Growth changes of the mandibular body with eruption of mandibular third molars: Analysis of anatomical morphometry and quantitative bone mineral content by using radiography

Abstract

This study aimed to analyze growth changes in mandibular body morphology and quantitative bone mineral content (QBMC) with eruption of mandibular third molars (M3s) and the relationship between those variables and posterior mandibular body length. Linear and angular measurements were conducted using standard lateral radiographs of 37 dried mandibles in Hellman's dental developmental stages IVA (14 specimens) to VA (23 specimens). Cortical and trabecular basal bone mineral contents (CBMC and TBMC) in the mandible were expressed in millimeter titanium equivalent values using a titanium step wedge. The largest significant change in the mandibular body morphology was an increase in the horizontal dimension (M2DP'-Go': 7.59mm), followed by vertical dimension - total height of the mandibular body (THOMB: 4.96mm) and mandibular cortical width (MCW: 1.22mm). The gonial angle (GA) decreased significantly by 6.72° between stages IVA and VA. The mandibular cortical index (MCI) was classified only as C1 or C2 in each stage. Among 4 types of line profile, types 1 and 2 were most commonly observed in both stages. Mean values for CBMC and TBMC increased significantly between stages IVA and VA. Posterior mandibular body length (MeF'-Go') correlated positively with M2DP'-Go', THOM, MCW, and CBMC (r=0.816, 0.698, 0.595, and 0.507), respectively and negatively with GA (r=-0.582). These results demonstrated that the morphological changes in the posterior mandibular body and the QBMC increased significantly with M3 eruption, while the GA became significantly smaller. The posterior mandibular body length had a linear correlation with these variables.