Effect of porcelain and enamel thickness on porcelain veneer failure loads in vitro.
BACKGROUND
Bonded porcelain veneers are widely used esthetic restorations. Although high success and survival rates have been reported, failures occur. Fracture is the most common failure mode. Fractures range from incomplete cracks to the catastrophic. Minimally invasive or thin partial veneers have gained popularity.


OBJECTIVE
The aim of this study was to measure the influences of porcelain veneer thickness and enamel substrate thickness on the loads needed to cause the initial fracture and catastrophic failure of porcelain veneers.


METHODS
Model discoid porcelain veneer specimens of varying thickness were bonded to the flattened facial surfaces of incisors, artificially aged, and loaded to failure with a small sphere. Individual fracture events were identified and analyzed statistically and fractographically.


RESULTS
Fracture events included initial Hertzian cracks, intermediate radial cracks, and catastrophic gross failure. Increased porcelain, enamel, and their combined thickness had like effects in substantially raising resistance to catastrophic failure but also slightly decreased resistance to initial Hertzian cracking. Fractographic and numerical data demonstrated that porcelain and tooth enamel behaved in a remarkably similar manner. As porcelain thickness, enamel thickness, and their combined thickness increased, the loads needed to produce initial fracture and catastrophic failure rose substantially. Porcelain veneers withstood considerable damage before catastrophic failure.


CONCLUSIONS
Increased enamel thickness, increased porcelain thickness, and increased combined enamel and porcelain thickness all profoundly raised the failure loads necessary to cause catastrophic failure. Enamel and feldspathic porcelain behaved in a like manner. Surface contact damage occurred initially. Final catastrophic failure followed flexural radial cracking. Bonded porcelain veneers were highly damage tolerant.
Assistant Professor, Peking University School of Stomatology, Peking China; and Visiting Scholar, UCLA School of Dentistry, Los Angeles, Calif.
Chunling
C
Ge
Student, UCLA School of Dentistry, Los Angeles, Calif.
Chad C
CC
Green
Laboratory technician, UCLA School of Dentistry, Los Angeles, Calif.
Dalene
D
Sederstrom
Adjunct Associate Professor, UCLA School of Dentistry, Los Angeles, Calif.
Edward A
EA
McLaren
Professor, UCLA School of Dentistry, Los Angeles, Calif. Electronic address: snwhite@dentistry.ucla.edu.
Shane N
SN
White
D000134:Acid Etching, Dental / Q000379:methods; D000538:Aluminum Silicates / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D003743:Dental Enamel / Q000648:ultrastructure*; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D006801:Humans; D006813:Humidity; D006858:Hydrofluoric Acid / Q000737:chemistry; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D018583:Pliability; D058105:Polymerization; D017680:Potassium Compounds / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry
C074864:All-Bond system; D000538:Aluminum Silicates; D003188:Composite Resins; D008689:Methacrylates; D017680:Potassium Compounds; D012821:Silanes; D014867:Water; D003776:Dental Porcelain; C016447:feldspar; D006858:Hydrofluoric Acid