Human mandibular prenatal growth: bivariate and multivariate growth allometry comparing different mandibular dimensions.

Mandibular growth was studied in 36 human fetuses (both sexes) ranging from 13 to 37 weeks of gestation by bivariate and multivariate analyses (bivariate allometry and principal components analysis, PCA). Several mandibular dimensions were measured and correlated with fetal weight. Considering the different mandibular dimensions in sequence of increasing component weights, PCA agreed with bivariate analysis. No mandibular dimension was considered to increase in isometric relationship. PCA showed the following distances with negative allometry: caput mandibulae-gnathion (both sides), gonion-processus coronoideus (both sides), caput mandibulae-processus coronoideus (both sides) and gonion-gnathion (right side). On the other hand, the following dimensions grew with positive allometry: gonion-gnathion (left side) and symphyseal height (both sides). PCA and bivariate analysis showed higher growth rates for the gonion-processus coronoideus distance and symphyseal height on the right side than on the left. All other mandibular dimensions presented more elevated growth rates on the left than on the right side. During the second and third trimesters of prenatal life the mandibular growth was allometrical; the mandibular body grew with more intensity than the ramus in both length and height. The greatest growth rate was found for the height at the symphysis. The angulus mandibulae presented a negative and slight correlation with the other linear dimensions of the mandible during prenatal life.