Scanning electron microscope observation of the endings of the odontoblast process in human and animal dentin

Abstract

Recent SEM studies have demonstrated that the odontoblast process occupies the dentinal tubules of fully formed dentin, up to the dentinal-enamel junction (Maniatopoulos and Smith, 1982, 1983; Yamada et al, 1983). There is however, still debate on how the processes end at the dentinal-enamel or dentinal-cementum junction. It was the purpose of this study to investigate the endings of the odontoblast process in these areas.Materials and Methods:Freshly extracted human and rat teeth were a) split mechanically by the use of a mallet and a chisel, b) decalcified in 18% E.D. T.A. for 6 hr, c) washed in PBS for 1 hr, d) digested with bacterial collagenase for 2 hr at 37°C, e) fixed in 2% glutaraldehyde with 0.1M cacodylate buffer for 12 hr, f) post-fixed in 1% osmium, g) dehydrated in a graded series of aqueous alcohol. All solutions had 0.1M sucrose added to maintain almost near physiological osmolarity, ph was 7.4. Then specimens were routinely processed for scanning electron microscopy (ISI-60).Results:Odontoblast processes were observed in the inner, middle and outer part of dentin, up to the dentin-enamel or dentino-cementum junction, in all specimens examined. These observations verify the findings of previous workers in the field. At the area of mantle dentin the odontoblast processes were observed to be divided, giving two or more terminal branches (schematically shown in fig 1-3). In this area the processes were observed to end forming spherical structures (fig 1-9). These spherical endings of the odontoblast processes were observed after the total removal of the enamel and part of the mantle dentin through demoralization. These structures were observed on the surface of the dentin in close relation to the openings of the dentinal tubules (fig 4,5,8 and 9) and presenting a true continuation to the odontoblast processes (fig 6,7). In some specimens (fig 5,6) spheres were collapsed probably due to specimen dehydration following fracture and SEM preparation, whereas in other specimens they appeared intact (fig 8,9). Some endings (fig 8,9) showed smaller spherical projections on the main sphere body. The spherical endings of the odontoblast processes were observed in both crown and root mantle dentin.Conclusions:The results suggest that i) the odontoblast processes occupy the full length of fully developed dentin in both human and rat teeth, up to the dentino-enamel or dentino-cementum junction, ii) The odontoblast processes end in the mantle dentin in the form of spherical structures.Acknowledgement:The authors are grateful to Dr. M. Sigal for the initial preparation of the specimens.