IESMBV-DEPARTAMENTODEINGLÉS

DENTAL PROSTHETICS

Prosthodontics, also known as dental prosthetics or prosthetic dentistry, is one of nine dental specialties recognized by the American Dental Association, Royal College of Dentists of Canada, and Royal Australasian College of Dental Surgeons. Prosthodontics is the dental specialty pertaining to the diagnosis, treatment planning, rehabilitation and maintenance of the oral function, comfort, appearance and health of patients with clinical conditions associated with missing or deficient teeth and/or oral and maxillofacial tissues using biocompatible substitutes.

Contents

1 Training

Training

According to the American College of Prosthodontists, a prosthodontist is a dentist who:^[2]

Specializes in the aesthetic (cosmetic) restoration and replacement of teeth.
Receives three to four years of additional training after dental school.
Restores optimum appearance and function to your smile. The treatment planning and restoration of implants, temporomandibular joint disorder (TMJ), and rehabilitation of occlusion with prostheses all fall under the field of prosthodontics.

Australia

Australian programs are accredited by the Australian Dental Council (ADC) and are 3 years in length and culminate with either a Master degree (MDS), a Master of Dental Science (MDSc) or a Doctor of Clinical Dentistry degree (DClinDent). Fellowship can then be obtained with the Royal Australasian College of Dental Surgeons, FRACDS (Pros).

Canada

Canadian programs are accredited by the (CDAC) and are a minimum of three years in length and usually culminate with a master (MSc or MDent) degree. Graduates are then eligible to sit for the Fellowship exams with the Royal College of Dentists of Canada (FRCD (C)).

In Canada, prosthodontics speciality programs are available at University of Montréal, University of Toronto and UBC.

USA

The American College of Prosthodontists (ACP) ensures standards are maintained in the field. Becoming a prosthodontist requires an additional three years of postgraduate specialty training after obtaining a dental degree. Training consists of rigorous clinical and didactic preparation in the basic sciences, head and neck anatomy, biomedical sciences, biomaterial sciences, function of occlusion (bite), TMJ, and treatment planning and experience treating full-mouth reconstruction cases, and esthetics. Due to this extensive training, prosthodontists are required to treat complex cases, full-mouth rehabilitation, TMJ-related disorders, congenital disorders, and sleep apnea by planning and fabricating various prostheses. There are only 3,200 prosthodontists in comparison to 170,000 general dentists in the United States.^[ Prosthodontists have been consistently ranked at 6th or 7th positions by Forbes among America's most competitive and highest salaried jobs.^[4][5][6][7]

Board certification is awarded through the American Board of Prosthodontics (ABP)^[8] and requires successful completion of the Part I written examination and Part 2, 3 and 4 oral examinations. The written and one oral examination may be taken during the 3rd year of speciality training and the remaining two oral examinations taken following completion of speciality training. Board eligibility starts when an application is approved by the ABP and lasts for six years.^[9] Diplomates of the ABP are ethically required to have a practice limited to prosthodontics. Fellows of the American College of Prosthodontists (FACP) are required to have a dental degree, have completed three years of prosthodontic speciality training, and be board certified by the ABP.

According to the ADA, specialties are recognized in those areas where advanced knowledge and skills are essential to maintain or restore oral health (Principles of Ethics and Code of Professional Conduct). Not all areas in dentistry will satisfy the requirements for specialty recognition. Acknowledged by the profession, the contributions of such and their endeavors are encouraged.

The American Dental Association does not recognize Cosmetic dentistry as a speciality.Prosthodontics is the only dental speciality under which the concentration of cosmetic/esthetic dentistry falls.General dentists may perform some simple cosmetic procedures. Consequently, there are questions regarding whether it is ethical for general dentists to treat "smile makeovers" or complex cosmetic and full-mouth reconstruction cases, as they are not qualified to address the complex needs of the patient. Likewise, there is no specialty recognized by the ADA for dental implants.

Maxillofacial prosthodontics/prosthetics

Maxillofacial prosthetics (Oral and Maxillofacial Prosthodontics) is a sub-specialty (or super-specialty) of Prosthodontics. It is the only recognized sub-specialty of all dental specialties by the American Dental Association. All Maxillofacial prosthodontists are prosthodontists first and then attain a fellowship training year) exclusively in Maxillofacial prosthetics that includes oral surgical and prosthodontic treatments. Maxillofacial prosthodontists treat patients who have acquired and congenital defects of the head and neck (maxillofacial) region due to cancer, surgery, trauma, and/or birth defects. Maxillary obturators, speech-aid prosthesis (formerly called as Pharyngeal/soft palate obturators) and mandibular-resection prostheses are the most common prostheses planned and fabricated by Maxillofacial prosthodontists.^[15] Other types of prostheses include artificial eyes, nose and other facial prostheses fabricated in conjunction with an anaplastologist.^[16]

Treatment is multidisciplinary, involving oral and maxillofacial surgeons, plastic surgeons, head and neck surgeons, ENT doctors, oncologists, speech therapists, occupational therapists, physiotherapists, and other healthcare professionals.

Due to their extensive training in prosthetic reconstruction, breadth of knowledge and capability of handling most types of complex cases, Maxillofacial prosthodontists have been referred to as "bullet-proof" dentists.

· Akers' clasp

An Akers' clasp is the classic direct retainer for removable partial dentures. Named after its inventor, Polk E. Akers, this suprabulge clasp consists of a rest, a guide plate, a retentive arm and a reciprocal arm. Akers' clasps, as a rule, face away from an edentulous area. Should they face the edentulous area, they are termed reverse Akers' clasps.

· Amalgam

In dentistry, amalgam is an alloy of mercury with various metals used for dental fillings. It commonly consists of mercury (50%), silver (~22-32% ), tin (~14%), copper (~8%), and other trace metals.^[ Dental amalgams were first documented in a Tang Dynasty medical text written by Su Kung in 659, and appeared in Germany in 1528.^[3][4] In the 1800s, amalgam became the dental restorative material of choice due to its low cost, ease of application, strength, and durability.^[^{citation needed}^]

Recently however, its popularity has diminished somewhat.^[^{citation needed}^] Concern for aesthetics, environmental pollution, health, and the availability of improved, reliable, composite materials have all contributed. In particular, concerns about the toxicity of mercury have made its use increasingly controversial. Due to a plan to phase out the use of mercury, Sweden, Norway and Denmark deliberated in 2008 on a ban of mercury dental amalgam, substituting it with composite fillings. Dentists in Denmark are no longer allowed to use mercury in fillings since April 1, 2008. The Swedish amalgam ban is for both environmental and health issues, according to the Swedish authorities.

Contents

1 History of use

1.1 Longevity and other advantages

History of use

There are, according to Geir Bjørklund, indications that dental amalgam was used in the first part of the T'ang Dynasty in China (618-907 A.D.), and in Germany by Strockerus in about 1528.^[3] Evidence of a dental amalgam first appears in the Tang Dynasty medical text Hsin Hsiu Pen Tsao written by Su Kung in 659, manufactured from tin and silver.^[4] Historical records hint that the use of amalgams may date even earlier in the Tang Dynasty.^[ It was during the Ming Dynasty that the composition of an early dental amalgam was first published, and a text written by Liu Wen Taiin 1505 states that it consists of "100 shares of mercury, 45 shares of silver and 900 shares of tin."^[4] Ever since its introduction in the Western World in the 1830s, amalgam has been the subject of recurrent controversies because of its mercury content. Early amalgam was made by mixing mercury with the filings of silver coins.

In 1833 the Crawcour brothers, two Frenchmen, brought amalgam to the United States, and in 1844 it was reported that fifty percent of all dental restorations placed in upstate New York consisted of amalgam. However, at that point the use of dental amalgam was declared to be malpractice, and the American Society of Dental Surgeons (ASDS), the only US dental association at the time, forced all of its members to sign a pledge to abstain from using the mercury fillings. This was the beginning of what is known as the first dental amalgam war.

The dispute ended in 1856 with the disbanding of the old association. The American Dental Association was founded in its place in 1859, which has since then strongly defended dental amalgam from allegations of being too risky from the health standpoint.^[10]

The ratio of the mercury to the remaining metallic mixture in dental amalgam has not always been 50:50. It was as high as 66:33 in 1930. Relative ratios between the other metals used in dental amalgams has also been highly variable. Conventional (or gamma 2)-amalgams have 32% silver and 14% tin, and they are most susceptible to corrosion due to their low copper content. Non-gamma-2 dental amalgams have been developed that were, however, found to release higher levels of mercury vapor compared with traditional amalgams. Amalgam is the dental material that has the strongest tendency to create galvanic currents and high electric potentials as it ages.^[^{citation needed}^] The rate of mercury release with the corrosion is accelerated when the amalgam filling is in contact with old restorations or coupled with gold artifacts present in the mouth.

Longevity and other advantages

Amalgam is "tolerant to a wide range of clinical placement conditions and moderately tolerant to the presence of moisture during placement". In contrast, the techniques for composite resin placement are more sensitive to many factors and require "extreme care".

Mercury has properties of a bacteriostatic agent whereas certain methacrylate polymers (for example TEGMA, triethylene glycol methacrylate) composing the matrix of resin composites "encourages the growth of microorganisms".

Recurrent marginal decay is a very important factor in restoration failure, but more so in composite restorations. In the Casa Pia study in Portugal (1986–1989), 1,748 posterior restorations were placed and 177 (10.1%) of them failed during the course of the study. Recurrent marginal decay was the main reason for failure in both amalgam and composite restorations, accounting for 66% (32/48) and 88% (113/129), respectively.Polymerization shrinkage, the shrinkage that occurs during the composite curing process, has been implicated as the primary reason for postoperative marginal leakage.

These are some of the reasons why amalgam has remained a superior restorative material over resin-base composites. The New England Children's Amalgam Trial (NECAT), a randomized controlled trial, yielded results "consistent with previous reports suggesting that the longevity of amalgam is higher than that of resin-based compomer in primary teeth^[11][16] and composites in permanent teeth. Compomers were seven times as likely to require replacement and composites were seven times as likely to require repair.

There are circumstances in which composite serves better than amalgam. For example, when a more conservative preparation would be beneficial, composite is the recommended restorative material. These situations would include small occlusal restorations, in which amalgam would require the removal of more sound tooth structure, as well as in "enamel sites beyond the height of contour." For cosmetic purposes, composite is preferred when a restoration is required on an immediately visible portion of a tooth.

Toxicity controversy

Controversy over the mercury component of dental amalgam dates back to its inception, when it was opposed by the United States dental establishment, but it became a prominent debate in the late 20th century, with consuer and regulatory pressure to eliminate it "at an all-time high". In a 2006 nationwide poll, 76% of Americans were unaware that mercury is the primary component in amalgam fillings, and this lack of informed consent was the most consistent issue raised in a recent U.S. Food and Drug Administration panel on the issue by panel members. Environmental concerns over external costs exist as well, as the use of dental amalgam is unregulated at the federal level in, for example, the United States. The WHO reports that in the United Kingdom mercury from amalgam accounts for 5% of total mercury emissions and that when combined with waste mercury from laboratory and medical devices, represents 53% of total mercury emissions.Separators may dramatically decrease the release of mercury into the public sewer system, where dental amalgams contribute one-third of the mercury waste.Although several states (NJ, NY, MI, etc.) require the installation of dental amalgam separators, they are not required by the United States government.As of 2008, the use of dental amalgam has been banned in Norway, Sweden and Denmark, and a committee of the US Food and Drug Administration (FDA) has refused to ratify assertions of safety.

In the 1990s, several governments evaluated the effects of dental amalgam and concluded that the most likely health effects would be due to hypersensitivity or allergy. Germany, Austria, and Canada recommended against placing amalgam in certain individuals such as pregnant women, children, those with renal dysfunction, and those with an allergy to metals. In 2004, the Life Sciences Research Office analyzed studies related to dental amalgam published after 1996. Concluding that mean urinary mercury concentration (μg of Hg/L in urine, HgU) was the most reliable estimate of mercury exposure, it found those with dental amalgam were unlikely to reach the levels where adverse effects are seen from occupational exposure (35 μg HgU). 95% of study participants had μg HgU below 4-5. Chewing gum, particularly for nicotine, along with more amalgam, seemed to pose the greatest risk of increasing exposure; one gum-chewer had 24.8 μg HgU. Studies have shown that the amount of mercury released during normal chewing is extremely low.^[^{citation needed}^] A tuna fish sandwich releases the same amount of mercury as 3-5 amalgam fillings.^[28]^[^{citation needed}^] However, from reviewing medical literature, the World Health Organization states mercury levels in biomarkers such as urine, blood, or hair do not represent levels in critical organs and tissues. Additionally, Gattineni et al. found that mercury levels do not correlate with the number or severity of symptoms. It concluded that there was not enough evidence to support or refute many of the other claims such as increased risk of autoimmune disorders, but stated that the broad and nonspecific illness attributed to dental amalgam is not supported by the data. Mutter in Germany, however, concludes that "removal of dental amalgam leads to permanent improvement of various chronic complaints in a relevant number of patients in various trials."^[

There is strong evidence that a certain percentage of lichenoid lesions are caused by amalgam fillings.

Under the Comments of the American Dental Association Before the Dental Products Panel of the Medical Devices Advisory Committee, the ADA supports the 2009 FDA ruling on dental amalgam.^[

After FDA’s deliberations and review of hundreds of scientific studies relating to the safety of dental amalgam, the FDA concluded that “clinical studies have not established a casual link between dental amalgam and adverse health effects in adults and children age six and older.” The FDA concluded that individuals age six and older are not at risk to mercury-associated health affects from mercury vapor exposure that come from dental amalgam.

On the controversy of dental amalgam toxicity, the ADA asserts the best scientific evidence supports the safety of dental amalgam. Clinical studies have not established an occasional connection between dental amalgam and adverse health effects in the general population.^[

The recent World Health Organization report reaffirms the safety and importance of maintaining the availability of dental amalgam. The comments of the ADA concluded that dental amalgam remains an excellent and valuable restorative material for both dentists and patients; other alternative tooth restorative materials haven’t been proven to be as effective as dental amalgam.^[

The comments of the ADA state that there is no scientific reason to revisit the 2009 FDA ruling; while high exposure to elemental mercury has been associated to adverse health effects, the mercury exposure in dental amalgam is not high enough to cause harm in patients.^[33] Dental amalgam is a safe restorative material which now have special controls on this device, imposed by the FDA to ensure the safety and effectiveness of dental amalgam. Also, in the FDA final regulation on dental amalgam in 2009, the FDA recommended the product labeling of dental amalgam. The suggested labeling included: a warning against the use of dental amalgam in patients with mercury allergy, a warning that dental professionals use appropriate ventilation when handling dental amalgam, and a statement discussion of scientific evidence on dental amalgam’s risks and benefits in order to make informed decisions amongst patient and professional dentists.

· Bridge

A bridge is a fixed dental restoration used to replace a missing tooth by joining an artificial tooth permanently to adjacent teeth or dental implants.

Types of bridges may vary, depending upon how they are fabricated and the way they anchor to the adjacent teeth. Conventionally, bridges are made using the indirect method of restoration. However, bridges can be fabricated directly in the mouth using such materials as composite resin.

A bridge is fabricated by reducing the teeth on either side of the missing tooth or teeth by a preparation pattern determined by the location of the teeth and by the material from which the bridge is fabricated. In other words, the abutment teeth are reduced in size to accommodate the material to be used to restore the size and shape of the original teeth in a correct alignment and contact with the opposing teeth. The dimensions of the bridge are defined by Ante's Law: "The root surface area of the abutment teeth has to equal or surpass that of the teeth being replaced with pontics".^[1]

The materials used for the bridges include gold, porcelain fused to metal, or in the correct situation porcelain alone. The amount and type of reduction done to the abutment teeth varies slightly with the different materials used. The recipient of such a bridge must be careful to clean well under this prosthesis.

When restoring an edentulous space with a fixed partial denture that will crown the teeth adjacent to the space and bridge the gap with a pontic, or "dummy tooth", the restoration is referred to as a bridge. Besides all of the preceding information that concerns single-unit crowns, bridges possess a few additional considerations when it comes to case selection and treatment planning, tooth preparation and restoration fabrication.

Contents

Case selection and treatment planning

When a single tooth requires a crown, the prosthetic crown will in most instances rest upon whatever tooth structure was originally supporting the crown of the natural tooth. However, when restoring an edentulous (without teeth) area with a bridge, the bridge is almost always restoring more teeth than there are root structures to support. For instance, in the photo at right, the 5-unit bridge will only be supported on three abutment teeth.

To determine whether or not the abutment teeth can support a bridge without failure from lack of support from remaining root structures, the dentist employs Ante's rule—which states that the roots of abutment teeth must have a combined surface area in three dimensions that is more than that of the missing root structures of the teeth replaced with a bridge. When the situation yields a poor prognosis for proper support, double abutments may be required to properly conform to Ante's rule.

When a posterior tooth intended for an abutment tooth already possesses an intracoronal restoration, it might be better to make that bridge abutment into an inlay or an onlay, instead of a crown. However, this may concentrate the torque of the masticatory forces onto a less enveloping restoration, thus making the bridge more prone to failure.

In some situations, a cantilever bridge may be constructed to restore an edentulous area that only has adequate teeth for abutments either mesially or distally. This must also conform to Ante's rule but, because there are only abutments on one side, a modification to the rule must be applied, and these bridges possess double abutments in the majority of cases, and the occlusal surface area of the pontic is generally decreased by making the pontic smaller than the original tooth.

Tooth preparation

As with preparations for single-unit crowns, the preparations for multiple-unit bridges must also possess proper taper to facilitate the insertion of the prosthesis onto the teeth. However, there is an added dimension when it comes to bridges, because the bridge must be able to fit onto the abutment teeth simultaneously. Thus, the taper of the abutment teeth must match, to properly seat the bridge. This is known as requiring parallelism among the abutments.

When this is not possible, due to severe tipping of one of more of the abutments, for example, an attachment may be useful, as in the photo at right, so that one of the abutments may be cemented first, and the other abutment, attached to the pontic, can then be inserted, with an arm on the pontic slipping into a groove on the cemented crown to achieve a span across the edentulous area.

Restoration fabrication

Full dental bridge being machined using WorkNC Dental CAD/CAM software.

As with single-unit crowns, bridges may be fabricated using the lost-wax technique if the restoration is to be either a multiple-unit FGC or PFM. Another fabrication technique is to use CAD/CAM software to machine the bridge.^[2] As mentioned above, there are special considerations when preparing for a multiple-unit restoration in that the relationship between the two or more abutments must be maintained in the restoration. That is, there must be proper parallelism for the bridge to seat properly on the margins.

Sometimes, the bridge does not seat, but the dentist is unsure whether or not it is only because the spatial relationship of the two or more abutments is incorrect, or whether the abutments do not actually fit the preparations. The only way to determine this is to section the bridge and try in each abutment by itself. If they all fit individually, it must have simply been that the spatial relationship was incorrect, and the abutment that was sectioned from the pontic must now be reattached to the pontic according to the newly confirmed spatial relationship. This is accomplished with a solder index.

The proximal surfaces of the sectioned units (that is, the adjacent surfaces of the metal at the cut) are roughened and the relationship is preserved with a material that will hold on to both sides, such as GC pattern resin. With the two bridge abutments individually seated on their prepared abutment teeth, the resin is applied to the location of the sectioning to reestablish a proper spatial relationship between the two pieces. This can then be sent to the lab where the two pieces will be soldered and returned for another try-in or final cementation.

· Centric relation

In dentistry, centric relation is the mandibular jaw position in which the head of the condyle is situated as far anterior and superior as it possibly can within the mandibular fossa/glenoid fossa.

It is defined as, "The maxillo-mandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterior-superior position against the slopes of the articular eminences. This position is independent of tooth contact. This position is clinically discernible when the mandible is directed superiorly and anteriorly. It is restricted to a purely rotary movement about the transverse horizontal axis". — GPT.

This position is used when restoring edentulous patients with removable or either implant-supported hybrid or fixed prostheses. Because the dentist want to be able to reproducibly relate the patient's maxilla and mandible, but the patient does not have teeth with which to establish his or her own vertical dimension of occlusion, another method has been devised to achieve this goal. The condyle can only be in the same place as it was the last time it was positioned by the dentist if it is consistently moved to the most superior and anterior position within the fossa.

It is a physiologic position that is used for reproducibility. The Temporomandibular Joint is not restricted to Centric Relation in function.
At the most superior position, the condyle-disc assemblies are braced medially, thus centric relation is also the midmost position. A properly aligned condyle-disc assembly in centric relation can resist maximum loading by the elevator muscles with no sign of discomfort. It also allows for the most repeatable and recordable position and therefore should be used when designing an appropriate occlusion.

Methods of Recording Centric Relation:

Physiological Methods:

Tactile or inter-occlusal check record method.
Pressureless method.
Pressure method.

Functional Methods:

Needlehouse method.
Patterson method.

Graphic Methods:

Intraoral methd.
Extraoral method.

Radiographic Method.

^[1]

· Crown

A crown is a type of dental restoration which completely caps or encircles a tooth or dental implant. Crowns are often needed when a large cavity threatens the ongoing health of a tooth.^[1] They are typically bonded to the tooth using a dental cement. Crowns can be made from many materials, which are usually fabricated using indirect methods. Crowns are often used to improve the strength or appearance of teeth. While inarguably beneficial to dental health, the procedure and materials can be relatively expensive.^[2]

The most common method of crowning a tooth involves using a dental impression of a prepared tooth by a dentist to fabricate the crown outside of the mouth. The crown can then be inserted at a subsequent dental appointment. Using this indirect method of tooth restoration allows use of strong restorative materials requiring time consuming fabrication methods requiring intense heat, such as casting metal or firing porcelain which would not be possible to complete inside the mouth. Because of the expansion properties, the relatively similar material costs, and the aesthetic benefits, many patients choose to have their crown fabricated with gold.

As new technology and materials science has evolved, computers are increasingly becoming a part of crown and bridge fabrication, such as in CAD/CAM Dentistry.

Contents

1 Other reasons to restore with a crown

2 Tooth preparation

8.1 Metal-containing restorations

8.1.1 Full gold crown

Other reasons to restore with a crown

There are additional situations in which a crown would be the restoration of choice.

Implants

Dental implants are placed into either the maxilla or mandible as an alternative to partial or complete edentulism. Once placed and properly integrated into the bone, implants may then be fitted with a number of different prostheses:

crowns or bridges
precision attachments for either removable partial dentures, complete dentures or a hybrid sort of prosthetic appliance.

Endodontically treated teeth

When teeth undergo endodontic treatment, or root canal therapy, they are devitalized when the nerve and blood supply are cut off and the space which they previously filled, known as the "pulp chamber" and "root canal", are thoroughly cleansed and filled with various materials to prevent future invasion by bacteria. Although there may very well be enough tooth structure remaining after root canal therapy is provided for a particular tooth to restore the tooth with an intracoronal restoration, this is not suggested in most teeth. The vitality of a tooth is remarkable in its ability to provide the tooth with the strength and durability it needs to function in mastication. The living tooth structure is surprisingly resilient and can sustain considerable abuse without fracturing. Consequently, after root canal therapy is performed, a tooth becomes extremely brittle and is significantly weaker than its vital neighbors.

http://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Clinical_Fracture_Rates_for_Nonvital_teeth.svg/525px-Clinical_Fracture_Rates_for_Nonvital_teeth.svg.png

Fractures of endodontically treated teeth increase considerably in the posterior dentition when cuspal protection is not provided by a crown.^[3]

The average person can exert 150–200 lbs (70-90 kg). of muscular force on his or her posterior teeth, which is approximately nine times the amount of force that can be exerted in the anterior. If the effective posterior contact area on a restoration is 0.1 mm², over 1 million PSI of stress is placed on the restoration. Therefore, posterior teeth (i.e. molars and premolars) should in almost all situations be crowned after undergoing root canal therapy to provide for proper protection against fracture (mandibular premolars, being very similar in crown morphology to canines, may in some cases be protected with intracoronal restorations). Should an endodontically treated tooth not be properly protected, there is a chance of it succumbing to breakage from normal functional forces. This fracture may well be difficult to treat, such as a "vertical root fracture" . Anterior teeth (i.e. incisors and canines), which are exposed to significantly lower functional forces, may effectively be treated with intracoronal restorations following root canal therapy if there is enough tooth structure remaining after the procedure.

Surveyed crown

Another situation in which a crown is the restoration of choice is when a tooth is intended as an abutment tooth for a removable partial denture, but is initially unfavorable for such a task. If the abutment teeth onto which the RPD is supposed to clasp do not possess the proper dimensions or features required, these aspects can be built into what is known as a surveyed crown.

Aesthetics

A fourth situation in which a crown would be the restoration of choice is when a patient desires to have his or her smile aesthetically improved but when partial coverage (i.e., a veneer/laminate) is not an option for one or more reasons. If the patient's occlusion does not permit for a mildly-retentive restoration, or if there is too much decay or a fracture within the tooth structure, a porcelain or composite veneer may not be placed with any adequate guarantee for its durability. Similarly, a "bruxer" (someone who clenches or grinds their teeth) may produce enough force to repeatedly dislodge or irreversibly abrade any veneer a dentist can plan for. In such a case, full coverage crowns can alter the size, shape or shade of a patient's teeth while protecting against failure of the restoration.

Makeover shows such as Extreme Makeover make extensive use of crowns, as the time-frame of the makeover is too short to allow up to 18 months for orthodontic treatment for problems that might otherwise be corrected more conservatively.

Tooth preparation

A full-arch Polyvinyl siloxane impression of the teeth prepared for the 5-unit PFM bridge shown in the photographs below. The salmon-colored impression material used near the crown preparations is of a lower viscosity than the blue, allowing for the capture of greater detail.

Preparation of a tooth for a crown involves permanently removing much of the tooth's original structure, including portions that might still be healthy and structurally sound. All currently available materials for making crowns are not as good as healthy, natural tooth structure, so teeth should only be crowned when an oral health-care professional has evaluated the tooth and decided that the overall value of the crown will outweigh the disadvantage of needing to remove some healthy parts of the tooth. This can be a very complex evaluation to make, so different dentists (trained at different institutions, with different experiences, and trained in different methods of treatment planning and case selection) may come to different conclusions regarding treatment.

Traditionally more than one visit is required to complete crown and bridge work, and the additional time required for the procedure can be a disadvantage; the increased benefits of such a restoration, however, will generally offset these considerations.

Dimensions of preparation

When preparing a tooth for a traditional crown, the enamel may be totally removed and the finished preparation should, thus, exist primarily in dentin. As elaborated on below, the amount of tooth structure required to be removed will depend on the material(s) being used to restore the tooth. If the tooth is to be restored with a full gold crown, the restoration need only be .5 mm in thickness (as gold is very strong), and therefore, a minimum of only .5 mm of space needs to be made for the crown to be placed. If porcelain is to be applied to the gold crown, an additional minimum of 1 mm of tooth structure needs to be removed to allow for a sufficient thickness of the porcelain to be applied, thus bringing the total tooth reduction to minimally 1.5 mm.

If there is not enough tooth structure to properly retain the traditional prosthetic crown, the tooth requires a build-up material. This can be accomplished with a pin-retained direct restoration, such as amalgam or a composite resin, or in more severe cases, may require a post and core. Should the tooth require a post and core, endodontic therapy would then be indicated, as the post descends into the devitalized root canal for added retention. If the tooth, because of its relative lack of exposed tooth structure, also requires crown lengthening, the total combined time, effort and cost of the various procedures, together with the decreased prognosis because of the combined inherent failure rates of each procedure, might make it more reasonable to have the tooth extracted and opt to have an implant placed.

In recent years, the technological advances afforded by CAD/CAM dentistry offer viable alternatives to the traditional crown restoration in many cases.^[4][5] Where the traditional indirectly fabricated crown requires a tremendous amount of surface area to retain the normal crown, potentially resulting in the loss of healthy, natural tooth structure for this purpose, the all-porcelain CAD/CAM crown can be predictably used with significantly less surface area. As a matter of fact, the more enamel that is retained, the greater the likelihood of a successful outcome. As long as the thickness of porcelain on the top, chewing portion of the crown is 1.5mm thick or greater, the restoration can be expected to be successful. The side walls which are normally totally sacrificed in the traditional crown are generally left far more intact with the CAD/CAM option. In regards to post & core buildups, these are generally contraindicated in CAD/CAM crowns as the resin bonding materials do best bonding the etched porcelain interface to the etched enamel/dentin interfaces of the natural tooth itself. The crownlay is also an excellent alternative to the post & core buildup when restoring a root canal treated tooth.

Taper

The prepared tooth also needs to possess 3 to 5 degrees of taper to allow for the restoration to be properly placed on the tooth. The taper should not exceed 20 degrees. Fundamentally, there can be no undercuts on the surface of the prepared tooth, as the restoration will not be able to be removed from the die, let alone fit on the tooth (see explanation of lost-wax technique below to understand of the processes involved in crown fabrication). At the same time, too much taper will severely limit the grip that the crown has on the prepared tooth, thus contributing to failure of the restoration. Generally, 6° of taper around the entire circumference of the prepared tooth, giving a combined taper of 12° at any given sagittal section through the prepared tooth, is appropriate to both allow the crown to fit yet provide enough grip.

Margin

The most coronal position of untouched tooth structure (that is, the continual line of original, undrilled tooth structure at or near the gum line) is referred to as the margin. This margin will be the future continual line of tooth-to-restoration contact, and should be a smooth, well-defined delineation so that the restoration, no matter how it is fabricated, can be properly adapted and not allow for any openings visible to the naked eye, however slight. An acceptable distance from tooth margin to restoration margin is anywhere from 40-100 μm^[^{citation needed}^]. However, the R.V. Tucker method of gold inlay and onlay restoration produces tooth-to-restoration adaptation of potentially only 2 μm^[^{citation needed}^], confirmed by scanning electron microscopy; this is less than the diameter of a single bacterium.

Naturally, the tooth-to-restoration margin is an unsightly thing to have exposed on the visible surface of a tooth when the tooth exists in the aesthetic zone of the smile. In these areas, the dentist would like to place the margin as far apical (towards the root tip of the tooth) as possible, even below the gum line. While there is no issue, per se, with placing the margin at the gumline, problems may arise when placing the margin too subgingivally (below the gumline). First, there might be issues in terms of capturing the margin in an impression to make the stone model of the prepared tooth (see stone model replication of tooth in photographs, above). Secondly, there is the seriously important issue of biologic width. Biologic width is the mandatory distance to be left between the height of the alveolar bone and the margin of the restoration, and if this distance is violated because the margin is placed too subgingivally, serious repercussions may follow. In situations where the margin cannot be placed apically enough to provide for proper retention of the prosthetic crown on the prepared tooth structure, the tooth or teeth involved should undergo a crown lengthening procedure.

http://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Periodontium.svg/330px-Periodontium.svg.png

The natural tooth's crown (the part visible in the mouth) meets the root (the part of the tooth in the bone) at the cementoenamel junction, and it is roughly at this point that the gingival attachment begins at the base of the gingival sulcus (G). The margin of the prosthetic crown may not violate the 2 mm of biologic width from the base of this sulcus to the height of the alveolar bone (C) if complications are to be avoided.

There are a number of different types of margins that can be placed for restoration with a crown. There is the chamfer, which is popular with full gold restorations, which effectively removed the smallest amount of tooth structure. There is also a shoulder, which, while removing slightly more tooth structure, serves to allow for a thickness of the restoration material, necessary when applying porcelain to a PFM coping or when restoring with an all-ceramic crown (see below for elaboration on various types of crowns and their materials). When using a shoulder preparation, the dentist is urged to add a bevel; the shoulder-bevel margin serves to effectively decrease the tooth-to-restoration distance upon final cementation of the restoration.

Ferrule effect

A very important consideration when restoring with a crown is the incorporation of the ferrule effect. As with the bristles of a broom, which are grasped by a ferrule when attached to the broomstick, the crown should envelop a certain height of tooth structure to properly protect the tooth from fracture after being prepared for a crown. This has been established through multiple experiments as a mandatory continuous circumferential height of 2 mm; any less provides for a significantly higher failure rate of endodontically-treated crown-restored teeth. When a tooth is not endodontically treated, the remaining tooth structure will invariably provide the 2 mm height necessary for a ferrule, but endodontically treated teeth are notoriously decayed and are often missing significant solid tooth structure. Because they are weaker after the additional removal of tooth structure that occurs during a root canal procedure, endodontically treated teeth require proper protection against vertical root fracture. Some have speculated that a shoulder preparation on an all ceramic crown that will be bonded in place may have the same effect as a ferrule.

Adequate and appropriate restoration of tooth structure

As crowns are fabricated indirectly (outside of the mouth) free of the encumbrances of saliva, blood, and tight quarters, they can be made to fit more precisely than restorative materials placed directly (inside the mouth). In regards to marginal adaptations (the circumferential seal which keeps bacteria out), anatomically correct contacts (touching adjacent teeth properly so food will not be retained), and proper morphology, the indirect fabrication of the restorations are unprecedented. Indirectly fabricated crowns may be fabricated one of two ways. In the traditional sense, the tooth in question is prepared, a mold is taken, a temporary crown is placed and then the patient leaves. The mold is then sent to a dental laboratory whereby a model is constructed from the mold, and a crown is created on the model (usually out of porcelain, ceramic, gold, or porcelain/ceramic fused to metal) to replace the missing tooth structure. The patient returns to the dental office a week or two later and then the temporary is removed and the crown is fitted and cemented in place. Alternatively, a crown may be indirectly fabricated utilizing technology and techniques relating to CAD/CAM dentistry, whereby the tooth is prepared and computer software is used to create a virtual restoration which is milled on the spot and bonded permanently in place an hour or two later.

3/4 and 7/8 crowns

There are even restorations that fall between an onlay and a full crown when it comes to preservation of natural tooth structure. In the past, it was somewhat common to find dentists who prepared teeth for 3/4 and 7/8 crowns. Such restorations would generally be fabricated for maxillary second premolars or first molars, which might only be slightly visible when a patient smiled. Thus, the dentist would preserve healthy natural tooth structure that existed on the mesiobuccal corner of the tooth for aesthetic purposes, the remainder of the tooth would be enclosed in restorative material. Even when porcelain-fused-to-metal and all-ceramic crowns were developed, preserving any amount of tooth structure adds to the overall strength of the tooth. Some dentists feel that the structural benefits of retaining some of the original tooth structure are more than offset by the potential problems of having a significantly longer marginal length (the "seam" on the surface between the crown and the tooth).

All-ceramic restorations

This section possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research may be removed. (February 2009)

Inlays, onlays, porcelain veneers, crownlays and all varieties of crowns can also be fabricated out of ceramic materials, such as in CAD/CAM Dentistry or traditionally in a dental laboratory setting. CAD/CAM technology can allow for the immediate, same day delivery of these types restorations which are milled out of blocks of solid porcelain which matches the shade or color of the patients teeth. Traditionally, all-ceramic restorations have been made off site in a dental laboratory either out of feldspathic porcelains or pressed ceramics. This indirect method of fabrication involves molds and temporaries, but can yield quite beautiful end-results if communication between the laboratory and the dentist is sound. The greatest difference between these two differing modalities lies in the fact that the CAD/CAM route does not require temporization, while the laboratory-fabricated route does. Some argue that this lack of temporization can result in a decreased need for root canal therapy, as there is no temporary leakage between visits.

Restorations that are all-ceramic require wide shoulder margins and reductions of at least 1.0 - 1.5 mm across the occlusal (chewing) surfaces of the teeth. There are times where this reduction would be considered excessive, just as there are times when previous restorations or pathology require this much removal or more. Arguments against using all-ceramic restorations include a greater chance of fracture, when little to no enamel remains for proper adhesive bonding, or potentially when the patient clenches or grinds their teeth ("bruxes") excessively. Indications for using all-ceramic restorations include more aesthetic results, when metal compatibility issues exist, and when removal of less tooth structure is desired. All-ceramic restorations do not require resistance and retention form and consequently less surface area need be removed and the restoration will still stay in place by virtue of micromechanical and chemical bonding.

Ceramic materials such as lithium disilicate dental ceramics have recently been developed which provide greater strength and life-expectancy of dental restorations.

Longevity

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Although no dental restoration lasts forever, the average lifespan of a crown is around 10 years. While this is considered comparatively favorable to direct restorations, they can actually last up to the life of the patient (50 years or more) with proper care. One reason why a 10 year lifespan is quoted is because a dentist can usually provide patients with this figure and be confident that a crown that the dental lab makes will last at least this long. Many dental insurance plans in North America will allow for a crown to be replaced after only five years.

The most important factor affecting the lifespan of any restorative is the continuing oral hygiene of the patient. Other factors are the skill of the dentist and their lab technician, the material used and appropriate treatment planning and case selection.

Full gold crowns last the longest, as they are fabricated as a single piece of gold. PFMs, or porcelain-fused-to-metal crowns possess an additional dimension in which they are prone to failure, as they incorporate brittle porcelain into their structure. Although incredibly strong in compression, porcelain is terribly fragile in tension, and fracture of the porcelain increases the risk of failure, which rises as the number of surfaces covered with porcelain is increased. A traditional PFM with occlusal porcelain (i.e. porcelain applied to the biting surface of a posterior tooth) has a 7% higher chance of failure per year than a corresponding full gold crown.

When crowns are used to restore endodontically treated teeth, they reduce the likelihood of the tooth fracturing due to the brittle devitalized nature of the tooth and provide a better seal against invading bacteria. Although the inert filling material within the root canal blocks microbial invasion of the internal tooth structure, it is actually a superior coronal seal, or marginal adaptation of the restoration in or on the crown of the tooth, which prevents reinvasion of the root canal.

Advantages and disadvantages

This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information. Such statements should be clarified or removed. (February 2009)

The main disadvantages of restoration with a crown are extensive irreversible tooth preparation (grinding away) and higher costs than for direct restorations such as amalgam or dental composite. The benefits, as described above, include long-term durability and evidence-based success as compared to other restorations or no treatment.

The crowning of two fairly large molars to sling a bridge between them for a missing tooth is a costly and sometimes oversold procedure. The increased food and bacteria trapping of the underside of the bridge often offsets the benefits of the bridge element in maintaining the positions of the opposing teeth and the loss of the ease of use and mouth feel of two big natural teeth.^[^{citation needed}^]

It is usually the damage to a tooth that dictates the need for a crown, and alternative treatments are usually less effective.^[^{citation needed}^] Risks and benefits can be weighed based on the priorities of the patient.

An example of this occurs when a patient would like to restore an edentulous area between healthy adjacent teeth. Before implants, there were three options:

· Fixed partial denture (bridge)

· Removable partial denture

· No treatment

Those who could afford it were usually told by their dentists that a bridge was their best choice, because it is much sturdier than removable dentures and requires less looking after. When implants became available, however, they were recommended as the best possible treatment, because the virgin teeth adjacent to the edentulous area no longer needed to be cut in order to fit the bridge. The affluent are thus told that a fixed partial denture is no longer desirable, now that implants are available. However, implants are significantly more expensive than a bridge, and the results are generally much less immediate.

Types and materials

http://upload.wikimedia.org/wikipedia/commons/f/f5/Comparison_-_Crowns_and_veneer.jpg

Comparison between a porcelain-metal dental crown, an all-porcelain dental crown and a porcelain veneer laminate

There are many different methods of crown fabrication, each using a different material. Some methods are quite similar, and utilize either very similar or identical materials.

Metal-containing restorations

Full gold crown

Full gold crowns (FGCs) consist entirely of a single piece of alloy. Although referred to as a gold crown, this type of crown is actually composed of many different types of elements, including but not limited to gold, platinum, palladium, silver, copper and tin. The first four elements listed are noble metals, while the last two listed are base metals. Full gold crowns are of better quality when they are high in noble content. According to the American Dental Association, full gold crown alloys can only be labeled as high noble when they contain at least 60% noble metal, of which at least 40% must be gold.

The process of constructing a full gold crown begins at the dentist's office. The clinician will begin by preparing the tooth by removing enough tooth tissue to allow for the crown. Once the preparation has been finalized the clinician will take an impression which is basically a mold of the patient's mouth. The impression and patient details are sent to a dental laboratory where the dental technician will flow dental gypsum into the impression to make a dental model. This model is an exact reproduction of the situation in the patient's mouth. The dental technician now has the information required to model a wax pattern of the final restoration allowing for the tooth shape, occlusion and preparation. The wax pattern can be removed from the model and a wax sprue pattern is attached. The pattern is now ready to use in the Lost-wax casting technique. It is invested in a gypsum or phosphate-bonded investment material, allowed to set then put into a furnace where the wax is completely burnt out leaving a hole for the gold to be poured in. Once the crown has cooled, the technician can remove the sprue, fit and polish the crown ready for cementation. The crown is returned to the dentists office where they can remove any temporary crown and cement the finished gold crown.

Porcelain-fused-to-metal crowns

http://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Porcelain_fused_to_metal_metal_crown.jpg/330px-Porcelain_fused_to_metal_metal_crown.jpg

Side view of porcelain-fused-to-metal crown for left mandibular first molar

Porcelain-fused-to-metal dental crowns (PFMs) have a metal shell on which is fused a veneer of porcelain in a high heat oven. The metal provides strong compression and tensile strength, and the porcelain gives the crown a white tooth-like appearance, suitable for front teeth restorations. These crowns are often made with a partial veneer that covers only the aspects of the crown that are visible. The remaining surfaces of the crown are bare metal. A variety of metal alloys containing precious metals and base metals can be used. The porcelain can be color matched to the adjacent teeth or gingivae.

Restorations without Metal

Chairside CAD/CAM Dentistry

The CAD/CAM method of fabricating all-ceramic restorations is by electronically capturing and storing a photographic image of the prepared tooth and, using computer technology, crafting a 3D restoration design that conforms to all the necessary specifications of the proposed inlay, onlay or single-unit crown; there is no impression. After selecting the proper features and making various decisions on the computerized model, the dentist directs the computer to send the information to a local milling machine. This machine will then use its specially designed diamond burs to mill the restoration from a solid ingot of a ceramic of pre-determined shade to match the patient's tooth. After about 20 minutes, the restoration is complete, and the dentist sections it from the remainder of the unmilled ingot and tries it in the mouth. If the restoration fits well, the dentist can cement the restoration immediately. A dental CAD/CAM machine costs roughly $100,000, with continued purchase of ceramic ingots and milling burs.

Typically, over 95% of the restorations made using Dental CAD/CAM and Vita Mark I and Mark II blocks are still clinically successful after 5 years.^[6][7] Further, at least 90% of restorations still function successfully after 10 years.^[6][7] Advantages of the Mark II blocks over ceramic blocks include: they wear down as fast as natural teeth,^[7][8] their failure loads are very similar to those of natural teeth,^[7][9] and the wear pattern of Mark II against enamel is similar to that of enamel against enamel.^[7][10][11]

Leucite Reinforced

Popularly known as the "Empress Crown," the leucite reinforced system is superficially similar to a gold crown technique in that a hollow investment pattern is made, but the similarities stop there. A specially designed pressure-injected leucite-reinforced ceramic is then pressed into the mold by using a pressable-porcelain-oven, as though the final all-ceramic restoration has been "cast." The crown that is constructed can be stained and glazed or cut-back and layered with feldspathic ceramic to match the patients natural color and shape.^[12]

A study by the Umeå University in Sweden, led by Göran Sjögren, sought to study the effectiveness of leucite-reinforced crowns. Titled “Clinical examination of leucite-reinforced glass ceramic crowns (Empress) in general practice: a restrospective study”, it found Empress crowns cracked at approximately only a 6% rate, with the integrity of 86% of the remaining samples being called "excellent."^[12][13]

Alumina

Alumina was introduced as a dental substructure (core) in 1989 when the material was slip cast, sintered, and infiltrated with glass. More recently, glass-infiltrated alumina cores are produced by electrophoretic deposition, a rapid nanofabricating process. During this process particles of a slip are brought to the surface of a dental die by an electric current, thereby forming a precision-fitting core greenbody in seconds. Margins are then trimed and the greenbody is sintered and infiltrated with glass. Glass-infiltrated alumina has significantly higher porcelain bond strength over CAD/CAM produced zirconia and alumina cores without glass.

Alumina cores without glass are produced by milling pre-sintered blocks of the material utilizing a CAD/CAM dentistry technique. Cores without glass must be oversized to compensate for shrinkage that occurs when the core is fully sintered.^[14] Milled cores are then sintered and shrink to the correct size.

All alumina cores are layered with aesthetic feldspathic porcelain to make true-to-life color and shape.^[14] Dental artists called ceramists, can customize the "look" of these crowns to individual patient and dentist requirements. Today, porcelain fused to alumina crowns set the standard for high aesthetics in dentistry.

Zirconia

Zirconia is a very hard ceramic that is used as a strong base material in some full ceramic restorations. The zirconia used in dentistry is zirconium oxide which has been stabilized with the addition of yttrium oxide. The full name of zirconia used in dentistry is yttria-stabilized zirconia or YSZ.

The zirconia substructure (core) is usually designed on a digital representation of the patients mouth, which is captured with a 3d digital scan of the patient, impression, or model. The core is then milled from a block of zirconia in a soft pre-sintered state. Once milled, the zirconia is sintered in a furnace where it shrinks by 20% and reaches its full strength of approximately 850MPa.

The zirconia core structure can be layered with aesthetic feldspathic porcelain to create the final color and shape of the tooth. Because bond strength of layered porcelain fused to zirconia is not strong, "monolithic" zirconia crowns are often made entirely of the zirconia ceramic with no aesthetic porcelain layered on top. Zirconia is the hardest known ceramic in industry and the strongest material used in dentistry. Monolithic zirconia crowns tend to be dense in appearance with a high value and they lack translucency and fluorescence. For aesthetic reasons, many dentists will not use monolithic crowns on anterior (front) teeth: "Where and When Is It Appropriate to Place Monolithic vs. Layered Restorations," Inside Dentistry, August 2012, Vol. 8, Issue 8, E. McLaren, R. Margeas, N. Fahl.

By using crowns made of metal zirconia, then merge the porcelain on the outside, zirconia crowns allow light to pass as a normal tooth would and that gives a natural look, unlike other metal cores that block the light. The normal too hot/cold sensations that can be felt with other crowns does not normally occur because of reduced thermal conductivity, this being another strong point for zirconia.

· Crown lengthening

Crown lengthening is a surgical procedure performed by a dentist to expose a greater amount of tooth structure for the purpose of subsequently restoring the tooth prosthetically.^[1] This is done by incising the gingival tissue around a tooth and, after temporarily displacing the soft tissue, predictably removing a given height of alveolar bone from the circumference of the tooth or teeth being operated on. While some general dentists perform this procedure, others frequently refer such cases to periodontists.

Contents

1 Biomechanical considerations

2 References

Biomechanical considerations

Biologic width

Biologic width is the natural distance between the gingival sulcus (G) and the height of the alveolar bone (I). The gingival sulcus (G) is a little crevice that lies between the enamel of the tooth crown and the sulcular epithelium. At the base of this crevice lies the junctional epithelium, which adheres via hemidesmosomes to the surface of the tooth, and from the base of the crevice to the height of the alveolar bone (C) is approximately 2 mm.

Biologic width is the distance established by "the junctional epithelium and connective tissue attachment to the root surface" of a tooth.^[1] In other words, it is the height between the deepest point of the gingival sulcus and the alveolar bone crest. This distance is important to consider when fabricating dental restorations, because they must respect the natural architecture of the gingival attachment if harmful consequences are to be avoided. The biologic width is patient specific and may vary anywhere from 0.75-4.3 mm.^[^{citation needed}^]

Based on the 1961 paper by Gargulio, the mean biologic width was determined to be 2.04 mm, of which 1.07 mm is occupied by the connective tissue attachment and another approximate 0.97 mm is occupied by the junctional epithelium.^[1][2] Because it is impossible to perfectly restore a tooth to the precise coronal edge of the junctional epithelium, it is often recommended to remove enough bone to have 3mm between the restorative margin and the crest of alveolar bone.^[3][4][5] When restorations do not take these considerations into account and violate biologic width, three things tend to occur:

chronic pain
chronic inflammation of the gingiva
unpredictable loss of alveolar bone

Ferrule effect

In addition to crown lengthening to establish a proper biologic width, a 2 mm height of tooth structure should be available to allow for a ferrule effect.^[6] A ferrule, in respect to teeth, is a band that encircles the external dimension of residual tooth structure, not unlike the metal bands that exist around a barrel. Sufficient vertical height of tooth structure that will be grasped by the future crown is necessary to allow for a ferrule effect of the future prosthetic crown; it has been shown to significantly reduce the incidence of fracture in the endodontically treated tooth.^[7] Because beveled tooth structure is not parallel to the vertical axis of the tooth, it does not properly contribute to ferrule height; thus, a desire to bevel the crown margin by 1 mm would require an additional 1 mm of bone removal in the crown lengthening procedure.^[8] Frequently, however, restorations are performed without such a bevel.

http://upload.wikimedia.org/wikipedia/commons/thumb/7/71/-5-CL-before_and_after.jpg/420px--5-CL-before_and_after.jpg

These two X-ray films depict the teeth of the upper right quadrant. In the upper film, there is a tooth, #5, with a large, defective DO composite restoration. The lower film depicts the ideal bone level after a crown lengthening procedure has been completed, as well as the margin of the prosthetic crown in relation to the reduced height of bone. Note that this is a dramatization of the procedure: the lower film is a digital manipulation of the upper film, and not an actual film of the teeth after a crown lengthening procedure and crown cementation have been performed.

Some recent studies suggest that, while ferrule is certainly desirable, it should not be provided at the expense of the remaining tooth/root structure.^[9] On the other hand, it has also been shown that the "difference between an effective, long-term restoration and a failure can be as small as 1 mm of additional tooth structure that, when encased by a ferrule, provides great protection. When such a long-lasting, functional restoration cannot be predictably created, tooth extraction should be considered."^[10]

Crown-to-root ratio

The alveolar bone surrounding one tooth will naturally surround an adjacent tooth, and removing bone for a crown lengthening procedure will effectively damage the bony support of adjacent teeth to some inevitable extent, as well as unfavorably increase the crown-to-root ratio. Additionally, once bone is removed, it is almost impossible to regain it to previous levels, and in case a patient would like to have an implant placed in the future, there might not be enough bone in the region once a crown lengthening procedure has been completed. Thus, it would be prudent for patients to thoroughly discuss all of their treatment planning options with their dentist before undergoing an irreversible procedure such as crown lengthening.

Treatment planning

Crown lengthening is often done in conjunction with a few other expensive and time-consuming procedures of which the combined goal is to improve the prosthetic forecast of a tooth. If a tooth, because of its relative lack of solid tooth structure, also requires a post and core, and thus, endodontic treatment, the total combined time, effort and cost of the various procedures, as well as the impaired prognosis due to the combined inherent failure rates of each procedure, might combine to make it reasonable to have the tooth extracted. If the patient and the extraction site make for eligible candidates, it might be possible to have an implant placed and restored with more esthetic, timely, inexpensive and reliable results. It is important to consider the many options available during the treatment planning stages of dental care.

A better alternative to surgical crown lengthening is orthodontic forced eruption, it is simple, it is non-invasive, does not remove or damage the bone and is cost effective. The tooth is extruded a couple of millimeters with simple bracketing of adjacent teeth and using light forces this will only take a couple of months. A simple fiberotomy is performed after crown lengthening and is easily performed by the general dentist. In many cases such as this one shown, surgery and extraction may be avoided if patient is treated orthodontically rather than periodontally.

· Crown-to-root ratio

Crown-to-root-ratio is the ratio of the length of the part of a tooth that appears above the alveolar bone versus what lies below it.^[1] It is an important consideration in the diagnosis, treatment planning and restoration of teeth, one that hopefully guides the plan of treatment to the proper end result.

Contents

1 Perspectives of different terminologies

Perspectives of different terminologies

Anatomical terms

All teeth have two general sections, the crown and the root. Because the crown is covered with enamel and the root is covered with cementum, the line at which these two sections join is called the cementoenamel junction. In health, the roots of teeth are entirely surrounded by and submerged in the alveolar bone of either the maxilla or the mandible, depending on whether the tooth in question is an upper or a lower tooth, up until the cementoenamel junction. Overlying the bone is the gingival soft tissue, which is, on average, about 1 millimeter in thickness.^[2] Because of this gingiva, the crown, which exists entirely outside of the surrounding bone, is somewhat obscured at the apical millimeter or so. Thus, crown and root can be used as anatomical terms, defining the actual parts of a tooth. Gingival recession is a related condition to decreased crown-to-root ratio, but referring to gingiva.

Clinical terms

These terms can also be used to refer to the clinical sense of the words, as relative crown and relative root, by describing how much tooth remains surrounded by bone. As the inflammation associated with periodontal disease causes the bone to resorb and disappear, revealing more of the root structure, the effective crown height in relation to the effective root height is reduced and the prognosis shifts from favorable to unfavorable.

Clinical importance

http://upload.wikimedia.org/wikipedia/commons/thumb/3/35/Mand_Right_Premolar_PA.JPG/413px-Mand_Right_Premolar_PA.JPG

This X-ray film displays horizontal bone loss of the mandible, in the lower right quadrant. Although the two premolars and the molar exhibit moderate to severe bone loss, there was no tooth mobility at the time this film was taken.

Clinically, the anatomical definitions don't really matter; what is important in terms of support for the teeth within the bone is how much of the teeth remain embedded; this is where the crown-to-root ratio becomes important.

Naturally, the cementoenamel junction exists much closer to the incisal or occlusal surface of a tooth than to the tip of the root or roots. Because of this fact, root length is considerably longer than crown length, and this helps allow for proper support of the teeth during normal function, not unlike a tree that has a root system hidden below ground which is more often than not considerably larger and more elaborate than the form taken by the growing branches. If a towering tree doesn't have enough support provided by its root system, it will easily be knocked over in even a slight wind; similarly, a tooth requires a sturdy root system encased in bone to protect it from being knocked out of the mouth.

The natural crown-to-root ratio is thus termed a favorable crown-to-root ratio, because the root system existing within the surrounding bone is more than sufficient to support the tooth under normal physiologic stresses. After some bone loss is incurred, though, and more root structure is visible outside of the supporting bone, not only is there less effecive root support, but there is an increased height of revealed tooth structure that this now diminished submerged root is responsible for supporting. In a way, then, each millimeter of lost bone contributes, for example, to a millimeter of less support and a millimeter of more structure to support. As can be extrapolated, this can easily become a very serious problem once three, four or five millimeters of bone have been lost due to periodontal disease.^[3] The minimum crown-to-root ratio necessary is 1:1; any less support provided by the roots drastically reduces the prognosis of the tooth and its restoration.

http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Jointtypodonts.jpg/375px-Jointtypodonts.jpg

Models of human teeth as they exist within the alveolar bone. The roots, as they can be seen through the transparent "bone", exist naturally in greater inciso-apical lengths than the crowns.

Teeth are constantly subject to both horizontal and vertical occlusal forces. With the center of rotation of the tooth acting as a fulcrum, the surface of bone adjacent to the pressured side of the tooth will undergo resorption and disappear, while the surface of bone adjacent to the tensioned side of the tooth will undergo apposition and increase in volume.^[4] When the amount of root remaining in the bone is so short that the entire surface of bone adjacent to the root surface is constantly under compression or tension (with no middle section acting as a stabilizer for the fulcrum), the prognosis for the tooth is deemed highly unfavorable. This is usually the outcome associated with untreated secondary occlusal trauma.

· Curve of spee

In anatomy, the Curve of Spee (called also von Spee's curve or Spee's curvature) is defined as the curvature of the mandibular occlusal plane beginning at the tip of the lower cuspid and following the buccal cusps of the posterior teeth, continuing to the terminal molar. According to another definition the Curve of Spee is an anatomic curvature of the occlusal alignment of the teeth, beginning at the tip of the lower canine, following the buccal cusps of the natural premolars and molars and continuing to the anterior border of the ramus. It is named for the German embryologist Ferdinand Graf von Spee (1855–1937), who was first to describe the anatomic relations of human teeth in the sagittal plane.

Details

The pull of the main muscle of mastication, the masseter, is at a perpendicular angle with the curve of Spee to adapt for favorable loading of force on the teeth. The long axis of each lower tooth is aligned nearly parallel to their individual arch of closure. The Curve of Spee is, essentially, a series of slipped contact points. It is of importance to orthodontists as it may contribute to an increased overbite. Larry Andrews, in his important paper: Six Keys to Normal Occlusion (1972), stated that a flat or mild curve of Spee was essential to an ideal occlusion.
The Curve of Spee is distinct from the Curve of Wilson, which is the upward (U-shaped) curvature of the maxillary and mandibular occlusal planes in the coronal plane.
The Curve of Spee is basically a part of a circle (8-inch diameter) which has its circumference as the anterior ramus of mandible. Ideally, it is aligned so that a continuation of this arc would extend through the condyles. The curvature of this arc would relate, on average, to part of a circle with a 4-inch radius. It is the only Anteroposterior curve of occlusion.

· Dental surgery

Dental surgery is any of a number of medical procedures that involve artificially modifying dentition, in other words surgery of the teeth and jaw bones.

Contents

Types

Some of the more common are:

Endodontic (surgery involving the pulp or root of the tooth)

Root canal

Pulpotomy The opening of the pulp chamber of the tooth to allow an infection to drain; Usually a precursor to a root canal
Pulpectomy - The removal of the pulp from the pulp chamber to temporarily relieve pain; Usually a precursor to a root canal.

Apicoectomy - A root-end resection. Occasionally a root canal alone will not be enough to relieve pain and the end of the tooth, called the apex, will be removed by entering through the gingiva and surgically extracting the diseased material.

Prosthodontics (dental prosthetics)

Crowns (caps) — artificial coverings of the tooth made from a variety of biocompatible materials, including CMC/PMC (ceramic/porcelain metal composite), gold or a tin/aluminum mixture. The underlying tooth must be reshaped to accommodate these fixed restorations
Veneers — artificial coverings similar to above, except that they only cover the forward (labial or buccal) surface of the tooth. Usually for aesthetic purposes only.
Bridges — a fixed prothesis in which two or more crowns are connected together, which replace a missing tooth or teeth through a bridge. Typically used after an extraction.
Implants — a procedure in which a titanium implant is surgically placed in the bone (mandible or maxilla), allowed to heal, and 4-6 months later an artificial tooth is connected to the implant by cement or retained by a screw.
Dentures (false teeth) — a partial or complete set of dentition which either attach to neighboring teeth by use of metal or plastic grasps or to the gingival or palatial surface by use of adhesive.
Implant-supported prosthesis — a combination of dentures and implants, bases are placed into the bone, allowed to heal, and metal appliances are fixed to the gingival surface, following which dentures are placed atop and fixed into place.

Orthodontic treatment

Implants and implant-supported prosthesis — also an orthodontic treatment as it involves bones
Apiectomy — also an orthodontic treatment as part of the underlying bone structure must be removed.
Extraction — a procedure in which a diseased, redundant, or problematic tooth is removed, either by pulling or cutting out. This procedure can be done under local or general anesthesia and is very common — many people have their wisdom teeth removed before they become problematic.
Fiberotomy — a procedure to sever the fibers around a tooth, preventing it from relapsing.

periodontics

Professional dental care

See also: Oral hygiene

http://upload.wikimedia.org/wikipedia/commons/thumb/2/28/Tooth_polishing_9332.JPG/330px-Tooth_polishing_9332.JPG

Dental hygienist polishing a patient's teeth

Regular tooth cleaning by a dental professional is recommended to remove tartar (mineralized plaque) that may develop even with careful brushing and flossing, especially in areas of the mouth that are difficult to clean. Professional cleaning includes tooth scaling and tooth polishing, as well as debridement if too much tartar has accumulated. This involves the use of various instruments and/or devices to loosen and remove tartar from the teeth. Most dental hygienists recommend having the teeth professionally cleaned at least every six months^[^{citation needed}^].

More frequent cleaning and examination may be necessary during the treatment of many different dental/oral disorders or due to recent surgical procedures such as dental implants. Routine examination of the teeth by a dental professional is recommended at least every year. This may include yearly, select dental X-rays. See also dental plaque identification procedure and removal.

Dental instruments and restorative materials

Main articles: Dental instruments and Dental restorative materials

Dental anesthesia

Main article: Dental anesthesia

Dentists inject anesthetic to block sensory transmission by the alveolar nerves. The superior alveolar nerves are not usually anesthetized directly because they are difficult to approach with a needle. For this reason, the maxillary teeth are usually anesthetized locally by inserting the needle beneath the oral mucosa surrounding the teeth. The inferior alveolar nerve is probably anesthetized more often than any other nerve in the body. To anesthetize this nerve, the dentist inserts the needle somewhat posterior to the patient’s last molar.

· Dentures

Dentures, also known as false teeth, are prosthetic devices constructed to replace missing teeth; they are supported by the surrounding soft and hard tissues of the oral cavity. Conventional dentures are removable. However, there are many different denture designs, some which rely on bonding or clasping onto teeth or dental implants. There are two main categories of dentures, the distinction being whether they are used to replace missing teeth on the mandibular arch or on the maxillary arch.

Contents

Causes of tooth loss

Patients can become entirely edentulous (without teeth) for many reasons, the most prevalent being removal because of dental disease typically relating to oral flora control, i.e., periodontal disease and tooth decay. Other reasons include tooth developmental defects caused by severe malnutrition, genetic defects such as dentinogenesis imperfecta, trauma, or drug use.

Advantages

Dentures can help patients through:

Mastication, as chewing ability is improved by replacing edentulous areas with denture teeth.
Aesthetics, because the presence of teeth gives a natural appearance to the face, and wearing a denture to replace missing teeth provides support for the lips and cheeks and corrects the collapsed appearance that results from the loss of teeth.
Pronunciation, because replacing missing teeth, especially the anteriors, enables patients to speak better. There is especially improvement in pronouncing words containing sibilants or fricatives.
Self-esteem, because improved looks and speech boost confidence in the ability to interact socially.

Types

Removable partial dentures

Removable partial dentures are for patients who are missing some of their teeth on a particular arch. Fixed partial dentures, also known as "crown and bridge" dentures, are made from crowns that are fitted on the remaining teeth. They act as abutments and pontics and are made from materials resembling the missing teeth. Fixed bridges are more expensive than removable appliances but are more stable.

Another option in this category is the Flexible partial, which is widely considered to be the most comfortable. The final restoration can now be made very quickly with innovations in digital technology. Flexible partials are becoming much more popular due to their aesthetic qualities. While the cost may be higher than a partial made with visible metal clasps, the results of the flexible partial are beautiful, with high levels of satisfaction. Flexible partial fabrication involves only non-invasive procedures, and serves as a virtually invisible tooth replacement option.

Complete dentures

Complete dentures are worn by patients who are missing all of the teeth in a single arch (i.e., the maxillary (upper) or mandibular (lower) arch).

History

Around 500 BC, Etruscans in northern Italy made dentures out of human or other animal teeth.

London's Peter de la Roche is believed to be one of the first 'operators for the teeth', men who advertised themselves as specialists in dental work. They were often professional goldsmiths, ivory turners or students of barber-surgeons.^[1] US President George Washington is famously known for his dentures, which were made with ivory from hippos and elephants as well as gold, rivets, spiral springs and even real human teeth.^[2]

The first porcelain dentures were made around 1770 by Alexis Duchâteau. In 1791, the first British patent was granted to Nicholas Dubois De Chemant, previous assistant to Duchateau, for 'De Chemant's Specification',

"a composition for the purpose of making of artificial teeth either single double or in rows or in complete sets, and also springs for fastening or affixing the same in a more easy and effectual manner than any hitherto discovered which said teeth may be made of any shade or colour, which they will retain for any length of time and will consequently more perfectly resemble the natural teeth."

He began selling his wares in 1792, with most of his porcelain paste supplied by Wedgwood.^[3][4]

In 1820, Samuel Stockton, a goldsmith by trade, began manufacturing high-quality porcelain dentures mounted on 18-carat gold plates. Later dentures from the 1850s on were made of Vulcanite, a form of hardened rubber (Claudius Ash’s company was the leading European manufacturer of dental Vulcanite) into which porcelain teeth were set. In the 20th century, acrylic resin and other plastics were used.^[5] In Britain sequential Adult Dental Health Surveys revealed that in 1968 79% of those aged 65–74 had no natural teeth; by 1998, this proportion had fallen to 36%.^[6]

Fabrication of complete dentures

Modern dentures are most often fabricated in a commercial dental laboratory or by a denturist using a combination of tissue shaded powders polymethylmethacrylate acrylic (PMMA). These acrylics are available as heat cured or cold cured types. Commercially produced acrylic teeth are widely available in hundreds of shapes and tooth colors.

The process of fabricating a denture usually begins with an initial dental impression of the maxillary and mandibular ridges. Standard impression materials are used during the process. The initial impression is used to create a simple stone model that represents the maxillary and mandibular arches of the patient's mouth. This is not a detailed impression at this stage. Once the initial impression is taken, the stone model is used to create a 'Custom Impression Tray' which is used to take a second and much more detailed and accurate impression of the patient's maxillary and mandibular ridges. Polyvinylsiloxane impression material is one of several very accurate impression materials used when the final impression is taken of the maxillary and mandibular ridges. A wax rim is fabricated to assist the dentist or denturist in establishing the vertical dimension of occlusion. After this, a bite registration is created to marry the position of one arch to the other.

Once the relative position of each arch to the other is known, the wax rim can be used as a base to place the selected denture teeth in correct position. This arrangement of teeth is tested in the mouth so that adjustments can be made to the occlusion. After the occlusion has been verified by the dentist or denturist and the patient, and all phonetic requirements are met, the denture is processed.

Processing a denture is usually performed using a lost-wax technique whereby the form of the final denture, including the acrylic denture teeth, is invested in stone. This investment is then heated, and when it melts the wax is removed through a spruing channel. The remaining cavity is then either filled by forced injection or pouring in the uncured denture acrylic, which is either a heat cured or cold-cured type. During the processing period, heat cured acrylics—also called permanent denture acrylics—go through a process called polymerization, causing the acrylic materials to bond very tightly and taking several hours to complete. After a curing period, the stone investment is removed, the acrylic is polished, and the denture is complete. The end result is a denture that looks much more natural, is much stronger and more durable than a cold cured temporary denture, resists stains and odors, and will last for many years.

Cold cured or cold pour dentures, also known as temporary dentures, do not look very natural, are not very durable, tend to be highly porous and are only used as a temporary expedient until a more permanent solution is found. These types of dentures are inferior and tend to cost much less due to their quick production time (usually minutes) and low cost materials. It is not suggested that a patient wear a cold cured denture for a long period of time, for they are prone to cracks and can break rather easily.

Problems with complete dentures

Problems with dentures may arise because patients are not used to having something in their mouth that is not food. The brain senses the appliance and interprets it as 'food', sending messages to the salivary glands to produce more saliva and to secrete it at a higher rate. This usually only happens in the first 12 to 24 hours, after which the salivary glands return to their normal output. New dentures can also be the cause of sore spots as they compress the denture bearing soft tissues (mucosa). A few denture adjustments in the days following insertion of the dentures can take care of this problem. Gagging is another problem encountered by a minority of patients. At times, this may be due to a denture that is too loose, too thick or extended too far posteriorly onto the soft palate. At times, gagging may also be attributed to psychological denial of the denture. Psychological gagging is the most difficult to treat since it is out of the dentist's control. In such cases, an implant-supported palateless denture may have to be constructed. Sometimes there could be a gingivitis infection under the completed dentures, caused by the accumulation of dental plaque. One of the most common problems for wearers of new upper complete denture is a loss of taste sensations.

Prosthodontic principles

Support

Support is the principle that describes how well the underlying mucosa (oral tissues, including gums) keeps the denture from moving vertically towards the arch in question during chewing, and thus being excessively depressed and moving deeper into the arch. For the mandibular arch, this function is provided primarily by the buccal shelf, a region extending laterally from the back or posterior ridges, and by the pear-shaped pad (the most posterior area of keratinized gingival formed by the scaling down of the retro-molar papilla after the extraction of the last molar tooth). Secondary support for the complete mandibular denture is provided by the alveolar ridge crest. The maxillary arch receives primary support from the horizontal hard palate and the posterior alveolar ridge crest. The larger the denture flanges (that part of the denture that extends into the vestibule), the better the stability (another parameter to assess fit of a complete denture). Long flanges beyond the functional depth of the sulcus are a common error in denture construction, often (but not always) leading to movement in function, and ulcerations (denture sore spots).

Stability

Stability is the principle that describes how well the denture base is prevented from moving in a horizontal plane, and thus sliding from side to side or front to back. The more the denture base (pink material) is in smooth and continuous contact with the edentulous ridge (the hill upon which the teeth used to reside, but now only residual alveolar bone with overlying mucosa), the better the stability. Of course, the higher and broader the ridge, the better the stability will be, but this is usually a result of patient anatomy, barring surgical intervention (bone grafts, etc.).

Retention

Retention is the principle that describes how well the denture is prevented from moving vertically in the opposite direction of insertion. The better the topographical mimicry of the intaglio (interior) surface of the denture base to the surface of the underlying mucosa, the better the retention will be (in removable partial dentures, the clasps are a major provider of retention), as surface tension, suction and friction will aid in keeping the denture base from breaking intimate contact with the mucosal surface. It is important to note that the most critical element in the retentive design of a maxillary complete denture is a complete and total border seal (complete peripheral seal) in order to achieve 'suction'. The border seal is composed of the edges of the anterior and lateral aspects and the posterior palatal seal. The posterior palatal seal design is accomplished by covering the entire hard palate and extending not beyond the soft palate and ending 1–2 mm from the vibrating line.

Implant technology can vastly improve the patient's denture-wearing experience by increasing stability and preventing bone from wearing away. Implants can also aid retention. Instead of merely placing the implants to serve as blocking mechanism against the denture's pushing on the alveolar bone, small retentive appliances can be attached to the implants that can then snap into a modified denture base to allow for tremendously increased retention. Available options include a metal "Hader bar" or precision balls attachments.

Complications and recommendations

The fabrication of a set of complete dentures is a challenge for any dentist/denturist. There are many axioms in the production of dentures that must be understood; ignorance of one axiom can lead to failure of the denture. In the vast majority of cases, complete dentures should be comfortable soon after insertion, although almost always at least two adjustment visits are necessary to remove the cause of sore spots. One of the most critical aspects of dentures is that the impression of the denture must be perfectly made and used with perfect technique to make an accurate model of the patient's edentulous (toothless) gums. The dentist or denturist must use a process called border molding to ensure that the denture flanges are properly extended. An array of problems may occur if the final impression of the denture is not made properly. It takes considerable patience and experience for a dentist to know how to make a denture, and for this reason it may be in the patient's best interest to seek a specialist, either a prosthodontist or denturist, to make the denture. A denturist is a trained and licensed professional who sees patients in need of dentures, partials, relines or repairs. A denturist not only takes the impression, but makes the entire denture in his or her own laboratory. The denturist then schedules a date for the delivery of the finished dentures to the patient. A general dentist may do a good job making dentures, but only if he or she is meticulous and experienced. Many dentists no longer make dentures themselves. but instead take an impression of the patients' mouth and then either send the impressions to a dental laboratory, which could be anywhere in the world, or send the patient to a denturist. Once the laboratory receives dental impressions of the patient's mouth, the laboratory creates plaster molds from them. The laboratory uses the molds to create the wax rims used to register the patient's bite. These wax rims are returned to the dentist, who uses them to register the patient's bite. The dentist may assist the patient in choosing the correct size of teeth for the dentures, or simply make the selection himself. Once bite registration is completed and the teeth are selected for the dentures, the wax rim is usually returned to the dental laboratory in order to have the denture teeth set into the wax. Once the teeth are set into the wax rim, the result is a prefinished denture that looks almost like the finished product. This prefinished denture is usually returned to the dentist's office and the patient usually has a chance to approve the setup (for immediate or standard dentures) or to try the denture before it is finished. After approval by the patient, the dentist returns the pre-denture to the laboratory for final processing. The finished denture is the returned to the dentist's office for delivery to the patient.

The maxillary denture (the top denture) is usually relatively straightforward to manufacture so that it is stable without slippage.

A lower complete denture should or must be supported by two to four implants placed in the lower jaw for support. An implant-supported lower denture is far superior to a lower denture without implants, because:

It is much more difficult to get adequate suction on the lower jaw.
The functioning of the tongue tends to break that suction, and
Without teeth the ridge tends to resorb and provides the denture less and less stability over time. It is routine to be able to bite into an apple or corn-on-the-cob with a lower denture anchored by implants. Without implants, this is quite difficult or even impossible.

In any case, implant-supported dentures have several advantages over conventional dentures.^[7] They offer improved comfort due to less irritation of the gums, confidence due to less risk of slipping out, and appearance due to less plastic required for retention purposes. Patients with implant-supported dentures have increased chewing efficacy and can speak more clearly.^[8]

However, like anything, there is a downside. Implant dentures tend to be fairly expensive. A cost of $15,000 to $30,000 for complete upper and lower implant dentures is not uncommon. Most dental insurance plans do not cover the total cost of implant dentures. Possible rejection of the implanted abutment can happen. If there is not enough bone, bone grafting may be required. Minimally invasive surgery may also be required. Treatment time can vary from three to six months.

In cases where a patient needs a complete upper and lower set of dentures, costs can be reduced by having a conventional non-implanted upper denture, since retention of upper dentures is much easier to achieve, and an implanted lower denture, since lower dentures tend not to fit as well otherwise.

Some patients who believe they have 'bad teeth' may consider having all of them extracted and replaced with complete dentures. However, statistics show that most patients who receive this treatment wind up regretting it. This is because complete dentures have only 10% of the chewing power of natural teeth, and it is difficult to get them fitted satisfactorily, particularly in the mandibular arch. Even if a patient retains one tooth there, that one tooth contributes significantly to the stability of the denture. However, retention of just one or two teeth in the upper jaw does not contribute much to the overall stability of a denture, since an upper complete denture tends to be very stable, in contrast to a lower complete denture. It is thus advised that patients keep their natural teeth as long as possible, especially in the case of lower teeth.

Costs

If dentures are medically necessary, insurance might pay 15%-80% of the costs (up to the plan's annual limit, if there is one). Some dental plans cover some of the cost of purchasing dentures and are typically determined by the fee guide of the regional dental legal authority.^[9] In countries where denturism is legally performed by denturists it is typically the denturist association that publishes the fee guide, in countries where it is performed by dentists, it is typically the dental association that publishes the fee guide. Some governments also provide additional coverage for the purchase of dentures by seniors. ^[10] Typically, only standard low-cost dentures are covered by insurance and because many individuals would prefer to have a premium cosmetic denture or a premium precision denture they rely on consumer dental patient financing options.^[11]

A low-cost denture starts at about $300–$500 per denture, or $600–$1,000 for a complete set of upper and lower dentures. These tend to be cold cured dentures, which are considered temporary because of the lower quality materials and streamlined processing methods used in their manufacture. In many cases, there is no opportunity to try them on for fit before they are finished. They also tend to look artificial and not as natural as higher quality, higher priced dentures.

A mid-priced (and better quality) heat cured denture typically costs $500–$1,500 per denture or $1,000-$3,000 for a complete set. The teeth look much more natural and are much longer lasting than cold cured or temporary dentures. In many cases, they may be tried out before they are finished to ensure that all the teeth occlude (meet) properly and look esthetically pleasing. These usually come with a 90-day to two-year warranty and in some cases a money back guarantee if the customer is unsatisfied. In some cases, the cost of subsequent adjustments to the dentures is included.

Premium heat cured dentures can cost $2,000-$4,000 per denture, or $4,000-$8,000 or more for a set. Dentures in this price range are usually completely customized and personalized, use high-end materials to simulate the lifelike look of gums and teeth as closely as possible, last a long time and are warranted against chipping and cracking for 5–10 years or longer. Often the price includes several follow-up visits to fine-tune the fit.

Care

Daily cleaning of dentures is recommended. Plaque and tartar can build up on false teeth, just as they do on natural teeth.^[12] Cleaning can be done using chemical or mechanical denture cleaners.

Fillings can be applied to decayed dentures - which may be the result of failure to clean.

When fillings are needed in dentures, it is standard practice to use amalgam. Bridge work on dentures can be complicated and costly, however.

· Fixed prosthodontics

Fixed prosthodontics in dentistry is a technique used to restore teeth, using fixed (that is, permanently attached) restorations (also referred to as indirect restorations), which include crowns, bridges, inlays, onlays, and veneers. Prosthodontists are specialist dentists who have undertaken training recognized by academic institutions in this field. Fixed prosthodontics can be used to restore single or multiple teeth, spanning areas where teeth have been lost. In general, the main advantages of fixed prosthodontics when compared to direct restorations is the superior strength when used in large restorations, and the ability to create an aesthetic looking tooth. As with any dental restoration, principles used to determine the appropriate restoration involves consideration of the materials to be used, extent of tooth destruction, orientation and location of tooth, and condition of neighboring teeth.

Contents

1 Preparation techniques

2 Restoration types

3 See also

Preparation techniques

Preparation of a tooth for a crown involves the irreversible removal of a significant amount of tooth structure. All restorations possess compromised structural and functional integrity when compared to healthy, natural tooth structure. Thus, if not indicated as desirable by an oral health-care professional, the crowning of a tooth would most likely be contraindicated. It should be evident, though, that dentists trained at different institutions in different eras and in different countries might very well possess different methods of treatment planning and case selection, resulting is somewhat diverse recommendations for treatment.

Dimensions of preparation

When preparing a tooth for a crown, the preparation should, ideally, exist entirely in enamel. As elaborated on below, the amount of tooth structure required to be removed will depend on the material(s) being used to restore the tooth. If the tooth is to be restored with a full gold crown, the restoration need only be .5 mm in thickness (as gold is very strong), and therefore, a minimum of only .5 mm of space needs to be made for the crown to be placed. If porcelain is to be applied to the gold crown, an additional minimum of 1 mm of tooth structure needs to be removed to allow for a sufficient thickness of the porcelain to be applied, thus bringing the total tooth reduction to minimally 1.5 mm.for porcelin or ceramic crowns the amount of tooth reduction is 2mm.for metal it is 1mm.

If there is not enough tooth structure to properly retain the prosthetic crown, the tooth requires a build-up material. This can be accomplished with a pin-retained direct restoration, such as amalgam or a resin like fluorocore, or in more severe cases, may require a post and core. Should the tooth require a post and core, endodontic therapy would then be indicated, as the post descends into the devitalized root canal for added retention. If the tooth, because of its relative lack of exposed tooth structure, also requires crown lengthening, the total combined time, effort and cost of the various procedures, together with the decreased prognosis because of the combined inherent failure rates of each procedure, might make it more reasonable to have the tooth extracted and opt to have an implant placed.

Taper

The prepared tooth also needs to possess a certain degree of taper to allow for the restoration to be properly placed on the tooth. Fundamentally, there can be no undercuts on the surface of the prepared tooth, as the restoration will not be able to be removed from the die, let alone fit on the tooth (see explanation of lost-wax technique below for understanding of the processes involved in crown fabrication). At the same time, though, too much taper will severely limit the grip that the crown has while on the prepared tooth, thus contributing to failure of the restoration. Generally, 6° of taper around the entire circumference of the prepared tooth, giving a combined taper of 12° at any given sagittal section through the prepared tooth, is appropriate to both allow the crown to fit yet provide enough grip.

Margin

The most coronal position of untouched tooth structure (that is, the continual line of original, undrilled tooth structure at or near the gumline) is referred to as the margin. This margin will be the future continual line of tooth-to-restoration contact, and should be a smooth, well-defined delineation so that the restoration, no matter how it is fabricated, can be properly adapted and not allow for any openings visible to the naked eye, however slight. An acceptable distance from tooth margin to restoration margin is anywhere from 40-100 nm. However, the R.V. Tucker method of gold inlay and onlay restoration produces tooth-to-restoration adaptation of potentially only 2 nm, confirmed by scanning electron microscopy; this is less than the diameter of a single bacterium.

Naturally, the tooth-to-restoration margin is an unsightly thing to have exposed on the visible surface of a tooth when the tooth exists in the esthetic zone of the smile. In these areas, the dentist would like to place the margin as far apical (towards the root tip of the tooth) as possible, even below the gum line. While there is no issue, per se, with placing the margin at the gumline, problems may arise when placing the margin too subgingivally (below the gumline). First, there might be issues in terms of capturing the margin in an impression to make the stone model of the prepared tooth (see stone model replication of tooth in photographs, above). Secondly, there is the seriously important issue of biologic width. Biologic width is the mandatory distance to be left between the height of the alveolar bone and the margin of the restoration, and if this distance is violated because the margin is placed too subgingivally, serious repercussions may follow. In situations where the margin cannot be placed apically enough to provide for proper retention of the prosthetic crown on the prepared tooth structure, the tooth or teeth involved should undergo a crown lengthening procedure.

Ferrule effect

The single most important consideration when restoring with a crown is, undeniably, the incorporation of the ferrule effect. As with the bristles of a broom, which are grasped by a ferrule when attached to the broomstick, the crown should envelop a certain height of tooth structure to properly protect the tooth from fracture after being prepared for a crown. This has been established through multiple experiments as a mandatory continuous circumferential height of 2mm; any less provides for a significantly higher failure rate of endodontically-treated crown-restored teeth. When a tooth is not endodontically treated, the remaining tooth structure will invariably provide the 2mm height necessary for a ferrule, but endodontically treated teeth are notoriously decayed and are often missing significant solid tooth structure. Contrary to popular belief, endodontically treated teeth are not brittle after being devitalized according to the following study -CM Sedglay & Messer 1992 Journal of Endodontics. Contrary to what some dentists believe, a bevel is not at all suitable for implementing the ferrule effect, and beveled tooth structure may not be included in the 2 mms of required tooth structure for a ferrule.

Restoration types

Crown

Main article: Crown (dentistry)

A crown is used to cover a tooth and may be commonly referred to as a "cap." Traditionally, the teeth to be crowned are prepared by a dentist, and records are given to a dental technician to construct the prosthesis. The records include models, which are replicas of a patient's teeth, and the impressions used to make these models. There are many different methods of crown fabrication, each using a different material. Some methods are quite similar, and utilize either very similar or identical materials. Crowns may be made of gold or other similar metals, porcelain, or a combination of the two. Crowns made of Zirkonia Oxide are being made more popular due to its high translucency and durability as opposed to chipping disadvantages of porcelain crowns.

Bridge

Main article: Bridge (dentistry)

A bridge is used to span, or bridge, an edentulous area (space where teeth are missing), usually by connecting to fixed restorations on adjacent teeth. The teeth used to support the bridge are called abutments. A bridge may also refer to a single-piece multiple unit fixed partial denture (numerous single-unit crowns either cast or fused together). The part of the bridge which replaces a missing tooth and attaches to the abutments is known as a "pontic." For multiple missing teeth, some cases may have several pontics.

Inlay

Main article: Inlays and onlays

An inlay is a restoration which lies within the confines of the cusps. These restorations are considered to be more conservative than onlays or crowns because less tooth structure is removed in preparation for the restoration. They are usually used when tooth destruction is less than half the distance between cusp tips.

Onlay

Main article: Inlays and onlays

An onlay is a method of tooth restoration, which covers, protects or reinforces one or more cusps. Onlays are methods for restoring teeth in an indirect way. Onlays are often used when teeth present extensive destruction due to caries or to trauma.

Veneer

Main article: Veneer (dentistry)

A veneer is a thin layer of restorative material placed over a tooth surface, either to improve the esthetics of a tooth, or to restore a damaged tooth surface. Materials used for veneers may include composite and porcelain. In some cases, removal of tooth structure is needed to provide sufficient space for the veneer, whereas sometimes a restoration may be bonded to a tooth without preparation of the tooth.

· Inlays and onlays

In dentistry, an inlay is an indirect restoration (filling) consisting of a solid substance (as gold, porcelain or less often a cured composite resin) fitted to a cavity in a tooth and cemented into place.^[1] An onlay is the same as an inlay, except that it extends to replace a cusp. Crowns are onlays which completely cover all surfaces of a tooth.

Contents

1 Inlays

1.1 Comparison of Inlays and direct fillings

Inlays

http://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/Inlay_imp.JPG/450px-Inlay_imp.JPG

An impression of preparation for restoration with a DO gold inlay on tooth #5. The "DO" designation indicates that the gold serves as a restoration for the distal and occlusal surfaces of the tooth. This tooth was prepared and the inlay will be fabricated according to the R.V. Tucker method of gold inlay preparation. Notice how the line angles of the impression for the inlay are very sharp and precise; this is achieved using carbon-tipped stainless steel instruments. The salmon-colored polyvinylsiloxane impression material is less viscous than the blue and is able to capture better detail for the tooth being restored.

Sometimes, a tooth is planned to be restored with an intracoronal restoration, but the decay or fracture is so extensive that a direct restoration, such as amalgam or composite, would compromise the structural integrity of the restored tooth or provide substandard opposition to occlusal (i.e., biting) forces. In such situations, an indirect gold or porcelain inlay restoration may be indicated.

Comparison of Inlays and direct fillings

When an inlay is used, the tooth-to-restoration margin may be finished and polished to a very fine line of contact to minimize recurrent decay. Opposed to this, direct composite filling pastes shrink a few percent in volume during hardening. This can lead to shrinkage stress and rarely to marginal gaps and failure. Although improvements of the composite resins could be archived in the last years, solid inlays do exclude this problem.^[2] Another advantage of inlays over direct fillings is that there is almost no limitations in the choice of material. While inlays might be ten times the price of direct restorations, it is often expected that inlays are superior in terms of resistance to occlusal forces, protection against recurrent decay, precision of fabrication, marginal integrity, proper contouring for gingival (tissue) health, and ease of cleansing offers. However, this might be only the case for gold. While short term studies come to inconsistent conclusions, a respectable number of long-term studies detect no significantly lower failure rates of ceramic ^[3] or composite ^[4] inlays compared to composite direct fillings. Another study detected an increased survival time of composite resin inlays but it was rated to not necessarily justify their bigger effort and price. ^[5]

http://upload.wikimedia.org/wikipedia/commons/6/67/MO_inlay_of_3.jpg

An MO gold inlay on tooth #3, the "MO" designation indicating that the gold serves as a restoration for the mesial and occlusal surfaces of the tooth. This tooth was also restored according to the R.V. Tucker method. Notice how the gold appears to flow into the tooth structure, almost perfectly mimicking the natural contours and even allowing the specular reflection to continue over the margin from tooth to gold.

Onlays

When decay or fracture incorporate areas of a tooth that make amalgam or composite restorations inadequate, such as cuspal fracture or remaining tooth structure that undermines perimeter walls of a tooth, an onlay might be indicated. Similar to an inlay, an onlay is an indirect restoration which incorporates a cusp or cusps by covering or onlaying the missing cusps. All of the benefits of an inlay are present in the onlay restoration. The onlay allows for conservation of tooth structure when the only alternative is to totally eliminate cusps and perimeter walls for restoration with a crown. Just as inlays, onlays are fabricated outside of the mouth and are typically made out of gold or porcelain. Gold restorations have been around for many years and have an excellent track record. In recent years, newer types of porcelains have been developed that seem to rival the longevity of gold. If the onlay or inlay is made in a dental laboratory, a temporary is fabricated while the restoration is custom-made for the patient. A return visit is then required to fit the final prosthesis. Inlays and onlays may also be fabricated out of porcelain and delivered the same day utilizing techniques and technologies relating to CAD/CAM dentistry. ^[6]

· Removable partial dentur

A removable partial denture (RPD) is for a partially edentulous dental patient who desires to have replacement teeth for functional or aesthetic reasons, and who cannot have a bridge (a fixed partial denture) for any number of reasons, such as a lack of required teeth to serve as support for a bridge (i.e. distal abutments) or due to financial limitations.

The reason why this type of prosthesis is referred to as a removable partial denture is because patients can remove and reinsert them when required without professional help. Conversely, a "fixed" prosthesis can and should be removed only by a dental professional.

Contents

Partially edentulous conditions

Depending on where in the mouth teeth are missing, edentulous situations can be grouped under four different categories, as defined by Dr. Edward Kennedy in his classification of partially edentulous arches.

Class I (bilateral free ended partially edentulous)
Class II (unilateral free ended partially edentulous)
Class III (unilateral bounded partially edentulous)
Class IV (bilateral bounded anterior partially edentulous)

Kennedy Class I RPDs are fabricated for people who are missing some or all of their posterior teeth on both sides (left and right) in a single arch (either mandibular or maxillary), and there are no teeth posterior to the edentulous area. In other words, Class I RPDs clasp onto teeth that are more towards the front of the mouth, while replacing the missing posterior teeth on both sides with false denture teeth. The denture teeth are composed of either plastic or porcelain.

Class II RPDs are fabricated for people who are missing some or all of their posterior teeth on one side (left or right) in a single arch, and there are no teeth behind the edentulous area. Thus, Class II RPDs clasp onto teeth that are more towards the front of the mouth, as well as on teeth that are more towards the back of the mouth of the side on which teeth are not missing, while replacing the missing more-back-of-the-mouth teeth on one side with false denture teeth.

Class III RPDs are fabricated for people who are missing some teeth such that the edentulous area has teeth remaining both posterior and anterior to it. Unlike Class I and Class II RPDs which are both tooth-and-tissue-borne (meaning they both clasp onto teeth, as well as rest on the posterior edentulous area for support), Class III RPDs are strictly tooth-borne, which means they only clasp onto teeth and do not need to rest on the tissue for added support. This makes Class III RPDs exceedingly more secure as per the three rules of removable prostheses that will be mentioned later, namely: support, stability and retention. (See the article on dentures for a more thorough review of these three fundamentals of removable prosthodontics.)

However, if the edentulous area described in the previous paragraph crosses the anterior midline (that is, at least both central incisors are missing), the RPD is classified as a Class IV RPD. By definition, a Kennedy Class IV RPD design will possess only one edentulous area.

Class I, II and III RPDs that have multiple edentulous areas in which replacement teeth are being placed are further classified with modification states that were defined by Oliver C. Applegate. Kennedy classification is governed by the most posterior edentulous area that is being restored. Thus, if, for example, a maxillary arch is missing teeth #1, 3, 7-10 and 16, the RPD would be Kennedy Class III mod 1. It would not be Class I, because missing third molars are generally not restored in an RPD (although if they were, the classification would indeed be Class I), and it would not be Class IV, because modification spaces are not allowed for Kennedy Class IV.

Components of an RPD

Rather than lying entirely on the edentulous ridge like complete dentures, removable partial dentures possess clasps of metal or plastic that "clip" onto the remaining teeth, making the RPD more stable and retentive.

The parts of an RPD can be listed as follows (and are exemplified by the picture above):

Major Connector (the thick metal "U" in the RPD above is a lingual bar, a type of major connector)
Minor Connector (the small struts protruding from the lingual bar at roughly 90 degree angles)
Direct Retainer (examples are in the upper left of upper photo and lower right of lower photo; the clasp arms act to hug the teeth and keep the RPD in place. The metal clasp and rest immediately adjacent to the denture teeth is also a direct retainer.)
Indirect Retainer (example is the little metal piece coming off the "U" at a 90 degree angle near the top of the upper photo, which is a cingulum rest on a canine.)

Physical Retainer (this is a mesh of metal that allows the pink base material to connect to the metal framework of the RPD. Some consider physical retainers their own component (making a total of seven), while others consider them within the indirect retainer category (thus making a total of six components.)

Base (the pink material, mimicking gingiva)
Teeth (plastic or porcelain formed in the shape of teeth)

Clasp design

Direct retainers may come in various designs:

Cast circumferential clasp (suprabulge)

Akers'
Half and half
Back-action
Ring clasp

Wrought wire clasp
Roach clasp (infrabulge)

I-bar
T-bar
Y-bar
7-bar

Both cast circumferential and wrought wire clasps are suprabulge clasps, in that they engage an undercut on the tooth by originating coronal to the height of contour, while Roach clasps are infrabulge clasps and engage undercuts by approaching from the gingival.

In addition there are a couple of specific theories which include the clasp design:

RPI: mesial rest, distolingual guide plate, I-bar

The RPI design was made for clasping a bilateral free end extension. These clasps are unique because they have to take into account extra torque force due to being tissue borne (and not tooth borne) at the posterior.
Described by Kratochvil in 1963 and modified by Krol in 1973

Kratochvil designed the abutment tooth with a long rest (from the mesial marginal ridge to the distal pit), long guide plane, and a regular I-bar clasp.
Krol modified this design with a short occlusal rest, short guide plane (touching only from occlusal to middle third), and a mesial-shifted I-bar. The theory behind Krol's decision was to allow for movement of the partial denture without placing too much torque on the abutment tooth.

An illustration of the RPI design function

RPA: mesial rest, distolingual guide plate, Akers' clasp-style retentive arm
RPC: mesial rest, distolingual guide plate, other type of cast circumferential clasp

So named in response to the RPI Philosophy introduced by Kratochvil and Kroll

APPENDIX COMMON TERMS IN DENTISTRY

Terms

http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Directions.jpg/450px-Directions.jpg

This X-ray film depicts some of the teeth in the lower right quadrant. The arrows point in the following directions: distal ←, mesial →, coronal ↑, apical ↓.

Anterior

the direction towards the front of the head or the lips, as opposed to posterior, which refers to the directions towards the back of an individual's head. The term anterior teeth refers to incisors and canines, as opposed to premolars and molars, which are posterior teeth.^[1]

Apical

The direction towards the root tip(s) of a tooth, as opposed to coronal, which refers to the direction towards the crown. It may also refer to something relating to the roots, such as apical support. When referring to direction in relation to entities on or of the crown, this term can be synonymous with both cervical and gingival.^[1]

Axial

A plane parallel to the surface of a tooth. For example, if a drill bur would be inserted into a tooth from any side (proximal, facial or lingual), the depth of the hole is defined by the axial wall of the hole.^[1]

Buccal

The side of a tooth that is adjacent to (or the direction towards) the inside of the cheek, as opposed to lingual or palatal, which refer to the side of a tooth adjacent to (or the direction towards) the tongue or palate, respectively. Although technically referring only to posterior teeth (where the cheeks are present instead of lips, use of this term may extend to all teeth, anterior and posterior), this term may be employed to describe the facial surface of (or directions in relation to) anterior teeth as well.^[1]

Cervical

Means neck in Latin (as in cervical vertebrae), and refers to the narrowing of the contours of the tooth surface at or near the CEJ, where the crown meets the root. When referring to direction in relation to entities on or of the crown, it is nearly synonymous with both apical and gingival.^[1]

Coronal

The direction towards the crown of a tooth, as opposed to apical, which refers to the direction towards the tip(s) of the root(s). It may also refer to something relating to the crown, such as coronal forces.^[1]

Distal

The direction towards the last tooth in each quadrant of a dental arch, as opposed to mesial, which refers to the direction towards the anterior midline. Each tooth can be described as having a distal surface and, for posterior teeth, a distobuccal (DB) and a distolingual (DL) corner or cusp.^[1]

http://upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Occlusal_of_denture_-_mod.jpg/450px-Occlusal_of_denture_-_mod.jpg

This photo shows an occlusal view of a complete maxillary denture. The green line, indicating the dental midline, is the defining line when it comes to mesial-distal direction. The blue arrow, which indicates a mesial direction, applies to the opposite side as well up until the green line. The red arrow is directly buccal to the right first maxillary molar, and the patient's name (Martin) label is embedded in the resin directly palatal to the same tooth.

Facial

The side of a tooth that is adjacent to (or the direction towards) the inside of the cheek or lips, as opposed to lingual or palatal, which refer to the side of a tooth adjacent to (or the direction towards) the tongue or palate, respectively. This term is an umbrella term for both the term buccal and labial.^[1]

Gingival

The direction towards the gingiva (gums), synonymous with cervical and similar to apical. However, locations on teeth already more apical to the interface of the crown and root, referred to as the CEJ, tend not to be described using this term, as it would lead to confusion, as the exact definition is ambiguous. Additionally, this term would not be used when referring to a tooth ex vivo.^[1]

Incisal

Either the direction towards the biting edge of anterior teeth, or to something relating to this edge, such as the terms incisal guidance or incisal edge. This is the sister term to occlusal, which related to the analogous location on posterior teeth.^[1]

Inferior

The direction towards the feet of a human's body, as opposed to superior, which refers to the direction towards the head. However, use of these terms should enjoy only limited usage when discussing features of a tooth, as, for example, something more inferior on a mandibular tooth will be situated more superior on a maxillary tooth, as they exhibit an inverted relationship. It is for this reason that the terms coronal and apical are substituted.^[1]

Interproximal

An adjective meaning between teeth. For example, interproximal teeth refers to the space between adjacent teeth.^[2][1]

Labial

The side of a tooth that is adjacent to (or the direction towards) the inside of the lip, as opposed to lingual or palatal, which refer to the side of a tooth adjacent to (or the direction towards) the tongue or palate, respectively. Although technically referring only to anterior teeth (where the lips are present instead of cheeks), use of the term buccal may extend to all teeth, anterior and posterior.^[2][1]

Lingual

The side of a tooth adjacent to (or the direction towards) the tongue, as opposed to buccal, labial, or facial which refer to the side of a tooth adjacent to (or the direction towards) the inside of the cheek or lips, respectively. Although this term is technically specific to the mandible, it enjoys extensive use in reference to the maxilla as well (see Palatal.)^[2][1]

Mandibular

Entities related to the mandible, or lower jaw.^[1]

Marginal

A number of different 'margins' that are involved in dentistry. The edge of tooth structure that is prepared to meet the edge of a prosthetic crown is called a margin, as is the aforementioned edge of the crown; an example of this usage would be "a poorly fitting crown might exhibit marginal leakage." The gingiva and bone that abut the teeth are referred to as 'marginal', as in marginal periodontitis. The bulk of tooth structure on the occlusal surface at the point of contact of posterior teeth is referred to as the marginal ridge.^[1]

Maxillary

Entities related to the maxilla, or upper jaw.^[1]

http://upload.wikimedia.org/wikipedia/commons/thumb/6/67/MO_inlay_of_3.jpg/300px-MO_inlay_of_3.jpg

This photo shows teeth #2-5 (Universal numbering system). Tooth #3, the upper right first molar, has an MO (mesial-occlusal) gold inlay. This molar is both posterior, as well as distal, to the premolars in front of it.

Mesial

The direction towards the anterior midline in a dental arch, as opposed to distal, which refers to the direction towards the last tooth in each quadrant. Each tooth can be described as having a mesial surface and, for posterior teeth, a mesiobuccal (MB) and a mesiolingual (ML) corner or cusp.^[1]

Occlusal

Either the direction towards the biting surface of posterior teeth, or to something relating to this surface, such as the terms occlusal interference or occlusal surface. This is the sister term to incisal, which related to the analogous location on anterior teeth.^[2][1]

Palatal

The side of a tooth adjacent to (or the direction towards) the palate, as opposed to buccal, labial or facial which refer to the side of a tooth adjacent to (or the direction towards) the inside of the cheek or lips, respectively. This term is strictly used in the maxilla.^[1]

Posterior

The direction towards the back of an individual's head, as opposed to anterior, which refers to the directions towards an individual's lips. The term posterior teeth refers to premolars and molars, as opposed to incisors and canines, which are anterior teeth.^[2][1]

Proximal

The surfaces of teeth that normally lie adjacent to another tooth. It is an umbrella term which includes both mesial and distal, such as when referring to the proximal surfaces of teeth.^[1]

Superior

The direction towards the head of a human's body, as opposed to inferior, which refers to the direction towards the feet. However, use of these terms should enjoy only limited use when discussing features of a tooth, as, for example, something more superior on a mandibular tooth will be situated more inferior on a maxillary tooth, as they exhibit an inverted relationship. It is for this reason that the terms coronal and apical are substituted^[1]

IESMBV-DEPARTAMENTODEINGLÉS

Monday, 20 January 2014

INTERMEDIATE REVISION B-1

DENTAL PROSTHETICS

Details