Influence of core buildup material on the fatigue strength of an all-ceramic crown

Clinically relevant variables and testing methods have not been used to investigate the effects of core buildup materials on the strength of all-ceramic restorations.

The aim of this study was to evaluate the compressive strength of Optimal Pressable Ceramic (OPC) all-ceramic crowns supported by 1 of 3 different core materials and subjected to static or cyclic loading in air or water.

A total of 135 human extracted third molar teeth were divided into 3 equal groups, and cores of amalgam, composite, and dentin (control) were fabricated. Complete crown preparations with a circumferential 90 degrees shoulder margin 1 mm deep were prepared to support complete crown restorations. Testing in compression was performed at a loading rate of 2.0 mm/min. Sixty teeth (20 with each type of core) were subjected to static loading, with equal numbers tested in air and water. The remaining 75 teeth (25 with each type of core) were subjected to cyclic loading in water. The compressive and diametral tensile strengths of 6 x 12-mm OPC cylinders also were tested in both air and water. The data were analyzed with 1-way analysis of variance followed by the Tukey multiple means comparison test (P<.05).

Analysis of the static fracture stress of OPC crowns indicated no significant differences among the core materials (values from testing in air and water, respectively: dentin core 22.7 +/- 4.5 MPa and 19.7 +/- 4.7 MPa; amalgam core 25.2 +/- 5.2 MPa and 21.6 +/- 6.3 MPa; and composite core 20.9 +/- 4.1 MPa and 18.7 +/- 4.9 MPa). Under wet conditions, static versus cyclic loading produced significantly different results for each of the core materials (dentin core 19.7 +/- 4.7 MPa vs. 9.5 +/- 1.5 MPa; amalgam core 21.6 +/- 6.3 MPa vs. 10.3 +/- 1.6 MPa; composite core 18.7 +/- 4.9 MPa vs. 13.3 +/- 3.2 MPa). A significant difference was observed for the solid compressive cylinders tested in water (793.8 +/- 280.1 MPa) versus in air (1473.6 +/- 527.4 MPa).

Within the limitations of this study, the mean compressive strength of OPC crowns tested in water was significantly different under cyclic versus static loading. No significant difference among the 3 core materials was found with respect to crown compressive strength.