278 MICROSCOPIC ANATOMY OF THE TEETH 



pulp are still depositing the dentine, delicate connective- 

 tissue fibres from the pulp are continuously being incor- 

 porated with the forming dentine. 



There seems to be every reason to believe that the principal 

 active agents in the separation and deposition of the lime 

 salts are the odontoblasts, and that they shed out their 

 product into the organic framework laid down to receive it, 

 and according to Von Ebner also contribute a delicate 

 fibrillar foundation to the matrix substance. 



Calcification of the Dentine. In young growing teeth there 

 is a portion of the matrix bordering on the pulp forming 

 a marginal band between the calcified dentine and the 

 odontoblast cells. This layer, the odontogenic zone, shown 

 in figs. 167 and 168, appears to consist of the collagenous 

 basis substance of the dentinal matrix in which the deposit 

 of the lime salts takes place. The uncalcified portion of 

 the matrix, in teeth that have not been treated with acids, 

 unlike the calcified part, takes the stain readily, and the 

 advancing calcification is seen encroaching upon it in the 

 form of rounded masses of the lime salts, or calcospherites, 

 some of these calcospherites lying free in the surrounding 

 uncalcified material (fig. 143). The spherites in this ad- 

 vancing layer are seen to be quite clear and to exhibit no 

 radial or concentric markings in the calcified preparations. 



When a young tooth is decalcified, the rounded contours 

 of the calcifying border have exactly the same appearance 

 as in the calcified tooth ; they appear structureless and 

 consist of the calcoglobulin basis of the spherites, which 

 takes stains readily. The interglobular spaces in imper- 

 fectly-developed dentine show also very clearly the advance 

 and coalescence of these bodies in the basis substance. 



In some sections prepared by Ramon y CajaPs silver- 

 nitrate method, and which were taken from an unerupted 

 human premolar, a further stage in the consolidation of 

 the matrix is revealed which appears to throw a strong light 

 on the mode of calcification of dentine, and to make clear 

 the meaning of certain appearances in the adult tissue 

 which had not received a satisfactory explanation. 



At the borders of carious cavities, a fine striation, very 

 much like muscle striation, is seen in the dentine in some 



