A further study of Dentine

Abstract

Summary Dentine is recognized as an acellular and a vascular calcified connective tissue matrix permeated by fine channels containing tissue fluid. The distribution of structures which fulfil this description of dentine is very wide, in fact it is present in all vertebrates with only one or two exceptions. It is seen in the shield of the ostracoderms, the earliest known vertebrates, in the scales or superficial calcified mesenchyme tissues of early fishes and in all teeth, to which in terrestrial animals it is restricted. Kindred structures to which a qualifying word is added to that of dentine, such as osteo‐dentine, are not discussed. Of the many names for the form of dentine described here that of tubular dentine is used. The greatly increased knowledge of the components of the connective tissues and recognition of a possession of basic properties in a closer degree than formerly, has advanced the interpretation of structural and functional features and certainly applies to dentine. Reference is made to the uncertain relation of reticular fibres to those of collagen. The former conception of cytoplasmic processes from the odontoblasts occupying the dentinal tubules is shown to be erroneous, so that tooth‐dentine, composed of a matrix or ground substance permeated by tissue fluid, is nearer in structure to other forms of connective tissue. The statement by Tomes is quoted showing that he is misinterpreted if the dentinal fibrils in the tubules described by him are regarded as processes from the odontoblasts. The contents of the dentinal tubules are now recognized in histologically fixed specimens as coagulated colloidal components of the tissue fluid. Odontoblasts, like fibroblasts, are fibrogenetic; they give rise to the collagen fibres and mucopolysaccharides forming the dentine matrix with which they are directly connected. Granules are present in the cells and in the forming dentine matrix, a continuity is such that distinction between the end of a cell and its connection with the predentine matrix cannot be determined and there is no evidence of a cell membrane in this position. Collagen fibres, completing the walls of the dentinal tubules in the formation of the dentine matrix have been mistaken for the fibrils of Tomes. The opinions expressed by many authorities upon the contents of the dentinal tubules are discussed, the statements are made almost entirely upon human dentine and laboratory animals. A study of the tissues over a wider field was undertaken, the teeth of vertebrates ranging from fishes to man are discussed and the arrangement in the diphyodonts and polyphyodonts considered. Development of tooth‐dentine is described in relation to the changed conception of its structure, and comparisons are made with the interpretations by other authorities. The development of other forms of tubular dentine is little known and is assumed to resemble the production of tooth‐dentine. The relation of the blood capillaries to the odontoblasts forming a Vaso‐cellular barrier is described and comparison made with bone formation. The production of dentine beyond this barrier gives rise to the characteristic a cellula r and a vascular structure. Attention is drawn to the importance of the pressure and variation of tension in the tissue fluid in determining the arrangement of the components of the matrix during development and the maintenance of the tissue fluid spaces, in mammalian dentine as tubules which are cylindrical due to fluid being laterally contained. During the development of dentine evidence is present indicating pressure in the tissues within the rigid layer of the internal dental epithelial cells of the enamel organ which determines their arrangement. The uniform appearance of dentine is due to the products of the odontoblasts blended and being moulded together by the tissue fluid pressure in the tubules or tissue spaces. There is no evidence of individual production of the matrix by an odontoblast in histological sections, the tubules cut transversely appear as empty rings in a homogeneous matrix. The functional importance of elasticity is commented upon in relation to sensation in teeth. The terminal nerve receptors are regarded as situated near the pulp surface and not at the outer aspect of the dentine. Tooth‐dentine is discussed almost entirely as other forms of dentine are too little known and generally are assumed to be similar in structure and probably in development. This is accounted for largely because nearly all forms in a satisfactory state of preservation are obtained with difficulty, particularly in the developmental stages.