Evaluation of Resin Clasps with Different Design by Retentive Force

Abstract

The aim of the present study was to apply acrylic resin for a removable partial denture (RPD) with resin clasps. The present study evaluated the changes in retentive forces of resin clasps with different designs composed of acrylic resin or polyester by repeated insertion/removal motion. Two resin clasp designs(length: 7.5 mm, width: 7.5 mm or 10 mm, thickness: 1.5 mm) made of acrylic resin or polyester(control) were used. An abutment tooth simulating the maxillary first premolar was prepared by using an 18-8 stainless steel model. The amount of undercut of the retentive arms was set at 0.5 mm, with half of the undercut area at the far zone as the contact surface. The initial retentive force and retentive force for each test specimen were measured. The changes of retentive force until 10,000 insertion/removal cycles were measured by an insertion/removal testing apparatus placed in distilled water at 37℃ and an insertion load to the abutment tooth of 9.8 N. The initial retentive force was not significantly different between each test specimen. During 9,001-9,015 and 10,001-10,015 insertion/removal cycles, the retentive force of acrylic resin clasps with width of 10 mm was significantly higher than that of polyester clasps with width of 7.5 mm(P<0.05). Our present study may suggest that an RPD with resin clasps composed of acrylic resin with dimensions of length of 7.5 mm, width of 10 mm, and thickness of 1.5 mm with half of the undercut area at the far zone as the contact surface has the potential for use in clinical application.