title: Thickness of CAD-CAM composite resin overlays influences fatigue resistance of endodontically treated premolars.
abstract: OBJECTIVE
  Evaluate the influence of composite resin CAD-CAM restoration thickness on the in vitro fatigue resistance and failure mode of overlay-type restoration in endodontically treated premolars.
  
  
  METHODS
  Thirty extracted premolars received root canal treatment followed by a standardized tooth preparation (1.5-, 2.5- or 3.5-mm cusp reduction, proximal gingival margins located 1.5mm below the CEJ, glass-ionomer base and immediately sealed dentin with Optibond FL). Restorations were milled using Cerec3 and FiltekMZ100 composite blocks. The intaglio surfaces of the overlays were sandblasted and silanated. Tooth preparations were sandblasted and etched before insertion of the restoration. All restorations were luted with Optibond FL and preheated FiltekZ100. A closed-loop servohydraulic unit was used for simulating cyclic isometric chewing at 5 Hz, starting with a load of 200 N (5000 cycles), followed by stages of 400, 600, 800, 1000, 1200 and 1400 N at a maximum of 30,000 cycles each. All samples were loaded until fracture or to a maximum of 185,000 cycles. Groups were compared using the Kaplan-Meier survival curves.
  
  
  RESULTS
  None of the restored premolars with the 1.5-mm cusp overlap restoration withstood all 185,000 loading cycles. With 2.5- and 3.5-mm cusp overlap, the survival rate was 30% and 40%, respectively. The rate of fracture below the CEJ was 60%, 60% and 30% for 1.5, 2.5 and 3.5 mm of cusp overlap, respectively. Survival of restored premolars with 2.5- and 3.5-mm cusp coverage was not significantly different (p=.23).
  
  
  CONCLUSIONS
  Thick FiltekMZ100 composite resin onlays showed higher fatigue resistance than thin ones and may be associated with fractures that are less subgingival.
authors.affiliation: Division of Primary Oral Health Care, School of Dentistry, University of Southern California, Los Angeles, CA 90089-7792, USA. magne@usc.edu
authors.forename: Pascal
authors.initials: P
authors.lastname: Magne
authors.forename: Alena
authors.initials: A
authors.lastname: Knezevic
mesh_terms: D000134:Acid Etching, Dental; D001641:Bicuspid / Q000473:pathology*; D001696:Biomechanical Phenomena; D001732:Bite Force; D003188:Composite Resins / Q000737:chemistry*; D017076:Computer-Aided Design; D003737:Dental Cavity Preparation / Q000379:methods; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D017220:Dentin-Bonding Agents / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D007284:Inlays / Q000379:methods; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D012390:Root Canal Therapy; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D016019:Survival Analysis; D019553:Tooth, Nonvital / Q000628:therapy*; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; D005899:Glass Ionomer Cements; C469607:OptiBond FL; D019279:Resin Cements; D012821:Silanes; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium