DENTIN. 



51 



contents, is made up of dentin or ivory, enamel, and cement or 

 crusta petrosa. 



Dentin. The main portion of a tooth is composed of dentin 

 which forms the walls of the pulp-chamber. It bears some resem- 

 blance to bone, though the Haversian canals and lacunae, which 

 characterize the latter, are not present ; it is, however, regarded 

 as modified bone. Chemically it consists of 10 per cent, water 

 and 90 per cent, solids, of which latter 27.70 per cent, is organic, 

 collagen and elastin, and 72.30 per cent, inorganic. Of this, 

 calcium carbonate and phosphate form 72 per cent, and magne- 

 sium phosphate and calcium fluorid the rest. 



Microscopically, dentin is made up of dentinal tubuli, hollow 

 tubes, which present a wavy appearance, between which is inter- 

 tubular tissue. In general, the tubules are parallel with one 



Cementum. < 



Dentin. 



FIG. 41. Cross-section of human tooth, showing cement and dentin ; X 212 

 (Bohm and Davidoff). At a are seen small interglobular spaces (Tomes' granular 

 layer). 



another, although in the upper part of the crown they are 

 arranged vertically, while in the neck and root they are oblique. 

 They extend from the enamel and cement to the pulp-chamber, 

 into which they open, and from the odontoblasts of which they 

 receive processes ; the dentin thus resembling bone in which bone- 

 corpuscles send processes into the canaliculi. At the ends, which 

 open into the pulp-chamber, the tubules are unbranched, but as- 

 they extend toward the enamel and cement they divide dicho- 

 tomously i. e., into two branches, each of which again divides 

 in the same manner. They terminate beneath the enamel and 

 cement in irregular communicating spaces, interglobular spaces 

 or the granular layer. 



The intertubular tissue contains the greater portion of the 

 inorganic constituents of the dentin. 



