title: Cyclic contact fatigue of a silver alternative to amalgam.
abstract: OBJECTIVE
  To purpose of this study was to compare the cyclic contact fatigue resistance of a novel mercury-free silver direct filling material to that of a dental amalgam (Dispersalloy).
  
  
  METHODS
  The silver specimens were made by pressing a precipitated powder at room temperature with a pressure of 150 MPa, which can be achieved in clinical hand-consolidation. To simulate clinical contact of restorations against enamel cusps, a cyclic contact fatigue methodology was employed. A spherical indenter was used to repeatedly indent the specimen, while the accumulation of deformation and damage was examined as a function of the number of cycles up to 5 x 10(5). Student's t test, analysis of variance (ANOVA) and Duncan's multiple range test were used to compare the specimen groups for significant differences in flexural strength, indentation impression diameter, and hardness. A type I error of alpha = 0.05 was considered as significant. Subsurface damage was examined by using a bonded-interface technique.
  
  
  RESULTS
  As a result of cyclic indentation, microcracks were produced in the amalgam, but no cracks were found in the silver filling material. At fewer numbers of cycles, indentation produced larger impressions in silver (e.g., diameter = [450 +/- 31] microns at 10(2) cycles) than in amalgam ([145 +/- 20] microns) due to a lower hardness of the former. However, with increasing number of cycles, damage accumulated more rapidly in the amalgam, while the silver beneficially work-hardened in repeated indentations. At 5 x 10(5) cycles, the difference in impression diameter between silver and amalgam ([582 +/- 20] microns vs. [568 +/- 42] microns) become insignificant (p > 0.1, Student's t test).
  
  
  CONCLUSIONS
  The mercury-free silver direct filling material is more resistant to microcracking and to cyclic contact fatigue than amalgam, and the indentation impression sizes in the consolidated silver and dental amalgam are not statistically different at large numbers of cycles.
authors.affiliation: Paffenbarger Research Center, American Dental Association Health Foundation, National Institute of Standards and Technology, Gaithersburg, MD, USA. hockin.xu@nist.gov
authors.forename: H H
authors.initials: HH
authors.lastname: Xu
authors.forename: F C
authors.initials: FC
authors.lastname: Eichmiller
authors.forename: A A
authors.initials: AA
authors.lastname: Giuseppetti
authors.forename: C E
authors.initials: CE
authors.lastname: Johnson
mesh_terms: D000704:Analysis of Variance; D019245:Compressive Strength; D003722:Dental Alloys / Q000737:chemistry*; D003723:Dental Amalgam / Q000737:chemistry; D003775:Dental Polishing; D003799:Dental Stress Analysis; D006244:Hardness; D008422:Materials Testing; D008628:Mercury / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D012834:Silver / Q000737:chemistry*