Relationships between mandibular joint size and craniofacial size in human groups

Area of Science:

• Anthropology
• Biomechanics
• Paleontology

Background:

• The temporomandibular joint (TMJ) is known to adapt morphologically in response to biomechanical forces during function.
• Understanding TMJ size variations can provide insights into past lifestyles and dietary habits.

Observation:

• Mandibular condyle and fossa sizes were measured in skulls from diverse subsistence groups, including hunter-gatherers, horticulturalists, and modern populations.
• Craniofacial dimensions were also recorded for comparative analysis.

Findings:

• Significant differences in TMJ size were observed between groups, correlating with presumed masticatory stress levels.
• Hunter-gatherers exhibited the largest joints, followed by horticulturalists, with 20th-century Americans and 17th-century British showing the smallest.
• Even when controlling for craniofacial size, distinct intergroup differences in TMJ size remained, notably larger in Eskimo populations compared to American Caucasoids.

Implications:

• The study suggests that environmental factors, particularly the intensity and nature of tooth use during development, play a crucial role in TMJ morphology.
• While genetic factors may contribute, functional adaptation appears to be a primary driver of observed joint size variations.
• These findings have implications for understanding human adaptation and evolution through the lens of biomechanical stress on the masticatory system.