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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 2  »  Developmental changes and regional differences in histochemical localization of hyaluronan and versican in postnatal molar dental pulp
Developmental changes and regional differences in histochemical localization of hyaluronan and versican in postnatal molar dental pulp
Discussion - References.



Discussion.
HA and versican were histochemically localized in all dental pulps studied during the postnatal period until 49 days of age, but the staining patterns for both molecules varied with age. Notably, strong reactions for both molecules appeared in the subodontoblastic layer of the coronal pulp by the completion of crown formation. However, the pattern in the radicular pulp was different; a strong reaction for HA and a weak reaction for versican were seen in the subodontoblastic layer of the radicular pulp. This was also the most common pattern observed in the radicular pulp in our previous study (Shibata et al. 1999).
During cavity preparation, odontoblasts are separated from the predentine, but not from the subodontoblastic layer, and shift inward together with it (Sato 1989, Ohshima 1990). Therefore, HA and versican in this layer may play a role in supporting and protecting odontoblasts. Yamauchi et al. (1997) made a similar conclusion based on the localization of versican and link protein in the subodontoblastic layer of the bovine dental pulp. Moreover, the subodontoblastic layer contains a nerve plexus (Maeda et al. 1987) and a capillary network (Nakamura 1986, Ohshima 1990), and hence HA and versican also seem to be involved in maintaining these structures.

Serial sections, respectively, and 4g is an adjacent section to a at day 21
Figures 4. Serial sections, respectively, and 4g is an adjacent section to a at day 21. HA staining (a,c,e) and immunostaining for 12C5 (b,d,f ) and for CS-56 (g) cut longitudinally (a,b,g), and transversely through the coronal pulp (c,d) and the radicular pulp (e,f ). In the coronal pulp, strong reactions for both HA and 12C5 are seen in the subodontoblastic layer (arrows in a-d). A strong reaction for 12C5 gradually shifted centripetally with increasing distance from the coronal pulp toward the root (arrowheads in b and f ), although a strong staining reaction for HA is still seen in the subodontoblastic region in the radicular pulp (arrowheads in a and e). Note a weak reaction for 12C5 is seen in the subodontoblastic layer of the radicular pulp (*in b and f ). Immunostaining for CS-56 shows an identical staining pattern to 12C5 (g). A weak reaction for CS-56 is also noted in the subodontoblastic layer of the radicular pulp (*in g). OB, odontoblasts. Bars = 100 m.

Compared to the radicular pulp, the coronal pulp has stronger defence mechanisms, including a higher number of immunocompetent cells (Okiji et al. 1992), and a more extensive subodontoblastic nerve plexus and capillary network (Nakamura 1986, Maeda et al. 1987, Sato 1989, Ohshima 1990). This is probably because the coronal pulp is more susceptible to exogenous stimuli than the radicular pulp. We suggest that the co-localisation of HA and versican seen in the coronal subodontoblastic layer can offer stronger support to the odontoblasts and can maintain more extensive nervous and/or vascular systems than HA alone seen in the radicular pulp.

Serial sections, respectively, at day 42. HA staining and immunostaining for 12C5 cut longitudinally, and transversely through the coronal pulp
Figure 5. Serial sections, respectively, at day 42. HA staining (a,c) and immunostaining for 12C5 (b,d) cut longitudinally (a,b), and transversely through the coronal pulp (c,d). Although the subodontoblastic layer in the coronal pulp shows strong reactions for both molecules (arrows in a-d), a 12C5-negative area is seen in the interior (arrowheads in b and d). In the corresponding area, HA staining was detectable but weak (arrowheads in a and c). The staining pattern in the root pulp for both molecules is identical to that at day 21. Bars = 100 m.

Serial sections showing HA staining and immunostaining for 12C5 at day 49
Figure 6. Serial sections showing HA staining (a) and immunostaining for 12C5 (b) at day 49. A versican-deficient, low-HA area in the central coronal pulp (arrows) expands at this age. Bars = 100 m.

Negative controls for immunostaining and HA staining (at day 21 never show positive reactions
Figure 7. Negative controls for immunostaining (a) and HA staining (b) at day 21 never show positive reactions. Bars = 100 m.

Versican is known to be involved in tissue formation by capturing a temporal space for succeeding tissues/cells in embryonic tissues (Shinomura et al. 1990, Landolt et al. 1995). Since the versican expression becomes extensively restricted in postnatal tissues (Bignami et al. 1993), its disappearance can be regarded as a sign of maturation. We think that versican in the dental pulp also has this function and that its disappearance in the interior of the coronal pulp shows the loss of this function with age, whereas its existence in the subodontoblastic layer contributes to supportive functions described above. Furthermore, since the coronal pulp is formed earlier, this change seems to occur earlier than in the radicular pulp.

References.

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