Anat Cell Biol.  2022 Dec;55(4):433-440. 10.5115/acb.22.081.

Geometric morphometric analysis of mandibular symphysis in Class III skeletal base

• Teo KF
• Nor MM
• Mohamed AM
• Pritam HMH

• KMID: 2537462
• DOI: http://doi.org/10.5115/acb.22.081

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.

Keyword

Geometric morphometric; Mandibular symphysis; Class III; Gonial angle; Shape

Figure

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  Fig. 1 Landmarks (numbered in white) sequences on mandibular symphysis.

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  Fig. 2 Procrustes superimposition of 254 samples. The blue circle encompassing landmarks (numbered in red) indicate landmark variation of the 254 samples.

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  Fig. 3 Shapes changes associated with the first three principal components (PCs), representing extremes PC scores along each PC axis. Light blue: mean shape of the samples. Dark blue: shape variation.

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  Fig. 4 Scatter plot of canonical variate (CV)1 vs. CV2. The groups are defined by gonial angle. The groups are defined by gonial angle. Light blue: mean shape of the samples. Dark blue: shape variation.

Reference

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