Temporal nature of periradicular bands ('Striae periradicales') on mammalian tooth roots

Periradicular bands, or fine circumferential lines on tooth roots, have received attention recently due to their prominence on hominin fossils and their potential utility for informing studies of root formation. In 1938, Komai and Miyauti [Dtsch Zahn Mund Kieferheilkd 1938;5:791-795] demonstrated that periradicular bands are related to dentine growth rather than cementum, suggesting that they were equal to accentuated lines in dentine ('dentine lamellae' or 'contour lines'). More recent indirect evidence from band spacing on primate roots suggests that they are temporally equal to other long-period lines in enamel (Retzius lines, perikymata) and dentine (Andresen lines). One of the main complications in understanding the relationship between Andresen lines and periradicular bands is the layer of cementum found on erupted teeth, which often obscures bands. Here we present both direct and indirect evidence that periradicular bands are temporally equivalent to internal long-period lines in the enamel and dentine. A sample of modern human teeth showing periradicular bands and accentuated rings was externally notched, molded, and sectioned; in one instance it was possible to show an equal number of long-period lines (internal Andresen lines and external periradicular bands) between isochrons (internal accentuated lines and external accentuated rings), confirming the temporal equivalence of these features. Furthermore, counts of long-period lines on crown and root surfaces of a Neanderthal anterior dentition showed approximately equal numbers of lines (113+/-1) between matching hypoplasias and accentuated rings across teeth. Despite their potential for studies of primate root growth, the etiology of these lines in mammalian roots requires further study.