The failure of amalgam dental restorations due to cyclic fatigue crack growth

In this study a restored mandibular molar with different Class II amalgam p reparations was examined to analyze the potential for restoration failure a ttributed to cyclic fatigue crack growth. A finite element analysis was use d to determine the stress distribution along the cavo-surface margin which results from occlusal loading of each restoration. The cyclic crack growth rate of sub-surface flaws located along the dentinal cavo-surface margin we re determined utilizing the Paris law. Based on similarities in material pr operties and lack of fatigue property data for dental biomaterials, the cyc lic fatigue crack growth parameters for engineering ceramics were used to a pproximate the crack growth behavior. It was found that flaws located withi n the dentine along the buccal and lingual margins can significantly reduce the fatigue life of restored teeth. Sub-surface cracks as short as 25 mu m were found capable of promoting tooth fracture well within 25 years from t he time of restoration. Furthermore, cracks longer than 100 mu m reduced th e fatigue life to less than 5 years. Consequently, sub-surface cracks intro duced during cavity preparation with conventional dental burrs may serve as a principal source for premature restoration failure. (C) 1999 Kluwer Acad emic Publishers.