Histology of Dental Hard Tissues

Biological hard tissue structures can only be fully comprehended through a thorough understanding of developmental mechanisms. This is possible to achieve through the study of living animals. We limit our coverage here to dental tissues in extant mammals. Opportunities for the study of fossils will necessarily be limited. Nevertheless, understanding some of the ranges of possibilities found today in the extraordinarily wide variety of dental tissue structure, arrangements, attachment mechanisms and tooth morphology within mammals will further our curiosity into what may have happened – and evolutionary sequences – in the distant past. Most knowledge of dental histology is in fact limited to human teeth and to those of common laboratory rodents. These are so profoundly different within themselves that it is a wonder that so much attention is paid to the latter. But this concentration has blinkered vision, and we hope to open a view to a wider horizon. We describe the nature of mammalian tooth germs, the embryonic origins of dentine, enamel and cementum and the basics of tooth form. We explore the histology of dental tissues in respect of variability in cell behaviours, matrix and mineralization strategies, their periodic and sometimes aperiodic growth expression, and the adaptive structural patterns that emerge. We also relay the advantages and pitfalls of preparation and imaging methods particularly useful to the paleohistologist. We are particularly focused upon the sophisticated heterodont dentitions of mammals among the gnathostomes. Yet, the diversity explored here is expected to be a vast underestimate of the real variability among living and extinct mammals. Ample room exists for advancement. In particular, comparative studies of cementum are practically non-existent, but such investigations would contribute the necessary integration with form and function of dentine and enamel histology in relation to tooth form. While paleohistologists have concentrated their attentions principally on bone, more research on dental hard tissues will be required to firm up the connections bridging the locomotor and feeding niches of toothed animals