THE TEETH 



323 



THE TEETH 



STRUCTURE 



Each tooth rests in a bony socket in the alveolar process of the maxil- 

 lary bone, and is also held in place by the periosteum of the alveolar 

 sac and the adjacent portion of the gum. The tooth is divisible into a 

 free portion or crown, and a concealed portion or root which usually 

 consists of from one to three fangs. The slightly constricted border 

 between the root and the 

 crown, which is surrounded by 

 the soft tissues of the gum, is 

 known as the neck of the tooth. 



The tooth consists of a su- 

 perficial calcareous portion and 

 a central medulla, the dental 

 or pulp cavity, which occupies 

 the axis of the tooth and which 

 contains a peculiar embryonal 

 type of connective tissue, very 

 similar to reticular tissue, the 

 dental pulp. At the tip of 

 each fang is an opening, the 

 foramen apicis dentis, leading 

 to a narrow canal which pene- 

 trates the wall of the tooth and 

 permits the entrance of the 

 nerves and blood-vessels Avhich 

 supply the pulp. 



The calcareous wall of the 

 tooth is formed by three dis- 

 tinct tissues: (1) dentin or 



ivory; (2) enamel; (3) cementum. The dentin incloses the entire pulp 

 cavity and is in turn covered by the enamel and cementum, the enamel 

 forming the superficial layer of the crown, the cementum that of the 

 root of the tooth. 



The Dental Pulp. The dental pulp is an embryonal type of con- 

 nective tissue which is rich in branching stellate cells and poor in 

 fibers. It contains no elastic fibrils,, and the delicate collagenous fibers 



Contour lines of Retzius 



( Prism stripes of 

 \ Schreger 



Contour lines of 

 Owen 



Dentinal tubules 



Granular layer of 

 Tomes 



Incremental lines of 

 Schreger 



loot canal 



FIG. 303. DIAGRAM OF AN AXIAL GROUND 

 SECTION OF TOOTH, SHOWING THE SEV- 

 ERAL STRIPES OF THE DENTIN AND THE 

 ENAMEL. 



