The Effect of Cementation Load, Unload Time, and Storage Time on Film Thickness and Microtensile Bond Strength...

This article aims to evaluate the effect of load weight, unload time, and storage duration on microtensile bond strength (µTBS) of dual-cure resin cement to CAD/CAM composite.

Forty-eight composite blocks (Grandio Blocs, n = 24 shade A1, and n = 24 shade A4) were randomly assigned to eight groups (n = 3 shade A1, and n = 3 shade A4) based on load weight (1, 3, 5, and 15 kg), and unload time (immediately before light curing or 10 minutes during/after light curing). Bonded blocks (n = 3/group) were sectioned into multiple sticks. Half of the sticks (n = 21) were tested after 24 hours, while the remaining 21 were stored in distilled water at 37°C and tested after 6 months. Sticks for film thickness were evaluated using a stereomicroscope (60 × ). However, the sticks for µTBS were pulled in tension at a 0.5-mm/min crosshead speed.

Data were analyzed using ANOVA and the Games-Howell post hoc test (α = 0.05).

There was no correlation between µTBS and FT (r = 0.035; p = 0.737). For the FT, only "unload time" had a significant effect (p < 0.001). For µTBS, "load weight," and "unload time" had no significant impact (p = 0.948 and p = 0.948, respectively). However, "storage time" significantly influenced the results (p < 0.001). Adhesive mode was significantly predominant (56.85%).

Unload time is a crucial factor controlling the film thickness of the dual-cure resin cement. However, it does not affect the resin cement µTBS to CAD/CAM composite.

Excessive seating load should be avoided when positioning CAD/CAM composite restorations, while a controlled short time may assist in preventing restoration rebound.