Recording and interpreting enamel hypoplasia in samples from archaeological and palaeoanthropological contexts

Enamel hypoplasia is often split into several macroscopic categories, including pit, localised, linear and plane-form defects. All types have been considered a sign of 'non-specific stress' during dental development in archaeological, as well as palaeoanthropological and other samples. There is growing evidence suggesting many defects may not be caused by illness or malnutrition during childhood, instead relating to trauma to the developing tooth, genetic conditions or specific environmental factors, i.e., may not be associated with 'stress' to the individual. In this study all types of macroscopic enamel hypoplasia were recorded, including pitting, linear, plane and localised type defects, in two extant great ape species and three fossil hominin species. The aim is to compare the characteristics and prevalence of different types of enamel hypoplasia among species and discuss potential differences in aetiology. The results show that samples have diverse prevalence's of different kinds of defects, and pitting, linear and localised defects likely have different aetiologies. Additionally, dental characteristics (e.g., tooth morphology, developmental timing/speed and enamel structure) heavily influence the likelihood of specific types of enamel hypoplasia forming. In sum, studies that include only one type of enamel hypoplasia, or focus on one tooth type, to generate a 'stress' rating for a sample may miss relevant information when comparing groups. Instead, it may be beneficial to record different types of defects separately, for all teeth, and then consider how genetic, environmental and tooth property factors may influence sample differences.