Enamel hypoplasia in molars of sheep and goats, and its relationship to the pattern of tooth crown growth

Abstract

Enamel is the most highly mineralized and durable tissue of the mammalian body. As enamel does not undergo remodeling or repair, disturbances of enamel formation leave a permanent record in the tissue that can be used for life history reconstruction. This study reports light and scanning electron microscope findings on hypoplastic enamel defects, and on the chronology of crown growth in the molars of sheep and goats. A marked reduction of enamel extension rates in cervical compared with more cuspal crown portions of sheep and goat molars was recorded, with formation of the cervical 25% of the crown taking about the same time as that of the upper 75% of the crown. This explains the more frequent occurrence of enamel hypoplasia in cervical compared with upper and middle crown portions. Regarding the identification of hypoplastic enamel defects by external inspection, our results suggest a dependence on the type of defect and the associated presence of smaller or larger amounts of coronal cementum. Defects considered to reflect a slight to moderate impairment of secretory ameloblast function can normally be correctly diagnosed as they are not occluded by thick layers of cementum. In contrast, defects denoting a severe impairment of enamel matrix secretion can typically not be correctly identified because they are occluded by large amounts of cementum, so that neither depth nor extension of the defects can be assessed on external inspection. In these cases, microscopic analysis of tooth sections is required for a correct diagnosis of the hypoplastic enamel defects.

Lines of Evidence–Incremental Markings in Molar Enamel of Soay Sheep as Revealed by a Fluorochrome Labeling and Backscattered Electron Imaging Study

“…Laminations were first described in aprismatic (prismless) surface enamel of human teeth [3], [30]–[32], and appear to be the most prominent incremental markings in the enamel of ungulate species [16], [33]–[36]. There is circumstantial and experimental evidence that laminations, like prism cross striations, constitute daily incremental markings [16], [33]–[36].…”

“…Laminations were first described in aprismatic (prismless) surface enamel of human teeth [3], [30]–[32], and appear to be the most prominent incremental markings in the enamel of ungulate species [16], [33]–[36]. There is circumstantial and experimental evidence that laminations, like prism cross striations, constitute daily incremental markings [16], [33]–[36]. Laminations run a course parallel to that of the striae of Retzius, but with a much closer spacing, and denote successive daily positions of the enamel forming front during the secretory stage of amelogenesis [16], [23], [34]–[36].…”

“…There is circumstantial and experimental evidence that laminations, like prism cross striations, constitute daily incremental markings [16], [33]–[36]. Laminations run a course parallel to that of the striae of Retzius, but with a much closer spacing, and denote successive daily positions of the enamel forming front during the secretory stage of amelogenesis [16], [23], [34]–[36]. The structural nature of laminations is debated.…”

Cementoblastoma in a red deer (Cervus elaphus) from the Late Pleistocene of Rochedane, France

“…Following capturing of the BSE-images, each tooth half was mounted with its polished side down on a glass slide, using the epoxy resin as glue. Two ground sections, each with a thickness of approximately 50 m, were produced as described in Kierdorf et al (2012). The cover-slipped sections were viewed and photographed in transmitted light in an Axioskop 2 Plus microscope (Zeiss, Jena, Germany) equipped with a digital camera (Canon PowerShot G2).…”

“…Subsequently, the tooth was embedded in epoxy resin (Biodur products, Heidelberg, Germany) and sectioned in a mesio-distal plane, using a rotary saw with a water-cooled, diamond-coated blade. The cut surfaces were smoothed and polished as described previously (Kierdorf et al, 2012). The polished, uncoated surfaces were then viewed in an environmental scanning electron microscope (ESEM; FEI Quanta 600 FEG, accelerating voltage 20 kV) operated in the backscattered electron (BSE) mode.…”