Scanning Electron Microscope Study of Composite Restorative Materials

Abstract

The relatively new class of dental restoratives, termed composites, contain thermosetting resin binders and various concentrations of several different types of inert fillers. Because of the difference in types and amounts of resins and fillers present in these materials, each restorative has unique surface characteristics. In addition, the various resin types and filler loading volumes cause differences in polymerization shrinkage and adaptation to the margins of cavity preparations. A combination of radioisotope leakage studies and scanning electron microscopy studies was used to investigate the surfaces and adaptation of four of these composite materials in comparison to an amalgam, silicate, and unfilled poly ( methyl methacrylate).

Adaptation of silicate and Adaptic to the margins of cavities

“…The above findings are in agreement wiih the results of recent studies which proved the existence of fissures between silicate fillings and the cavity walls (Lee & Swartz, 1970). The present work has in addition proved that etching of the cavity walls does not result in higher adaptability of the silicate filling to the cavity margins.…”

“…Adaptic,* a composite dental filling material, has been studied to find out its physical and chemical properties in vitro and in vivo (Lee & Swartz, 1970;McLutidie & Murray, 1972;Liatukas, 1972). The material is composed of a resin matrix and an inorganic filler, the latter serving to reduce shrinkage at the stage of polymerization and provide a closer marginal adaptation (Lee & Swartz, 1970). Studies on the marginal fillingcavity relationship with the scanning electron microscope (SEM) revealed an average fissure of 0-5 ^m between the material and the cavity wall.…”

“…Studies on the marginal fillingcavity relationship with the scanning electron microscope (SEM) revealed an average fissure of 0-5 ^m between the material and the cavity wall. For silicate fillings these gaps were found to be of 3 jxva in width (Lee & Swartz, 1970). An attempt to overcome this disadvantage was made with the introduction of etching techniques.…”

Microleakage Testing

“…This method of microscopy is often used together with direct observation ( 15). These techniques do not quantity diffusion or penetration, and no direct correlation has been demonstrated between visible fissure size and depth of leakage ( 16).…”

The effects of cyclic stress on dental polymethylmethacrylate

“…The parameters of testing, initially very simple, have become increasingly sophisticated so far as temperature and cycle duration are concerned (Nelsen, Woolcott & Paffenbarger, 1952;Going & Sawinski, 1966;Peterson, Phillips & Swartz, 1966;Tani & Buonocore, 1969;Guzman, Swartz & Phillips, 1969;Lee & Swartz, 1970;Asmussen, 1974: Morley & Stockwell, 1977Glyn Jones, Grieve & Kidd, 1978;Kidd, Harrington & Grieve, 1978;Glyn Jones, Grieve & Harrington, 1979). Accelerated or extreme cycling may well be adequate for comparing the behaviour of different materials, but when only small changes are brought about, their clinical significance can only be accurately evaluated if all the test procedures have resembled service conditions as closely as possible.…”