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Purpose: To study the changes of hyoid position in infants with Robin sequence before and after mandibular distraction osteogenesis, and to explore the related factors., Material and Methods: Twenty-six infants with Robin sequence underwent bilateral mandibular distraction osteogenesis from May 2016 to April 2020. Three-dimensional computed tomography data of patients before and after surgery were analyzed with Materialise Mimics 17.0. Changes in the three-dimensional position of the hyoid bone were studied., Results: The angle between the long axis of the tongue body and hard palate plane, and the angle between the long axis of the tongue body and mandibular plane were significantly decreased after surgery than before surgery. The hyoid bone-cranial base vertical distance, hyoid bone-mental point distance, and hyoid bone - epiglottis distance were significantly increased after surgery. The differences in the above-mentioned data were statistically significant ( P  < 0.05). Changes in the angle between the long axis of the tongue body and the hyoid bone - mental point line correlated with changes in the position of the hyoid bone relative to the cervical spine ( P   =  0.006). Postoperatively, the hyoid bone moved forward and the increase in the hyoid bone - mental point osseous distance interval (41.28%) was significantly greater than the increase in the hyoid bone-epiglottis distance (18.73%). Differences in the total mandibular length and the hyoid bone - cranial base vertical distance are related to the age at the operation ( P  < 0.05). The younger the age at the time of surgical intervention, the greater the difference before and after surgery for the same follow-up interval., Conclusions: The three-dimensional direction of the hyoid bone changes after the distraction osteogenesis of the mandible, and the hyoid bone moves downward and forward. Because the mandibular length and airway changed, the relative positions of the long axis of the tongue body on the sagittal plane rotated clockwise., Competing Interests: The authors report no conflicts of interest., (Copyright © 2021 by Mutaz B. Habal, MD.)

Purpose: There is a lack of uniformity in the diagnostic criteria and system for the morphologic classification of micrognathia in infants with isolated Pierre Robin sequence (IPRS). Therefore, the aim of this study was to create a morphologic classification system for IPRS-affected mandibles that may guide surgical management and osteotomy design., Patients and Methods: We designed and implemented a retrospective cross-sectional study. The study sample included infants with IPRS. The predictor variables included shape variables of the IPRS-affected mandibles. The outcome of interest was morphologic differences among the IPRS-affected mandibles in the infancy stage. The original coordinate data of the mandibular images were analyzed by a generalized Procrustes analysis and 2-block partial least squares analysis to identify the focal and nonfocal areas in the IPRS-affected mandibles. The original feature points were modified according to the results of 2-block partial least squares analysis. The modified feature points were further analyzed by principal component analysis, K-means cluster analysis, and canonical variate analysis to obtain a morphologic classification of the IPRS-affected mandibles., Results: One hundred fifty infants with IPRS were enrolled in this study. Principal component analysis showed that the variations among IPRS-affected mandibles were mostly in terms of the shapes of the mandibular ramus, mandibular body, and angle of the mandible. On the basis of the results of K-means cluster analysis and canonical variate analysis, the mandibles in group A3 showed characteristics such as a simply shorter mandibular body. Group B3 was adjusted to show characteristics such as a shorter mandibular body with a more obtuse mandibular angle, whereas group C3 showed characteristics such as a shorter mandibular body with a shorter mandibular ramus., Conclusions: Our study confirmed the hypothesis that there are quantifiable morphologic differences among the IPRS-affected mandibles, and it provided a morphologic classification of the IPRS-affected mandibles that will help to promote the clinical diagnosis and treatment., (Copyright © 2020 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.)