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 inclinations 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 nonextraction mandibular arch from 2013-2019 were selected. Dental models at the initial scan, the ClinCheck prediction, 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 buccolingual 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.