Adhesion of dental porcelain to cast, milled, and laser-sintered cobalt-chromium alloys: shear bond strength and sensitivity to thermocycling.

STATEMENT OF PROBLEM: New technologies have led to the introduction of new materials, so an evaluation of the adhesion of ceramics to these materials is needed. PURPOSE: The purpose of this study was to compare the shear bond strength of dental porcelain to cast, milled, and laser-sintered cobalt-chromium alloys, and to investigate the adhesive bond and failure type after thermocycling, 90 metal cylinders (10 mm diameter and 10 mm height) were prepared from cast (30 specimens), milled (30 specimens), and laser-sintered (30 specimens) alloys. MATERIAL AND METHODS: Ceramic cylinders (2.5 mm diameter and 4 mm length) were fused to the alloy cylinders. For each group, 15 specimens were thermocycled 5500 times at temperatures between 4°C and 60°C before testing. After testing, the specimen surfaces were visually examined to determine the failure mode. Differences in adhesion values according to manufacturing method, testing condition (thermocycling or no thermocycling), and interaction between the factors were evaluated with a 2-way ANOVA. The χ(2) test (95% confidence level) was performed to determine whether the failure mode was associated with the testing condition. RESULTS: Adhesion strengths for the nonthermocycled specimens were 42.79 ±14.14 MPa (cast), 37.56 ±9.18 MPa (milled), and 29.09 ±6.95 MPa (laser-sintered), and, for the thermocycled specimens, 16.52 ±8.96 MPa (cast), 22.21 ±13.25 MPa (milled), and 24.28 ±10.13 MPa (laser-sintered). Two-way ANOVA results indicated no statistically significant differences in adhesion among the manufacturing methods (P=.257), but statistically significant differences were observed according to both testing conditions (P<.001) and interaction between the factors (P=.015). The χ(2) test indicated that the failure mode was not associated with the testing condition (thermocycled, P=.280; nonthermocycled, P=.240). CONCLUSIONS: The porcelain adhesion values for all the materials were adequate for clinical applications. No significant adhesion differences were observed between cast, milled, and laser-sintered specimens, or among thermocycled and nonthermocycled laser-sintered specimens. However, significant adhesion differences were observed among the thermocycled and nonthermocycled cast and the milled specimens.