The fabrication of a precisely fitting removable partial denture is one of the more challenging tasks in restorative dentistry. Without a careful all-inclusive diagnosis and well-designed treatment plan, the chances of success are minimal. Patients who require a removable prosthesis (Fig. 21-1) usually have sustained extensive damage as a consequence of caries, periodontal disease, or trauma. They also may exhibit acquired or congenital intraoral defects. As a result of prolonged loss of arch integrity, there may be drifting or tipping, and the occlusion is often less than ideal.
Treatment plans that include a removable prosthesis may require additional diagnostic procedures besides those described in Chapters 1 and 2. The importance of accurate diagnostic casts mounted in centric relation can hardly be overemphasized. If all posterior teeth are absent, it will be much more difficult to relate opposing diagnostic casts, and stable record bases must be made under these circumstances (Fig. 21-2).
The use of a dental surveyor (Fig. 21-3) is essential during treatment planning for the following reasons:
1. To help assess the relative alignment of the long axes of teeth that support an RPD.
2. To help determine the optimum path of placement and removal.
3. To help evaluate tissue undercuts and their influence on RPD design.
The most appropriate anteroposterior and mediolateral tilt of the cast needs to be selected. Careful analysis is essential because a compromise often must be made between the requirements of an ideal tooth preparation (see Chapter 7) and the requirements for a particular tooth to be used as an abutment to support and retain an RPD. The path of insertion is the single most important factor in determining how much tooth reduction is needed to meet mechanical and esthetic requirements simultaneously (Fig. 21-4).
When surveying the diagnostic cast, the antero-posterior tilt should be established first. The lateral inclination is then determined. The operator should focus on the relative alignment of selected abutment teeth, any tissue undercuts, and the available
occlusocervical dimension for anticipated proximal and reciprocal guide planes. The feasibility of re-contouring axial walls and the possible consequences of such recontouring must also be considered. For instance, it may be necessary to treat a malposed tooth orthodontically or endodontically if recontouring is not feasible. Similarly, removal of a tooth that unnecessarily complicates RPD design should be considered and carefully weighed against its effect on the stability of the prosthesis. If future loss of an already compromised tooth would render the RPD useless, it may be better to remove that tooth before initiating any prosthetic treatment.
When a patient has missing anterior teeth, the path of insertion of an RPD should be parallel to the proximal surfaces of the abutment teeth adjacent to the space (Fig. 21-5). This results in superior esthetics because it minimizes the space between the artificial and natural teeth. Sometimes esthetics can be improved by using a rotational insertion path.'
Apparently complex decisions as to the best tooth preparation-path of withdrawal combination can be greatly simplified by using diagnostic tooth preparation, waxing, and denture tooth setting (Figs. 21-6 and 21-7). These trial procedures on diagnostic casts help determine how to arrive at the best mechanical and esthetic result without deviating from the principles of occlusion or making excessively bulky restorations that inevitably causes periodontal complications. The concept is to determine before treatment the precise end point in re-
gard to occlusion and appearance with interchangeably articulator-mounted casts of the pre- and post-treatment condition. These cross-mounted casts also enable the treatment sequence to be simplified by allowing one arch to be treated at a time. The restorations on the first arch to be restored are fabricated against the diagnostically waxed opposing cast (Fig. 21-8 and Fig. 3-34).
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