Evaluation of ISO9693 Bond Tests with Zirconia Ceramics

Objectives: To evaluate the applicability of the ISO 9693 Schwickerath bond strength test, developed for metal ceramic bond strength evaluation, in the case of ceramic-ceramic bonds with transformation toughened zirconia ceramics. Methods: To date, metal ceramic bond strength tests have not been applicable to the evaluation of ceramic bond strength, due to the high stiffness and brittle nature of ceramic core materials. The introduction of transformation toughened zirconia ceramics with a relatively low elastic modulus (200 GPa, comparable to stainless steel) offers an opportunity to evaluate the applicability of this test. Samples of transformation toughened zirconia (Cercon, Dentsply Prosthetics) were prepared with three commercially available veneering porcelain materials - Ceramco PFZ (Dentsply Prosthetics), Cercon Ceram S (Dentsply DeguDent) and Cerabien CZR (Noritake Dental). The ISO 9693 procedure was then used to test the bond strengths in flexure. Results: Bond strengths comparable to those for metal ceramics (~ 25 MPa) were achieved with the ceramic-ceramic systems. However significantly different behavior was observed due to the higher elastic modulus, even compared to stiff NP alloys. The effect of surface preparation of the ceramics was significant. Conclusions: Though initial results are encouraging, more refinement related to elastic modulus behavior may be necessary before the ISO 9693 test is applicable to zirconia ceramic systems.