Long-term Bond-strength of CAD/CAM Composite Samples and a Universal Adhesive

Objectives: In adhesive cementation of indirect restorations, clinical success of the luting system is often correlated with shear bond strength (SBS). However, initial SBS offer little information regarding long-term-stability of the bonded interface. To ensure a clinically performing cementation of milled CAD/CAM composite restorations, stable SBS provided by the luting-materials employed is paramount.
This study evaluated the effect of up to 6 month water-storage on the SBS between a new CAD/CAM composite and clinically well-established universal adhesive and luting composite.
Methods: SBS was tested according to ISO-29022. CAD/CAM composite blocks Tetric-CAD (Ivoclar Vivadent) were sandblasted with 50 µm corundum at 1.5 bar (Renfert) to obtain a visibly matt surface. This surface was then contacted with Adhese Universal ("AU", Ivoclar Vivadent) under 20s of microbrush agitation, and the adhesive thinned to an immobile layer with compressed air (4bar). The specimen was then carefully introduced into the sample jig and the luting composite Variolink Esthetic DC ("VLE", Ivoclar Vivadent) applied to the bonded surface via the jig mould. The specimen was then light-cured using a Bluephase Style curing unit at 1200 mW/cm² (Ivoclar Vivadent) through a Tetric-CAD disc (3mm, MT A3.5) for 30 s.
Specimens were aged (24h, 3 and 6 months, 37°C, water) before testing SBS (ZWICK-ROELL, Z010, 1mm/s crosshead-speed).
Results: SBS showed that Adhese Universal and Variolink Esthetic DC on sandblasted Tetric-CAD provided stable high values for at least 6 months. There was no discernible influence of storage period on bond-strength performance.
Conclusions: Within the limitations of this investigation, shear bond strength obtained with Tetric-CAD, Adhese Universal and Variolink Esthetic DC proved to be tolerant to at least 6 months of water storage.