title: Subsurface compression fatigue in seven dental composites.
abstract: OBJECTIVE
  The purpose of this study was to evaluate subsurface fatigue in seven dental composites.
  
  
  METHODS
  Cylindrical test pieces were subjected to 2000 compression cycles with a load of 120 N. The area of stained subsurface was measured, and subsequently, the specimens were examined by scanning electron microscopy.
  
  
  RESULTS
  The greatest staining occurred in the composites with large quartz fillers, whereas there was little staining in the microfilled materials. Electron microscopy demonstrated very little evidence of cracks, suggesting that silver nitrate stained a network of crazes and microcracks in the subsurface. The pattern of staining indicated that the microcracks formed within the depth of the subsurface rather than by direct nucleation from the indenter.
  
  
  CONCLUSIONS
  The different patterns of subsurface damage occurring as a result of compression should be considered when studying the wear and degradation of these materials.
authors.affiliation: Department of Clinical Dental Sciences, University of Liverpool, England, UK.
authors.forename: L H
authors.initials: LH
authors.lastname: Mair
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011140:Polyurethanes / Q000737:chemistry; D011312:Pressure; D014520:Urethane / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; D011140:Polyurethanes; C056413:Occlusin; C092420:Clearfil Photo Posterior; C074741:Silux Plus; C048711:P-30 composite resin; D014520:Urethane; D017438:Bisphenol A-Glycidyl Methacrylate; C033469:profile resin