Variation in the timing of enamel formation in modern human deciduous canines

Abstract

Objectives: Deciduous canines are now used increasingly in archaeological and forensic studies to establish the time of birth and as a retrospective source of trace elements incorporated into enamel before and after birth. However, data on the variability of deciduous enamel formation times are scarce. Our objectives were to use daily incremental markings to estimate daily secretion rates, the timing of prenatal, postnatal and total enamel formation and any changes in enamel coverage or prism and stria orientation that occur during enamel formation. Materials and Methods: Longitudinal ground sections of 81 deciduous canines were studied with transmitted light microscopy. High-resolution digital images were imported from an Olympus VS-120 virtual slide scanning system into a geographic information system (ArcGIS, ESRI USA) for quantitative and statistical analyses of linear, angular and area measurements of buccal enamel. Results: Daily rates of enamel secretion close to the EDJ were faster than in permanent enamel (3.23 µm/day, SD=0.54). Prism and stria angles subtended to the EDJ both increased through crown formation. Enamel coverage was low in the cusp and cervix but maximal ~150 days after birth. The mean prenatal enamel formation time was 118 days (range SD, 29.2, n=24). The overall mean postnatal enamel formation time was 319 days (range 210-420, SD 50.6, n=67). Conclusions: Daily enamel secretion rates compared well with previous studies of deciduous enamel, however, enamel extension rates in deciduous cuspal enamel were notably lower. The variability of both prenatal and postnatal deciduous enamel formation times was greater than previously reported.

Synchrotron X-ray fluorescence imaging of strontium incorporated into the enamel and dentine of wild-shot orangutan canine teeth

“…Transmitted light micrographs were recorded both in polarised and non-polarised light using a range of objective lenses (2.5x, 6.3x, x12.5x, 25x, 50x). The methods used to calculate enamel formation time and root formation time in this study have previously been described and illustrated in detail (Dean, 2012a;Guatelli Steinberg, Floyd, Dean & Reid, 2012;Dean & Cole, 2013;Dean, Humphrey, Groom & Hassett, 2020) but are briefly outlined again here. Regions of inner enamel within 200 µm of the enamel dentine junction (EDJ) were identified that showed clear daily enamel cross striations.…”

Growth of Neanderthal infants from Krapina (120–130 ka), Croatia

“…Full methodological details for calculating extension rates, and creating thin sections, can be found in the electronic supplementary material, methods. We used two standard methodologies to calculate enamel extension rates from a portion of the EDJ length divided by the time required by ameloblasts to form a corresponding portion of an enamel prism located between the EDJ and neonatal line [38,41]. The first method provided an average extension rate over a set period of time leading up to birth.…”

Tooth Enamel and Its Dynamic Protein Matrix

“…For example, the proteomic analysis of dental enamel has allowed addressing the phylogenic relationship of the Eurasian Rhinocerotidae and additional information from other fauna from 1.77-Myr old tooth [ 25 ]. This is because the mineral-bound protein is less likely to be lost and located between densely packed mineral crystals remains well preserved for longer duration than nucleic acids [ 26 , 27 , 28 ]. The study of ancient proteins preserved in fossils is named paleoproteomics.…”