IV. On the process of calcification in enamel and dentine

Abstract

In considering the process of calcification in dentine and enamel I have endeavoured to carry further my investigations as to the structure and development of dentine commenced in 1892, the object of that paper having been to show the existence of a connective tissue foundation derived from the tooth pulp, in which calcification takes place much as it does in membrane bone. The actual mode of deposition of the lime salts I did not then consider, except to express the opinion that the calcification took place by a process of secretion from the cells of the pulp. Since that date and following the previous investigations of von Ebner and others, the conversion theory of the formation of dentine has been to a great extent abandoned, this conversion theory being that the odontoblast cell became actually converted into dentine matrix, its centre remaining uncalcified as the soft fibril, and the rest of the cell forming in different degrees of calcification the Neumann’s sheath and the matrix. The view held in this paper and by numerous histologists at the present day is that the cells of the pulp secrete a material which calcifies, they themselves not entering into the calcified substance, but receding farther and farther into the pulp as calcification advances, and the fibril becomes more and more elongated. The odontoblast cell has had many functions assigned to it, one of them being that it is a nerve end-organ, and that its prolongation, the dentinal fibril, conducts sensation from the dentine. As Mr. Chas. Tomes says, writing in 1904 (1), “the difference of opinion as to the function of the odontoblast cells never can be finally settled until the nerve endings of the pulp are finally demonstrated.” As I hope it is now satisfactorily proved that true nerve fibres are distributed to the dentine, the ground is cleared for a further investigation of the real nature and functions of the cells and dentinal fibrils. We can no longer look upon the odontoblasts as being in any sense nerve end-organs, or consider their processes, the dentinal fibrils, as transmitters of sensation from the hard substance of the dentine. From their position and structure we may confidently consider them to be actively engaged in the formation of dentine, and I shall endeavour to produce evidence of this and of the way in which their functions are carried out, drawing special attention to certain processes of a purely physical nature which are concerned in calcification, and their co-ordination with the action of the living cells.