Background: The objective of this study was to assess the correlation between maxillary sinus proximity to root apices of maxillary molars and changes in molar angulation (tipping), inclination (torque), and rotation during molar distalization using clear aligner therapy (CAT).
Methods: This study evaluated 38 cone beam computed tomography (CBCT) images obtained pre (T0) and post (T1) treatment from 19 adult patients who underwent maxillary molar distalization using Invisalign aligners (Align Technology, Inc., San José, CA, USA) with at least 2mm distalization. Only those who wore the aligner for at least 22 hours daily were included in the study. Sinus proximity and the changes in tip, torque and rotation were measured for 61 molars. Spearman coefficient analysis was used to appraise the correlation between sinus proximity and each of the other measured variables. The level of significance was set at p≤ 0.05. The reproducibility of measurements was assessed by the intraclass correlation coefficient (ICC).
Results: Spearman coefficient revealed a significant positive correlation between maxillary sinus proximity to root apices and molar inclination (buccal crown torque) (p=0.044). Palatal root proximity to the sinus was the only individual root eliciting a positive correlation with molar inclination (p=0.022). No significant correlation was found between sinus proximity and molar angulation (tipping) nor rotation (p= 0.381 and p=0.124, respectively).

Conclusion: Proximity of maxillary molars root apices to the maxillary sinus causes more buccal crown torque during distalization using CAT, while it has no significant effect on molar tipping nor rotation.