Mandibular rotation and occlusal development during facial growth
PURPOSE: Mandibular growth rotation is an important phenomenon in human facial growth. However, changes in the vertical height of the dentition, the inclination of the occlusal plane, and subsequent mandibular rotation during growth, are only poorly established. This study was designed to examine the inter-relation among occlusal plane rotation, mandibular growth rotation, and the establishment of tooth axis during growth and development. MATERIALS AND METHODS: The materials used consisted of 351 lateral cephalograms from 39 children who belonged to a longitudinal growth study. We observed their growth changes in the developmental stages from first molar eruption (Initial stage) until the completion of permanent dentition (Final stage). We measured values regarding the posture of the lower face, including mandibular rotation, occlusal plane, and tooth axis. The tangent law was applied for the sagittal organization of the mandibular teeth by geometrical analyses. RESULTS: Results showed that mandibular growth rotation is associated with occlusal plane rotation, which is caused by greater vertical height increase in the molars than in the anterior incisors. It was also shown that the mandibular incisors followed the tangent law, but the long axis of the posterior mandibular teeth exhibited almost the same angle, approximately 15° with the direction of the tangent. This tooth axis arrangement was very much dependent upon occlusal plane rotation and mandibular rotation during growth. CONCLUSION: The results of this cephalometric study could help dentists to determine a more suitable organization of occlusion in the sagittal plane, as required in orthodontics, prosthodontics, and implant dentistry.