3D assessment of morphological changes, maxillary central incisor-incisive canal relationship, and root resorption in extraction fixed appliance therapy considering demographic and skeletal classifications.

Background: This study aimed to assess changes in morphology, the relationship between the maxillary central incisor (U1) and the incisive canal (IC) and estimate root resorption following extraction orthodontic treatment with fixed appliances, considering gender, age, and skeletal sagittal and facial classifications.

Methods: The sample comprised eighty-four maxillary central incisors from 42 patients treated with maxillary incisors retraction using fixed appliances with first premolars extraction. Measurements, including IC width, root-IC distance, cortical bone width, IC height, and root resorption, were taken before (T1) and after (T2) treatment at specified heights (H1, H2, and H3; 2, 4, and 6 mm above the labial cementoenamel junction of U1).

Results: Significant differences in IC width, U1 length, and U1 root-IC distance were observed across genders, age groups, and skeletal classifications. Root resorption was greater in females (2.60 ± 1.82 mm vs. 1.25 ± 1.20 mm, P = 0.008), adults (2.53 ± 1.71 mm vs. 1.28 ± 1.45 mm, P = 0.009), Class II subjects (2.30 ± 1.86 mm vs. 1.47 ± 1.22 mm, P = 0.040), and the high angle facial group (3.41 ± 1.49 mm vs. 1.10 ± 1.23 mm vs. 0.90 ± 0.75 mm, P < 0.001). Root-IC proximity increased after treatment, showing a positive correlation with resorption, especially at H2 level for approximation (66.7%) and contact (31%), and at the H1 level for invasion (25%). Multivariate regression identified U1 tooth movement and IC height as key factors in negative U1-IC relationships.

Conclusions: Extraction orthodontic treatment with fixed appliances significantly impacts the U1-IC relationship and contributes to root resorption, with variations across demographic and skeletal groups. These findings underscoring the need for precise treatment planning to reduce risks of root resorption and unfavorable U1-IC proximity.

Clinical relevance: These findings enhance orthodontic treatment planning by identifying factors influencing root resorption and preserving dental health during anterior teeth retraction.