SUMMARY The size and shape of the cells in the basal cell layer of the oral epithelium in 100 specimens from oral mucosa were studied by using an interactive image analysis system (IBAS-1). Four groups of white lesions (traumatic keratosis, lichen planus, leucoplakia, and a "risk group") in addition to two control groups (normal mucosa and squamous cell carcinoma) were studied retrospectively. The results showed a progressive increase in the dimensions (area, perimeter, and maximum diameter) of the nuclei from normal mucosa through traumatic keratosis, lichen planus, leucoplakia and the "risk group" to carcinoma, with considerable differences. The nucleus in squamous cell carcinoma was twice as large as in normal mucosa. A substantial increase in the dimensions of both the cell and the nucleus was found in the "risk group." The nucleo:cytoplasmic ratio, contrary to what might have been anticipated in risk lesions, did not show considerable differences between the diagnostic groups. Furthermore, it was slightly decreased in the risk group compared with the normal mucosa. The shape factors (form PE and contour index) seemed to be less helpful in the identification of the "risk group." The size of the basal cell and its nucleus can be of diagnostic value for lesions with a high risk of malignant transformation.

Analysis of the histological findings on an objective basis, using a cluster analysis programme, provided an encouraging degree of separation into the diagnostic groups. When a number of known carcinoma cases were included in the cluster analysis as " markers ", a small number of leukoplakia and keratosis cases were placed by the computer into the same cluster as these " markers ". Of the original 187 cases originally diagnosed as leukoplakia or keratosis, 4.8% are known to have developed a carcinoma, but of the 11 cases the computer placed in the same cluster as the " marker " cases of carcinoma, 36% have subsequently developed carcinoma. Thus, in the cluster analyses, the computer is tending to " recognize " those cases that later developed carcinoma, and to separate them from the bulk of the cases in which malignant change has not occurred.

The changes in a permanent central incisor of a patient suffering from hypophosphatasia, were investigated light microscopically and compared with those of two of his primary teeth. In addition his other central incisor was studied with transmission and scanning EM. The changes in permanent teeth were similar to those of the primary dentition, including loss of cementum and the presence of deep resorption areas in dentin. Afibrillar cementum was detected with EM, and was attached to dentin surface. The presence of a thick layer of bacterial plaque was a prominent feature in all the teeth examined. A large number of bacteria was also found in resorption bays. It is suggested that bacteria may play an important role in the destruction of soft and hard tissues leading to loss of teeth in hypophosphatasia.

Muscle changes were investigated ultrastructurally in 2 groups of patients having oral submucous fibrosis. One group was from patients with no evidence of restricted mouth opening and the other was from patients with restricted mouth opening. Electronmicroscopically, the majority of muscle fibres taken from the first group appeared normal with only occasional muscle fibres showing accumulation of homogeneous material and compression of the sarcomeres closest to this material. In contrast, the tissues from patients with restricted mouth opening showed severe changes and necrosis in a high proportion of muscle fibres. The necrotic muscle fibres exhibited complete loss of their plasma membrane, but in which the outline was maintained by an intact basal lamina. It is suggested from this study that restricted mouth opening in submucous fibrosis might depend not only on the sub‐epithelial fibrosis but also on the extent of muscle degeneration.

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