The Prevalence and Possible Causes of Third Molar Agenesis in Post-Medieval Chichester

Third molars are the last permanent tooth to develop, the most variable in size and morphology, and are also the most commonly congenitally absent tooth. According to Sujon et al. (2016), approximately 50% of modern (20th century onwards) human third molars are anomalous, either unerupted, partially erupted or absent. Congenital absence is known as dental agenesis, which results from a developmental anomaly in the dental epithelium or the underlying mesenchyme (Bhutta et al., 2014). Grewal’s (1962) analysis of agenesis in the third molars of mice revealed that congenitally absent teeth begin as tooth germs but growth formation ceases at or before the cap stage of development, at which point the tooth germ resorbs. It may occur unilaterally, bilaterally, in combinations of three teeth, or completely, with all four absent. In their meta-analysis of modern data, Carter & Worthington (2015) found that 22.63% of people worldwide have some degree of third molar agenesis. The samples included in their analysis were gathered from various ethnicities and socioeconomic groups, with prevalence ranging from 5.32% 56.0%. The exact etiology of third molar agenesis is unknown, but a genetic component is well established (Carter & Worthington, 2015; FrazierBowers et al., 2002), and it is thought that delayed growth or a lack of space in the jaw may result in epigenetic absence (Anderson & Popovich, 1981; Kajii et al., 2004; Suri et al., 2004). Disease and nutrition have also been shown to affect the eruption and formation of third molars (Anderson & Popovich, 1981; Garn et al., 1961; Suri et al., 2004), adding to the already complex etiology of this trait. Grüneberg’s (1951) experiments with mice indicate that agenesis is the phenotypic result of the extreme end of a size continuum. Mice with absent third molars more often displayed small and variable remaining third molars, and as the dental lamina became smaller, the more likely growth and tooth formation were to cease development and resorb. It has frequently been reported that third molar agenesis occurs more often in modern populations than in the past (Alam et al., 2014; Kajii et al., 2004), ABSTRACT Third molar agenesis is a dental anomaly that occurs in approximately 25% of people worldwide and results in the complete absence of one or more of the third molars. A rise in the prevalence of congenitally absent third molars has been noted in modern clinical data, and it has been proposed as an evolutionary step in the dental reduction of the human dentition. Whilst research has been conducted in extant cohorts, relatively little has been published on third molar agenesis in archaeological assemblages. A post-medieval assemblage (AD 1550-1850), from Chichester, United Kingdom, was visually and radiographically analyzed to determine the prevalence of this anomaly. Mesiodistal and buccolingual measurements were taken on retained third molars to determine if there was an association between agenesis and reduced tooth size. Prevalence of agenesis was found to be comparatively high (42.7%) relative to contemporary and modern European samples, and tooth size reduction was documented. Consequently, it can be said that high rates of third molar agenesis are not simply a modern clinical phenomenon, as many prevalence rates in recent populations are lower. Temporal and regional patterns are, therefore, unclear. In order to better understand the trajectory and evolution of this anomaly, more archaeological assemblages ought to be examined.