Tooth Structure and Replacement of the Triassic Keichousaurus (Sauropterygia, Reptilia) From South China

The small-sized sauropterygian Keichousaurus hui was one of the most abundant marine reptiles from the Triassic Yangtze Sea in South China. Although Keichousaurus has been studied in many aspects, including the osteology, ontogeny, sexual dimorphism, and reproduction, the dentition of this marine reptile was only briefly described in external morphology. In this study, we provide new information on Keichousaurus tooth implantation, histology, and replacement based on a detailed examination of well-preserved specimens collected in the past decades. The tooth histology has been investigated for the first time by analyzing cross-sections of premaxillary teeth and the tooth attachment and implantation have been further revealed by X-ray computed microtomography. We refer the tooth replacement of Keichousaurus to the iguanid replacement type on the basis of the observed invasion of small replacement tooth into the pulp cavity of the functional tooth. Given the resemblance to other extinct and modern piscivorous predators in the morphology and structure of teeth, Keichousaurus might mainly feed on small or juvenile fishes and some relatively soft-bodied invertebrates (e.g., mysidacean shrimps) from the same ecosystem.

Human Primary Tooth Histology Six Months after Treatment with Silver Diamine Fluoride

Objective: To describe the histological characteristics of a human primary tooth with deep caries next to the dental pulp 6 months after being treated with silver diamine fluoride (SDF). Study design: A tooth that was considered to be not restorable 6 months after being treated with SDF was examined with light microscopy. Results: the histologic examination revealed no carious pulp exposure, tertiary dentin, a flattened odontoblastic layer adjacent to irregular tertiary dentin, dentinal tubules with silver deposits to a depth of 1 mm and no bacteria, and a pulp with no significant inflammation. Conclusions: The use of silver diamine fluoride as an interim treatment of deep caries on vital carious primary teeth of children, leads to histologic changes that prevent pain and pulp deterioration, and most likely facilitate pulp healing. These unique findings expand the knowledge about the effect of SDF on the human dental tissues.

Saurichthys (Pisces, Actinopterygii) teeth from the Lower Triassic of Spitsbergen, with comments on their stable isotope composition (δ13C and δ18O) and X−ray microtomography

A rich collection of exceptionally preserved Lower Triassic fossil fish remains obtained during the Polish Spitsbergen Expedition of 2005 includes many isolated teeth be− lieved to belong to a saurichthyid actinopterygian. Stable isotope analysis (δ13C and δ18O) of putative Saurichthys teeth from the Hornsund area (South Spitsbergen) acting as a paleoenvironmental proxy has permitted trophic−level reconstruction and comparison with other Lower Triassic fish teeth from the same location. The broader range of δ13C values ob− tained for durophagous teeth of the hybodont selachian, Lissodus, probably reflects its mi− gratory behaviour and perhaps a greater feeding diversity. X−ray microcomputed tomogra− phy (XMT), a non−destructive technique, is used for the first time in order to elucidate de− tails of tooth histology, the results of which suggest that the method has considerable poten− tial as a future analytical tool.

Tooth histology patterns in early tetrapods and the presence of ‘dark dentine’

ABSTRACTThe presence of a petaloid pattern (previously known as ‘dark dentine’) in cross sections of teeth of the embolomere Pholiderpeton attheyi has been used as a synapomorphy of the embolomeres or of the embolomeres plus the stem tetrapod, Crassigyrinus scoticus. Among the taxa studied, dentine that appears dark results from closely packed dentine tubules and can be found in any part of a tooth section in which such crowding occurs. The petaloid pattern is restricted to tooth sections of a particular diameter, and is obliterated in larger sections of teeth that show complex folding. Petaloid dentine has been found in all tetrapod teeth with plicidentine that were sectioned in this study, whether from stem tetrapods, the Embolomeri, Temnospondyli, or Stereospondyli, and has been recognised in some sarcopterygian fish, an extant actinopterygian fish, ichthyosaurs, and Varanus. The presence of petaloid dentine is neither a synapomorphy of the tetrapod node nor of any node within tetrapods