Influence of overlay restorative materials and load cusps on the fatigue resistance of endodontically treated molars.
OBJECTIVE
To assess the influence of restorative materials and load cusps on the fatigue resistance of endodontically treated molars.


METHODS
Thirty extracted molars received root canal treatment followed by a standardized tooth preparation (3-mm cuspal reduction and immediate dentin sealing). Twenty Cerec 3 overlays (Sirona Dental Systems) were milled in the ceramic Vita MKII block (Vident; groups MKIIGL and MKIIGL-Z, oven-glazed), and 10 restorations were duplicated with a composite resin (Miris 2, Coltane/Whaledent; group M2). The fitting surfaces of the restorations were hydrofluoric acid etched (porcelain only) and silanated. Preparations were airborne-particle abraded and etched. All restorations were luted with preheated Filtek Z100 (3M ESPE) and subjected to cyclic isometric chewing (5 Hz) starting at 200 N (5,000 cycles), followed by stages of 400, 600, 800, 1,000, 1,200, and 1,400 N at a maximum of 30,000 cycles each. A stainless steel load sphere was used for groups MKIIGL and M2, while a composite resin load sphere was used in group MKIIGL-Z. All samples were loaded until fracture or to a maximum of 185,000 cycles. Groups were compared using the Kaplan-Meier survival curves (P = .05).


RESULTS
None of the molars restored with porcelain withstood all 185,000 loading cycles (survival = 0%). The mean fracture load for MKIIGL was 1,060 N and for MKIIGL-Z, 1,280 N. In group M2, the survival rate was 50%. The rate of fracture below the CEJ was 40%, 30%, and 20% for MKIIGL, MKIIGL-Z, and M2, respectively.


CONCLUSIONS
Miris 2 overlays showed higher fatigue resistance than MKII porcelain (P = .01) when loaded with a stainless steel antagonist.
Don & Sybil Harrington Foundation Chair of Esthetic Dentistry, Division of Primary Oral Health Care, School of Dentistry, University of Southern California, Los Angeles, Californa 90089-7792, USA. magne@usc.edu
Pascal
P
Magne
Alena
A
Knezevic
D000134:Acid Etching, Dental; D000537:Aluminum Oxide / Q000737:chemistry; D001732:Bite Force; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D001840:Dental Bonding; D045662:Dental Etching; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D006801:Humans; D006858:Hydrofluoric Acid / Q000737:chemistry; D007284:Inlays; D008422:Materials Testing; D008963:Molar / Q000503:physiopathology*; D012390:Root Canal Therapy; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D016019:Survival Analysis; D013997:Time Factors; D019246:Tooth Preparation / Q000379:methods; D019553:Tooth, Nonvital / Q000503:physiopathology*; D015040:Zirconium / Q000737:chemistry
D003188:Composite Resins; D003764:Dental Materials; D012821:Silanes; C083568:Z100 composite resin; D003776:Dental Porcelain; D013193:Stainless Steel; D012822:Silicon Dioxide; D015040:Zirconium; D000537:Aluminum Oxide; D006858:Hydrofluoric Acid