Biological clocks and incremental growth line formation in dentine

Abstract

Dentine-and enamel-forming cells secrete matrix in consistent rhythmic phases, resulting in the formation of successive microscopic growth lines inside tooth crowns and roots. Experimental studies of various mammals have proven that these lines are laid down in subdaily, daily (circadian), and multidaily rhythms, but it is less clear how these rhythms are initiated and maintained. In 2001, researchers reported that lesioning the so-called master biological clock, the suprachiasmatic nucleus (SCN), halted daily line formation in rat dentine, whereas subdaily lines persisted. More recently, a key clock gene (Bmal1) expressed in the SCN in a circadian manner was also found to be active in dentine-and enamel-secretory cells. To probe these potential neurological and local mechanisms for the production of rhythmic lines in teeth, we reexamined the role of the SCN in growth line formation in Wistar rats and investigated the presence of daily lines in Bmal1 knockout mice (Bmal1 −/− ). In contrast to the results of the 2001 study, we found that both daily and subdaily growth lines persisted in rat dentine after complete or partial SCN lesion in the majority of individuals.

An inconstant biorhythm: The changing pace of Retzius periodicity in human permanent teeth

“…Local cellular clocks are thought to release multiple oscillations representing different biorhythms, rather than only one central timekeeper, such as the suprachiasmatic nucleus (Hastings, 1998). Evidence from analysis of daily circadian clocks in mammalian enamel point toward a similar situation (Papakyrikos et al, 2020; Ray et al, 2020). Furthermore, quantitative genetics has demonstrated in various animal models, including primates, that anterior teeth can develop under independent genetic control relative to posterior teeth (Grieco et al, 2013; Hlusko & Mahaney, 2007), supporting a modular approach to understanding dental development and enamel formation.…”

“…Quantitative genetic research as well as studies investigating clock genes increasingly point to the role of local developmental influences during odontogenesis (Grieco et al, 2013; Hlusko & Mahaney, 2007; Papakyrikos et al, 2020; Ray et al, 2020). Local cellular clocks are thought to release multiple oscillations representing different biorhythms, rather than only one central timekeeper, such as the suprachiasmatic nucleus (Hastings, 1998).…”

Teeth reveal juvenile diet, health and neurotoxicant exposure retrospectively: What biological rhythms and chemical records tell us

“…[ 97–99 ] Teeth record Pb exposure very rapidly, particularly in dentine, leading to its use as an artificial time‐maker in foundational studies of incremental tooth development. [ 13 ]…”

“…[1,2,4] Experimental studies have proven that mammalian teeth have microscopic subdaily, daily, and supradaily structures in their hard tissues. [12,13] These incremental features can be visualized by cutting a tooth lengthwise to expose an internal plane (Figure 1). Analyses of growth lines in well-preserved and well-sectioned teeth may provide estimates of tooth formation timing that is accurate to within a few weeks or, in some cases, days.…”

Using primary teeth and archived dried spots for exposomic studies in children: Exploring new paths in the environmental epidemiology of pediatric cancer

“…This arises from the developmental biology of teeth—deciduous teeth begin mineralization prenatally towards the end of the first trimester and then continue to develop in an incremental manner forming daily (and even sub‐daily) markings. [ 38 ] Thus, naturally shed deciduous teeth are perhaps the only stable fetal tissue that can be attained in childhood non‐invasively, which can then be used to reconstruct exposure history at fine‐scale temporal resolution.…”