Tubular Dentin Research Articles

Ultrastructure of wound healing following direct pulp capping with calcium-beta-glycerophosphate (Ca-BGP).

Tissue changes in rat incisors after direct pulp capping with calcium-beta-glycerophosphate (Ca-BGP) have been studied using light and electron microscopy. Immediately after pulp capping, Ca-BGP was converted to hydroxyapatite (HAP) at the cavity floor. At Day 1, the exposure site was covered with Ca-BGP-mediated mineralized tissue. Osteodentine had developed below this mineralized tissue at Day 3. Matrix vesicles (MV) were observed in the extracellular matrix between large cells and osteodentine. At Day 5, tubular dentine was observed below the osteodentine. Three days after the application of Ca(OH)2 in a control experiment, osteodentine had formed below the necrotic zone; however, tubular dentine was not observed at Day 5. These findings suggest that the applied Ca-BGP might be the source of Ca and inorganic phosphate (Pi) through hydrolysis by alkaline phosphatase (ALP), and that Ca-BGP-mediated mineralized tissue induces the early formation of tubular dentine.

Ability of hydroxyapatite-bone morphogenetic (corrected from morphologenetic) protein (BMP) complex to induce dentin formation in dogs.

This histological investigation examined the formation and differentiation of pulp cells under the influence of HAP/BMP complex. HAP/BMP complex was implanted in exposed pulp of the mandibular premolars and alveolar bone defect in the dog. Sequential changes in these areas were examined mainly under a light microscope and partly under a scanning electron microscope. Two weeks after the operation, fibroblast-like cells proliferated right beneath the implanted complex, and after 3 weeks, dentin including dentin tubules grew in the pulp. After four weeks a dentin bridge composed of osteoid dentin was found, and after 8 weeks this dentin calcified and covered the defective surface of the root and adhered to new bone surrounding the HAP granules. The results indicated that the dentin induced by HAP/BMP complex may be of two types: tubular dentin and osteodentin. This complex exhibited outstanding ability to induce dentinogenesis and osteogenesis.

Pulp capping with synthetic hydroxyapatite in human premolars

AbstractClassically, calcium hydroxide is used as a pulp capping agent in humans to form a dentinal bridge over vital dental pulp tissue. The aim of the present study was to determine whether synthetic hydroxyapatite could be used as a substitute. For this purpose, pulp capping with microsized hydroxyapatite (mean size = 38 nm ± 15 nm) was done under lacal anesthesia in 12 normal premolars, to be extracted for orthodontic purposes form 12 different young patients, having given their informed consent. Clinically, the healing was uneventful in all patients, having given their informed consent. Clinically, the healing was uneventful in all patients. Half of the teeth were extracted at 3 months and the other half at 6 months. The pulps were studied under light microscopy and under scanning and transmission electron microscopy using nondecalcified sections. In all cases, a continuous, well‐calcified bridge was observed and no inflammatory cells were present in the residual pulp. In some cases denticles containing some synthetic hydroxyapatite crystals were found in the radicular pulp. The calcified bridge was made up by osteodentine and near the pulp tubular dentine with a layer of predentine and odontoblasts were noted. Odontoblastic processes were lacated in deninal tubules and the intertubular dentine showed interwoven calcified collagen fibrils and hydroxyapatite crystals with a mean length of 0.1 μm along their c axis.

Unique odontogenic tumor with dentinogenesis and features of unicystic plexiform ameloblastoma

A case of an atypical odontogenic tumor with features of unicystic plexiform ameloblastoma and odontoblastic differentiation with deposition of tubular dentin matrix is reported. The significance of dentinogenesis, amelogenesis, and calcification in odontogenic tumors is discussed.

Multiple functions for NGF receptor in developing, aging and injured rat teeth are suggested by epithelial, mesenchymal and neural immunoreactivity

We have used immunocytochemistry to analyse expression of nerve growth factor receptor (NGFR) in developing, aging and injured molar teeth of rats. The patterns of NGFR immunoreactivity (IR) in developing epithelia and mesenchyme matched the location of NGFR mRNA assayed by in situ hybridization with a complementary S35-labeled RNA probe. The following categories of NGFR expression were found. (1) There was NGFR-IR in the dental lamina epithelium and in adjacent mesenchyme during early stages of third molar formation. (2) NGFR-IR nerve fibers were posterior and close to the bud epithelium. (3) During crown morphogenesis NGFR expression was prominent in internal enamel epithelium and preodontoblasts; it faded as preameloblasts elongated and as odontoblasts began to make predentin matrix; and it was weak or absent from outer enamel epithelium, the cervical loop, and differentiated ameloblasts and odontoblasts. (4) When NGFR-IR nerve fibers entered the molars late in the bell stage, they innervated the most mature peripheral pulp and dentin in an asymmetric pattern which correlated more with asymmetric enamel synthesis than with mesenchymal NGFR-IR distribution. (5) The mesenchymal pulp cells continued to have intense NGFR expression in adult teeth, especially near coronal tubular dentin. (6) The pulpal NGFR-IR decreased in very old rats or subjacent to reparative dentin (naturally occurring or experimentally induced). (7) During root formation, the preodontoblasts had NGFR-IR but most root mesenchymal cells and Hertwig's epithelial root sheath did not. This work suggests that there are important epithelial and mesenchymal targets of NGF regulation during molar morphogenesis that differ for crown and root development and that do not correlate with neural development. The continuing expression of NGFR-IR by pulpal mesenchymal cells in adult rats was most intense near coronal odontoblasts making tubular dentin; and it was lost during aging, or subjacent to sites of dentin injury that caused a phenotypic change in the odontoblast layer.

The induction of reparative dentine in the amputated dental pulp of the dog by bone morphogenetic protein

Reparative dentine was formed in the cavity of the amputated pulp when capped with crude allogeneic BMP. This began with a slight cell-mediated immune response and was followed by resorption of BMP and proliferation of migratory spindle-shaped mesenchymal cells, together with vascular invasion. Four weeks postoperatively, there were osteodentinoblasts embedded in forming matrix and/or osteodentinocytes trapped within osteodentine in some parts of the cavity. Other parts were filled with pulpal tissue. Eight weeks postoperatively, odontoblasts were forming tubular dentine next to the osteodentine. In albumin-implanted controls, a little osteodentine and no tubular dentine were seen. These findings suggest that dissolved BMP stimulates mitosis of mesenchymal cells and may induce differentiation of osteodentinocytes. The resultant osteodentine may play some role in the differentiation of odontoblasts.

Differentiation of odontoblasts in mouse dental papillae recombined with normal or chemically-treated dentinal matrices

Separation and recombination experiments were made with manually or trypsin-dissociated dental papillae (day 15, 16, 17, 18 in utero and 2, 7, 14 postnatal) and manually isolated hard tissues of the third molar crown (14 postnatal days). Several series of hard tissues were further treated with citric acid, hyaluronidase or sodium hypochlorite. The recombinations were transplanted into the subcutaneous tissue of new-born mice. Grafts were removed 7, 14 and 21 days later and prepared for light and electron microscopy. Whatever the age of the papilla and whatever the treatment of the crowns, well-characterized odontoblasts differentiated and deposited new layers of tubular dentine, except when the recombined dental papilla was 15 days old. These findings indicate that odontoblasts are very early committed (since day 16 in utero) and that they may differentiate in dental papillae in contact with chemically altered dentinal matrices.

Dentin induction by implants of autolyzed antigen-extracted allogeneic dentin on amputated pulps of dogs.

Implantation of autolyzed antigen-extracted allogeneic (AAA) dentin matrix gelatin powder caused homeoinduction on amputated dental pulps. This event began with migration of spindle-shaped mesenchymal cells into the cavity on the amputated pulp. This was followed by proliferation of undifferentiated large cells concomitantly with vascular invasion and attachment of spindle-shaped cells and large cells to the AAA dentin. The adhering cells differentiated into osteodentinoblasts and/or preodontoblasts to form osteodentin matrix and predentin respectively. Osteodentinocytes and odontoblasts, then, formed osteodentin and tubular dentin. The healing of pulp dressed with inactivated AAA dentin using guanidine HCl was delayed. These results suggested that AAA dentin matrix powder may have chemotactic and mitogenic activity for undifferentiated mesenchymal cells and may provide a suitable scaffolding for fixation of these cells. Compartments of microenvironment formed by AAA dentin and the enveloping hard substances may play some role in differentiation into odontoblasts.

Morphogenesis of mineralized tissues induced by neonatal mouse molar pulp isografts in the spleen

Tooth pulps dissociated intact with EDTA were isografted for up to 40 days, and examined by light and electron microscopy for hard tissue morphodifferentiation. Grafts formed tubular dentine and osteodentine. Tubular dentine, penetrated regularly by elongated odontoblast processes, resembled normal dentine and was formed when the original odontoblasts continued normal matrix secretion. Osteodentine was formed by spindle-shaped cells with large round nuclei which presumably were transformed pulp cells, and incorporated the same elements as found in cells of non-tubular dentine. Occasionally, odontoblasts were contiguous with both the regular dentine and the osteodentine. Thus in EDTA-dissociated pulps transplanted to the spleen, the original odontoblasts produce tubular dentine and other pulp cells differentiate to form osteodentine.

Ultrastructure of a new generation of odontoblasts in grafted coronal tissues of mouse molar tooth germs

Third molar tooth germs were removed from 14-day-old mice and freed from the enamel organ and follicle. After section of the apical tissues, including Hertwig's sheath, they were transplanted in 1-day-old newborn mice of the same lineage. Electron microscopy of grafts removed 7, 14 and 21 days later showed that, following the disappearance of the initial layer of odontoblasts and a period of adaptation, 14 days after transplantation newly differentiated odontoblasts deposited tubular dentine. The dentine matrix production was increased over that of controls, demonstrating that synthesis was accelerated, possibly because of lack of nerves in the grafts. Numerous characteristic structures that might be involved in the transit of proteoglycans from the Golgi apparatus were seen, as far as the extremity of the odontoblast processes. The particular experimental conditions allowed the observation in the neck region of the odontoblast of a concentration of coated vesicles which might be involved in cellular lengthening. Thus, in the presence of a fine and regular vascular network, a new generation of odontoblasts may differentiate, even in the absence of epithelial and nervous elements, and so predentine may contain inductive factors that allow the odontoblastic differentiation of pulp cells in contact with it.

Effects of various calcium phosphate biomaterials on reparative dentin bridge formation

This article reports on various calcium phosphate materials placed directly on the dental pulp of pig primary teeth. The following capping agents were tested, using light microscopy and microradiography of undecalcified sections: tricalcium phosphate plus magnesium, 50% tricalcium phosphate-50% hydroxylapatite, and octocalcium phosphate, with calcium hydroxide being used as a reference material. The results show that tricalcium phosphate plus magnesium and octocalcium phosphate induce formation of a dystrophic dentin similar to that of dentinogenesis imperfecta or even vasodentin. Compared with calcium hydroxide, the 50% tricalcium phosphate plus 50% hydroxylapatite compound provides the best dentinogenetic effects, resulting in a thicker reparative dentin bridge and quicker formation of normal tubular dentin.

Mandibular dentinoma

Dentinoma is a rare odontogenic tumor showing the inductive effects of odontogenic epithelium on the connective tissue. A case of the tumor occurring in the region of the missing right mandibular second permanent premolar of an 11-year-old male is described. The tumor and the impacted right mandibular second deciduous molar were surgically removed. Histologically, areas of hyalinized collagen, osteodentin and tubular dentin were seen in a stroma varying from mesenchymal to more mature. Immunostaining for the distinct types I, III and IV collagens were negative in the hyalinized areas. Type IV collagen stained as a halo corresponding to the basal membrane zone surrounding the groups of odontogenic epithelial cells. Recovery was uneventful. There was no recurrence of the tumor during the first 10 months of follow-up.

Ghost cells in complex odontoma: A light microscopic and SEM study

Ghost cells in complex odontoma were studied by light microscopic and scanning electron microscopic examination of decalcified sections. They were found at different locations in odontomas: next to tubular dentin, at the site where enamel would be expected; adjacent to remnants of enamel matrix or surrounded by enamel matrix; within granular calcified masses in contact with bone or tubular dentin; in contact with ameloblasts or adjacent to small rests of odontogenic epithelium. They were either isolated or arranged in groups. Their cytoplasm presented a fibrillar component and a lack of keratohyaline. In a complex odontoma, ghost cell keratinization occurs as a result of metaplastic transformation. The calcifying process in these cells was found to be a passive one, with the cells becoming gradually entrapped within the calcified material—bone, osteoid, dentin, dystrophic osteodentin, or dystrophic granular or lamellar types of calcification. Complex odontomas contain both normal and metaplastic odontogenic epithelial cells, which may have lost their developmental and inductive properties.

Differentiation of pulpal cells and inductive influences of various matrices with reference to pulpal wound healing.

Based on recent literature, the dynamics of mesenchymal cells in transplantation of various tissues and matrices, as well as the origin of new odontoblasts which participate in the formation of the dentin bridge, are described. Experiments involving implantation of pulp, periosteum, perichondrium, treated dentin, and bone matrices were performed to emphasize the capability of these cells to produce hard tissue. Light and electron microscopic and autoradiographic studies were carried out to clarify the origin of replacement odontoblasts. It appears that the pulp cells, endothelial cells, and pericytes become undifferentiated mesenchymal cells following pulp exposure. These mesenchymal cells differentiate into odontoblasts, which subsequently produce a dentin matrix. Pulp tissues autografted to non-pulpal sites, elaborated bone (or osteodentin) matrix, but they did not graft to tubular dentin. An experiment on dentin bridge formation, using germ-free rats, demonstrated that the pulp tissue has intrinsic healing potential. Therefore, it was concluded that the ability of pulp tissue to elaborate hard tissues depends on its environment.

歯髄の創傷治ゆにおける歯髄細胞の分化と誘導

The dynamics of mesenchymal cells in transplantation of vital pulp tissues and dentin matrices, as well as the origin of new odontoblasts which participate in the formation of the dentin bridge, based upon our experiments and recent literature, are described.Experiments involving implantation of pulp and treated dentin matrix were performed to emphasizethe capability of these cells and matrices to produce hard tissue and were compared with those of implantedperiosteum, perichondrium and treated bone matrix. Light and electron microscopic and autoradiographicstudies were carried out to clarify the origin of replacement odontoblasts. It appears thatthe pulp cells, endothelial cells, and pericytes become undifferentiated mesenchymal cells following pulpexposure. These mesenchymal cells differentiate into odontoblasts, which subsequently produce a dentinmatrix. Pulp tissues auto-grafted to non-pulpal sites, elaborated the bone (or osteodentin) matrix, butdid not produce to the tubular dentin. An experiment on dentin bridge formation, using germ-free rats, demonstrated that the pulp tissue has intrinsic healing potential. Therefore, it was concluded that theability of pulp tissues depends on its micro-environment as inductive agents. This conclusion may notcontradict the idea induced by our experiments on implantation of periosteum, perichondrium and treatedbone matrices.

Micromorphology of mineralization deposits in the pulps of human teeth.

Summary. The dental pulp may contain a considerable amount of calcified material. This originates from the pulp and takes the form of rods or tubules in the radicular pulp, or concentric spherical deposits in the coronal pulp. Chains of oval deposits may also form at the coronal end of the radicular pulp.Obliteration of the root canal may be due to dentinogenesis or to a massive diffuse pulpal calcification which has a herring‐bone structure and contains small spaces which could harbour bacteria. Growths of tubular dentine may be observed which take the form of flakes along the walls of the root canal and nodules around the walls of the coronal pulp chamber. These tubular excrescences may be observed invading the diffuse pulpal calcification to form a complicated cross‐linked calcified structure.

覆髄剤に対する無菌飼育ラットきゅう歯露出歯髄の反応

The response of the dental pulp to calcium hydroxide or zinc oxide and eugenol cement was investigated histopathologically, using the germ-free and conventional rats. The upper first molar pulp was exposed with a p1/2 round bur through the mesial surface of the teeth and covered with the capping agents. The observation period was 1, 2, 4, 7, 10, 14 and 28 days postoperatively. The results obtained were as follows: 1) In the conventional rats, severe inflammation of the pulp was observed as the result of bacterial contamination throughout the observation period. The response of the pulp itself to the capping agents could not be assessed exactly. 2) In the germ-free rat pulp covered with calcium hydroxide, the inflammation was slight and a higher calcified tubular dentin bridge was observed 28 days postoperatively. 3) In the germ-free rat pulp covered with zinc oxide and eugenol cement, the inflammation was moderate and a relatively poorly calcified dentin bridge without the dentinal tubules was observed 28 days postoperatively. 4) In the germ-free rat whose pulp was left open to the oral environment, the response of the pulp was the mildest of all the experimental groups. The calcification of the dentin bridge of this group was slightly higher than that of the pulp capped with zinc oxide and eugenol cement 28 days postoperatively. 5) The presence of the dentin chips weakened the response of the pulp tissue to the agent, but the formation of the dentin bridge was delayed.

A histological investigation of isografts of immature mouse molars to an intrabony and extrabony site

Partially-developed teeth with remnants of their periodontal ligaments isografted to the tibial shaft medulla and renal subcapsular site were capable of progressive regeneration characterized by renewed tubular dentine formation. Bone formation occurred in relation to grafts at the renal site as well as the tibial shaft; evidence of periodontal fibre reorganization was observed in grafts at both sites. Despite post-transplantation dentine and cementum formation, continued development of roots of normal morphology did not occur, perhaps due to disappearance of epithelial root sheath.

A histological investigation of allografts of mature mouse molars to an intrabony and an extrabony site.

Fully developed mandibular third molar teeth, allografted across an H-2 plus multiple non-H-2 barrier to the tibial shaft medulla and renal subcapsular site in mice, were examined histologically over a 12-month period after transplantation. Cellular degeneration within the pulp chamber occurred in the immediate post-transplantation period and was followed by pulp chamber repopulation by a vascular fibrous connective tissue during the first 14 days after transplantation. Progressive regeneration of the grafts occurred and was characterized by irregular tubular dentine formation followed by more organized tubular dentine deposition on the pulp chamber walls. Allografts at both sites eventually underwent rejection, and it was apparent that grafts at the subcapsular kidney site were rejected in a shorter time (35 to 56 days) than those at the tibial shaft site (56 to 70 days). When mature teeth were allografted to the tibial shaft medulla across multiple minor (non-H-2) barriers alone, similar changes were observed with grafts undergoing rejection 56 to 70 days after transplantation. External root resorption and ankylosis were not prominent features and periodontal ligament reorganization was not observed in any of the grafts.

Continued development of 5-day old tooth-germs transplanted to syngeneic hamster ( Mesocricetus auratus) cheek pouch

One developing maxillary second molar tooth-germ from a 5-day old golden hamster was transplanted into the cheek pouch of each of 41 5–7-week old hamsters of the same inbred strain. Host animals were killed at intervals from 4 days up to 24 weeks after transplantation. 86 per cent of the transplants survived to show signs of further growth and development, as assessed by additional formation of enamel and dentine matrix. Each surviving germ showed only mild infiltration by inflammatory cells. Soon after transplantation, the enamel organ partially degenerated, occasionally undergoing squamous metaplasia and cyst formation. Nevertheless, new enamel was deposited, mainly in the cervical region, by freshlydifferentiated ameloblasts. After irregular or cellular dentine deposition, regular tubular dentine reappeared. Approximately 50 per cent of the transplants cultivated for more than 3 weeks developed roots. Acellular and cellular cementum, woven and lamellar bone, and periodontal ligament were all found in relation to some formed roots. The dentinogenesis of a further 10 (out of 16) transplants was assessed by tetracycline hydrochloride administration (10 mg/kg wt) at weekly intervals for 6 weeks to label newlyformed dentine. These transplants showed 3–5 discrete fluorescent lines in coronal dentine; thus dentinogenesis in the transplants occurred in a normal incremental manner.