Influence of ceramic thickness and type on micromechanical properties of light-cured adhesive bonding agents

Objective. The aim of this study was to evaluate the micromechanical properties of different adhesive bonding agents when polymerized through ceramics. Materials and methods. Sixty sound extracted human third molars were selected and the crowns were sectioned perpendicular to the long axis in order to obtain dentin slices to be bonded with one of the following adhesives: Syntac/Heliobond (Ivoclar-Vivadent) or Adper-Scotchbond-1XT (3M-ESPE). The adhesives were cured by using a LED-unit (Bluephase (R), Ivoclar Vivadent) with three different curing times (10 s, 20 s and 30 s) under two ceramics (IPS-e. max-Press, Ivoclar-Vivadent; IPS-Empress (R) CAD, Ivoclar-Vivadent) of different thicknesses (0 mm, 0.75 mm, 2 mm). Thirty groups were included, each containing 60 measurements. Micromechanical properties (Hardness, HV; indentation modulus, E; and creep, Cr) of the adhesives were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). Data were statistically analyzed by using one-way ANOVA and Tukey's post-hoc test, as well as a multivariate analysis to test the influence of the study parameters (SPSS 18.0). Results. Significant differences were observed between the micromechanical properties of the adhesives (p < 0.05). The ceramic type showed the highest effect on HV (Partial-eta squared (eta(2)) = 0.109) of the tested adhesives, while E (eta(2) = 0.275) and Cr (eta(2) = 0.194) were stronger influenced by the adhesive type. Ceramic thickness showed no effect on the E and Cr of the adhesives. Conclusions. The adhesive bonding agents used in this study performed well by curing through different thicknesses of ceramics. The micromechanical properties of the adhesives were determined by the adhesive type and were less influenced by ceramic type and curing time.