Dental Wear and Molar Pulp Volume Reduction in Macaca fascicularis

Odontoblasts lining the pulp cavity deposit dentine throughout life, meaning the volume of the pulp cavity decreases with age. Primates with more abrasive diets have relatively higher molar pulp volume in their unworn molars than those with less abrasive diets. We propose that species with more abrasive diets deposit additional dentine across their lifespans to help resist wear and extend the effective lifespan of their molars. Whereas both age and wear affect dentine deposition, it is unknown which of these two variables has the greater impact.

We measured pulp volume and calculated wear from micro-CT scans of lower first molars of captive-bred Macaca fascicularis (n = 13) of known age. We used reduced major axis regressions (alpha = 0.05) to test if age or wear was a better predictor of pulp volume.

Both variables have a significant negative relationship with pulp volume (age: p = 0.004, R² = 0.546; wear: p < 0.001, R² = 0.890). A mixed linear model of pulp volume against wear as main effect and age as covariant had a non-significant interaction effect (p = 0.078) and confirmed that both age (p = 0.030) and wear (p = 0.004) are significantly negatively correlated with pulp volume.

Results suggest that whereas pulp volume decreases with age, wear is more strongly correlated with decreasing pulp volume. These findings have implications for interpreting odontoblast activity in response to sensory feedback and the relationship between pulp volume and diet. These results also have implications for using molar pulp volume to estimate age at death in humans.