Impact of thermal misfit on shear strength of veneering ceramic/zirconia composites.
OBJECTIVE
Thermal misfit is discussed as one reason for chipping of veneered zirconia restorations. The aim of the investigation was to assess the effect of thermal misfit on the shear strength of zirconia/veneering ceramic composites.


METHODS
Shear strengths of 12 different veneering ceramic/zirconia composites were measured (n=10). The veneering ceramics were fired onto polished Y-TZP. In order to create a strong thermal mismatch, one of the veneering ceramics was intended for use on alumina and one for the metal-ceramic technique. The glass transition temperatures of the veneering ceramics and the coefficients of thermal expansion of all ceramics were measured (n=6). Statistical analysis was performed with one-way ANOVA and a post hoc Bonferroni test (p<0.05).


RESULTS
Shear strength ranged from 21.9+/-6.2 to 31.0+/-7.1 MPa. The ceramic for the metal-ceramic technique showed spontaneous debonding. The differences in the coefficients of thermal expansion of core and veneer (Delta alpha) were calculated. In addition the differences between glass transition temperatures of the veneering ceramics and room temperature (Delta T) as the effective temperature range for stress formation were calculated. Highest shear strength was observed when Delta alpha Delta T approximately 1000 x 10(-6).


CONCLUSIONS
Thermal expansion and glass transition temperature of the veneering ceramic have an impact on the shear strength of veneer/zirconia composites.
Fischer
Jens
J
Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Center for Dental and Oral Medicine, University of Zurich, Plattenstrasse 11, CH-8032 Zurich, Switzerland. jens.fischer@zzmk.uzh.ch
Stawarzcyk
Bogna
B
Trottmann
Albert
A
Hämmerle
Christoph H F
CH
D000537:Aluminum Oxide; D001840:Dental Bonding; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D003801:Dental Veneers; D003804:Dentin; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys; D033081:Shear Strength; D044366:Transition Temperature; D015019:Yttrium; D015040:Zirconium
D016876:Metal Ceramic Alloys; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide