Influence of cement thickness on resin-zirconia microtensile bond strength

Abstract

Purpose: The aim of this study was to evaluate the influence of resin cement thickness on the microtensile bond strength between zirconium-oxide ceramic and resin cement.

Materials and methods: Thirty-two freshly extracted molars were transversely sectioned at the deep dentin level and bonded to air-abraded zirconium oxide ceramic disks. The specimens were divided into 8 groups based on the experimental conditions (cement type: Rely X UniCem or Panavia F 2.0, cement thickness: 40 or 160 µm, storage: thermocycled or not). They were cut into microbeams and stored in 37℃ distilled water for 24 h. Microbeams of non-thermocycled specimens were submitted to a microtensile test, whereas those of thermocycled groups were thermally cycled for 18,000 times immediately before the microtensile test. Three-way ANOVA and Sheffe's post hoc tests were used for statistical analysis (α=95%).

Results: All failures occurred at the resin-zirconia interface. Thermocycled groups showed lower microtensile bond strength than non-thermocycled groups (P<.001). Differences in cement thickness did not influence the resin-zirconia microtensile bond strength given the same resin cement or storage conditions (P>.05). The number of adhesive failures increased after thermocycling in all experimental conditions. No cohesive failure was observed in any experimental group.

Conclusion: When resin cements of adhesive monomers are applied over air-abraded zirconia restorations, the degree of fit does not influence the resin-zirconia microtensile bond strength.

Keywords: Cement thickness; Microtensile bond strength; Resin cement; Zirconia.

Fig. 1

Schematic image of customized jig for zirconia-resin-tooth bonding. Two lateral fixation screws stabilized Tofflemire matrix bands. A vertical fixation screw immobilized the cut tooth specimen and maintained constant torque during polymerization of the resin cement.

Fig. 2

Preparation of microbeams. A customized holding device was used to rotate the specimen 90 degrees, resulting in microbeams with a rectangular cut surface.

Fig. 3

Measurement of cement thickness. Microbeams with cement thicknesses of 40 (A) and 160 µm (B).

Fig. 4

SEM images of fractured non-thermocycled microbeams. The fractured surface reflects the mixed failure mode at the resin-zirconia interface (A: U40NTC; B: P160NTC).

Fig. 5

SEM images of fractured microbeams which were thermally cycled 18,000 times. Both fractured surfaces represent adhesive failures at the resin-zirconia interface (A: U40TC, B: P40TC).