Homeostatic and reparative functions of the periodontal ligament are most significant in respect to periodontal therapy and transplantation and/or replantation of tooth. Based on our experimental studies and currently published studies, this review article discusses the mechanism of both tissue regeneration and homeostatic function of the periodontal ligament from the viewpoint of periodontal treatment and tooth transplantation. The involvement of cell proliferation, differentiation, growth factors, microenvironment including the guided tissue regeneration, osteogenic progenitor cells, bone morphogenetic protein are discussed. In relation to transplantation or replantation of tooth and periodontal regeneration, we describe the following characteristics of the periodontal ligament; volume of the periodontal ligament attached to root surface of extracted teeth, characteristics of cells in the periodontal ligament, cell constituting the regenerated periodontal ligament, mechanism maintaining a certain width, particularly the function of Malassez's epithelial rests and mechanism of ankylosis.

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The immunohistochemical expressions of epidermal growth factor receptor (EGFR) and Proliferating Cell Nuclear Antigen (PCNA) were studied in the epithelialization process of bare flaps, the fascial flap and the deepithelialized mucoperiosteal flap, used for reconstruction of the oral mucosa in rat models. The intense expression of EGFR and PCNA was detected in the tip area of the migrating epithelium during the early period of the healing process in both flaps, and differing distributions of EGFR and PCNA positive cells were identified. In the fascial flap, a signifi-cantly high positive rate of EGFR was detected in comparison with the deepithelialized mucoperiosteal flap. The expression of EGFR in both flaps may be attributed to the influences of different connective tissue substrates which induce a control mechanism to maintain the equilibrium between differentiation and proliferation of epithelium.

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This paper's purpose is to analyze temporally and spatially differential roles of Notch-1, -2 and -3 in the neurogenesis of mouse embryos. In Northern blot hybridization, Notch-1 and -3 were expressed in the nervous tissue and increased in the level from 12 to 14 day post coitum (dpc). Notch-2 was more weakly expressed than Notch-1 and -3 on 12 and 14 dpc. In in situ hybridization, Notch-1 and -3 expressions appeared early on 6 dpc. On 12, 14, and 15 dpc, high level of Notch-1 expression was observed in the ventricular zone, and Notch-3 was diffusely expressed in the ventricular, intermediate and marginal zones of the brain, and Notch-2 expression was in the lower level. These findings suggest that Notch-1, -2 and -3 play individu-ally complementary and combinatorial roles in the neurogenesis of mouse embryos.

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The histological features of recurrent aphthous ulcer (RAU) are consistent with increased number and activation of T cells in the diseased areas. A previous study suggested that 13-23% of the cells express IL-2 and transferrin receptors, which implies potential for local proliferation. The aim of the study was to to evaluate the proliferation activity in 10 RAU lesions compared to 9 oral traumatic ulcer (TU) lesions. Demonstration of proliferating cells was performed by application of affinity-purified rabbit anti-human Ki-67 antibodies in avidin-biotin-peroxidase complex (ABC) staining to both RAU and TU biopsies. We found that the basal/suprabasal layers of RAU epithelium away from the ulcer contained 30% more proliferating cells (127±24 vs 97±19 cells/0.2mm², P<0.01) than the epithelium of TU. Furthermore, 9±4% (115±29 cells/0.2 mm²) of the infiltrating inflammatory cells in RAU lesions were Ki-67-positive proliferating cells, compared to only 3±1% (37±14 cells/0.2 mm²) in TU inflammatory infiltrates. These findings suggested that the mitotic activity is increased in RAU epithelium and that the relatively longer persistence of RAU cannot be explained by a lack of new epithelial cell production. Furthermore, mononuclear inflammatory cells replication in situ represent one mechanism for the expansion of the inflammatory cell infil-trates at sites of RAU and TU lesions.

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A 67-year-old male was admitted to the Clinic of Oral and Maxillofacial Surgery II, Dental Hospital, Matsumoto Dental University, with a chief complaint of a painless swelling of the mandibular gingiva. Under a clinical diagnosis of an epulis of the gingiva, surgical excision was performed. The material was then diagnosed histopathologically as a poorly differentiated carcinoma. After reporting the biopsy results, we obtained important information that the patient had been tentatively diagnosed as having hepatocellular carcinoma by clinical examination. Therefore, the tumor was further examined immunohistochemically. The immunohistochemical examination used some useful markers for the diagnosis of hepatocellular carcinoma, i.e., CEA, EMA, α-1-ACT, α-1-AT, albumin, AFP, and CK 7, 8, 18, 19. The examination results were positive for many immunohistochemical profiles of hepatocellular carcinoma, although there was no so-called “hepatoid pattern” in the histopathological observation. Finally the gingival carcinoma was considered to be a poorly differentiated metastatic carcinoma that had originated from a “hepatocellular carcinoma”, as judged from our histopathological and immunohistochemical examinations. This was determined although the histopathological observation of the primary lesion in the liver was not carried out. No additional treatment was undertaken as according to the wishes of the family.

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A relative rare case of a cytomegalovilus (CMV) infectious disease is reported. Recently, CMV infection has attracted increasing clinical attention due to an increase in susceptible hosts, and CMV infections are usually manifested by serious symptoms. This patient showed multiple fistulae in the lower gingiva and the enlargements of gingiva and submandibular lymph nodes, but no other serious systemic complications. Cytomegaloviral infection caused intractable fistula formation in an immunoconpromised host.

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A rare case of desmoplastic ameloblastoma is presented with an immunohistochemical study of epithelial cell markers. A 42-year-old Japanese woman was admitted with a complaint of painless swelling in the anterior mandible. Radiological examination revealed an ill-defined lesion with a mixed radiolucent-radiopaque appearance. Tumor extirpation was performed, and no sign of recurrence has been confirmed. Histological examination exhibited proliferative epithelial islands surrounded by extensive dense fibrous connective tissue stroma. Most of the tumor cells lacked ameloblastic cellular polarization. The tumor cells showed positive immunoreactivities for anti-cytokeratin 8, 13 and 19, filaggrin and ameloblastoma antibodies, retaining the odontogenic epithelial characteristics.

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We report a case of lingual osseous choristoma at the immature stage of development in a 25-year-old female. The present findings suggest that a pure osseous lesion originates from entrapped ectomesenchyme which may give rise to osteogenic tissue without endochondral ossification.

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Spindle cell carcinoma is a rare malignant tumor which is generally considered to be a variant of squamous cell carcinoma. A case of spindle cell carcinoma of the tongue occurring in a 50-year-old Chinese male is reported. Immunohistochemical technique was used as an adjunct to the diagnosis of this unusual type of carcinoma. The immunohistochemical expression of keratin was recognized in the spindle cells, as well as in the carcinomatous cells. Moreover, the spindle cell component expressed vimentin. These findings suggest an epithelial origin with squamous differentiation and mesenchymal participation in the genesis of spindle cell carcinoma. Additionally, the differential expression of low and high molecular weight keratin was demonstrated. The possible causes of coexpression of keratin and vimentin are also briefly reviewed, which may be because some epithelial tumor cells were transformed into mesenchymal (vimentin-positive) spindle cells; or due to dedifferentiation, with regression to vimentin, an embryonal type of intermediate filament; or attributed to the cellular adaptation to environmental influences; or be related to reduced cell-to-cell contact.

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A diffuse large B-cell lymphoma exhibiting multinodular proliferation appeared in the parotid gland of a 69-year-old Japanese male. A well-capsulated mass embedded in the parotid gland showed a diffuse large cell lymphoma demonstrating multinodular or trabecular proliferation. This lesion partially consisted of epithelioid cells with CD20-positivity, but negative reactions for CD30 and epithelial membrane antigen. Diffuse large cell lymphomas rarely show a nodular pattern or other unusual variants so that a careful examination should be required for an accurate diagnosis.

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