Vertical growth pattern and posterior eruption space of the developing mandibular second molar: A retrospective cross-sectional study

Abstract

Background The role of the vertical growth pattern in the etiology of mandibular second molar eruption disturbance is controversial; this relationship has mostly been examined through whether or not the tooth erupts, and the eruption space left anterior to the ramus for the second molar has not been directly measured and compared across different growth patterns. The aim of this study was to evaluate whether the available posterior eruption space and molar angulation for the developing mandibular second molar differ among individuals with vertical, normal, and horizontal growth patterns.

Methods A total of 132 individuals (aged 9–18 years), in whom at least two-thirds of the second molar root development was complete, were included in this retrospective cross-sectional study. Individuals were divided into vertical (n = 44), normal (n = 44), and horizontal (n = 44) growth pattern groups according to SN/GoGn° and FMA° values. On lateral cephalometric radiographs, the gonial angle, Y-axis, posterior/anterior facial height ratio, ramus height, mandibular corpus length, and effective mandibular length were measured; on panoramic radiographs, the first molar–ramus distance, ramus distance/second molar mesiodistal width ratio, molar inclination angle, second molar mesiodistal width, and eruption depth were measured. One-way ANOVA and eta-squared (η²) effect size were used for between-group comparisons, and Pearson correlation analysis was used to assess associations.

Results The groups differed markedly in gonial angle (p < 0.001; η²=0.497), Y-axis (p < 0.001; η²=0.444), and posterior/anterior facial height ratio (p < 0.001; η²=0.671). In contrast, none of the panoramic measurements differed significantly among the groups: molar inclination angle (p = 0.584), first molar–ramus distance (p = 0.260), second molar mesiodistal width (p = 0.274), ramus distance/mesiodistal width ratio (p = 0.390), and eruption depth (p = 0.976); all effect sizes were negligible (η²=0.000–0.021). Before adjustment for multiple testing, the first molar–ramus distance and second molar width correlated positively with mandibular corpus length, effective mandibular length, and ramus height in all three groups (r = 0.33–0.64); after Benjamini–Hochberg correction, the associations of second molar width with mandibular corpus length and effective mandibular length remained significant in all three groups, whereas those of the first molar–ramus distance were retained in the normal and horizontal groups but not in the vertical group.

Conclusion The available posterior eruption space and molar angulation for the developing mandibular second molar did not differ among cephalometrically distinct vertical growth pattern groups. In this cross-sectional sample, the available posterior eruption space was associated with mandibular size, whereas no association with the vertical facial pattern was identified.