Mandibular projection in Class II Division 2 subjects following maxillary incisor proclination, overbite correction and dentoalveolar expansion using clear aligners
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Introduction: The purpose of this study was to evaluate the dental and skeletal treatment effects of maxillary incisor proclination, overbite correction and maxillary dentoalveolar expansion with no planned Class II mechanics on the magnitude of mandibular growth or/and projection in growing patients with Class II Division 2 using Invisalign® clear aligners (Align technology, Santa Clara, CA, USA). Methods: Records of 32 patients (12.86 ± 2.01) with Class II Division 2 dental and Class II skeletal relationship were studied retrospectively. Pre (T1) and Post-treatment (T2) CBCT-generated lateral and posterioanterior cephalograms were retrospectively obtained for the treatment group (n=16) and were compared with the T1 and T2 records of an untreated control group (n=16). Proclination and protrusion of the maxillary incisors, as well as maxillary dentoalveolar expansion with no other Class II mechanics were planned in the treatment mechanics. A customized cephalometric analysis was performed. Unpaired t-test and Analysis of Covariance (ANCOVA) regression models were used to compare the linear and angular measurements at both time points for both treatment and control groups to determine if significant skeletal Class II correction was achieved (p < 0.05). Results: An increase in skeletal mandibular growth and forward projection was observed in the treatment group when compared to the control group (mean differences: SNB (2.55°, p=0.0002), Ar-Go (2.08mm, p=0.0311), Go-Pog (2.64mm, p<0.0001), and Co-Pog (4.55mm, p<0.0001). The skeletal jaw relationship parameters showed improvements in the treatment group toward Class I compared to the control group as evidenced by a mean difference increase in ANB (2.5°, p<0.0001) and Wits (3.04mm, p<0.0001). In comparison to the control group, the treatment group also showed an increase in intermolar width (3.16mm, p<0.0001) while the overbite reduced significantly in the treatment group (-2.97mm, p<0.0001). The maxillary incisors were proclined and protruded (U1-SN: 12.48°, p<0.0001; U1-NA: 11.7° and 3.53mm, p<0.0001) in the treatment group as they were initially retroclined and retruded. Conclusion: Proclination of the maxillary incisors, correction of deep overbite and maxillary dentoalveolar expansion using clear aligners in growing patients with Class II Division 2 malocclusions were effective in improving the dental and skeletal Class II relationship.