Replacement Of Several Missing Teeth

Fixed prosthodontics becomes more difficult when several teeth must be replaced. Problems will be encountered when restoring a single long, uninterrupted edentulous area or multiple edentulous areas with intermediate abutment teeth (Fig. 3-20), especially when anterior and posterior teeth are to be replaced with a single fixed prosthesis. Underestimation of the problems involved in extensive prosthodontics can lead to failure. One key to ensuring a successful result is to plan the prostheses by waxing the intended restorations on articulated diagnostic casts. This is essential for complex fixed prosthodontic treatments, particularly where an irregular occlusal plane is to be corrected, the vertical dimension of occlusion is to be altered, an implant-supported prosthesis is recommended, or a combination of fixed and removable prostheses are to be used. The precise end point of such compli-

Supraeruption Tooth

Fig. 3-19. Square section orthodontic wire can be used as a simple stabilizing appliance to prevent drifting of abutment teeth after exodontia. The wire is retained by placing small restorations. As an alternative, orthodontic bands can be used as the retainer. NOTE: These simple stabilizers do not prevent supraeruption of opposing teeth; in areas where this is anticipated, a provisional FPD is needed.

Fig. 3-19. Square section orthodontic wire can be used as a simple stabilizing appliance to prevent drifting of abutment teeth after exodontia. The wire is retained by placing small restorations. As an alternative, orthodontic bands can be used as the retainer. NOTE: These simple stabilizers do not prevent supraeruption of opposing teeth; in areas where this is anticipated, a provisional FPD is needed.

cated treatments can be far from evident, even to an experienced prosthodontist (see Fig. 2-39).

Overloading of Abutment Teeth. The ability of the abutment teeth to accept applied forces without drifting or becoming mobile must be estimated and has a direct influence on the prosthodontic treatment plan. These forces can be particularly severe during parafunctional grinding and clenching (see Chapter 4), and the need to eliminate them becomes obvious during the restoration of such a damaged dentition. Although it may be hoped that a well-reconstructed occlusion will reduce the duration and strength of any parafunctional activity, there is little scientific evidence to support this. It is unwise to initiate treatment on the assumption that new restorations will reduce parafunctional activity, unless this has been demonstrated with treatment appliances over a significant period .23

Direction ofForces. Whereas the magnitude of any applied force is difficult to regulate, a well-fabricated fixed partial denture can distribute these forces in the most favorable way, directing them in the long axis of the abutment teeth. Potentially damaging lateral forces can be confined to the anterior teeth, where they are reduced by the longer lever arm (see Chapter 4).

Root Surface Area. The root surface area of potential abutment teeth must be assessed when planning treatment for fixed prosthodontics. Ante14 suggested in 1926 that it was unwise to provide a fixed partial denture when the root surface area of the abutment was less than the root surface area of the teeth being replaced; this has been adopted and reinforced by other authors25-27 as Ante's law. Average values for the root surface area of permanent teeth are given in Table 3-1.28 As an example of Ante's law, consider the patient who has lost a first molar and second premolar (Fig. 3-21). In this situation, a four-unit FPD is an acceptable risk, as long as there has not been bone loss from peri-odontal disease, because the second molar and first premolar abutments have root surface areas approximately equal to those of the missing teeth. If the first molar and both premolars are missing, however, an FPD is not considered a good risk because the missing teeth have a greater total root surface area than the potential abutments.

Nyman and Ericsson, 29 however, cast doubt on the validity of Ante's law by demonstrating that teeth with considerably reduced bone support can be successfully used as fixed partial denture abutments. The majority of the treatments presented by

Intermediate Abutment Fixed Prosth

Fig. 3-20. A, A five-unit FPD replacing the maxillary first molar and first premolar. The middle abutment can act as a fulcrum during function, with possible unseating of one of the other abutments. To be successful, this type of FPD needs extremely retentive retainers. B, An alternative approach is a nonrigid dovetail connector between the molar pontic and the second premolar. C, Where periodontal support is adequate, a much simpler approach would be to cantilever the first premolar pontic. (Redrawn from Rosenstiel SF: In Rayne J editor: General dental treatment, London, 1983, Kluwer Publishing.)

Fig. 3-20. A, A five-unit FPD replacing the maxillary first molar and first premolar. The middle abutment can act as a fulcrum during function, with possible unseating of one of the other abutments. To be successful, this type of FPD needs extremely retentive retainers. B, An alternative approach is a nonrigid dovetail connector between the molar pontic and the second premolar. C, Where periodontal support is adequate, a much simpler approach would be to cantilever the first premolar pontic. (Redrawn from Rosenstiel SF: In Rayne J editor: General dental treatment, London, 1983, Kluwer Publishing.)

Root Surface Area Molar

Fig. 3-21. To assess the support of a fixed partial denture, Ante's law has been invoked. It proposes a relationship between the root surface areas of the missing teeth and those of the potential abutment teeth. (The numbers represent root surface area percentages.) If the first molar (22) and second premolar (11) are missing, the abutments for a four-unit FPD will have slightly greater total root surface area (34%) than the teeth being replaced. Then, in the absence of other detrimental factors, an FPD's prognosis will be favorable. However, if the first premolar (12) is also missing, the loss of potential abutment root surface area will comprise 45%, whereas the remaining abutments have only 36%, which is much less favorable.

Fig. 3-21. To assess the support of a fixed partial denture, Ante's law has been invoked. It proposes a relationship between the root surface areas of the missing teeth and those of the potential abutment teeth. (The numbers represent root surface area percentages.) If the first molar (22) and second premolar (11) are missing, the abutments for a four-unit FPD will have slightly greater total root surface area (34%) than the teeth being replaced. Then, in the absence of other detrimental factors, an FPD's prognosis will be favorable. However, if the first premolar (12) is also missing, the loss of potential abutment root surface area will comprise 45%, whereas the remaining abutments have only 36%, which is much less favorable.

these authors had an abutment root surface area less than half that of the replaced teeth, and there was no loss of attachment after 8 to 11 years. They attributed this success to meticulous root planing during the active phase of treatment, proper plaque control during the observed period, and the oc-

Fig. 3-22. A, A misaligned abutment tooth may be difficult or impossible to prepare for an FPD abutment and provides poor support. B and C, Where possible, this should be corrected with orthodontic treatment before restoration.

(Courtesy Dr. G. Gruendeman.)

Fig. 3-22. A, A misaligned abutment tooth may be difficult or impossible to prepare for an FPD abutment and provides poor support. B and C, Where possible, this should be corrected with orthodontic treatment before restoration.

(Courtesy Dr. G. Gruendeman.)

clusal design of the prostheses. Others have confirmed that abutment teeth with limited periodontal bone can successfully support fixed prostheses .30,31

Root Shape and Angulation. When tooth support is borderline, the shape of the roots and their angulation should be considered. A molar with divergent roots will provide better support than a molar with conical roots and little or no interradicular bone. A single-rooted tooth with an elliptic cross-section will offer better support than a tooth with similar root surface area but a circular cross-section. Similarly, a well-aligned tooth will provide better support than a tilted one. Alignment can be improved with orthodontic uprighting (Fig. 3-22).

Periodontal Disease. After horizontal bone loss from periodontal disease, the PDL-supported root surface area can be dramatically reduced 32 Because of the conical shape of most roots (Fig. 3-23), when one third of the root length has been exposed, half the supporting area is lost. In addition, the forces applied to the supporting bone are magnified because of the greater leverage associated with the lengthened clinical crown. Thus potential abutment

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    What is ante s law for missing teeth replacement?
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