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 »  Home  »  Endodontic Articles 13  »  Location, arrangement and possible function of interodontoblastic collagen fibres in association with calcium hydroxide-induced hard tissue bridges
Location, arrangement and possible function of interodontoblastic collagen fibres in association with calcium hydroxide-induced hard tissue bridges
Discussion - References.



Discussion.
During root dentinogenesis in the rat molar, the occurrence of collagen is irregular and does not contribute to predentine formation (Hayward&Webb1984, Salmon et al.1991). During secondary physiologic dentine formation, the pattern of interodontoblastic collagen fibre occurrence is irregular in cats (Bishop et al.1991). In this study, argyrophilic stained VKF within the dentine matrix of early dentine bridges were routinely detected. Classic von Korff fibres were postulated to help guide the odontoblasts in their pulp ward migration during dentinogenesis and to bind the soft tissue pulp and odontoblasts to the dentine (von Korff 1906). In the case of a pulp exposure, although the VKF is different from classical von Korff fibres in some ways, they are important for initial dentine bridging to induce and support a dentinogenesis framework, helping to guide the ‘preodontoblastoid’ cells in their migration, adhesion and arrangement, and dentine bridge formation. Furthermore, the VKF may provide a biological/mechanical tie that binds the fibres of the central pulp and newly formed odontoblastoid cells, become embedded in the predentine and are finally incorporated to serve asmatrix fibres in the early formed dentine bridge (Fig. 4).
VKF were quite different from classic von Korff fibres in their thickness and their silver staining intensity. Moreover, they consist of two types of collagen fibrils, a thick fibril (_240 nm in diameter) and a thin fibril portion (_80 nm in diameter). Since no similar findings have been described in the literature, this may be a unique structural feature beneath a hard-setting Ca(OH)2 agent as the capping material. Yoshiba et al. (1994) have suggested that the fibronectin-positive fibres may correspond to von Korff fibres. Fibronectin is an extracellular matrix glycoprotein distributed in the tissues and blood and has been demonstrated to induce reparative dentinogenesis (Seux et al. 1991, Tziafas et al.1992b). Yoshiba et al. (1996) suggested a fibronectin-rich matrix served as a reservoir for cell migration and attachment following direct pulp capping in human teeth. The results of this study shows the VKF stained positive for fibronectin, and this most likely corresponds with VKF fibres. Additional matrix components such as proteoglycans, fibronectin, or other collagen types may be important in the control of collagen-fibril structure (Birk & Trelstad 1984). Further immunohistochemical staining studies are needed to more precisely define, distinguish and differentiate VKF from classic von Korff fibres.
Initially, we observed VKF extending from the original dentine, passing through the odontoblastoid cells with a close relationship to the central pulp. Therefore, both odontoblastoid and pulp broblasts appear to be involved in the formation of VKF. Bishop et al. (1991) suggested a similar possibility with interodontoblastic fibres during secondary physiologic dentine formation in the root dentine. However, as the odontoblastoid cells begin organizing and attaching to each other, the VKF appear to lose their close relationship with fibres of the central pulp. After that, the VKF are no longer observed near odontoblastoid cells. These data strongly suggest that pulp broblasts are mainly involved in the formation of the thin fibril portions of VKF, and the thick fibril portion extends directly from the original dentine, possibly being produced by odontoblastoid cells.
Dentine and predentine contain only type I collagen (Takita et al.1987) whereas the pulp contains mostly type I, with up to 45% type III (Lechner & Kalnitsky 1981) and smaller amounts of type V collagen (Tsuzaki et al. 1990). Based on the thickness of fibrils, Bishop et al. (1991) speculated the interodontoblastic fibre was type I collagen. The thickness (80-240 nm in diameter) and immunohistochemical staining indicates the VKF in this study are type I collagen. Shroff & Thomas (1992) showed that the distribution of type I and III collagen is related to the degree of odontoblast differentiation and the reactivity of type I collagen observed between the cells. Thus, the reactivity of type I collagen is possibly related to initial dentine bridge formation.

Figure 6. Composite drawing of the sequence of VKF during early dentine bridge formation. This figure is made from (A) 14-, (B) 21-,(C) 30-day section, at some distance from the exposure area and (D) 30-day section, at the periphery of the exposure area.
(A) The VKF consisting of a thick and a thin fibril portion extends from the original dentine, passes through the odontoblastoid cells, and has a close relationship with the central pulp.
(B) As the predentine expands, the VKF becomes embedded in it.
(C) As odontoblastoid cells differentiate, they begin displaying well-organized cell processes and attaching to each other, and hence the VKF loses its close relationship with the central pulp.
(D) As the formation of dentine bridge advances, the VKF is embedded in the calcified dentine bridge and no longer observed near the odontoblastoid cells.

Immunostaining for type I collagen is detected in the VKF and the central pulp fibres

Tziafas et al. (1992a) suggested that the physicochemical properties of a surface to which pulp cells attach is a critical requirement for expression of their odontoblastic potential. The presence of residual dentine chips at the wound surface might be effective to promote a surface to which pulp cells will attach and differentiate into new odontoblastoid cells (Kitasako et al. 2000b). In this study, dentine chips remained at the wound surface and VKF extended perpendicularly from the remaining dentine chips. On the other hand, in the absence of dentine chips at the wound surface, VKF were randomly arranged with some defects observed within the new dentine bridge. At the periphery of the exposure, VKF seemed to serve as a guide for cell arrangement following tubular dentine bridge formation. In the absence of a basement membrane, adhesion of pulp cells onto an appropriate surface may be the critical requirement for the appearance of elongated, polarized, odontoblastoid cells (Veis1985).The small surface recesses like a tubular structure within dentine may support a favorable surface to which VKF can attach and so enhance pulp cell adhesion, arrangement and differentiation. Conclusions Interodontoblastic collagen fibres were routinely detected throughout early dentine bridges. Interodontoblastic collagen fibres may be important for initial dentine bridging to induce and support a dentinogenesis framework.

References.

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