A histological study of enamel developmental defects in a chacma baboon (Papio ursinus) incisor

Physiological stress disrupts normal growth creating visible grooves on the enamel surface (i.e., linear enamel hypoplasia or LEH). Hypoplastic defects often, but not always, co-occur with internal accentuated lines (AL). Monkeys reportedly exhibit fewer enamel defects than hominoids as their presumably faster-growing teeth produce shallower LEH defects that are harder to macroscopically identify. In this case study of a chacma baboon (Papio ursinus) incisor, we assessed whether AL are matched by LEH defects; how enamel extension rates and striae angles relate to the surface distribution of LEH defects; and whether striae angles are shallow and rates of enamel extension fast compared to hominoid anterior teeth. We found a higher prevalence of internal AL (N = 48) compared to external LEH defects (N = 10), which co-occurred in all instances of LEH. However, 79.2% of AL defects do not co-occur with LEH defects. The spatial distribution of AL is more consistent, ranging from 3-10/decile, while LEH defects occur mainly in the midcrown and cervical regions. This incisor exhibits faster extension rates (mean = 23.6 µm/day) and shallower striae angles (11-16°) compared to hominoids, likely creating shallower LEH defects and contributing to the discrepancy between AL and LEH defects.