Validation of the Adhesive Remnant Index (ARI) using quantitative 3D scanner analysis on in vitro samples

Background: Residual adhesive left on enamel after orthodontic bracket removal can compromise aesthetics and enamel integrity. The Adhesive Remnant Index (ARI) is commonly used to visually assess these residues, but its correlation with true adhesive volume has not been quantitatively validated. Objective: This study aimed to validate the visual ARI using 3D optical scanning and test the hypothesis of no correlation between ARI scores and adhesive remnant volumes. Methods: Seventy-five extracted human third molars were bonded with molar tubes using BrackFix Adhesive. After 24 h, tubes were debonded, and ARI scores (0–3) were assessed visually under 6.0× magnification. Residual adhesive was scanned pre- (T0) and post-debonding (T1) using a structured-light 3D scanner (ATOS Compact). Volumes were calculated and analyzed with Kendall's tau correlation. Results: A strong correlation was found between ARI scores and adhesive remnant volumes (Kendall's τ = 0.649; p < 0.001). Median volumes increased with ARI scores: 0.048 mm3 (score 0), 0.401 mm3 (score 1), 1.025 mm3 (score 2), and 2.893 mm3 (score 3). Conclusion: Visual ARI scores significantly reflect the actual adhesive remnant volume as quantified by 3D scanning, supporting ARI's clinical validity for assessing residual adhesive after debonding.