Discussion - References.
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 â€˜preodontoblastoidâ€™ 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.
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.
Birk DE, Trelstad RL (1984) Extracellular compartments in matrix morphogesis: collagen fibril, bundle and lamellar formation by corneal broblasts. Journal of Cell Biology 99, 2024-33.
Bishop MN, Malhotra M, Yoshida S (1991) Interodontoblastic collagen (von Korff fibres) and circumpulpal dentin formation: an ultrathin section study in the cat. American Journal of Anatomy191, 67-73.
Cox CF, Bergenholtz G, FitzgeraldM, Heys DR, Heys RJ, Avery JK (1982) Capping of the dental pulp mechanically exposed to the oral microflora - a 5-week observation of wound healing in the monkey. Journal of Oral Pathology 11, 327-39.
Cox CF, Keall CL, Keall HJ, Ostro E, Bergenholtz G (1987) Biocompatibility of surface-sealed dental materials against exposed pulps. Journal of Prosthetic Dentistry 57,1-8.
Fitzgerald M (1979) Cellular mechanics of dentinal bridge repair using 3H-Thymidine. Journal of Dental Research 58,2198-206.
Furseth R (1971) The fine structure of the odontoblast predentin area in the root. Scandinavian Journal of Dental Research 79, 141-50.
Gomori G (1937) Silver impregnation of reticulum in parafin sections. American Journal of Pathology 13,993-1002.
Hayward AF, Webb BW(1984) Interodontoblastic collagen fibres in the roots of molar teeth of rats. Journal of Anatomy 138, 581-2 (abstract).
Higashi T, Okamoto H (1996) Electron microscopic study on interodontoblastic collagen fibrils in amputated canine dental pulp. Journal of Endodontics 22,116-9.
Kitasako Y, Shibata S, Arakawa M, Cox CF, Tagami J (2000a) A light and transmission microscopic study of mechanically exposed monkey pulps: dynamics of fibre elements during early dentin bridge formation. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 89,945-53.
Kitasako Y, Shibata S, Pereira PNR, Tagami J (2000b) Short-term dentin bridging of mechanically exposed pulps capped with adhesive resin systems. Operative Dentistry 25,155-62.
von Korff K (1906) Die entwicklung der zahnbeingrundsubstanz der saugetiere. Archiv Fur Mikroskopischen Anatomie 67,1-17.
Lechner JH, Kalnitsky G (1981) The presence of large amounts of type III collagen in bovine dental pulp and its significance with regard to the mechanism of dentinogenesis. Archives of Oral Biology 26, 265-73.
Lester KS, Boyde A (1968) The question of von Korff fibres in mammalian dentine. Calcified Tissue Research1, 273-87.
Reith EJ (1968) Collagen formation in developing molar teeth of rats. Journal of Ultrastructure Research 21, 383-414.
Salmon JP, Septier D, Goldberg M (1991) Ultrastructure of interodontoblastic fibres in the rat molar. Archives of Oral Biology 36,171-6.
Seux D, Couble ML, Hartmann DJ, Gauthier JP, Magoloire H (1991) Odontoblast-like cytodifferentiation of human dental pulp cells in vitro in the presence of a calcium hydroxide-containing cement. Archives of Oral Biology 36,117-28.
Shibata S, Fukuda K, Suzuki S, Yamashita Y (1997) Immunohistochemistry of collagen types II and X, and enzyme-histochemistry of alkaline phosphatase in the developing condylar cartilage of the fetal mouse mandible. Journal of Anatomy191,561-70.
Shroff B, Thomas HF (1992) Investigation of the role of von Korff fibres during murine dentinogenesis. Journal de Biologie Buccale 20,139-44.
Silva DG, Kalis DG (1972) Ultrastructural studies on the cervical loop and the development of the amelodentinal junction in the cat. Archive of Oral Biology17, 279-89.
Sogaard-Pedersen B, Boye H, Matthiessen ME (1990) Scanning electron microscope observations on collagen fibres in human dentin and pulp. Scandinavian Journal of Dental Research 98,89-95.
Takita K, OhsakiY, Nakata M, Kurisu K (1987) Immunofluorescence localization of type I and type III collagen and fibronectin in mouse dental tissue in late development and during molar eruption. Archives of Oral Biology 32, 273-9.
Tsuzaki M, Yamauchi M, Mechanic GL (1990) Bovine dental pulp collagens: characterization of type III and V collagen. Archives of Oral Biology 35,195-200.
Tziafas D, Alvanou A, Kaidoglou K (1992a) Dentinogenic activity of allogenic plasma fibronectin on dog dental pulp. Journal of Dental Research 71,1189-95.
Tziafas D, Kolokuris I, Alvanou A, Kaidoglou K (1992b) Shortterm dentinogenic response of dog dental pulp tissue after its induction by demineralized or native dentine, or predentine. Archives of Oral Biology 37,119-28.
Veis A (1985) The role of dental pulp - thoughts on the session on pulp repair processes. Journal of Dental Research 64,552-4.
Yoshiba N, Yoshiba K, Iwaku M, Nakamura H, Ozawa H (1994) A confocal laser scanning microscopic study of the immunofluorescent localization of fibronectinin the odontoblast layer of human teeth. Archives of Oral Biology 39,395-400.
Yoshiba K, Yoshiba N, Nakamura H, Iwaku M, Ozawa H (1996) Immunolocalization of fibronectin during reparative dentinogenesis in human teeth after pulp capping with Ca(OH)2. Journal of Dental Research 75,1590-7.