title: Effects of cyclic loading on occlusal contact area wear of composite restoratives.
abstract: OBJECTIVE
  To investigate the effects of cyclic loading on occlusal contact area (OCA) wear and the possible presence of fatigue wear mechanisms in four composite resins (Silux, Z100, Ariston and Surefil) using a reciprocal compression-sliding test apparatus.
  
  
  METHODS
  Six specimens were made for each composite material and the amalgam alloy (Dispersalloy) control. The wear specimens were subjected to wear testing at 20 MPa with artificial saliva as lubricant. Wear depth (microm) was measured using profilometry every 20,000 cycles up to 120,000 cycles. The worn specimens were subjected to SEM to determine the presence of fatigue wear mechanisms. Results were analyzed using ANOVA/Scheffe's test (P<0.05) and Pearson's Correlation (P<0.01).
  
  
  RESULTS
  Dispersalloy had the lowest wear at all cyclic intervals. For all materials, OCA wear increased with increased number of cycles. Although Dispersalloy, Ariston and Surefil experienced no significant increase in wear between each 20,000 cycles increment, a significant increase was observed with Silux. For Z100, a significant difference was observed only from 40,000 cycles onwards. Both Z100 and Dispersalloy exhibited fatigue wear after wear testing for 120,000 cycles. Cyclic loading resulted in deep and wide microcracks in Silux. Fatigue wear was not observed with Silux, Ariston and Surefil.
  
  
  CONCLUSIONS
  The effects of cyclic loading on wear is material dependent. While some restorative materials exhibit fatigue wear, others exhibit deep microcrack formation with extended cyclic loading. The latter may precipitate catastrophic failure despite the low wear observed. Care should, therefore, be exercised when selecting materials for posterior stress-bearing areas.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074, Republic of Singapore. rsdyapuj@nus.edu.sg
authors.forename: A U J
authors.initials: AU
authors.lastname: Yap
authors.forename: S H
authors.initials: SH
authors.lastname: Teoh
authors.forename: C L
authors.initials: CL
authors.lastname: Chew
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D001732:Bite Force; D003188:Composite Resins / Q000737:chemistry*; D019245:Compressive Strength; D003722:Dental Alloys / Q000737:chemistry; D003723:Dental Amalgam / Q000737:chemistry; D019232:Dental Restoration Failure; D019554:Dental Restoration Wear; D003793:Dental Restoration, Permanent; D006801:Humans; D008153:Lubrication; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D011312:Pressure; D012464:Saliva, Artificial / Q000737:chemistry; D012822:Silicon Dioxide; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium
chemical_list: C409382:Ariston pHc; D003188:Composite Resins; D003722:Dental Alloys; D008689:Methacrylates; D012464:Saliva, Artificial; C403464:SureFil packable composite; C083568:Z100 composite resin; C033470:Dispersalloy; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D003723:Dental Amalgam; D015040:Zirconium