Sexual dimorphism of the mandibular conformational changes in aging human adults: A multislice computed tomographic study by geometric morphometrics

Abstract

The aging process has an impact on mandibular bone morphology and can therefore affect shape sexual dimorphism. Understanding the effect of senescence on mandibular shape changes is particularly important to correctly estimate the sex of an individual and predict age-related conformational modifications. The purpose of this study was to assess age-related changes in mandibular shape and sexual dimorphism. The study sample comprised 160 Multi Slice Computed Tomography examinations of individuals aged 40 to 79 years. Geometric morphometric analysis of fourteen osteometric landmarks was used to examine sexual dimorphism and patterns of mandibular shape variation with age. Results showed that mandibular sexual dimorphism of shape remained significant with aging. Conformational changes occurred between 50 and 70 years and were different for male and female individuals. Females presented earlier and more marked age-related shape changes than males. These observations suggest that mandibular senescence is a sexually dimorphic process since its onset, rate, and the areas subjected to conformational changes differ from male to female individuals. Senescence-related changes present substantial variability, and further investigation is required to determine precisely the age that marks their onset.

Fig 1. Mandibular landmarks used in the present study.

Landmark’s definitions are listed in Table 2.

Fig 2. Landmark placement in Horos DICOM Viewer.

(a) Multiplanar reconstruction on Horos showing the placement of the Pogonion (Pg) landmark. (b) 3D volume rendering displaying the mandibular landmarks as coloured dots.

Fig 3. Principal Component Analysis of male and female mandibular shape.

Each sex is divided into two age cohorts: 40–64 years vs. 65–79 years for males, and 40–54 years vs. 55–79 years for females. The effect of age on mandibular conformation is more marked for females.

Fig 4. Male and female mandibular aging rates.

An acceleration of female mandibular shape changes can be observed between 50–60 years. The rate of conformational changes is estimated in Procrustes distance / year.

Fig 5. Lateral view of male and female mandibular shape variations with age.

On the left: male mean shapes: 40–64 years (solid lines) vs 65–79 years (dashed lines). On the right: female mean shapes 40–54 years (solid lines) vs 55–79 years (dashed lines). The arrows represent the major directions and magnitude of changes in conformation with age.

Fig 6. Anterior view of male and female mandibular shape variations with age.

On the left: male mean shapes: 40–64 years (solid lines) vs 65–79 years (dashed lines). On the right: female mean shapes 40–54 years (solid lines) vs 55–79 years (dashed lines). The arrows represent the major directions and magnitude of changes in conformation with age.

Fig 7

Left lateral view of male (blue) and female (red) mean shape superimposition. On the left: 40–59 year group. On the right: 60–79 year group. Males are represented as solid lines, females are represented as dashed lines. Arrows represent the main trend of variation for female individuals between age groups.

Fig 8

Anterior view of male (blue) and female (red) mean shape superimposition. On the left: 40–59 year group. On the right: 60–79 year group. Males are represented as solid lines, females are represented as dashed lines. Arrows represent the main trend of variation for female individuals between age groups.