[A systematic approach for removable partial denture design].
Patients' attitudes, medical, surgical and financial considerations lead to the use of a removable partial denture (RPD) as the chosen prosthetic restoration even in the "dental implant era". The aim of this article is to describe a systematic approach to RPD design, so the RPD will be a long-term solution that will not harm the remaining oral tissues. There is an unlimited RPD design options. Choosing the right one involves considering biochemical factors, aesthetics and patients' comfort. A systematic approach starts with a correct diagnosis of the remaining hard and soft tissues, followed by a careful planning of support, stability and retention in that order. Additional elements should be added only at a later stage. A systematic track starting with a preliminary design, surveying of the model and analyzing the preliminary design on that surveyed model. If needed, that track should be reversed until an acceptable design is found. Support should ideally be achieved by using metal rests on healthy tooth structure. Tooth supported RPD are the most convenient ones and have a very good long-term prognosis. Old restorations or caries might impose changes from the ideal supporting rests. When posterior teeth are missing or when the edentulous area is vast, tooth-tissue supported RPD are used. In these cases one should gain initial support from the teeth and an additional support from the soft tissues. A denture base that is similar to a full denture base that would have been prepared for a fully edentulous patient should achieve this. If the prognosis of the potential supporting teeth is poor, a tissue-tooth supported RPD is considered. In these cases, the denture base is the primary supporting element, and stress relieving clasp-assemblies such as the RPI/RPA should be considered. Stability is achieved primarily by metal contacts between teeth and the metal framework of the RPD. In fact, any embracing part of the clasp assembly and a correct denture base can contribute to the stability. The distal parts of the retentive clasps produce the active retention. Since these parts generate lateral forces on the abutment teeth, a reciprocating element should be used. True reciprocation can only be achieved if the reciprocating element touches the tooth before the retentive clasp. After designing support, stability and retention, other parts should be considered. When a distal extension RPD is considered, an indirect retainer should be incorporated into the framework in order to prevent upward rotational movement of the denture. The major connector converts forces from one side to the other. In the upper jaw, that part acts also as a supporting element in Kennedy class I and class II cases. In other cases, a minimal type of a major connector should be chosen. As for minor connectors, these should only be added if other parts--such as guiding planes--couldn't be used for the purpose of connecting functional elements to the major connector. In any case, a 5 mm distance between two adjacent minor connectors should be allowed in order to prevent food from being trapped in that space. A systematic approach starts with diagnosis of the remaining tissues and with finding the correct prosthetic solution with the patient. If a RPD is the chosen solution, start designing with analysis of support, followed by stability and only then, decide upon the necessary retentive elements. All other parts should be considered later. Such a systematic approach will ensure a long-term solution and a happy patient.