Does the maxillary sinus floor affect orthodontic tooth movement and root resorption after premolar extraction? A...

This study aimed to evaluate the impact of maxillary sinus-root relationship (SRR) on orthodontic tooth movement and root resorption measured by using cone-beam computed tomography (CBCT) during first premolar extraction space closure in adults receiving traditional treatment (TT) and clear aligner therapy (CAT).

This retrospective study analyzed pre and posttreatment CBCT scans of 80 Chinese adults (type I vs type V SRR; TT vs CAT), with 40 patients in each SRR type and equal allocation to TT and CAT groups. All measurements were performed on CBCT images at T1 and T2 using InVivo 6.0.3 software (Anatomage, San Jose, Calif).

Greater mesial molar movement was observed in type I SRR than in type V SRR. In the TT group, mesial root movement was greater in type I SRR (between-group mean difference [ΔΔT] = -1.24 mm; confidence interval = -2.35 to -0.13; P = 0.029). In the CAT group, type I SRR showed greater mesial root movement (ΔΔT = -1.12 mm; confidence interval = -1.84 to -0.41; P = 0.003) and larger cusp displacement at mesial and distal cusps (ΔΔT = -2.12 mm; ΔΔT = -1.54 mm). Within type I SRR, the CAT group produced greater cusp movement than TT (ΔΔT = 1.29 mm; ΔΔT = 0.90 mm). No significant TT vs CAT group differences were observed in type V SRR. All groups had significant root resorption; TT group was associated with greater resorption than CAT group, particularly in the second premolar (ΔΔT = 0.36 mm; P = 0.010), palatal root of the first molar in type I SRR (ΔΔT 0.37 mm; P = 0.006), and distobuccal root in type V SRR (ΔΔT = 0.30 mm; P = 0.013).

The findings suggest that molar movement may be greater when the sinus floor is farther from the roots, and CAT may induce more tipping, whereas TT may cause more root resorption. Sinus proximity did not appear to increase resorption risk. However, the imbalance in treatment duration between TT and CAT remains a potentially biasing limitation.