Abstract
Introduction: Class II malocclusion, particularly its unilateral presentation, poses significant challenges in orthodontics because of asymmetrical occlusal relationships and associated midline deviations. Although clear aligner therapy offers esthetic and practical benefits, its predictability in achieving complex movements, such as unilateral molar distalization, remains limited.
Methods: This retrospective study included 51 adult patients treated with clear aligners for Class II subdivision malocclusion taken from the Australasian Aligner Research Database. Digital models at baseline, from the virtual treatment plan (planned), and at the outcome achieved after a single course of aligner treatment were analyzed using Geomagic Control X software to assess unilateral molar Class II correction, overjet changes, and midline discrepancy. A subgroup of 12 patients was further analyzed to evaluate unilateral maxillary molar distalization and associated mesiodistal tipping of the maxillary molars.
Results: On average, 36.8% of the planned molar relationship correction and 23.8% of the planned midline correction were achieved. Overjet increased rather than decreased, representing a 28.8% shortfall in the planned overjet correction. Subgroup analysis indicated that 53% of the planned molar distalization was achieved (mean, 1.6 mm vs 3.0 mm planned), with a strong correlation (r = 0.98) between distalization and molar tipping, averaging 2.6° per millimeter.
Conclusions: Clear aligner therapy demonstrates limited predictability in achieving unilateral Class II molar correction, overjet reduction, and midline improvement in subdivision malocclusions. Substantial unilateral molar distalization remains challenging and is frequently accompanied by undesirable crown tipping. Age was also identified as a significant predictor of distalization efficiency.