302 



CHEMISTRY OF A TOOTH. 



a 



Fig. 125. 



Transverse section of the fang a, 

 cement with bone-corpuscles ; b, 

 dentine with dentiiial tubules ; c, 

 boundary between both. 



Chemistry Of a Tooth. The teeth consist of a gelatine-yielding matrix infil- 

 trated with calcium phosphate and carbonate (like bone). 1. The dentine con- 

 tains organic matter, 27'70; calcium phosphate and carbonate, 72'06; magnesium 

 phosphate, 0'75, with traces of iron, fluorine, and sulphuric acid (Aeby, Hoppe- 

 Seyler). 



2. The enamel contains an organic 

 proteid matrix allied to the substance 

 of epithelium. It contains 3 '60 organic 

 matter and 96 '00 of calcium phosphate 

 and carbonate, 1*05 magnesium phos- 

 phate, with traces of calcium fluoride 

 and an insoluble chlorine compound. 



3. The cement is identical with 

 bone. 



The pulp in a fully-grown tooth re- 

 presents the remainder of the dental 

 papilla around which the dentine was 

 deposited. It consists of a very vas- 

 cular indistinctly fibrillar connective- 

 tissue, laden with cells. The layers of 

 cells, resembling epithelium, which lie 

 in direct contact with the dentine are 

 called odontoblasts (Waldeyer, 1865), 

 i.e., those cells which build up the 

 dentine. These cells send off long 

 branched processes into the dentiiial tubules, whilst their nucleated bodies 

 lie on the surface of the pulp and form connections by processes with other cells 

 of the pulp and with neighbouring odontoblasts. Numerous non-medullated 

 nerve-fibres (sensory from the Trigerniuus) whose mode of termination is unknown, 

 occur in the pulp. 



The periosteum or periodontal membrane of the fang is, at the same 



time, the alveolar periosteum, and consists of delicate connective-tissue with few 

 elastic fibres and many nerves. 



The gums are devoid of mucous glands, are very vascular, and often pro- 

 vided with long vascular papillae which are sometimes compound. 



Development Of a Tooth. It begins at the end of the second month of foetal 



life. Along the whole length of the foetal gum is a 

 thick projecting ridge (Fig. 126, a) composed of many 

 layers of epithelium. A depression, the dental 

 groove also filled with epithelium, occurs in the 

 gum, and runs along under the ridge. The dental 

 groove becomes deeper throughout its entire length, 

 and on transverse section presents the appearance of 

 a dilated flask (6), while at the same time it is filled 

 with elongated epithelial cells, which form the 

 "enamel-organ." A conical papilla (the "dentine- 

 germ ") grows up from the mucous tissue, of which 

 the gum consists, towards the enamel-organ (Fig. 

 127, c), so that the apex of tLe papilla comes to have 

 the enamel-organ resting upon it like a double cap. 

 Afterwards, owing to the development of connective- 

 tissue, the parts of the enamel-organ lying between 

 and uniting the individual dentine-germs disappear, 

 and gradually the connective-tissue forms a tooth- 

 sac enclosing the papilla and its enamel-organ (d). 



, Dental ridge ; b, enamel- 

 organ ; c, beginning of 

 the dentine-germ ; d, first 

 indication of the tooth - 

 sac. 



