Comparison of shear bond strengths of clear aligner attachments to full-contour zirconia crowns with different sandblasting times and primers: An in vitro study.

Introduction: This study investigated the effect of sandblasting time and primer type on the shear bond strength of composite attachments to full-contour zirconia crowns.

Methods: A total of 108 zirconia specimens were fabricated and divided into 9 groups (n = 12) according to sandblasting time (10, 30, and 60 seconds) and primer type (silane, 10-methacryloyloxydecyl dihydrogen phosphate [MDP], universal). After sandblasting with 110-μm alumina particles, specimens were primed, and attachments were bonded using a packable composite. Surface roughness was measured, and scanning electron microscopy analysis was performed on an additional 36 specimens. Specimens underwent thermocycling before shear bond strength testing. Failure modes were assessed using a digital microscope and categorized based on the Adhesive Remnant Index (ARI) as adhesive, cohesive, or mixed. Data analyses were conducted using 2-way analysis of variance and chi-square tests.

Results: Surface roughness and microirregularities peaked at 30 seconds. Both sandblasting time and primer type significantly influenced the shear bond strength (P <0.001). MDP and universal primers consistently outperformed silane. Optimal bond strength varied with primer type and sandblasting time: 30 seconds with MDP yielded 12.02 MPa, whereas 60 seconds with universal primer reached 14.56 MPa. Silane resulted in predominantly adhesive failures (ARI, 0). Mixed failures (ARI, 1) were more common with MDP and universal primers, particularly at 60 seconds of sandblasting with the universal primer.

Conclusions: This study highlights the importance of sandblasting duration and primer selection in optimizing bond strength to zirconia. Both MDP and universal primers achieved clinically acceptable bond strength, with their performance influenced by sandblasting time.