Transverse dimensions and molar torque patterns of first molars in Chinese adolescents: a 3D digital dental analysis

To investigate age-related differences in transverse intermolar width and crown torque of maxillary and mandibular first permanent molars in adolescents, and to explore whether molar torque changes are associated with differential transverse growth.

A total of 410 dental casts and corresponding posteroanterior cephalograms from 108 Chinese subjects (38 males and 70 females) aged 8-18 years were analyzed using a retrospective observational design with partially repeated measures. For subjects with records available at multiple ages, all eligible records were included to improve age-group representation. Maxillary and mandibular basal bone widths were measured on posteroanterior radiographs. Dental casts were digitized and analyzed to obtain intermolar width and molar crown torque. Statistical analyses included linear mixed-effects models for sex comparisons, one-way ANOVA with Bonferroni correction for age-group comparisons, Pearson correlation analysis, and sensitivity analysis.

Both maxillary and mandibular basal bone widths were greater in older age groups, with mandibular basal width exceeding that of the maxilla. Despite this skeletal pattern, maxillary intermolar width increased more than mandibular intermolar width (3.16 mm vs. 1.44 mm). Maxillary first molars exhibited a progressive shift toward palatal angulation of 7.43°, whereas mandibular first molars showed a buccal angulation change of 14.04°, both tending toward a more neutral buccolingual angulation.

In this Chinese population aged 8-18 years, transverse skeletal growth of the mandible exceeded that of the maxilla, whereas maxillary intermolar width increased more than mandibular intermolar width. Coordinated molar torque adjustments were observed alongside this skeletal-dental discrepancy and may reflect a dentoalveolar compensatory adaptation contributing to transverse occlusal coordination.