Effect of various intermediate ceramic layers on the interfacial stability between zirconia core and veneering ceramics

Abstract

Objectives: The purposes of this study were to evaluate the effects of intermediate ceramics on the adhesion between the zirconia core and veneer ceramics.

Materials and methods: The polished surfaces of fully sintered Y-TZP blocks received three different treatments: 1) connector (C), 2) liner (L), or 3) wash layer (W). All the treated zirconia blocks were veneered with either a) fluorapatite glass-ceramic (E) or b) feldspathic porcelain (V) and divided into four groups (CE, CV, LE and WV). For the control group, the testing surfaces of metal blocks were veneered with feldspathic porcelain (VM). All veneered blocks were sectioned into bars (3 mm × 3 mm × 7 mm), perpendicularly to the interface. A half of the samples in each group (n = 21) were exposed to thermocycling for 20,000 cycles. The temperature was altered between 5°C and 55°C with an immersion time of 30 seconds and a transfer time of 2 seconds. The other half of the specimens were stored at room temperature under dry conditions. All specimens were subjected to the shear test, and the failed surfaces were microscopically examined. The elemental distribution at the zirconia core/veneer interface was analyzed. The bond strength data of the groups were compared with one-way analysis of variance (ANOVA) and the post hoc analyses were conducted using a Tukey test (α=0.05).

Results: The specimens in Group CE and CV exhibited significantly greater mean bond strength values than those in Group LE and WV, respectively (P<0.05). However, the mean bond strengths significantly decreased in the connector groups (CE and CV) after thermocycling (P<0.05). The elemental analysis suggested diffusion of ceramic substances into the zirconia surface.

Conclusions: A glass-ceramic based connector is significantly more favorable to core/veneer adhesion than the other intermediate ceramics evaluated in the study. However, thermocycling affected the bond strength at the core/veneer interface differently according to the intermediate ceramics.