Longitudinal changes of crown inclination in juveniles with normal occlusion / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the longitudinal changes in crown inclination of permanent incisors and first molars in juveniles with normal occlusion.</p><p><b>METHODS</b>The untreated sample comprised 20 subjects (6 males and 14 females) with normal occlusion from the Research Centre for Craniofacial Growth and Development of Peking University School and Hospital of Stomatology. Crown inclination was evaluated with Biaggini Rayset in two stages, stage I with first molars and four incisors in occlusion (mean, 9.5 +/- 0.9 years) and stage II with the second molars in occlusion (mean, 13.7 +/- 1.3 years).</p><p><b>RESULTS</b>No significant difference was found between sexual groups. The crown inclination of the upper central incisors decreased (P < 0.001). The crown inclination of the lower central and lateral incisors increased (P < 0.01 and P < 0.05, respectively). The crown inclination of maxillary molars decreased with growth (P < 0.001), whereas that of mandibular molars increased with growth (P < 0.001).</p><p><b>CONCLUSIONS</b>Maxillary molars tended to become upright lingually, whereas mandibular molars upright buccally with growth.</p>

Longitudinal changes of posterior available spaces of lower dental arch in adolescents with normal occlusion from 13 to 18 years of age / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the changes of available spaces of posterior arch segments in mandibular dentition from 13 to 18 years of age, which would provide information for space analysis of whole dental arch in adolescents.</p><p><b>METHODS</b>Twenty-six adolescents (12 males, 14 females) with normal occlusion were selected. All of the subjects had lateral cephalograms taken at the same time each year for 6 years. Longitudinal cephalometry and statistic analysis were conducted for all subjects.</p><p><b>RESULTS</b>Significant differences of available space were found between males and females. The growth of available space from 13 to 18 years of age was 5.12 mm in females and 5.79 mm in males. The completion of mandibular remodeling in males lagged behind females for about 1 year. No significant increase was found in girls beyond 16 years and in boys beyond 17 years. There was a 1.22 mm increase on each side per year in females until 16 years and a 1.45 mm increase in males until 17 years. The increase of available space was made partly by resorption of bone from the anterior border of the ramus and partly by mesial movement of the first molar. The mesial movement of dental arch was probably stimulated by the eruption of the third molars.</p><p><b>CONCLUSIONS</b>The prediction of available space should be based on age and sex.</p>