Effect of attachment design and light-curing duration on shear bond strength in clear aligners

The objective of this study was to evaluate the effects of various attachment geometries and light-curing durations on shear bond strength and Adhesive Remnant Index (ARI) scores. A total of 90 extracted human premolars were divided into three groups based on attachment shape: rectangular, bevel, and ellipsoid (n = 30). Each group was further subdivided by curing time: 3 s (high-intensity LED, 2300–2500 mW/cm²) and 15 s (conventional LED, 1000–1200 mW/cm²), with 15 samples per subgroup. Attachments were designed in a CAD environment and bonded using customized transfer trays. Following bonding, samples were subjected to shear bond strength testing using a universal testing machine. Adhesive remnants were evaluated using the Adhesive Remnant Index (ARI). Data were analyzed using two-way ANOVA and Tukey HSD test (p < 0.05), with statistical processing performed in R (v4.4.0). No significant difference was found in shear bond strength based on curing time [F(1,84) = 0.286, p = 0.594]. Under 3-second curing, rectangular attachments showed significantly greater shear bond strength than ellipsoids (p < 0.001). With 15-second curing, rectangular attachments also yielded significantly greater strength than both ellipsoid (p < 0.001) and bevel (p = 0.007) types. Ellipsoid attachments exhibited significantly higher ARI scores compared to the other groups (p < 0.05). Attachment geometry significantly influenced shear bond strength, with rectangular attachments demonstrating the highest resistance in both curing durations. Curing duration alone did not produce a statistically significant effect. These findings underscore the importance of attachment selection in clinical treatment planning.