Do mid-crown enamel formation front angles reflect factors linked to the pace of primate growth and development?

Enamel formation front (EFF) angles represent the leading edge of enamel matrix secretion at particular points in time. These angles are influenced by rates of enamel extension (the rates at which tooth crowns grow in height), rates of enamel matrix secretion and the angles that prisms make with the enamel-dentine junction. Previous research suggests, but has not yet established, that these angles reflect aspects of primate biology related to their pace of growth and development, most notably brain and body size. The present study tested this possibility on histological sections using phylogenetically-controlled and Bonferroni-corrected analyses spanning a broad taxonomic range. Ten species were represented in the analysis of anterior teeth; 17 in the analysis of posterior (postcanine) teeth (with varying sample sizes). Also, tested was the relationship of EFF angles to striae of Retzius periodicity (long period growth rhythms in enamel) and degree of folivory, as both factors are related to primate developmental rates. Finally, several analyses were conducted to investigate whether tooth size (operationalized as EDJ length) might mediate these relationships. Central results are as follows: (1) Relationships between EFF angles and brain weight (anterior teeth) and between EFF angles and body mass (anterior and posterior teeth) are statistically significant and (2) Mid-crown EFF angles are not statistically significantly related to EDJ lengths. These results suggest that tooth size does not mediate relationships between EFF angles and brain weight/body mass and are discussed with respect to underlying enamel growth variables (especially rates of enamel extension and secretion).