CBCT assessment of maxillary molar distalization and root length changes during clear aligner therapy

This prospective CBCT case series evaluated the pattern of maxillary molar movement during sequential distalization with clear aligners and vertical attachments, without adjunctive Class II elastics or skeletal anchorage, and assessed associated orthodontically induced inflammatory root resorption.

Ten maxillary quadrants from seven adult patients with Class II molar relationships were included. All patients were treated using a standardized sequential molar distalization protocol with clear aligners. CBCT scans were obtained at baseline (T0) and immediately after completion of molar distalization (T1). Linear crown and root positional changes, as well as molar root length changes, were assessed using three-dimensional CBCT superimposition. Descriptive statistics and paired t-tests were used, with significance set at P < 0.05.

The maxillary first and second molars demonstrated significant distal displacement at the mesiobuccal cusp tips: 1.24 ± 0.64 mm and 1.02 ± 0.82 mm, respectively. Root apex displacement was limited, suggesting crown-dominant distal movement rather than true bodily distalization. The maxillary central incisors showed significant labial incisal-edge displacement of 1.93 ± 1.27 mm, while root apex position remained stable, indicating partial anterior anchorage loss under the tested protocol. Small but statistically significant reductions in molar root length were detected, ranging from 0.19 ± 0.21 mm to 0.47 ± 0.68 mm.

Within the limitations of this exploratory prospective case series, sequential maxillary molar distalization with clear aligners and vertical attachments produced modest crown-dominant distal molar movement. Mild anterior anchorage loss was observed under a protocol without adjunctive elastics or skeletal anchorage. Molar root length reductions were small and remained below 1 mm. Larger controlled studies incorporating planned vs. achieved movement analysis are required.