Longitudinal Quantitation of Tooth Displacement in Chinese Adolescents with Normal Occlusion

This longitudinal study aims to analyze the different modes of the maxillary and mandibular tooth displacement in subjects, who were aged 12.5-17.5 years (150-210 months), with untreated normal (Class I) occlusion. Longitudinal lateral cephalograms for a set of 10 subjects (7 females and 3 males) at consecutive annual time points were selected and monitored. Data were analyzed on the basis of the superimpositions of serial tracings of lateral cephalograms on stable anterior cranial base, the anatomies of the maxillary and mandibular structures. The horizontal and vertical displacements of the first molar and incisor were assessed by t-test. The local and the secondary tooth displacements with growth contributed to the total horizontal and vertical displacements of the molars and incisors of the subjects. In the total tooth displacement, the horizontal growth of maxilla and mandible had the same contribution as the local tooth displacements. The vertical maxillary growth played a smaller role than the local drift, and mandibular remodeling went in a reverse direction with the local tooth drift. The first molars moved more forward than the incisors in the upper and lower arches. Both the upper and lower first molars showed forward tipping. The analysis of tooth displacement may be utilized in making orthodontic treatment plan, including anchorage or torque control.