Prosthodontics is a specialty area of dentistry, which deals with the replacement and restoration of extensively damaged or missing teeth. It may be associated with or without replacement of soft tissues.
The field of Prosthodontics can be divided into two main categories termed fixed prosthodontics and removable prosthodontics.
Fixed prosthodontics involves replacing the damaged or missing teeth with crowns and bridges which are cemented into a patient’s mouth.
Removable Prosthodontics replaces missing teeth and soft tissues, utilizing full and partial dentures which can be removed from the mouth by the patient. There are also situations in which a patient needs total mouth restoration requiring a combination of both fixed and removable Prosthodontics.
Prosthodontics also deal with maxillofacial reconstruction which involves reconstruction of head and neck anomalies resulting from congenital, surgical, or traumatic events.
Fixed prosthodontics is the science of restoring severely damaged teeth or replacing missing teeth. This can be accomplished by the fabrication of single unit crowns to restore individual teeth or bridges to replace missing teeth.
There are certain criteria which must be met in order to successfully utilize fixed prosthodontics for oral restoration, which can be evaluated with a thorough diagnosis, by the following methods:
• Patient history
• Full mouth radiographs
• Intraoral examination
• Diagnostic casts mounted on an articulator.
INDICATIONS FOR FIXED PROSTHODONTICS
The fixed Prosthodontics can be indicated in the patients showing the following favourable general conditions:
(a) Good general health.
(b) Controlled health problems.
(c) Adequately controlled oral hygiene.
In addition to these three basic conditions, the prosthodontist also looks for the following:
• Adequate bone structure demonstrated in the radiographic evaluation.
• No apparent radiographic pathosis of teeth or supporting structures,
• Healthy hard and soft tissues that will support the fixed prosthesis.
If any of the above conditions are not met, the success of the fixed restoration may be jeopardized; thus, it must be addressed before any treatment can be implemented.
CONTRAINDICATIONS OF FIXED PROSTHODONTICS
The review process of a patient’s health history can reveal many possible contraindications to a treatment plan with fixed Prosthodontics. Some of the possible contraindications are as follows:
(1) Any undiagnosed or uncontrolled medical and/or dental problem which can jeopardized the success of fixed restoration treatment.
Poor oral hygiene or a periodontal condition. Teeth that are damaged and unrestorable and require extraction or require an endodontic evaluation prior to the definitive restorative work.
(4) Inadequate dentition which can pose grave problems for the longevity of fixed restorations.
(5) Inadequate space for the restorations.
VARIOUS TYPES OF FIXED PROSTHESES
There are the four basic types of fixed prostheses:
The crown is the basic unit of fixed Prosthodontics restorations. The extensively damaged crowns of natural teeth, which need additional restoration beyond basic filling repair, are restored with crown. A full coverage crown may be composed of several different materials including precious metal (gold), non-precious metal, plastics, porcelain, or a combination of metal and porcelain. A crown is used to replace the damaged coronal aspect of a natural tooth. It is permanently cemented to the remaining prepared tooth structure.
Crowns can be used to restore a single tooth or to serve as part of a multiunit bridge. Crowns can be designed in different ways in order to suit the needs of each individual case. Three of the most widely utilized crowns are full cast crowns, partial cast crowns, and the veneer crowns.
Full Cast Crowns
In general, the full cast crown is an all-metal restoration. It can be cast in a variety of metals ranging from non-precious metals (base alloys) to yellow or white gold. Cast crowns can be used where heavy occiusal wear is present, such as the molar area. Also, metal crowns can be used in conjunction with a removable partial denture, in which the crown is known as a survey crown.
Partial Cast Crowns
The partial crown is usually cast in precious metals. As its name implies, it covers less than 100 percent of the crown of a tooth. Common examples are the 3/4 and 7/8 crowns. The preparation of the tooth for the partial cast crown is very meticulous, requiring precise skills by the dental practitioner.
Veneer crowns are full cast metal crowns with a tooth-coloured material applied to the esthetically critical areas. The tooth-coloured material is usually acrylic resin or porcelain. The acrylic resin or porcelain is usually applied on the buccal or facial aspect of the tooth. A veneer crown is used when esthetics is an important issue. This is due to the fact that the veneer material can be matched to the colour of the patient’s natural dentition, thus camouflaging or disguising the presence of the Prosthodontics restoration if done successfully.
A bridge is a prosthetic device used to replace a missing tooth or several teeth. This is done by utilizing a combination of crowns and pontics and linking them together. Abridge is permanently cemented in the patient’s mouth.
A bridge is a definitive restoration used to replace one or more missing teeth. It is cemented in the patient’s mouth and is not easily removed. There are certain criteria that must be met in order for such a procedure to be performed. These are as follows:
1. The area to be replaced must have at least one healthy tooth in front of and one healthy tooth behind the empty space. The soft tissue and bone structure must be adequate and healthy.
2. The patient must be motivated to keep the area healthy and clean to ensure the life of the bridge.
A bridge has three basic components: a retainer, pontic(s), and connectors.
A retainer is the anchoring position of the bridge. It is the portion of the bridge that attaches to the natural, healthy tooth (abutment) next to the space being filled. The retainer usually takes the form of a full coverage crown and is cemented in place.
The pontic is the portion of the bridge that replaces the missing tooth. It is a solid structure, which is attached to the adjacent retainers. It sits in very close proximity to the soft tissue on its gingival side. The occlusal side is fabricated to be anatomically correct. It resembles the surface of a full coverage crown.
The pontic can be constructed in several different forms. The difference is usually in the gingival shape. This shape is dictated by the position of the bridge in the patient’s mouth and the shape of the underlying soft tissue and bone. One of the most common pontic shapes is the sanitary pontic.
The sanitary pontic is usually employed only in posterior areas. As the name suggests, this type of pontic is easy for the patient to clean. It sits in close proximity to the underlying ridge without touching it. It may sit approximately 1 mm above the gingiva to facilitate cleaning or lightly touch the edentulous ridge.
The pontic most often employed for tooth replacement in the anterior regions of the mouth is the modified ridge lap design. This pontic is also convex on the side proximal to the edentulous ridge so that the patient can clean the surface with floss. It lightly contacts the ridge. From the facial view the ridge lap pontic appears to emerge from the gums rendering a natural appearance.
The connector is the link between the other components of the bridge. It links the abutment to the pontic. The connector can be one of two types, rigid or non-rigid.
A rigid connector is a solid mass between pontic and abutment. It is very strong and non-flexible.
It’s used in short bridge spans in both anterior and posterior areas.
A non-rigid connector also links the retainer and the pontic as does a rigid connector. It can be used in more complex and longer span bridges to introduce some flexibility. This allows some play in the bridgework and acts as a stress breaker and reducer.
An inlay is a casted metal or metal restoration utilized to restore a partially damaged tooth, exclusive of its cusps. An inlay can be used when the cusps of the tooth are still intact. It is fabricated by taking an impression of the prepared tooth and sent to a dental laboratory for construction. The completed inlay is then inserted onto the prepared tooth and is permanently cemented.
An onlay has characteristics similar to that of inlay, but it is used to restore a tooth with damaged cusps. Preparation and restoration using a cast onlay is performed similarly to that of an inlay.
THE LABORATORY INSTRUCTIONS
The dental laboratory is a vital part of all prosthetic construction. All facets of the laboratory’s procedures must be done with complete precision to ensure an exact fit for the patient. To accomplish this goal, the laboratory must be given very exact instructions from the dentist.
This information is conveyed to the laboratory in the form of a prescription. The laboratory prescription is the detailed instructions sent to the dental laboratory by the dentist for restoration construction. The prescription contains the following information:
1. Patient Information.
2. Type of Prosthesis.
4. Type of Alloy (Metal).
5. Type of Pontic.
6. Date for return of the step.
7. Dentist’s Information.
Infection control is vital in all aspects of dentistry, with no exception to crown and bridge preparation. Some of the guidelines that are specific to prosthesis fabrication are as follows:
• All impressions must be disinfected upon removal from a patient’s mouth. This includes final impressions, preliminary impressions, impressions of the opposing arch, and bite registrations.
• All casting must be disinfected prior to try-in. Also, once a try-in is completed, the casting must be disinfected before it can be shipped back to the dental laboratory.
• Finally, all packing and wrappings sent with the labwork are removed and discarded by the dentist or lab when the work is received.