Orthopedic effects of maxillary protraction combined with chin cap appliance

Objective: The objective of this study is to investigate and provide the morphological changes of the Class III mandible after orthopedic therapy, such as a maxillary protraction (occipito-mantal appliance, OMA) combined with a chin cap. Methods: The subjects of the Class III malocclusion were consisted of 20 male and 20 female Taiwanese children. The mandibular mean configurations of the pre-treated and post-treated stage were obtained by Procrustes analysis. The strain tensor analysis was employed to localize morphological changes of the Class III mandible. The Goodall's F test of statistical analysis will be utilized to determine whether mandibular mean configurations differed significantly between stages. Results: The probability of statistical difference between the mandibular mean configurations of the pre-treated and post-treated stage occurred at the level of p < 0.05 for all comparisons. The size change of Class III mandible showed that a size reduction was detected in the regions of symphysis, incisor alveolus, as well as the lower portion of the ascending ramus (maximum diminution in size by 10% approximately). For the shape change was detected in the regions of mandibular corpus, especial in the region of incisor alveolus and symphysis, exhibiting significant anisotropy of 54.7% in maximum. The compression vectors of the mandibular growth were significantly detected at local regions, including symphysis and incisor alveolus. The expansion growth in the mandible was redirected toward the perpendicular direction of the mandibular plane. Conclusions: The size change for mandibular configuration evidenced a positive allometry all over the mandible. The morphological change showed that not only the size and shape changes of the mandible could reveal the correction effects, but the directions of mandibular growth are important to identify the treatment outcomes. This work was supported by the National Science Council of Taiwan, NSC 96-2221-E-214-056-MY2.