T. C. WHITE ON THE SO-CALLED " NERVe" OF THE TOOTH. 9 



examination than tlie limits of a paper like this can afford ; but it 

 may be interesting to show the part it plays in the formation of the 

 dentine. 



About the sixth or seventh week of embryonic life a groove is 

 formed in either jaw^, at the bottom of which, after the lapse of a 

 few weeks, papillae begin to arise, and shortly after transverse par- 

 titions in this groove shut off and separate each papilla, which then 

 becomes the representative of the future temporary tooth. About 

 the seventh month of foetal life the ossification of the tooth com- 

 mences, and the dentine is represented by a cup-shaped scale cap- 

 ping the crown, and ultimately extending down the sides and em- 

 bracing the whole of the upper surface of the pulp. Jt is at this 

 period of their growth that the odontoblasts are most active, for 

 they have the development of the dentine before them, and deriving 

 a plentiful supply of nutrition from the plexus of bloodvessels 

 beneath them, dentine is formed through their agency from without 

 inwards, till the pulp being reduced to the size at which we gene- 

 rally see it by the gradual formation of the dentine, the odonto- 

 blasts become dormant, but capable of awaking to activity under 

 the influence of certain circumstances of irritation ; thus if caries 

 attacks a tooth at a particular spot the tubuli in the dentine, 

 through the fibrillae in them, become consolidated at an equal dis- 

 tance from the j)oint of attack all round it, and a barrier seems 

 to be thus thrown up against the inroads of the advancing 

 enemy ; but unless such a remedial measure as the careful excava- 

 tion of the carious portion of the tooth and subsequent plugging of 

 the cavity be adopted, barrier after barrier may be thrown up but 

 to be overcome. Even then the odontoblasts of the pulp resist by 

 forming new dentine in its very substance, and it is only when in- 

 flammation and suppuration destroy the odontoblasts that this re- 

 parative process is annihilated. In some cases of general irritation 

 of the pulp, as where the crown of a tooth is worn through by the 

 grinding down and wear of mastication, the whole of the pulp may 

 be converted into an irregular dentine. Sometimes nodules of 

 ossific matter are found in the meshes of the areolar tissue of the 

 pulp, but these do not partake of the character of the dentine, but 

 are semi-transparent and structureless, testifying to the amount of 

 bone-producing matter in the homogenous plasma saturating the 

 body of the pulp, but which it is the legitimate office of the odon- 

 toblasts to build up as dentine. 



