1554 



HUMAN ANATOMY, 



Fig. 



-Odonto- 

 blasts 





The Pulp. — The contents of the pulp-cavity is the modified tissue of the 

 mesoblastic dental papilla remaining after the completed formation of the dentine. 

 The major part of the adult pulp consists of a soft, very vascular connective tissue 

 containing few or no elastic elements, but numerous irregularly distributed cells of 

 uncertain form. The general type of the tissue resembles the embryonal, both in the 

 character of the fibrous tissue and of the cells, which are round, oval, or stellate with 

 long processes. The fibrous bundles and the more elongated cells are most regu- 

 larly disposed around the blood-vessels and nerves, which they invest in delicate 

 fibrous sheaths. 



The peripheral zone of the pulp, next the dentine, presents the greatest special- 

 ization, since in this situation lie the direct descendants of the dentine-producing 

 cells, the odontoblasts. In this locality the pulp, especially in older teeth, presents 



three layers. The outer (.04— .08 mm. thick) 



consists of several rows of large cylindrical 



elements, of which the most superficial are 



arranged vertically to the free surface of 



the pulp, after the manner of an epithelium. 



-Dentine These are the odoyitoblasts, now no longer 



active, about .025 mm. in length and .005 



mm. broad, which send out long, delicate 



^*^S' ^^J^^^'^'"^ ' ^ % processes (the dentinal fibres) inio the den- 



^\'^S ^^^^'^^^%^^ 'i / O' ^^^ tubules externally, and shorter ones 



N a. i \vAt . t^^'^)*? '^^ "^/z .' ^^ towards the pulp-tissue. When very young 



they probably possess also lateral processes. 

 The deeper cells of the odontoblastic layer 

 are less regularly disposed and less cylindri- 

 cal in form. The second, or Weir s layer, 

 best seen in older teeth, is characterized 

 by absence of cells, the fibrous tissue and 

 the cell-processes forming a clear, cell-free 

 zone which separates the striking layer of 

 odontoblasts from the subjacent third or in- 

 terniediate layer. The latter consists of nu- 

 merous small round or spindle-cells, closely 

 placed, but irregularly disposed, which grad- 

 ually blend with the ordinary pulp-tissue. 

 The blood-vessels supplying the pulp are from three to ten small arteries which 

 soon after entering the pulp-cavity break up into very numerous branches from which 

 a rich capillary net-work is derived. In human teeth the capillaries usually do not 

 invade the layer of odontoblasts, although at times the vascular loops may extend 

 between these cells. The venous radicles form larger veins which follow the course 

 of the arteries. Lymphatics have been demonstrated as networks within the pulp. 

 The ;z^rz^<f.s are numerous, each fang receiving a main stem and several additional 

 smaller twigs, which in a general way accompany the blood-vessels in their coarser 

 distribution. On reaching the crown-pulp the larger twigs are replaced by finer 

 branches, which divide into innumerable interwoven fibres. The latter, on reaching 

 the margin of the pulp, form a peripheral plexus beneath the layer of odontoblasts, 

 from which terminal non-medullated fibrillae are given off. Some of these end 

 beneath the odontoblasts in minute knot-like swellings ; others penetrate the odonto- 

 blastic layer to terminate in pointed free endings. There is no trustworthy evidence 

 supporting the view that the nerves directly communicate with the odontoblasts, but 

 they have been traced into the dentinal tubules. 





'A» 



-Pulp- 

 tissue 



.Blood- 

 vessel 



Section of periphery of pulp-tissue of young tooth 



X 175- 



IMPLANTATION AND RELATIONS OF THE TEETH. 



The Permanent Teeth. — Each fang is implanted in a socket corresponding 

 to it in shape, so that the pressure is transmitted from the surface of the conical fang 

 throughout, except at the very tip, which has a hole for the vessels and nerves. A 

 corresponding hole in the socket communicates with the dental canals. The human 



