The mutual abrasion of light-cured composites and clasps: an in vitro study

Abstract

A reciprocating abrasion testing machine was used to measure the mutual abrasion of light-cured composites and clasps in vitro. Composite specimens were produced by packing the material into hemispherical wells in a polytetrafluoroethylene block, light-curing for 20 seconds and conditioning in distilled water for one week. The composites tested included ultrafine, hybrid and conventional types. Nine clasp types were studied including cast and wrought, round and half-round, cobalt-chromium, stainless steel and gold. The tests were carried out at 37 °C. The vertical overlap (undercut) of composite and clasp was set at 0.25mm. Ten specimens were subjected to 14,500 traverses in each test Abrasion of composite was measured as weight loss and reduction in thickness of the specimens, while abrasion of clasps was measured as weight loss. Abrasion of the composites was greatest for the conventional type and least for the ultrafines, but in all cases the changes were small and unlikely to impair the clinical performance of clasps during several years' usage. The abrasion of the clasps by conventional composite was considerable and would be expected to cause a significant reduction in retention clinically.