The predictability of the mandibular curve of Spee leveling with the Invisalign appliance

The purpose of this study is to provide an initial investigation into the predictability and characteristics of the mandibular curve of Spee (COS) leveling using the Invisalign appliance (Align Technology, Santa Clara, Calif) and any regions of ineffectiveness in the dental arch.

This study used a retrospective sample of patients treated by a single experienced Invisalign provider in private practice. All adult patients with Class I or II Angle malocclusions treated using a minimum of 14 Invisalign aligners without intermaxillary elastics, bite ramps, or auxiliaries and a nonextraction mandibular arch from 2013 to 2019 in the practice were selected. Dental models at the initial scan, the ClinCheck prediction, and the actual outcome were analyzed with Geomagic Control X software (version 2017.0.3; 3D systems, Rock Hill, SC). The COS and extrusion of posterior teeth relative to the occlusal plane were measured and compared.

Forty-two subjects met the selection criteria. ClinCheck predicted 0.55 mm (P < 0.0001) more COS leveling than the actual outcome. The mean COS leveling accuracy using Invisalign was 35%, and ClinCheck overestimated the leveling in 86% of the patients. The first molars had the lowest accuracy and extrusion relative to the occlusal plane.

To achieve desired clinical treatment goals, there should be a prescribed overcorrection of the mandibular COS leveling within the ClinCheck treatment plan, and the extrusion of mandibular first molars should be a region of focus. The clinician should consider using auxiliary appliances to improve mandibular COS leveling.