Basic Study on Laser Joining of Resin for Denture Base and Dental Alloy

Abstract

Dentures are comprised of resin and metal materials. These materials are joined using chemicals or mechanically by making under-cuts, but spaces remaining between the materials cause denture fracture and oral bacterial infection. To solve this problem, we performed a basic study to evaluate the applicability of laser-assisted metal and plastic (LAMP) joining for the direct joining of cobalt-chromium alloy for casting (COBALTAN, Shofu Inc., Kyoto, Japan) and acrylic resin for a thermoplastic base (ACRYJET, High-Dental Japan, Osaka, Japan). LAMP joining is a technique that facilitates the laser joining of resin and metal and was developed by the Laser Welding and Materials Processing, Welding Research Institute, Osaka University. LAMP joining achieves a very strong joint between acrylic resin and cobalt-chromium alloy. As a result, most samples of thermoplastic acrylic resin for denture suffer plastic deformation in tensile shear tests, and some samples broke at a position away from the joint interface on thermoplastic acrylic resin for dentures, prior to fracture at the joint interface. Although it was not possible to measure the bonding strength to line profile, in this experiment, the joints possessed very strong tensile shear strengths of not less than 4.9 MPa. Sufficient bonding strength was obtained between the thermoplastic acrylic resin for dentures and the cobalt-chromium alloy for casting by LAMP joining. When the bonded interface was observed under SEM, fine air bubbles characteristic of LAMP joining were observed, and no micro-level space was present in the bonded interface. It is suggested that cobalt-chromium alloy for casting and acrylic resin for a thermoplastic base can be joined with no space in the bond interface by using LAMP joining without special surface processing. (J. Jpn. Soc. Laser Dent. 23:131 ~ 136, 2012 Reprint requests to Dr. NAITO) Key words= Laser joining, Dissimilar materials joining, Thermoplastic acrylic resin, Cobalt-chromium cast alloy キーワード=レーザー接合,異材接合,熱可塑性アクリル樹脂,コバルトクロム合金