STRUCTURE OF THE DENTINE. 



785 



The central cavity of a tooth is called the pulp-cavity, because it is occupied 

 and accurately filled by a soft, highly vascular, and sensitive substance, 



Fig. 543. 



Fig. 543. SECTIONS OP AN INCISOR AND 

 MOLAR TOOTH. 



The longitudinal sections show the whole 

 of the pulp-cavity in the incisor and molar 

 teeth, its extension upwards within the crown 

 and its prolongation downwards into the fangs 

 with the small aperture at the point of each ; 

 these and the cross section show the relation 

 of the dentine and enamel. 



called the dental pulp. This pulp con- 

 sists of areolar filaments, amongst 



which numerous nuclei and cells are rendered visible by the action of acetic 

 acid. It is well supplied with vessels and nerves, which are derived from 



Fig. 544. MAGNIFIED LONGITUDINAL SECTION OF A Fig. 544. 



BICUSPID TOOTH (after Ketzius). 



1, the ivory or dentine, showing the direction and pri- 

 mary curves of the dental tubuli ; 2, the pulp-cavity with 

 the small apertures of the tubuli into it ; 3, the cement or 

 crusta petrosa covering the fang as high as the border of 

 the enamel at the neck, exhibiting lacunae ; 4, the enamel 

 resting on the dentine ; this has been worn away by use from 

 the upper part. 



the internal maxillary artery and the fifth pair, and 

 which enter the cavity through the small aperture 

 at the point of each fang. 



The solid portion of the tooth is composed of 

 three distinct substances, viz. the proper dental 

 substance, ivory or dentine, the enamel, and the 

 cement or crusta petrosa. The dentine constitutes 

 by far the larger part of the hard substance of a 

 tooth ; the enamel is found only upon the exposed 

 part or crown ; and the cement covers with a thin 

 layer the surface of the implanted portion or fang. 

 A fourth variety of tissue, osteodentine, is formed 

 within the dentine, at the expense of the pulp, as 

 age advances. 



A. The dentine, (Owen,) forming the principal 

 mass or foundation of the body and root of a tooth, 

 gives to both of these parts their general form, 

 and immediately encloses the central cavity. It 



resembles very compact bone in its general aspect and chemical relations, 

 but is not identical with it in structure, or in the exact proportions of its 

 earthy and animal constituents. 



According to the analyses of Berzelius and Bibra, the dentine of human 

 teeth consists of 28 parts per cent, of animal, aud 72 of earthy matter. 

 The former is resolvable into gelatin by boiling. The composition of the 

 latter, according to Bibra, is as follows, viz. , phosphate of lime 66 '7 per cent., 

 carbonate of lime 3 '3, phosphate of magnesia and other salts, including a 

 trace of fluoride of calcium, ! 8. Berzelius found 5 *3 carbonate of lime. 



3 F 



