The implants in implant-supported removable partial dentures (RPDs) are placed in the edentulous ridge to stabilize the RPD and minimize the resultant rotational movement. This study investigated the effect of implant placement on RPD stability. A model simulating a mandibular bilateral distal extension missing was fabricated using epoxy resin and silicone impression material as thin (1 mm) and thick (2 mm) soft tissues. Five pressure sensors (PS-10K, Kyowa, Tokyo, Japan) were attached near the left and right first molars (#36 and #46), first premolars (#34 and #44) and medio-lingual alveolar crest. Five bilateral distal extension RPDs with Co-Cr frameworks were conventionally fabricated. After the implants were placed at the bilateral second molar areas, healing caps (4.5 mm high) were connected to the denture base with autopolymerized resin to support the RPD. As in a conventional RPD, sealing screws were placed without connecting them. Loads up to 5 kg were applied, and the pressure and displacement of the RPDs (n = 5) were simultaneously measured and analysed using the Wilcoxen test (alpha = 0.05). There was less pressure on both thin and thick soft tissues, the #36, #46 and the medio-lingual alveolar crest from the implant-supported RPD than from the conventional RPD (P < 0.05). There were no significant differences in pressure on #34 and #44 between the two RPDs (P > 0.05). There was significantly less denture displacement of the implant-supported RPD than of the conventional denture (P < 0.05). Implant support helped prevent the displacement of distal extension RPDs and decreased the pressure on soft tissues.

This position paper proposes a definition and naming standard for removable partial dentures (RPDs) using thermoplastic resin, and presents a guideline for clinical application. A panel of 14 experts having broad experience with clinical application of RPDs using thermoplastic resin was selected from members of the Japan Prosthodontic Society. At a meeting of the panel, "non-metal clasp denture" was referred as the generic name of RPDs with retentive elements (resin clasps) made of thermoplastic resin. The panel classified non-metal clasp dentures into two types: one with a flexible structure that lacks a metal framework and the other having a rigid structure that includes a metal framework. According to current prosthetic principles, flexible non-metal clasp dentures are not recommended as definitive dentures, except for limited cases such as patients with a metal allergy. Rigid non-metal clasp dentures are recommended in cases where patients will not accept metal clasps for esthetic reasons. Non-metal clasp dentures should follow the same design principles as conventional RPDs using metal clasps.

This study evaluated the marginal and internal gaps of Procera AllCeram crowns in vivo using silicone materials. Ninety Procera AllCeram crowns were evaluated before final cementation. White and black silicone materials were used to record the marginal and internal fit; then the crowns were sectioned bucco-lingually and mesio-distally to measure the thickness of the silicone layer using a microscope. Sixteen reference points were measured on each specimen. Mean marginal gaps among anterior, premolar and molar teeth, and mean gaps at the reference points within the groups were compared by analysis of variance and Dunnett T3 test. The mean values at the margins were the smallest in all tooth groups, whereas those at the rounded slope of the chamfer were the largest. There were significant differences (P < 0.001) in the mean gaps at the four reference points (margin, rounded slope of the chamfer, axial wall and occlusal surface) in each group, except for the molar teeth. The mean marginal gaps of the Procera AllCeram crowns were within the range of clinical acceptance.

Within the limits of this in vitro study, it can be concluded that the investigated overdenture attachment systems are sufficiently resistant to wear. However, the Dalbo(®) -Plus- and SFI(®) -Bar- exhibit higher retentive capacities than the Locator(®) -attachment over time. The fixation screw of the SFI(®) -Bar may loosen during long-term use, but these observations might be less important if 1-year recall intervals are respected. An angulation of up to 12° between implants does not seem to have a significant effect on attachment wear.

This position paper reviews physical and mechanical properties of thermoplastic resin used for non-metal clasp dentures, and describes feature of each thermoplastic resin in clinical application of non-metal clasp dentures and complications based on clinical experience of expert panels. Since products of thermoplastic resin have great variability in physical and mechanical properties, clinicians should utilize them with careful consideration of the specific properties of each product. In general, thermoplastic resin has lower color-stability and higher risk for fracture than polymethyl methacrylate. Additionally, the surface of thermoplastic resin becomes roughened more easily than polymethyl methacrylate. Studies related to material properties of thermoplastic resin, treatment efficacy and follow-up are insufficient to provide definitive conclusions at this time. Therefore, this position paper should be revised based on future studies and a clinical guideline should be provided.