Evaluate The Crown/Root Ratio Of Clear Aligners After Expansion

To investigate the expression efficiency of the crown/root of maxillary posterior teeth by clear aligner. In this research, through a retrospective study, 41 adult patients with tooth non-extraction, the average age of 25.67±7.07 years, the application of clear aligner (Invisalign) for maxillary expansion treatment of posterior teeth. There were 7 males and 34 females with permanent dentition, complete eruption of the second molar, good tooth morphology and no bad prosthesis. The horizontal, sagittal and coronal planes were determined on CBCT, and the crown and root width of 264 teeth were measured before (T0) and after (T1) arch expansion. When using Invisalign for maxillary expansion, the efficiency of crown expansion decreased gradually from the first premolar to the second molar. The first premolar was 74.47%±21.78%, the second premolar was 68.55%±23.26%, the first molar was 63.09%±10.56%, and the second molar was 66%±31.87%. Buccal inclination was 4.84°±1.71 in group A (crown/root ≤1:2). The crown/root ratio of 0.46:1 should be designed to achieve buccal overall movement of the first premolars. A crown/root ratio of 0.58:1 should be designed to achieve buccal overall movement of the second premolars. The overall buccal movement of the first molar was realized. The design crown/root ratio was 0.51:1. The crown/root ratio of 0.52:1 should be designed to achieve the overall buccal movement of the second molar.