Geometric morphometric analysis of mandibular symphysis in Class III skeletal base

Abstract

This study aimed to investigate the general mandibular symphysis (MS) shape variation among Class III skeletal base, using geometric morphometric analysis. Pre-treatment lateral cephalometric radiographs of 254 patients aged 11-40 years old, with Class III skeletal base (ANB <1 o ) and lower incisor angle (<99 o ) were included. Nine-landmarks with x and y coordinates were identified on MS using TPSDig2 software, then exported into Morpho J for shape and statistical analysis. Principal component analysis showed that three main shape dimensions with a total variance of 74.6% represented the majority variation of samples. Procrustes Anova showed the shape of MS in Class III skeletal base to be mainly influenced by gonial angle, incisor inclination and sex (P<0.0001). Canonical variate analysis showed that high gonial angle groups had significantly narrower and elongated MS whereas low gonial angle groups had wider, bulbous and rounded MS (P<0.0001). The ratio of alveolar part to basal part was 1:5 in low gonial angle and 2:3 in high gonial angle. Males had significantly taller MS with narrower B point area compared to females (P<0.0001). Retroclined incisors exhibited taller and retroclined alveolar parts (P<0.0001). The shape of MS in Class III skeletal base varied at the alveolar part, basal part or both and it is influenced by gonial angle, incisor inclination and sex. Hence, understanding the shape variation of MS is important to aid orthodontic treatment planning.

Geometric Morphometric Analysis of Mandibular Symphysis Growth between 12 and 15 Years of Age in Class II Malocclusion Subjects

“…The evidence would suggest that the vertical skeletal/facial pattern has a significant influence on the morphologic variation of the mandibular symphysis [ 26 , 27 ]. In addition, a recent study investigating the morphology of the mandibular symphysis in Class III subjects would confirm the relation between the skeletal pattern and the morphology of the symphysis [ 28 ]. However, these studies did not evaluate how the form of the symphysis may change during growth and whether this change is related to the initial craniofacial pattern.…”

“…Two approaches are documented in the pertinent literature for the study of mandibular symphysis. Following Klingenberg’s work [ 30 ], it is possible to use a homology-free approach that does not envisage semi-landmarks but exploits the surrounding anatomical structures to identify the points used in the analysis [ 28 ]. It is also possible to take advantage of a more traditional approach that involves the use of semi-landmarks [ 9 ].…”

“…However, considering the limited observational timing of the present study, it is unlikely that the mandibular symphysis may have shown MS’form changes due to ex novo occurrences of morphological features. In this regard, both methodologies have been previously used to investigate symphysis morphology [ 9 , 28 ].…”

Association of Symphyseal Morphology with Lower Incisor Inclination in Sagittal and Vertical Growth Patterns

“…In a study of the symphysis, different scales of measurement were used to calculate the vertical growth in relation to the inclination of incisors. Then 3-D radiography [13][14][15] was used for further analyses, this study is not similar to the respective study but some points were comparable like the symphyseal height is relative to the inclination of incisors. But in our case, it is only true with vertical class I.…”