Cells different from all others the enamel knot found again
The enamel knot is formed during early tooth morphogenesis in the centre of the tooth germ epithelium Figure 2.1 . It forms at the late bud stage and this also marks the beginning of tooth shape development. Moreover, the cells of the enamel knot cease to proliferate Jernvall et al., 1994 . This was our initial discovery or rediscovery, there was disagreement in the literature on this matter, see Butler, 1956 for review , which drove our attention to this area ofthe tooth germ. Before the...
Cytological aspects of odontoblast terminal differentiation
The terminal differentiation of odontoblast is initiated at the tip of the cusps, progressing in an apical direction and occurs in each cusp according to a specific temporo-spatial pattern Figure 3.1 . The preodontoblasts located adjacent to the basement membrane, beneath the inner dental epithelium, show no special orientation and contain few cisternae of rough endoplasmic reticulum, only small Golgi apparatus and few mitochondriae Garant and Cho, 1985 . These preodontoblasts probably withdraw...
Dentine terminology
There is considerable terminological confusion in the literature describing exoskeletal tissues, and almost as much in describing the histological variation found in the teeth of living and fossil fishes. Much of this stems from the concept that dentine should be compared with Figure 5.1. Schematic of four patterns in dentines of early vertebrate dermal armour. Variations of cell arrangement and their interconnecting cell processes were proposed as an imagined evolutionary progression from...
Control of odontoblast terminal differentiation
Odontoblasts overtly differentiate according to a cusp-specific temporospatial pattern. That means that preo-dontoblasts will be able to express sequentially a specific cytological and metabolic phenotype. Such behaviour requires both epigenetic signalling and specific competence. To the best of our knowledge, preodontoblasts never give rise to a functional odontoblast layer when dental papillae, isolated by treatment with proteolytic enzymes, are either cultured in vitro in conventional media...
Developmental aspects of dentines in lower vertebrates
With the benefit of recent work on the structural development of dentines in extant lower vertebrates, it is possible to offer some suggestions about the growth, patterning and phenotypic expression amongst fossil tissues. In an attempt to explain the developmental basis ofsome of this diversity in early dentines, with regard to a potential difference in the odontoblast cells, we have taken an example of new information on odontogenesis in the shark tooth to illustrate a later diversification....
Earliest dentines
The fossil record of dentine now extends back to the Late Cambrian, approximately 510 million years ago Smith, M.P. et al., 1996 , followed by a rapid diversification of dentinous tissues into the succeeding Ordovician and Lower Silurian periods. The variety of dentinous tissues encountered in this time interval appears to greatly exceed the diversity seen in the subsequent 450 million year history of vertebrate development. 5.3.1. Fossil tissue characters Interpretation offossil tissues...
Acknowledgements Wub
The authors thank Harold C. Slavkin DDS, for his never ending enthusiasm and capacity for research into the mechanisms of biomineralization that has touched each of our professional lives. His vision for the future of dental research materialized in the formation of the Center for Craniofacial Molecular Biology at the University of Southern California School of Dentistry, a site where scientists from many different disciplines unite their expertise in order to advance knowledge ofcraniofa-cial...
Enamel Knot
switches that can cause the cell to progress to the next developmental phase differentiation, mitosis and to manufacture new sets of signalling molecules. These signalling molecules, on the other hand, may trigger the neighbouring cells to proceed to the next developmental phase, which may or may not be the same as that of the signalling cells. Also the signalling cells themselves may respond to a signal called autocrine induction in contrast to paracrine - between populations of cells . The...
Patterning of tooth position and shape
Mammalian teeth have characteristic shapes for each position in the jaws. The shape and position are important for dietary requirements and have evolved and diversified for particular specialised feeding functions. Incisors are conical, or chisel-shaped and located at the front of the jaws, where they are used not only for obtaining and cutting food, but also for grooming or defence functions. Molars are triangular, rectangular and multicuspid in shape and are located towards the back of the...
i2 Homeobox genes and tooth bud initiation
The first morphological sign of tooth development is a narrow band ofthickened epithelium primary epithelial band on the developing mandible and maxilla that forms four zones, one in each quadrant. These bands specify the area of epithelium from which teeth are Figure 1.1. Insitu hybridisation of a section in a dorsoventral plane with anterior at the top, of a day 10.5 gestation mouse embryo head showing Msx-2 gene expression in the ectomesenchyme and oral epithelium in relation to the...
Contributors
Barry K Berkowitz GKT School of Biomedical Science Henriette Raphael House, Guy's Campus, London Bridge, London SEI 1UL, UK P. M. Butler 23 Mandeville Court, Strode Street, Egham, Surrey TW20 9BU, UK Mike I. Coates Biological Sciences, University College London, Gower Street, London WC1E 6BT, UK M. C. Dean Evolutionary Anatomy Unit, Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK George H. Dibdin MRC Dental Group, Dental School,...