Stress relaxation of dental amalgam alloys

Short-term stress relaxation of four dental amalgam alloys was studied. Test materials included two conventional lathe-cut restoratives, a spherical alloy, and a dispersed phase product. Specimens were 24-hr-old 4 X 8-mm cylinders. The specimens were compressed and held at constant strain on development of a stress (So) of 28 MN/m2. Subsequent stress relaxation (Dt) was recorded for 60 sec. Data were obtained at eight nominal temperatures between 0 and 55 degrees C. Over the experimental temperature range, fractional stress losses at 60 sec (Dt/So/60) for specimens made from lathe-cut alloys increased from 10% to 58%. The spherical material and the dispersed phase alloy showed fractional stress losses (Dt/So/60) ranging from 9% to 47% and 9% to 31%, respectively. It would appear that particle morphology and alloy composition affect stress-relaxation behavior of dental amalgam. Stress decay patterns enhance significantly the mechanical characterization of amalgam alloys.