Harder foods make hardier heads among post-weaning rats
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Purpose: The impact that material properties of foods have on the mammalian skull has been studied extensively. However, research that compares cranial morphologies in response to dietary shifts during growth is limited. We analyzed the crania of Sprague-Dawley rats raised on contrasting post-weaning diets. Methods: Four groups of rats were fed different diets from weaning (week 4) to adulthood (week 16): powdered pellets only (SS); hard pellets only (HH); powdered pellets followed by a switch to hard pellets at week 10 (SH); and hard pellets switched to powdered pellets. We employed shape analysis (Geometric Morphometrics) and computational biomechanics (Finite Element Analysis) to quantify the impact of food hardness on the morphology of their crania. Results: We found significant differences in cranial shape between SS and HH groups, and SH and HH groups. In both cases, similar shape differences were found in the region of the temporal zygomatic root, suggesting that a diet of hard foods may have a consistent impact on morphology. Biomechanical modelling demonstrated clear differences in bone stress distributions during incisor biting between diet groups, indicative of bone remodeling in response to the introduction/removal of hard foods; groups fed hard pellets experienced less stress indicating bone deposition for reinforcement. Conclusions: These findings suggest juvenile diets are an important predictor of intraspecific cranial morphology. More extensive analyses incorporating larger sample sizes will help to further elucidate the nature of these relationships and will contribute to our understanding of mammalian osteology and mastication, post-weaning development, and orthodontics.