An investigation into the role of core porcelain thickness and lamination in determining the flexural strength of In-Ceram dental materials.

Purpose: A biaxial flexure test was conducted to evaluate the effect of reducing the thickness of In-Ceram core material and veneering with Vitadur α dentine porcelain on its flexural strength.
Materials and Methods: Four groups of 10 discs were tested; group I discs were In-Ceram discs with mean thickness of 1.58 ± 0.08 mm, group II discs were In-Ceram discs with mean thickness of 1.0 ± 0.11 mm, group III discs were laminated In-Ceram core porcelain/Vitadur α discs with a mean total thickness of 2.06 ± 0.15 mm and core porcelain thickness of 1.0 ± 0.11 mm; group IV discs were Vitadur α discs with a mean thickness of 2.08 ± 0.16 mm.
Results: Mean flexural strength values decreased between groups: 436 ± 38 MPa for group I, 352 ± 30 MPa for group II, 237 ± 24 MPa for group III, and 77 ± 14 MPa for group IV. The result of ANOVA and Tukey tests indicated that the mean flexural strength of group II was significantly less than group I, indicating that thickness of the In-Ceram core provides critical flexural strength to the final product. The addition of ≈ 1 mm of Vitadur α veneering porcelain to In-Ceram core significantly (p= 0.05) reduced the flexural strength as compared to the nonveneered In-Ceram core specimens (group II). The Vitadur α specimens (group IV) were significantly weaker than all the other groups.
Conclusion: This study indicates that lamination should be avoided in areas where maximum strength is required for In-Ceram all-ceramic crowns and bridges.
(© 2011 by the American College of Prosthodontists.)