A Histological Examination of Enamel Microevolution over 2000 Years of Human History using British Populations

The study of permanent enamel thickness and secretion rates of ameloblasts have yielded insights into the evolution of enamel when compared between hominin species. However, the study of modern human permanent tooth enamel has received far less attention, particularly regarding daily secretion rates (DSRs) and changes over time between populations. Moreover, enamel thickness and DSRs have rarely been analysed in conjunction for human samples. The research here uses dental histological thin sections to examine inner, mid, and outer DSRs for lateral and cuspal enamel, and the average (AET), relative (RET), cuspal (CT), and lateral (LT) thickness, for permanent first molar, upper canine, and upper first incisor crowns, from five British populations spanning the last 2000 years of history. The populations cover the Roman period (1-4AD) to modern day. A total of 265 teeth were analysed: first molar (n=115), upper canine (n=69), and upper first incisor (n=81). Results display consistent and significant trends towards decreasing DSRs from the ancient to modern populations. This was observed in all first molar cuspal regions (inner p<0.001, mid p<0.001, and outer p<0.001) and the inner and outer lateral regions (inner p=0.01 and mid p<0.001), in all upper first incisor cuspal and lateral regions (all p<0.001), and in all upper canine cuspal and lateral regions (all p<0.001). Enamel thickness features revealed less inter-population variation in first molars. The Early Anglo-Saxon RET was significantly larger than that of the Late Anglo-Saxon (p<0.001) and Medieval (p<0.001) populations. The Modern-day population LT was significantly thicker than the Roman populations (p=0.04). These differences allude to potential differences in diet between these populations. Alongside the differences seen between populations, the data provides the first major evidence for changes in the daily rate of enamel growth in human permanent dentition between populations. That similar variation was not observed in enamel thickness suggests thickness and growth can vary significantly and independently between human population.