ename 

 interglobular spaces 

 contour lines of Retzius 



dentine 



contour lines of growth 

 bom 



pulp 



acellular cementum 

 root 



bone osteon- 

 periodontal membrane 

 (vascular) 



cellular cementum 

 (laminate bone) 



collagenous fibers which continue 

 into bone as Shorpey's fiber 



Figure 8-49. Section of a mammalian tooth set in the jaw. (After 

 Ham, 1957) 



opening of the cup. The dental lamina at this stage has a 

 second generation of tooth germs extending down from it 

 medial to the initial tooth germs. 



The enamel-producing epithelium is bell-shaped and 

 formed of columnar ameloblasts or ganoblasts. The amelo- 

 blasts induce the formation of odontoblasts in the adjacent 

 dermal papilla, and these then produce the first layer 

 of dentinal material, a soft fibrous material called preden- 

 tine. The fibers of the odontoblasts extend between columns 

 of the predentine. The appearance of the predentine next to 

 the basal membrane of the ameloblasts induces the forma- 

 tion of enamel. The soft pre-enamel material accumulates 

 at the base of each ameloblast as a Tome's process; either 

 this material is secreted through the basement membrane 

 or that part of the cell containing it breaks down (merocrine 

 secretion). As the ameloblasts move away from the secreted 

 pre-enamel, new layers of Tome's processes appear and the 

 long wavy and spiraled column is produced. The produc- 

 tion of the soft material is periodic as is its calcification; this 

 periodism produces the cross lines of Retzius seen in the 

 rods. 



Inside of the enamel-dentine interface, the dentine is laid 

 down in layers toward the pulp cavity, first as a soft pre- 

 dentine and later as a calcified, hard dentine. Dentinal 

 tubules containing the processes of the odontoblast are left 

 behind as this process continues, and the processes elongate 

 as the cells move further and further from the interface. 



The tooth structure of vertebrates can now be reviewed 

 beginning with the fishes. 



Agnath fishes 



The agnath fishes are unique in that they do not have 

 teeth of the gnathostome type. Some of the anaspids per- 

 haps had small denticles similar to those of the body 

 armor on the tooth plate in the floor of the mouth. In the 



dental lamella of permanent tooth 



rimordium of ename 



disintegrating dental lamella disintegrating enamel organ 



bone 



dental papilla 

 odontoblasts 



^C,v--,-=.v7~'^ \', * dental sac of mesenchyme'^ '-'c'^T 



^."Yrc- 



A 4th MONTH 



B 



5th MONTH 



C BIRTH 



Figure 8-50. Three stages in the development of human (mammalian) tooth. A, cap stage of tooth 

 bud, fourth month; B, bell stage, fifth month; C, milk and permanent teeth at birth. (After Ham, 1957) 



TEETH 



245 



