Tomoyuki Onishi

Immunohistochemical localization of calbindin D28k during root formation of rat molar teeth.

Abstract The present study was undertaken to examine the localization of calbindin D28k (CB)-like immunoreactivity (-LI) during the root formation of the rat molar. In the adult rat, CB-LI was detected in some of the cells of the epithelial rest of Malassez at the bifurcational region and in certain cells between the root dentin and cementum at the apical region. These cells had indented nuclei and many tonofilaments, and cementocytes lacked CB-LI. Moreover, CB-LI was observed in the periodontal fibroblasts in the alveolar half of the apical region. During root formation, the cells in the Hertwig’s epithelial root sheath (HERS) lacked CB-LI, but most fragmented cells along the root surface began to express CB-LI when HERS was disrupted. Preodontoblasts and odontoblasts at the apical portion of the root also showed CB-LI. After the formation of cellular cementum, the CB-immunoreactive (-IR) cells were entrapped between the root dentin and cementum in the apical portion of the root. The number of CB-IR cells at the root surface decreased gradually, while that between the root dentin and cementum increased. The fibroblasts in the periodontal ligament began to express CB-LI after commencement of the occlusion, and the number and the staining intensity of CB-IR fibroblasts increased gradually with the passage of time. The present results suggest that CB may play an important role in the survival of the epithelial cells, in the cellular responses of periodontal fibroblasts against mechanical forces caused by the occlusion, and in the initial mineralization by the odontoblasts through the regulation of intracellular Ca2+ concentration.

Histopathological characteristics of eruption mesenchymal calcified hamartoma: two case reports

Odontogenic calcified masses were present in the opercula of lower first molars that were delayed in eruption. The masses were relatively small, opaque, white in color with a smooth texture. Histopathological examinations revealed that they contained osteodentin, cementum, and pulp-like components; however, not odontogenic epithelial cells or enameloid. Further, mesenchymal multinucleated giant cells and dysplastic dental matrices were observed in the connective tissues surrounding the masses. These clinical and histopathological findings disagree with the features of pericoronal odontogenic hamartoma lesions, including odontoma, ameloblastic fibroma, and ameloblastic fibro-odontoma. Therefore, we propose to categorize this odontogenic mass as a new variety of hamartoma, eruption mesenchymal calcified hamartoma.

Hyper-expression of Osteocalcin mRNA in Odontoblasts of Hyp Mice

The Hyp mouse is a murine homologue of human X-linked hypophosphatemia that displays hypo-mineralization in bone and dentin. In this study, we tested the hypothesis that the defect in Hyp mice leads to alterations in the expression of dentin matrix proteins that may be associated with the hypo-mineralization changes in the tissues. Quantitative RT-PCR analyses showed that expression of the osteocalcin gene in Hyp mice tooth germ samples was significantly higher than in wild-type mice, whereas the gene expressions of osteonectin, osteopontn, dentin matrix protein 1, and type I collagen in both types of mice were similar. Further, cultured Hyp mice tooth germ samples exhibited a higher expression of the osteocalcin gene than did those from wild-type mice, which was in accord with the results of our in vivo analysis. These findings suggest that osteocalcin mRNA is highly expressed in Hyp mice odontoblasts and may be associated with dentin hypo-mineralization.

Immunohistochemical localization of heat shock protein 25 (HSP 25) during root formation of the rat molar

The present study investigated the immunohistochemical localization of heat shock protein 25 (HSP 25) of rat molar teeth during root formation. Most, probably all, cells of the epithelial rest of Malassez (ERM cells) had immunoreaction for laminin, a marker protein for basement membrane. During root formation, HSP 25 immunoreactivity was observed in odontoblasts, cells at the subodontoblastic layer, and those in close proximity to the acellular cementum. HSP 25‐immunopositive cells at the subodontoblastic layer were present only at the apical region. Most HSP 25‐immunoreactive cells in close proximity to the cementum lacked laminin immunoreactivity. However, at postnatal day 28 a small number of cells showed immunoreaction for both HSP 25 and laminin at the cervical and bifurcational regions. Under the electron microscope, most HSP 25‐immunoreactive cells along the surface of the cementum were round and contained rich organelles such as mitochondria and rough endoplasmic reticulum. They lay between fiber bundles of the periodontal ligament. The localization and morphological features of these HSP 25‐immunoreactive cells resemble those of cementoblasts. On the other hand, HSP 25‐immunoreactive cells at the cervical region were oval and contained few cell organelles. They were closely apposed to each other, and separated from the surrounding tissues with basal lamina. These features were similar to those of mature ERM cells. In contrast, cells with microvillus‐like processes and relatively rich mitochondoria, which were similar to immature ERM cells, had no immunoreaction for HSP 25. These results suggest that HSP 25 may be involved in shape alterations of ERM cells, cementoblasts, and odontoblasts during differentiation. Anat Rec 267:321–329, 2002.

Identification and characterization of integrin-binding sialoprotein (IBSP) genes in reptile and amphibian.

Integrin-binding sialoprotein (IBSP) is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family; and the whole SIBLING family is further included in a larger secretory calcium-binding phosphoprotein (SCPP) family. SIBLING proteins are known to construct a part of the non-collagenous extracellular matrices of calcified tissues, and considered to have arisen by duplication and subsequent divergent evolution of a single ancient gene. To understand the alterations of SIBLING molecules associated with the evolution of calcified tissues in vertebrates, we initiated a search for lower vertebrate orthologs of SIBLING genes. In the present study, an IBSP ortholog from a reptile (caiman) and two distinct orthologs from an amphibian (African clawed toad) were identified and characterized. As expected, the toad IBSP genes were transcribed only in calcified tissue (jaw and tibia), as also seen in mammals. The caiman, toad, avian, and mammalian IBSPs share several unique features specific for IBSP and apparently have similar properties. Furthermore, analysis of the sequences suggested that the IBSP molecule might have gradually intensified its functions related to calcification during its evolutionary process through tetrapods.

Calbindin D28k‐like immunoreactivity during the formation of the enamel‐free area in the rat molar teeth

Previous studies have demonstrated the presence of calbindin D28k in the ameloblasts derived from the inner enamel epithelium. The occlusal surfaces of the rodent molars partly lack the enamel covering, which is referred to as enamel‐free area (EFA). In the present study, we compared the immunohistochemical localization of calbindin D28k‐like immunoreactivity (CB‐LI) in the cells at the EFA (EFA cells) and ameloblasts of the rat molar teeth at the light microscopic level. CB‐LI was strong in the ameloblasts of the presecretory through the protective stages, while it was faint at the late secretory to transitional stages. However, some mature ameloblasts lacked the immunoreactivity. On the other hand, the majority of EFA cells showed distinct polarization and elongation that were absent in few cells at the early stage of EFA formation. At all stages, the EFA cells adjacent to the ameloblasts showed CB‐LI, however, some cells adjacent to the mature ameloblasts lacked the reaction. Intensive CB‐LI was demonstrated in EFA cells at the reduced enamel epithelium. These immunohistochemical findings suggest EFA cells have cytochemical properties similar to those of ameloblasts. Anat Rec 258:384–390, 2000.

Histopathological characteristics of primary teeth in pre-term very low birth-weight child: Case report

Abstract Several studies have reported that the prevalence of enamel hypoplasia in pre-term low birth-weight children is higher than that in normal birth-weight children. However, the features of primary teeth dentin in pre-term low birth-weight children are rarely reported. We clinically examined a pre-term very low birth-weight child, and performed histopathological examinations of the extracted primary incisors. Hypomineralized enamel was observed in the permanent upper central incisors, while enamel defects were not detected in primary teeth. In the histopathological examinations, several features of dentin defects, such as irregular dentinal tubules and globular dentin, were observed on the pulpal side of dentin. These findings indicated that dentin formation in the present low birth-weight children was mainly affected during the natal and postnatal periods. Our results provide the evidence that tooth formation in low birth-weight children is affected by postnatal systemic derangement.

Intentional replantation of maxillary molar affected by an intractable periapical abscess related to a radicular groove: A case report

We presented a case of an intractable periapical abscess in the area of the maxillary first molar. The tooth had no evidences of dental caries, restoration, or fracture, and responded well to a pulp vitality test. However, a radiographic examination revealed radiolucency in the apical portion of the distal root. Computerized tomography (CT) revealed that the tooth had 1 buccal and 2 palatal roots fused together, expressing a U-shaped. Further, a radicular groove that reached to the crown portion of the distal surface was found. Radiolucency was observed in the area adjacent to the radicular groove and in the U-shaped region. We finally performed an intentional replantation, since conventional periodontic and endodontic procedures were unsuccessful. One year postoperatively, the patient had no clinical or radiographic symptoms.