The predictability of the mandibular curve of Wilson, buccolingual crown inclination, and transverse expansion expression with Invisalign treatment

Introduction: This study aimed to provide an initial investigation into the mandibular curve of Wilson (COW) handling using the Invisalign appliance (Align Technology, Santa Clara, Calif). Individual buccolingual crown in-clinations and transverse expansions were also investigated to detect any regions of ineffectiveness in the dental arch. Methods: A retrospective sample of patients treated by an experienced Invisalign provider in private practice was used. All adult patients with Class I or II Angle malocclusions and mild to moderate crowding treated using a minimum of 14 Invisalign aligners without intermaxillary elastics, bite ramps, or auxiliaries and a nonex-traction mandibular arch from 2013-2019 were selected. Dental models at the initial scan, the ClinCheck predic-tion, and the outcome after the initial series of aligners were analyzed with Geomagic Control X software (version 2017.0.3; 3D systems, Rock Hill, SC). The COW, buccolingual crown inclination relative to the occlusal plane and cusp tip expansion were compared between ClinCheck changes and achieved changes. Results: Forty-two subjects met the selection criteria. 74% of subjects experienced a flatter COW than ClinCheck predictions, and the mean difference was 0.76 mm (P = 0.0149). The first molars encountered 0.52 mm (P \0.001) more buccal crown inclination than ClinCheck predictions. No other teeth experienced statistically significant bucco-lingual inclination differences to ClinCheck. The second molars were the only teeth to experience significantly more arch expansion than ClinCheck at 0.68 mm (P = 0.0046). Conclusions: The Invisalign appliance tended to over-flatten the mandibular COW compared with ClinCheck because of the lack of buccal root torque in the mandibular first molars during expansion. The mandibular second molars were the only teeth to experience more expansion than ClinCheck. (Am J Orthod Dentofacial Orthop 2023;163:109-16)

Automated summary

This study aimed to investigate the mandibular curve of Wilson (COW) handling using the Invisalign appliance. The study also assessed the buccolingual crown inclinations and transverse expansions to identify any ineffective regions in the dental arch. Results showed that the Invisalign appliance tends to over-flatten the mandibular COW, and only the mandibular second molars experienced more expansion than predicted by ClinCheck.