DENTINE 237 



Rose includes under his vitrodentine the outer layer of the 

 teeth of Selachia, which Tomes considers to be enamel. There 

 are certain objections to Rose's classification which are con- 

 sidered by Tomes in a paper on the subject in 1898 (226), 

 and as his classification of dentines appears to be the simplest 

 and least open to objections, it has been adopted in the present 

 work. As Tomes points out, the term-' trabecular dentine ' 

 is perhaps a better descriptive term than ' osteodentine ', 

 and we may conveniently describe this variety as osteo- or 

 trabecular dentine. 



Orthodentine (tubular dentine). To the naked eye typical 

 orthodentine, as seen in human teeth, is a yellowish white 

 semi-translucent substance covered by enamel in that por- 

 tion of the tooth which is raised above the gum margin, 

 and in contact externally with the overlying cement at 

 the neck and root of the tooth. 



If a tooth is placed in an acid solution, such as a 3 to 5 per 

 cent, solution of nitric or hydrochloric acid, the lime salts are 

 removed and the collagen basis substance alone remains and 

 still exhibits the general structure and appearance of the calci- 

 fied dentine ; it is soft and elastic and can be penetrated by 

 a needle. The resulting substance is collagen, which is 

 converted into gelatine by boiling, thus having the same 

 characteristics as bone. 



When both bone and dentine are treated with strong 

 acids a residue remains which consists of elastin, and is 

 probably present in the dentine in the Neumann's sheaths 

 of the tubules. 



Chemical Composition. As in enamel, the salt which greatly 

 predominates in dentine is calcium phosphate, the other 

 salts present being calcium carbonate and magnesium phos- 

 phate, and according to Von Bibra (2) traces of calcium 

 fluoride . The same author also gives the percentage of animal 

 matter as 27-61, while the percentage of organic matter in 

 enamel according to recent analysis is from 1 to 2. 



Tomes, however, considers that the amount of organic 

 matter in dentine has been over-estimated, and would place 

 it at about 19 per cent., as he considered that the water 

 retained in combination with dentine, even when dried at 

 212 F., amounts to about 8 per cent, of the whole, and he 



