Masaru Yatabe

Clinical application of removable partial dentures using thermoplastic resin. Part II: Material properties and clinical features of non-metal clasp dentures

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.

A comparison of the fitting accuracy of thermoplastic denture base resins used in non-metal clasp dentures to a conventional heat-cured acrylic resin

Abstract Objective. To incorporate a metal framework into removable partial dentures, the dimensional accuracy of thermoplastic resins requires precision equivalent to conventional acrylic resins. This study aimed to evaluate the fitting accuracy of thermoplastic resins compared to heat-cured acrylic resin. Materials and methods. Four thermoplastic resins (polyethylene terephthalate [EstheShot, ES; EstheShot Bright, ES-B], polyamide [Lucitone FRS, LF], polycarbonate [Reigning Resin N, RN] and a heat-curing acrylic resin [Acron, AC]) were used. The specimens were created on master casts constructed of high-strength stone that simulated a maxillary edentulous ridge. Additionally, high-expansion stone was used as the master cast for RN specimens. The ES-B, LF and RN specimens were prepared with and without annealing after injection molding. The gaps between the molded resin and the cast were measured. Results. ES had the smallest gap and was significantly smaller than AC (p < 0.05). The gap sizes of ES-B, LF and RN (high-expansion stone) without annealing were similar to AC (p > 0.05), while the gap size of RN (high-strength stone) with and without annealing was significantly greater than AC (p < 0.001). The gap sizes of ES-B and LF with annealing were significantly less than AC (p < 0.05). Further, the gap sizes of ES-B, LF and RN with annealing were significantly smaller than the gaps without annealing (p < 0.05). Conclusions. The results suggested that ES, ES-B and LF have adequate fitting accuracy for incorporating metal framework into dentures and that annealing effectively improved the fitting accuracy of ES-B, LF and RN.