A review of the properties of some denture base polymers

Abstract

INTRODUCTION Acrylic denture base materials have been widely available in the United Kingdom for about 40 years. The loss of rubber supplies to the United Kingdom in 1942 completed the change over to acrylic resins which had really begun in 1935 with the introduction of Kallodent, in its injection moulded form, by Imperial Chemical Industries Ltd. The production of acrylic resin for dentistry is the now familiar dough moulding technique which was introduced by Kulzer shortly after Kallodent. This basic material and technique has remained as the denture base material of choice since that time, although various polymers have been developed for use in dentistry to overcome the strength deficiencies of polymethylmethacrylate (PMMA). Polymers such as the polyamides, epoxy resin, polystyrene, vinyl-acrylic, rubber graft polymers and polycarbonate have been used. Modification of PMMA and the addition of fillers has also been attempted. Over the past few years acrylic resin polymers have also been modified so that they could be used in a more versatile fashion and a review of the properties of these pour-type denture base resins has been published (Bates et al., 1977). The total amount of money spent on repairs to acrylic dentures in the National Health Service of England and Wales between 1948 and 1978 is reliably estimated at a figure of g27.9 million at a cost of JZ28.1 million (not allowing for variations in monetary value) (Dental Estimates Board, 1979) and so the strength of these resins is still a cause for concern. Further recent efforts have been made to improve these deficiencies by developing different polymers based upon dental PMMA, with the addition of rubbers. This produces a resin that consists of a matrix of PMMA within which is dispersed an interpenetrating network of rubber and PMMA. This leads to a situation where a developing crack accelerates in the PMMA, but decelerates whilst crossing the rubber phase, thus increasing the fracture resistance. It is therefore useful to review some of the physical and mechanical properties of a range of these higher strength polymers and compare them with other acrylic denture base resins.