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.

Clinical application of removable partial dentures using thermoplastic resin-part I: definition and indication of non-metal clasp dentures.

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.

Evaluation of brittleness of porcelain fused to pure titanium by fracture toughness, hardness and fracture energy.

To elucidate the cause of brittleness of porcelain fused to pure titanium (PFPT) which leads to chipping and cracking similar to that of conventional porcelain in clinical use, fracture toughness KIc, hardness (Hv and Hk) and fracture energy gamma reflecting the bonding energy of atoms were evaluated. In KIc there were no differences between PFPT and conventional porcelain, nor for Hv and Hk, but for the gamma of PFPT calculated from the KIc and the Young modulus measured by the resonance method there was less than that of conventional porcelain. These results indicate that mechanical properties such as KIc and hardness cannot always substantiate the brittleness of PFPT experienced in practical use. However, a comparatively small gamma of PFPT may suggest a fatigue crack growth as a more likely phenomenon as it occurs more easily than the conventional one in oral.