Stability of Mini-Screw Assisted Orthopedic Correction of Growing Retrognathic Hyperdivergent Patients

Purpose: To determine if non-surgical posterior dental intrusion produces stable orthodontic and orthopedic correction in growing retrognathic hyperdivergent patients. The primary aim of this study was to compare the vertical dental and skeletal changes that occurred during treatment and after treatment to untreated control subjects. Methods: The sample included of 14 subjects (5 males and 9 females), who were 13.4 ± 0.7 years pre-treatment (T1), 16.8 ± 1.3 years post-treatment (T2), and 20.4 ± 0.9 years at long-term recall (T3). During the initial orthopedic phase, 150 gram Niti coil springs were attached to two palatal mini-screw implants (MSI’s) for maxillary intrusion, and two buccal mandibular MSI’s were used for posterior mandibular vertical control. Full orthodontic therapy was initiated to correct the malocclusion during the orthodontic phase. Patients were recalled a minimum of 1 year post-treatment (mean recall 3.6 ± 1.6 years) for stability records. The subjects were compared to matched untreated controls. Results: During treatment and retention, the maxillary and mandibular molars underwent 2.8 mm and 3.7 mm of relative posterior intrusion, respectively. The maxillary incisor was extruded 2.85 mm during treatment, while the untreated control incisor erupted only 1.25 mm. Orthopedic changes included a reduction in the MPA (3.25°), an increase in SN-Pg (2.4°), an increase in S-N-B (2.1°), and a 5 mm relative reduction in anterior facial height. With the exception of the maxillary incisor (0.6 mm of relative intrusion post-treatment), post-treatment dental and orthopedic changes were not statistically significant between the treated and control subjects. Conclusions: Except for maxillary incisor position, the substantial dental intrusion and associated orthopedic corrections that occurred during treatment remained stable post-treatment