Mineral Apposition Rates in Coronal Dentine of Mandibular First Molars in Soay Sheep: Results of a Fluorochrome Labeling Study

Abstract

We studied the spatio-temporal variation of mineral apposition rate (MAR) in postnatally formed coronal dentine of mandibular first molars from Soay sheep repeatedly injected with different fluorochromes. MAR declined along the cuspal to cervical crown axis, and from early to late formed dentine, that is, from the dentine at the enamel-dentine-junction (EDJ) to the dentine adjacent to the dentine-pulp-interface (DPI). Highest mean MARs (about 21 µm/day) were recorded in cuspal dentine formed in the period of 28-42 days after birth. Lowest values (<2 µm/day) were recorded in late-formed (secondary) dentine close to the DPI. The high MARs recorded in the dentine of the cuspal crown portions enable the formation of a large tooth crown within a relatively short period of less than one year. The established MARs in the dentine of the different crown portions of sheep molars will allow a precise determination of the timing of stress events affecting dentine formation. They are also helpful for devising sampling protocols in studies of trace element or stable isotope distributions in sheep dentine aimed at assessing temporal variation of incorporation into forming dentine. Such data are useful in a variety of contexts, including, for example, the exposure to pollutants and the reconstruction of husbandry practices or feeding regimes. Anat Rec, 301:902-912, 2018. © 2017 Wiley Periodicals, Inc.

Intra‐tooth isotopic analysis (δ13C and δ15N) of dentine collagen in high‐crowned teeth: A new experimental study with modern sheep specimens

“…DIET2 and DIET3 periods are represented in the isotopic sequences over a different length (in mm) between second and third molars, despite representing the same time span in both molars (4 months span each period). This fact is well consistent with the variable tooth growth rates existing along the crown, where the deposition rate of dentine is higher during the first months of tooth development than towards the latest growth stages when the growth rate decreases (Kahle et al, 2018;Witzel et al, 2018). This histological feature (i.e., attenuation of the crown growth rate) results in a more prolonged representation of a certain isotopic signature in the upper part of the crown, while the same time span would be cramped in the last part of the tooth.…”

“…In the sheep specimens analyzed in this study, these effects are well evident in the representation of the first change of diet—occurring at the 13th month of life—along the M2 crown. The ascending trend in isotopic values starts around 25 mm from ERJ, while it would be expectable that this moment of life would be represented much onwards in the crown, in the last 1/5 part according to crown growth rates reported in sheep in previous studies (Kahle et al, 2018; Witzel et al, 2018). When considering these dentine growth timings reported for M2 and M3 crowns, in contrast, the moments on sheep's life when diet shifts occurred seem to fix better with the final position of ascending/descending trends instead of the starting point of variation (Figure 5).…”

“…Sequential analysis on dentine is nowadays barely understood because the technique needs to face an isotopic average resulting from mixing different dentine layers during sampling. In high‐crowned teeth, dentine growth front is oblique to the vertical axis of molars, growing in width while the tooth is growing in length (Balasse et al, 2001; Kahle et al, 2018; Zazzo et al, 2006). This growth geometry complicates sampling following the natural deposition of dentine while obtaining samples with enough size to implement the standard collagen purification methods (Guiry et al, 2016).…”

The pay-off of hypsodonty - timing and dynamics of crown growth and wear in molars of Soay sheep

“…With the methods used in this study, it was not possible to exactly determine the prenatal onset of enamel formation in the studied M 1 . However, based on mineral apposition rates in dentine we have previously reconstructed the onset of prenatal hard tissue formation in these teeth as occurring between 20 and 40 days prior to birth [50]. This matches quite well with the period of 49 days for prenatal crown formation in the M 1 recorded for a sheep (Dorset breed) on the basis of lamination counts in prenatal enamel and a calculation of the EER [51].…”

“…This approach can be viewed as a retrospective longitudinal growth study. Studies with a similar design were previously conducted to characterize crown growth rates and incremental patterns in enamel and dentine of different mammalian specie s [42, 45–50].…”