Cyclic contact fatigue of a silver alternative to amalgam

Objective. The purpose of this study was to compare the cyclic contact fati gue resistance of a novel mercury-free silver direct filling material to th at of a dental amalgam (Dispersalloy). Methods. The silver specimens were made by pressing a precipitated powder a t room temperature with a pressure of 150 MPa, which can be achieved in cli nical hand-consolidation. To simulate clinical contact of restorations agai nst enamel cusps, a cyclic contact fatigue methodology was employed. A sphe rical indenter was used to repeatedly indent the specimen, while the accumu lation of deformation and damage was examined as a function of the number o f cycles up to 5x10(5) Student's t test, analysis of variance (ANOVA) and D uncan's multiple range test were used to compare the specimen groups for si gnificant differences in flexural strength, indentation impression diameter , and hardness. A type I error of alpha = 0.05 was considered as significan t. Subsurface damage was examined by using a bonded-interface technique. Results. As a result of cyclic indentation, microcracks were produced in th e amalgam, but no cracks were found in the silver filling material. At fewe r numbers of cycles. indentation produced larger impressions in silver (e.g ., diameter = [450 +/- 31] mu m at 10(2) cycles) than in amalgam ([145 +/- 20] mu m) due to a lower hardness of the former. However, with increasing n umber of cycles, damage accumulated more rapidly in the amalgam, while the silver beneficially work-hardened in repeated indentations. At 5 x 10(5) cy cles, the difference in impression diameter between silver and amalgam ([58 2 +/- 20] tcm vs. [568 +/- 42] mu m) became insignificant (p > 0.1, Student 's t test). Significance. The mercury-free silver direct filling material is more resis tant to microcracking and to cyclic contact fatigue than amalgam, and the i ndentation impression sizes in the consolidated silver and dental amalgam a re not statistically different at large numbers of cycles. (C) Published by Elsevier Science ltd on behalf of the Academy of Dental Materials.