A multivariable model for treatment duration in nonextraction clear aligner therapy

The objective of this study was to evaluate the associations between pretreatment dentoalveolar characteristics and treatment duration in nonextraction clear aligner therapy (CAT).

This retrospective cohort study included 296 patients treated with nonextraction CAT. Pretreatment variables were extracted from Invisalign ClinCheck (Align Technology, Santa Clara, Calif) digital treatment planning software and included deviations in overjet and overbite from a 3 mm reference, arch irregularities, midline deviation, and posterior crossbite. Treatment duration was defined as the time from initial aligner delivery to the completion of all refinement stages. Multivariable linear regression analysis was performed to evaluate the associations between pretreatment characteristics and treatment duration. Internal validation was performed using bootstrap resampling (5000 iterations).

The 11 pretreatment variables collectively explained 32.8% of the variability in treatment duration (R² = 0.328; adjusted R² = 0.302). Overbite showed the strongest association with treatment duration, followed by mandibular crowding, midline deviation, and posterior crossbite (P <0.001). Each 1 mm increase in overbite and overjet was associated with increases of approximately 41 and 15 days in treatment duration, respectively. The presence of posterior crossbite was associated with an approximately 89-day increase. Bootstrap analysis demonstrated the stability of the regression estimates.

Pretreatment dentoalveolar characteristics were significantly associated with treatment duration in nonextraction CAT. Although several baseline characteristics independently contributed to treatment duration, the model explained approximately one-third of its variability, highlighting the influence of biological, behavioral, and treatment-related factors beyond pretreatment records.