Removable partial dentures with double crowns - biological and prophylactic value and potential complications

Abstract

Correctly indicated and accurately made, partial denture with double crowns is a dental restoration of the highest biological, prophylactic and aesthetic values. However, insufficient knowledge of double crowns systems, as well as errors and omissions in the clinical and laboratory work invalidate this type of restoration and can have negative effects on the supporting tissues. Double crowns may come in form of telescope crowns and conical crowns. Double crowns as connecting elements should provide: retention, stabilization, physiological transmission of occlusal loads through the abutment teeth as well as the prophylactic value, comfort for the patient, durability and aesthetics. In order to achieve these qualities, it is necessary, among other things: to make proper indication, to execute adequate tooth preparation (grinding), to make the choice of materials for the construction, to establish proper connection of the outer crown and the metal framework and to choose a suitable aesthetic material for veneering. It is necessary to understand the mechanism of double crowns retention so that the optimal value of the retention force which should be 5-9 N per each patrix can be established. Insufficient retention force will reduce the comfort for the patient because would make the separation too easy, whereas an excessive force may negatively affect the periodontium of the abutment teeth. Retention force and durability of restorations with telescope and conical crowns depend also on the characteristics of the material they are made of. The most frequently used are gold and palladium-silver alloys. In recent years, titanium and the combination of ceramic and galvanized gold are used. Prophylactic effect of double crowns is also provided by a proper planning that will enable the physiological transfer of the forces on the abutment teeth and the health of free gingiva. A special challenge is to plan the connection of outer crown with the metal framework. The best results showed optimized approximal extensions. Double crown production demands experience of a clinician and dental technician in the performance of clinical and laboratory phases. A removal of sufficient tooth tissue during grinding in order to avoid getting oversized artificial teeth and a formation of the appropriate demarcation line which will provide sufficient stability of the system in the gingival area represent a particular challenge. Errors in laboratory work can be avoided with a good knowledge of the milling proceedings, a selection of a suitable material for the external crowns modeling and acquisition of precision castings.