Effect of thermocycling on the flexural strength of porcelain laminate veneers

The aim of this study was to examine the impact of thermocycling on the flexural strength and development of surface flaws on the glazed surface of porcelain laminate veneer restorations with and without resin luting cement.

80 Vitadur alpha dentin porcelain discs (10 mm diameter, 0.9 mm thickness) were glazed on one side and divided into two groups: A (porcelain laminate veneer only without resin luting cement) and B (porcelain laminate veneer luted with resin cement), each containing 40 discs. The discs in groups A and B were then thermocycled at different temperatures and were subjected to SEM analysis to evaluate the effect of thermocycling on crack propagation. Mean flexural strength was determined by using the ball-on-ring test. Student's t -test was used to find out the difference between strength values of the thermocycled porcelain discs and discs luted with resin cement.

SEM analysis revealed crack propagation in the subgroups subjected to extremes of temperature, i.e., 4 +/- 1 degrees C, 37 +/- 1 degrees C and 4 +/- 1 degrees C, 65 +/- 1 degrees C in the porcelain laminate veneers luted with resin cement. Flexural strength analysis revealed superior flexural strength for porcelain laminate veneers: 88.58 +/- 6.94 MPa when compared to porcelain laminate veneers luted with resin cement: 8.42 +/- 2.60 MPa. Results were tabulated and statistically analyzed using Student's t -test.

Laminate veneer specimens exhibited greater flexural strength than those which were luted with resin cements. Laminate veneer specimens luted with resin cement and subjected to extremes of temperature, 4 +/- 1 degrees C and 37 +/- 1 degrees C and 4 +/- 1 degrees C and 65 +/- 1 degrees C, showed a marked decrease in flexural strength. After thermocycling at extremes of temperature, laminate veneer specimens luted with resin cement showed crack propagation. Fit of laminate veneers cannot / should not be compensated by the thickness of luting agent.