STRUCTURE AND DEVELOPMENT OF THE TEETH. 



273 



FIG. 100. Transverse Sec- 

 tion through Dentine. 

 The light rings are the 

 dentinal sheaths, the 

 dark centers with the 

 bright points are the 

 dentinal fibrils lying in 

 the dentinal tubules. 



of the enamel as a structureless membrane, i /n or 2 fi thick, which, in the case of 

 young teeth, exhibits an epithelium-like arrangement, and is derived from the outer 

 epithelial layer of the enamel organ. 



The cement (osseous substance) consists of a thin bony layer covering the 

 root of the tooth, with a nbrillated ground-substance and provided with Shar- 

 pey's fibers (Fig. 103, a). Haversian canals and 

 lamellae are found only in the thick layers of cement 

 at the apex of the root, the former at times leading 

 into the tooth-cavity. Thin layers of cement may 

 even be unprovided with bone-corpuscles. 



Chemistry of the Solid Constituents of the Tooth. 

 The teeth consist of a framework of calcareous sub- 

 stance, infiltrated with calcium phosphate and car- 

 bonate, like the bones, (i) The dentine contains of 

 organic matter 27.7, of calcium phosphate and car- 

 bonate 72.06, of magnesium phosphate 0.75, with 

 traces of iron, fluorin and sulphuric acid, potassium, 

 sodium, and carbon dioxid. (2) The enamel pos- 

 sesses as its organic basis a substance resembling 

 the proteid of epithelial cells. It contains of inor- 

 ganic matter in addition to 3.60 of organic matter 

 calcium phosphate and carbonate 96.00, magnesium 

 phosphate 1.05, with traces of calcium fluorid, an in- 

 soluble chlorin-combination, potassium, sodium, and 

 carbon dioxid. (3) The composition of the cement is 

 identical with that of true bone. 



The Soft Parts of the Tooth. The tooth-pulp in the 



adult tooth represents the remains of the dental papilla, about which the hard- 

 ening layer of dentine has been deposited. It consists of connective tissue, at 

 times not distinctly fibrous, and rich in capillaries, with connective-tissue cells 

 and leukocytes. The most superficial layer of cells, which, not unlike epithelium, 

 lie close together next to the dentine, is formed of unencapsulated odontoblasts, 



25 // long by 2 fi wide, from which the 

 production of the dentine proceeds. 

 They send long processes into the den- 

 tinal tubules, while the nucleated cell- 

 body, resting on the surface of the 

 pulp, forms a connection with the pulp 

 and with neighboring odontoblasts by 

 means of other processes. Numerous 

 medullated nerve-fibers, becoming non- 

 medullated after repeated division, 

 penetrate between the odontoblasts and 

 end beneath the dentine in free ex- 

 tremities presenting nodular thickening 

 in places. Other nerve-fibers lie partly 

 in the dentinal tubules, in part in the 

 substance of the dentine. Most of them 

 appear to end free, in a brush-like 

 radiation. A plexus of fine nerve-fibers 

 lies beneath the enamel. The epidenti- 

 nal canal-system is provided with a 

 special nerve-apparatus, which in part 

 penetrates into the enamel. The ar- 

 teries of the tooth often lie in grooves 

 in the nerve-branches. The capillaries 

 even penetrate to the odontoblast-layer. 

 The periosteum of the root of the tooth 

 and, at the same time, of the alveolar cavity, is of a delicate structure, without 

 elastic fibers, but rich in nerves and blood-vessels. The gums have no mucous 

 glands and are characterized by their long, vascular papillae. 



The development of the teeth begins as early as the fortieth day (Rose). 

 Throughout the entire length of the alveolar margin there is a projecting ridge, 

 formed of a thick epithelial layer, the denial ridge (Ing. 104, a). From this epitne- 

 18 



FIG. 101. Interglobular Spaces in the Dentine. 



