266 R. M. Frank 



et al. (1964), using microradiography and by Rouiller (1951), Frank (1959), 

 Plackova and Stepanek (1960), Takuma (1960), Awazawa (1962), Johansen and 

 Parks (1962) with the electron microscope. The presence of peritubular dentine has 

 been noted in fetal dentine (Takuma, 1960; Frank and Nalbandian, 1963 a) and 

 in young third molars (Frank, 1959) so that this zone has to be considered as a 

 normal constituent of developing and adult dentine. 



In the present study, the peritubular dentine appeared in non-decalcified sections 

 as a electron dense annular zone (Fig. 6), which at higher magnification was seen to 

 be built up by a grouping of dark dots more apparent on transverse section (Fig. 6) 

 and predominantly as dark long profiles on longitudinal section. Electron diffraction 

 of peritubular dentine shows ring patterns typical of the apatite group and when 

 selective area electron diffraction patterns from this region are made with a small 

 selection diaphragm, the presence of line arcing is noted on the pattern indicating a 

 preferential orientation of the apatite crystals (Fig. 11). 



It has been shown that this peritubular dentine has a loose fibrillar matrix, easily 

 destroyed by histological decalcifying methods (Frank, 1959). According to Takuma 

 (1960) and Johansen and Parks (1962), the fibrils of the peritubular zone are colla- 

 gen fibrils. However Awazawa (1962) did not find any collagen striations and Brad- 

 ford (1963) noticed after ethylene diamine maceration, followed by decalcification in 

 weak buffered formic acid that a larger part of the peritubular matrix still remained. 



In the present study our findings agree with Plackova and Stepanek (1960) who 

 state that the peritubular dentine contains more minerals, less fibrils and more ground 

 substance than the intertubular dentine. The rich content of acid mucopolysaccharides 

 in the peritubular matrix has been confirmed by histochemical methods (Wislocki 

 et al., 1948; Wislocki and Sognnaes, 1950; Weill, 1959; Symons, 1961). 



In the young premolar teeth examined in the present investigation, we noticed 

 that the peritubular zone is formed and enlarges progressively by calcification of its 

 inner wall at the expense of the tubular lumen. The presence of collagen fibrils in the 

 periodontoblastic organic space (Fig. 8) and their subsequent calcification and em- 

 bedding in the peritubular zone points to the fact that the loose fibrillar matrix of 

 this zone is collagen. In the peripheral layer of dentine complete obliteration of the 

 tubular content occucrs in some tubules. Therefore, dentinal sclerosis which has been 

 noted in different pathological conditions as well as in old dentine (Dreyfuss et al., 

 1964), is also present in young coronal dentine under physiological conditions. 



The intertubular dentine immediately surrounds the lumen of tubules in areas 

 where no pertitubular dentine is present and also fills the regions between the outer 

 parts of the peritubular zones. Compared with the latter the intertubular dentine 

 contains less apatite crystals and ground substance, but is richer in collagen fibrils 

 with 640 A periodicity. Johansen (1964) considers the apatite crystals of the inter- 

 tubular dentine as plates of 1000 A in length and 20 — 35 A in thickness. Like HoH- 

 LiNG (1963), we have also noticed the absence of preferential orientation of the elec- 

 tron diffraction pattern of large areas of intertubular dentine (Fig. 10). However, 

 with selective area electron diffraction pattern performed with a small selection 

 aperture, preferential orientation of the crystals has been noticed. Electron micro- 

 graphs of human amelo-dentinal junction (Fig. 9) show that the intertubular dentine 

 is closely interconnected with enamel and it is difficult to follow the exact limit of 

 both tissues. 



