Cuspal Enamel Growth and Crown Enamel Thickness in Modern-Day African Pastoralists and Farmers

European and African populations have exhibited limited variation in dental development. However, it remains unclear whether tooth growth, specifically enamel formation, varies between modern human populations with differing diets. Enamel growth and thickness were compared between two modern human ethnic populations, the Fulbe and Nso, from Cameroon. There is a cultural focus on milk-drinking and consuming milk-based products in the Fulbe which is not present in the Nso, who have a broad-based modern diet including agricultural produce. This study aimed to determine whether enamel formation differed between these populations and, if so, whether these variations correlated with their diets.

Standard histological methods were used to analyse cuspal enamel growth rates, average enamel thickness and tooth crown size in 35 permanent molars (Fulbe n= 9; Nso n= 26). Prism widths were measured using scanning electron microscopy. Cuspal enamel growth rates and average enamel thickness were also measured in a comparative European (British) sample.

The speed at which tooth crowns extended in height was significantly (p= 0.005) faster in the Fulbe (n= 7, mean= 23.61µm/day) than the Nso (n= 7, mean= 14.41µm/day). Prism widths were also larger (Fulbe mean= 5.68µm; Nso mean= 5.24µm). The comparative European sample had accelerated extension rates (n= 20, mean= 28.39µm/day) which were more similar to the results for the Fulbe than the Nso. Tooth crown size was significantly (p< 0.005) larger in the Nso molars than the Fulbe molars. Crown enamel thickness was greater in the combined African (Fulbe and Nso) molars (mean= 1.49 mm) than the European molars (mean= 1.14 mm) from this study, as well as other comparative datasets from previous publications. No consistent differences were found between pre-weaning (first molars) and post-weaning (second and third molars) cuspal enamel growth rates in either the pastoralists or farmers.

These results imply there is more variation in modern human tooth growth than previously reported. Further research into cuspal enamel growth rates across geographic and regional populations is necessary to establish the full extent of human variation. The lack of difference between the first and distal molars suggests post-weaning diets, including those which emphasise the continued consumption of milk and milk-based products, have a limited effect on enamel formation. This means dietary shifts, such as weaning, may not be easily detected from dental samples in the fossil hominin record using histological techniques.