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The various cytokeratin polypeptides in oral epithelia are expressed in dependence on site and formation of a stratum corneum. Certain cytokeratins occur permanently and others occasionally. In fibrous hyperplasia and Lichen ruber planus, patterns of cytokeratins did not deviate significantly from normal. In some but not all cases of squamous cell carcinoma and leukoplakia studied, marked aberrations of pattern were characterized by (i) appearance of cytokeratin No. 19, (ii) somewhat more frequent occurrence of cytokeratins Nos. 8 and 18, (iii) proteolytic modifications of cytokeratins, and (iv) partial loss of a few site-specific cytokeratins. The aberrations may be taken as additional diagnostic criteria for differentiation between non-aggressive and potentially aggressive leukoplakic lesion, even if they are not correlated with the conventional histological grading of dysplasia.

The frequency of the occurrence of cytokeratins analyzed SDS-electrophoretically in 20 leukoplakic lesions and 14 squamous cell carcinomas of the oral mucosa has shown a picture of "restlessness" with some quantitative, some qualitative deviations from the locally normal pattern of cytokeratins. In most cases the basic pattern typical for the oral mucosa was still recognizable, except for three highly undifferentiated carcinomas. The variations of the cytokeratin pattern existed independently of the clinical form of leukoplakia and of its histological degree of dysplasia. The striking findings in some, but not all cases were: --the presence of cytokeratin no. 18 as a major component which normally appears rarely and faintly, and of cytokeratin no. 19, which is not normally detectable electrophoretically within the whole oral mucosa; --the absence of cytokeratins no. 1-3 despite of the cornification which was reliably proved by histology; --the appearance of the proteins having molecular mass values of 42 kDa and less which very probably may be the products of partial keratinolysis as evidenced by immunoblotting with monoclonal and polyclonal antibodies to cytokeratins. Among these proteins a proteolytically modified cytokeratin no. 19 of only 38 kDa was found.

From 1969 to 1980 the authors examined 587 histological specimens of oral leukoplakia obtained from 424 patients. The histological findings were assessed in classification numbers qualitatively and quantitatively characterizing the subepithelial inflammation, epithelial hyperplasia, keratosis, the grade of epithelial dysplasia an the degree of infiltration when carcinoma had already developed. From this histological classification a classification number resulted which allows conclusions on the prognosis of the leukoplakia under study. Besides the grade of dysplasia also the features of the subepithelial inflammation are important for the prognostic assessment of leukoplakia. The classification numbers are suitable for data processing. In the grading system reported, the most important morphological findings are represented with qualitative and quantitative objectiveness. The classification number leads to more reliable comparison and evaluation of the results obtained by different research groups.

The direct effects of different alcohol concentrations (20%, 40%, 96%) upon the oral mucosa of rabbits were proved in short-term and long-term experiments. The direct toxic action of the alcohol in short-term experiments leads to a local damage of the mucous membrane which is proportional to the degree of alcohol concentration. The alcohol-toxic irritation in long-term studies produced in the course of 12 months a leukoplakia-like epithelial dysplasia (dyskeratosis, keratosis, increased density of the basal layer, slightly increased number of mitotic figures) but there was no loss of polarity of cells and the basement membrane was always intact. No animal developed a spontaneous tumour. The repeated local tissue damage by high local alcohol concentration is in connection with other etiologic factors (excessive tobacco usage) an important initiating factor of cancer of the mouth.

Rabbits were exposed repeatedly to formalin irritation using a new oral tank which allows a chronical contact with the oral mucosa. In long-term experiments (11 months) a preneoplastic unrest of the epithelium with dyskeratosis could be produced. This new model of "oral tank" can be used for soluble and insoluble test substances for analyzing pathogenetic processes in the oral cavity.