Crack propensity of porcelain laminate veneers: A simulated operatory evaluation

Statement of problem. Anterior teeth are especially subject to the thermal variations of ingested food and drinks. Postoperative cracks of porcelain l aminates are considered a possible consequence of polymerization shrinkage, function, and thermocycling. Purpose. This investigation was conducted to define the parameters associat ed with the development of cracks in porcelain veneers using cyclic thermal fatigue. Material and methods. Twenty-seven maxillary incisors were restored with po rcelain 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 s pecimens. 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 luti ng composite thicknesses. Most cracked samples exhibited a ratio at the fac ial location below 3.0 (2.6 +/- 0.35), whereas most noncracked specimens we re above this value (3.9 +/- 0.19). Incisal and especially proximal measure ments alone were not significantly different between cracked versus uncrack ed 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 developm ent of flaws in porcelain veneers. Control of tooth reduction and the appli cation of die spacers during laboratory procedures undoubtedly represent ke y elements; a sufficient and even thickness of ceramic combined with a mini mal thickness of luting composite will provide the restoration with a favor able configuration with regard to crack propensity, namely, a ceramic and l uting composite thickness ratio above 3.