TISSUES (CONNECTIVE) 



Fig. 19. Section of dentine near pulp. The tubule contents have been removed and the section decal- 

 cified, showing the arrangement of collagen fibrils around the tubule. Embedding medium removed. 

 Stereoscopic photograph. X 10,000. 



some time (M. Deakins, J. Dent. Res., 27, 

 429, 1942) that there is a water loss in the 

 matrix immediately before calcification. A 

 changed appearance of the calcified matrix, 

 in response to pressure or caries is often ob- 

 served, and Von Th. Spreter {Schweiz. Med. 

 Woch., 88, 635, 1958) has shown that 12- 

 13 % dentine by w^eight is a liquor contain- 

 ing adequate amounts of protein, amino 

 acids, sugars and minerals for further pol- 

 ymerization or precipitation. As a reaction 

 to caries, crystallites of the same size as those 

 in enamel have been observ^ed randomly 

 precipitated within the dentine matrix. 



Near the pulp, the tubules are observed to 

 be completely filled by the odontoblast proc- 

 esses. Towards the enamel, between the 

 matrix proper and the odontoblast process, 

 a 'peritubular zone' has frequently been re- 

 ported. Its nature is as yet unresolved. A 

 good factual description has been given by 

 R. Frank (Arch. Oral Biol, 1, 29, 1959). 



Dental Enamel. Tooth enamel has a 

 matrix and crystallites which are completely 

 unhke any of the other calcified tissues, 

 doubtless because it is the only calcified 

 ectodermal structure. The matrix consists of 

 two main compounds, which from chemical 



analysis and X-ray diffraction studies can 

 probably be regarded as members of the 

 keratin group. Some reports indicate that a 

 small proportion of polysaccharide may be 

 present. The prismatic appearance of enamel 

 in sections prepared for the light microscope 

 is due to the arrangement of these two com- 

 pounds. Since the composition of neither is 

 certainly known, they will be referred to 

 here by the names of the workers who first 

 provided an adequate description of each — 

 the less soluble and denser as Pincus' pro- 

 tein, and the less dense and more unstable 

 as Stack's protein. Fig. 20 shows the arrange- 

 ment in a section of developing enamel 

 shortly before the calcification commences. 

 Both proteins form an oriented network, and 

 during calcification apatite crystallites are 

 laid down in pockets of these networks. Cal- 

 cification in Stack's protein occurs shortly 

 before calcification of Pincus' protein at the 

 same level in the enamel. When fully calci- 

 fied, enamel has a very much higher propor- 

 tion of apatite to matrix than is found in any 

 other tissue. There are considerable difficul- 

 ties in cutting thin sections (diamond knives 

 chip easily) and most published photographs 

 of mature enamel are of replicas. When 



289 



