Evaluation of thermal compatibility between core and veneer dental ceramics using shear bond strength test and contact angle measurement

Objectives. To test the hypotheses that shear bond strength (sigma(s)) and contact angle (theta) are influenced by the thermal expansion/contraction behavior of bilayered all-ceramic systems. Methods. Glass-infiltrated ceramics (A - In-Ceram ALUMINA) and zirconia-reinforced alumina (Z - In- Ceram ZIRCONIA) were veneered with feldspathic ceramics (7 - VM7; 9 - VM9; 13 - VM13), yielding 6 experimental groups. Surface roughness (Ra) of A and Z core ceramic disks (12 mm diameter x 1.2 mm high) was measured to assure that values were similar. A cylinder of veneer (2 mm diameter x 2 mm high) was fired onto the center of all core disks, cooled under identical conditions and tested for sigma(s) to failure (n = 20). For the theta evaluation (n = 10) similar specimens (veneer 1 mm high) were overfired to develop an equilibrium theta that was then measured from digital images (AutoCAD 2006). Published thermal expansion data were used. Results. The mean values of sigma(s) (MPa) and theta(degrees) for the core-veneer ceramic groups were, respectively: A7 (19.4 +/- 4.7; 49 +/- 4.7); Z7 (23.4 +/- 6.2; 56 +/- 4.9); A9 (0.9 +/- 1.6; 55 +/- 5.8); Z9 (9.8 +/- 5.7; 59.8 +/- 2.9); A13 (0; 70 +/- 6.0); Z13 (0; 67.2 +/- 6.3). As the difference in coefficient of thermal expansion (coreveneer) increases, the theta value increases (r = 0.95) and the sigma(s) value decreases (r = -0.92), p <= 0.01. Conclusion. The contact angle measurement and the shear bond strength test of core-veneer ceramics are influenced by the thermal expansion behavior of these all-ceramic systems. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.