Effect of vitamin A on epitheliomesenchymal interaction during odontogenesis and oncogenesis in NMU-treated hamster.

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1) NMU-induced disturbances in odontogenesis of the cut mandibular incisors was hypoplasia ranging in extent from loss of pigment of enamel and enamel hypoplasia to loss of enamel and irregular hypoplastic dentin formation. These changes of the incisors were more prominent in animals treated with retinol palmitate (RP) plus NMU than those in the animals treated with NMU alone.2) When RP was administered in combination with NMU,there was an increase frequency of odontogenic epithelial cell nests' proliferation with dysplastic dentin formation at the incisal region.3) In RP plus NMU-treated hamsters, the frequency and degree of neoplastic changes of the odontogenic epithelium with dentin formation were increased.4) In NMU-treated hamsters, an excess of beta-carotene slightly prevented the disturbances in odontogenesis, atypical proliferation of odontogenic epithelium, and keratinization of epithelial component.5) NMU inhibited ameloblast differentiation, whereas, the differentiation of odontoblasts and cell-to-cell contact between preameloblasts and odontoblasts were not prevented. RP and beta-carotene did not prevent NMU-induced inhibition of ameloblast differentiation but inhibited NMU-induced keratinization of odontogenic epithelium. Atypical proliferation of odontogenic epithelium with inductive dentin formation caused by RP + NMU treatment resulted from the inhibition of squamous metaplasia with keratinization of the epithelium.6) RP plus NMU treatment resulted to a decrease in incidence of neoplastic invasion of the epithelium in the gingiva or forestomach.7) beta-carotene has moderate suppressive effect on tumor growth of the gingival squamous cell carcinoma and slight effect on squamous cell carcinoma of the forestomach.8) Administration of large quantity of beta-carotene induced adenofibrosislike proliferation of the bile ducts and proliferation of spindle-shaped cells in the submucosa of the glandular stomach in NMU-treated hamsters.