Adhesion to a new CAD/CAM resin composite: Effects of the machining roughness simulation, surface treatments, and long-term aging.

To evaluate the effect of surface treatments, finishing condition (polished vs. ground) and aging on the microtensile bond strength of a CAD/CAM resin composite to resin cement. CAD/CAM resin composite blocks (Tetric CAD HT) were sectioned (7 × 12 × 4 mm), randomly divided according to finishing condition (polished or ground) and surface treatment groups (Ctrl: no treatment; AA: air-abrasion with 110 μm Al 2 O 3 powder; TBS: tribochemical silica coating). A coupling agent corresponding to each surface treatment was applied for cementation (Ctrl and AA groups: ExciTE F DSC; TBS group: RelyX Ceramic Primer) and each block was adhesively cemented (Variolink N) with another one from the same conditioning. Next, 1 mm2 cross-section beams were produced after sectioning, with half being tested under microtensile test after 24 h, while the other half was aged (25,000 cycles of thermocycling + 90 days of storage) (n = 50). Contact angle and Scanning Electron Microscopy (SEM) analysis were performed. Bond strength data (MPa) were statistically analyzed using Three-way ANOVA and Tukey tests (α = 0.05). The failure types were examined and classified as predominantly adhesive, cohesive or mixed under stereomicroscopy. The surface treatments (AA and TBS) promoted higher bond strength than the Ctrl group. Grinding finishing improved the bond strength only when no treatment was performed (Ctrl group), having a negative effect for the TBS treatment. The long-term aging damaged the resin bond, independent of the condition. The failure analysis showed that 92% of the failures were classified as adhesive in the baseline conditions, and 94.7% in aged specimens. TBS showed the lowest contact angle among the tested groups for both conditions (baseline and aged). Surface conditioning with alumina particle air-abrasion or tribochemical silica coating improves the bond strength. CAD/CAM milling roughness induces better surface condition for adhesion, in particular when no treatment is performed. Bond degradation occurs after long-term aging for all the test conditions. When luting CAD/CAM resin composite restorations, the surface treatment and roughness due to the grinding by burs in the manufacturing process influence the adhesion of restoration to resin cement. • The machining roughness simulation influences the bond strength of the CAD-CAM resin composite to resin cement. • Alumina particle air-abrasion lead to the higher bond strength for a milled composite resin surface. • Treated polished surfaces has higher reduction in bond strength after long-term aging. • Tribochemical surface treatment has the lowest reduction in bond strength after aging. [ABSTRACT FROM AUTHOR]