Abnormal melanin pigmentation of the oral mucosa has been linked to smoking and has been designated smoker melanosis. Since the incidence of smoker melanosis varies among races, we investigated the incidence of melanin pigmentation in 280 Bangladeshi individuals. The incidence of melanin pigmentation was 82.0% in the smoker group and 58.3% in the non-smoker group. Melanin pigmentation frequently occurred in participants aged from 20-49 years old in the smoker group, while it occurred in participants aged from 30-59 years old in the nonsmoker group. Gingiva and buccal mucosa were frequently affected sites in both the smoker and non-smoker groups. The smoker group had tendency to show more intense melanin pigmentation than that in the non-smoker group. Since the present study is the first extensive survey of smoker melanosis in Bangladesh, these results provide important information for investigating the effects of smoking habits on melanin pigmentation of the oral mucosa among various ethnic groups.

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The metastasis of squamous cell carcinoma (SCC) as it invades surrounding tissue is a complex process that requires cancer cells to interact with stromal fibroblasts. During that interaction, cancer cells cause stromal fibroblasts to secrete and activate matrix metalloproteinases that degrade the extracellular matrix. Our experimental goal is to clarify the mechanisms by which MMP-9 is expressed and activated as SCC cells invade adjacent tissue. A human oral SCC cell line (HSC-3) and an embryonal lung fibroblast cell line (MRC-5) were co-cultivated in type I collagen gel. The expression and activation of MMPs in the culture supernatants were detected by gelatin zymography and Western blot analysis. We histologically examined the pattern of cancer-cell invasion in specimens harvested from our in vitro invasion model. Gelatin zymography and Western blot analyses showed that MMP-9 and MMP-2 were secreted by HSC- 3 and MRC-5, respectively. When HSC-3 cells were co-cultured with MRC-5 in the in vitro invasion model, pro-MMP-9 (92 kDa) was converted to the activated form (67 kDa), and we observed HSC-3 cells growing invasively into the collagen gel. In contrast, when HSC-3 cells were cocultivated with MRC-5 fixed with 2.5% glutaraldehyde solution, pro-MMP-9 was not activated, and no invasion of HSC-3 cells was observed. Cancer cell invasion requires the presence of fibroblast-derived factors that plays an important role in fully activating MMP-9, and we showed that MRC-5 fibroblasts secrete MMP-3, which is a potent MMP-9 activator, in this co-culture system.

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Immunohistochemical expression of vascular endothelial growth factor (VEGF) and proliferating cell nuclear antigen (PCNA) in oral squamous cell carcinomas (OSCCs) was investigated comparatively between the original and the metastatic lymph node lesions of the same tumor. Tissue samples of both the original and regional lymph node lesions were obtained from 11 patients who did not receive preoperative radiotherapy. The percentage of VEGF immunopositive area (PVIA) in the tumor was determined through computer image analysis. Proliferative activity of tumor cells was assessed in terms of the labeling index (LI) of PCNA. PCNA LI showed no correlation between the original and metastatic tumors, whereas the PVIA appeared to be similar between the original and regional lymph node lesions. These results suggest that immunohistochemical expression of VEGF in the original tumor shows the characteristic behavior of a metastatic tumor, thus providing therapeutic information.

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Surgery on tumorous bone often requires resection of the corresponding normal tissues including the periosteum, particularly for malignancies. The periosteum supplies nutrition to the bone and is an essential tissue as a recipient bed for mucosa grafting. The conditions necessary for survival of a mucosa graft include a well-vascularized host bed and rapid serum imbibition occurring immediately after grafting. This study was designed to reveal the regenerative process of the periosteum. Forty mice were used. A defect of the periosteum was surgically created following the elevation of the skin flap on the cranium of mice under general anesthesia. The histological findings of elastic as well as collagen fibers and the immunohistochemical expression of parathyroid hormone (PTH)/PTH-related peptide (PTH/PTHrP) receptor and proliferating cell nuclear antigen (PCNA) at the postoperative intervals were investigated. At 7 days postoperatively, the periosteal defect was occupied by a periosteum-like tissue (PLT) composed of two layers (a collagen layer and an elastic layer), which was different from the normal periosteum. A positive reaction to PTH/PTHrP receptor was seen in the PLT, similar to that shown for the normal periosteum. The immunoreaction of PCNA as well as PTH/PTHrP receptor reached its peak at 5 or 7 days and gradually decreased till 84 days postoperatively. At 84 days postoperatively, the PLT was remodeled to have almost the same features as the normal periosteum composed of a collagen layer. These results suggest that an adequate healing period is needed for the periosteal defect site where the transplanted bone will be subjected to mucosa grafting.

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An unusual case of pigmented ameloblastic fibro-odontoma with prominent odontoma components in a 7-year-old Japanese boy is reported. In addition to the characteristic histopathologic features of ameloblastic fibro-odontoma, deposition of melanin pigments was found in the ameloblastic cells, mesenchymal cells resembling the dental papilla and calcified tissue including mature dentin. The pigments were stained positively with Fontana-Masson, and the pigment-laden cells in mature dentin were positive for HMB-45 by immunohistochemical staining. Such findings have not been described so far in any previously reported cases.

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