Thio-urethane Oligomer Additives to Resin Cements Affect Ceramic-composite Bond Strengths

Objectives: The aim of this study was to evaluate the effect of thio-urethane (TU) additives to resin cements on the microtensile bond strength (µTBS) of the ceramic, luted with the experimental and commercial resin cements, after mechanical fatigue (Mf) and thermal cycling (Tc).
Methods: Ninety-six ceramic blocks (IPS e.max Press) were made and assigned to 12 groups (n=8): Groups 1-3 - bonded with experimental control cement (EC) without thio-urethane; Groups 4-6 – bonded with experimental cement with 20 wt% of aliphatic TU; Groups 7-9 – bonded with experimental cement with 20 wt% of aromatic TU; and Groups 10-12 – bonded with commercial cement, RelyX Ultimate-RU. Ceramic surfaces were etched (20s-10% hydrofluoric acid) and treated with silane before being cemented to composite blocks (Z250). Composite surfaces were treated with adhesive (Single Bond Universal). After 24 hours in distilled water at 37°C, the specimens of groups 2, 5, 8 and 11 were subjected to Tc (10,000, 5°C-55°C) while groups 3, 6, 9 and 12 to Mf (300,000). Specimens were sectioned to obtain sticks (1mm²) and subjected to µTBS at a crosshead speed of 1.0 mm/min. Data were analyzed with ANOVA/Tukey’s test (α=0.05).

Results: The µTBS (MPa) of the resin cements after 24 hours, Tc and Mf for aliphatic TU (38.6±1.9; 34.2±3.3; 33.1±1.7) and RU (38.8±2.5; 33.1±2.1; 30.5±2.6) were significantly higher than for aromatic TU (36.5±1.1; 29.9±1.7; 28.6±1.7), which were higher than EC (30.2±2.2; 24.9±2.5; 23.8±1.5). Bond strength decreased significantly (~15-20%) after the Tc and Mf for all groups.

Conclusions: The use of thio-urethane oligomers, mainly the aliphatic version, was able to increase the µTBS of composite-ceramic specimens. Tc and Mf reduced µTBS for all resins cements.