Calbindin D28K-like immunoreactive nerve fibres in the predentine of rat molar teeth

Dental neuroplasticity, neuro-pulpal interactions, and nerve regeneration

This review covers current information about the ability of dental nerves to regenerate and the role of tooth pulp in recruitment of regenerating nerve fibers. In addition, the participation of dental nerves in pulpal injury responses and healing is discussed, especially concerning pulp regeneration and reinnervation after tooth replantation. The complex innervation of teeth is highly asymmetric and guided towards specific microenvironments along blood vessels or in the crown pulp and dentin. Pulpal products such as nerve growth factor are distributed in the same asymmetric gradients as the dentinal sensory innervation, suggesting regulation and recruitment of those nerve fibers by those specific factors. The nerve fibers have important effects on pulpal blood flow and inflammation, while their sprouting and cytochemical changes after tooth injury are in response to altered pulpal cytochemistry. Thus, their pattern and neuropeptide intensity are indicators of pulp status, while their local actions continually affect that status. When denervated teeth are injured, either by pulp exposure on the occlusal surface or by replantation, they have more pulpal necrosis than occurs for innervated teeth. However, small pulp exposures on the side of denervated crowns or larger lesions in germ-free animals can heal well, showing the value of postoperative protection from occlusal trauma or from infection. Current ideas about dental neuroplasticity, neuro-pulpal interactions, and nerve regeneration are related to the overall topics of tooth biomimetics and pulp/dentin regeneration.

The Ruffini ending as the primary mechanoreceptor in the periodontal ligament: its morphology, cytochemical features, regeneration, and development

The periodontal ligament receives a rich sensory nerve supply and contains many nociceptors and mechanoreceptors. Although its various kinds of mechanoreceptors have been reported in the past, only recently have studies revealed that the Ruffini endings--categorized as low-threshold, slowly adapting, type II mechanoreceptors--are the primary mechanoreceptors in the periodontal ligament. The periodontal Ruffini endings display dendritic ramifications with expanded terminal buttons and, furthermore, are ultrastructurally characterized by expanded axon terminals filled with many mitochondria and by an association with terminal or lamellar Schwann cells. The axon terminals of the periodontal Ruffini endings have finger-like projections called axonal spines or microspikes, which extend into the surrounding tissue to detect the deformation of collagen fibers. The functional basis of the periodontal Ruffini endings has been analyzed by histochemical techniques. Histochemically, the axon terminals are reactive for cytochrome oxidase activity, and the terminal Schwann cells have both non-specific cholinesterase and acid phosphatase activity. On the other hand, many investigations have suggested that the Ruffini endings have a high potential for neuroplasticity. For example, immunoreactivity for p75-NGFR (low-affinity nerve growth factor receptor) and GAP-43 (growth-associated protein-43), both of which play important roles in nerve regeneration/development processes, have been reported in the periodontal Ruffini endings, even in adult animals (though these proteins are usually repressed or down-regulated in mature neurons). Furthermore, in experimental studies on nerve injury to the inferior alveolar nerve, the degeneration of Ruffini endings takes place immediately after nerve injury, with regeneration beginning from 3 to 5 days later, and the distribution and terminal morphology returning to almost normal at around 14 days. During regeneration, some regenerating Ruffini endings expressed neuropeptide Y, which is rarely observed in normal animals. On the other hand, the periodontal Ruffini endings show stage-specific configurations which are closely related to tooth eruption and the addition of occlusal forces to the tooth during postnatal development, suggesting that mechanical stimuli due to tooth eruption and occlusion are a prerequisite for the differentiation and maturation of the periodontal Ruffini endings. Further investigations are needed to clarify the involvement of growth factors in the molecular mechanisms of the development and regeneration processes of the Ruffini endings.

Alteration in the expression level of calbindin D28k in the periodontal ligament of the rat molar during experimental tooth movement

The present immunohistochemical study was designed to investigate changes in the distribution and expression level of calbindin D28k in the periodontal ligament during experimental tooth movement in the rat molar to clarify the physiological role of this protein in the ligament. In normal animals, calbindin D28k-like immunoreactivity appeared sparsely in spindle-shaped cells in the alveolar half of the periodontal ligament. Electron microscopic observations showed that these immunoreactive cells were characterized by well-developed rough-surfaced endoplasmic reticulum and phagosomes--which often contained collagen fibers--suggesting that these cells could be categorized as periodontal fibroblasts. Twelve hours following the onset of the experimental tooth movement, cells positive for calbindin D28k increased in number in the periodontal ligament, especially in the alveolar half of the pressured side. Immunoelectron microscopy showed that the calbindin D28k-immunopositive cells had morphological features similar to those of fibroblasts in the normal ligament, and that these cells occasionally made contact with immunonegative macrophage-like cells. Immunopositive cells gradually decreased in number, and the distribution of the cells and intensity of the immunoreactivity returned to normal levels by 14 days following the induction of the experimental tooth movement. The present results suggest that calbindin D28k plays an important role in the homeostasis and cyto-protection of fibroblasts in the periodontal ligament at the initial phase of experimental tooth movement.

Immunohistochemical localization of S-100beta in the dental pulp of the rat molar

The present study was undertaken to reveal whether S-100alpha or S-100beta or both are present in the nerve fibers in the rat molar tooth pulp. No immunoreactivity for S-100alpha was observed in the molar pulp. In the root pulp, thick smooth-surfaced structures accompanying the blood vessel showed S-100beta-like immunoreactivity (-LI), and occasionally a very few thin beaded elements exhibited S-100beta-LI. In the coronal pulp, S-100beta-like immunoreactive (-IR) structures arborized repeatedly and extensively; they had a predominantly thick, smooth-surfaced appearance, though parts appeared thin and beaded. Numerous thin varicose S-100beta-IR structures ran through the odontoblast cell layer, and further penetrated into the predentin alongside the dentinal tubules. They could be traced for approximately 10-20 micrometers into the predentin from the pulp-predentin border. Immunoelectron microscopy revealed that the Schwann cells in the root pulp showed S-100beta-LI, and that S-100beta-LI was present in the axoplasm as well as Schwann cells in the coronal pulp. The S-100beta-IR axons were rarely surrounded by S-100beta-IR Schwann cells. In the predentin, S-100beta-IR nerve fibers terminated in a position close to the odontoblast processes. The present findings indicate that S-100beta, not S-100alpha, is present in the axon in the dental pulp and predentin as well as in the Schwann cells.