Crack propensity of porcelain laminate veneers: A simulated operatory evaluation.
BACKGROUND
Anterior teeth are especially subject to the thermal variations of ingested food and drinks. Postoperative cracks of porcelain laminates are considered a possible consequence of polymerization shrinkage, function, and thermocycling.


OBJECTIVE
This investigation was conducted to define the parameters associated with the development of cracks in porcelain veneers using cyclic thermal fatigue.


METHODS
Twenty-seven maxillary incisors were restored with porcelain laminate veneers and subjected to thermocycling (5 degrees C to 50 degrees C) for 1000 cycles. Ceramic cracks were reported for 11 of the 27 specimens. Teeth were sectioned and prepared for SEM analysis. Measurements of the ceramic and the luting composite thicknesses were performed for each specimen at different restoration locations (facial, incisal, and proximal).


RESULTS
No significant differences in the ceramic or the luting composite thicknesses were observed between cracked and uncracked specimens. However, significant differences were observed in the ratio of the ceramic and luting composite thicknesses. Most cracked samples exhibited a ratio at the facial location below 3.0 (2.6 +/- 0.35), whereas most noncracked specimens were above this value (3.9 +/- 0.19). Incisal and especially proximal measurements alone were not significantly different between cracked versus uncracked specimens. Ceramic was slightly thinner in the facial aspect than in the proximal aspect, which was also thinner than the incisal aspect. Composite in the facial aspect was thinner in the cervical area than in the incisal third of the tooth.


CONCLUSIONS
Significant cyclic temperature changes can induce the development of flaws in porcelain veneers. Control of tooth reduction and the application of die spacers during laboratory procedures undoubtedly represent key elements; a sufficient and even thickness of ceramic combined with a minimal thickness of luting composite will provide the restoration with a favorable configuration with regard to crack propensity, namely, a ceramic and luting composite thickness ratio above 3.
Magne
P
P
School of Dentistry, University of Minnesota, Minneapolis, Minn., USA. pascal@web.dent.umn.edu
Kwon
K R
KR
Belser
U C
UC
Hodges
J S
JS
Douglas
W H
WH
D000704:Analysis of Variance; D001628:Beverages; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003801:Dental Veneers; D005502:Food; D006801:Humans; D007180:Incisor / Q000648:ultrastructure; D016014:Linear Models; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011108:Polymers / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics
D003188:Composite Resins; D011108:Polymers; D019279:Resin Cements; D003776:Dental Porcelain