Molar occlusion and mandibular rotation: a longitudinal study.
The human dentition undergoes a process of complex development. Growth of the skeleton, morphology and function of the soft tissues (muscles in particular and airway), space considerations, and other factors influence the development of the dentition. The present study considered two of the factors involved: molar relationship in the sagittal plane and mandibular rotation. Forty-two persons from the Burlington sample were studied to determine whether changes in molar relation between the mean of ages 7 to 12 years were correlated with the rotational growth pattern of the mandible. The sample was divided into forward rotators (FR) and backward rotators (BR), based on the changes in the SN-corpus axis angle over time. The statistically significant difference of 4.04 degrees in change of the SN-CA angle over time, between the FRs and BRs, indicates that this method of characterizing the two different types of growers is useful. It is interesting to note, however, that the FRs and BRs, on an average, initially had the same SN-corpus axis angles. The molar relationship was determined on the basis of the cusp-fossa relationship in the sagittal plane. In the twenty-eight forward rotators and fourteen backward rotators the molar relationship did not change in a predictable fashion. Statistically significant correlations were not found between molar occlusion and growth direction patterns. Also, the SN-corpus-axis angle, at a single point in time, is not a good predictor of whether an individual is going to exhibit a forward or backward mandibular rotational growth pattern. The change in molar occlusion during the process of growth and development is a multifactorial phenomenon and cannot be predicted on the basis of the direction of mandibular growth rotation between the ages of 7 and 12 years.
D002508:Cephalometry; D002648:Child; D003766:Dental Occlusion; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008310:Malocclusion / Q000503:physiopathology; D008334:Mandible / Q000254:growth & development*; D008963:Molar / Q000033:anatomy & histology*; D012399:Rotation; D014716:Vertical Dimension