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Histopathologic examination of oral leukoplakias has a major impact on the assessment of prognosis and treatment planning. We investigated the extent of agreement in grading epithelial dysplasia between pathologists with the same or different educational backgrounds. Two general pathologists and two oral pathologists were each given 100 sections of oral leukoplakia to grade from no dysplasia to carcinoma in-situ. The interobserver agreement rates were in the range of 49% to 69%. The calculated kappa values were in the range of 27% to 45%, showing poor to moderate agreement between the pathologists. When comparing the kappa values between the two pairs of pathologists with the same education, these values did not diverge from the general level of kappa values, indicating that the interobserver variability was due to individual differences rather than to educational background.

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16 cases of calcifying odontogenic cysts (C.O.C.) were studied and reevaluated. It could be concluded, that the group contained two entities, a cyst and a neoplasm. The cyst occurs as three variants. 1. A simple unilocular cyst with moderate mural proliferations of epithelium and no, or sparse amounts of dentinoid (dysplastic dentin); it seems to occur during man's entire life span. 2. A unilocular cyst which produces compound or complex odontomas in its luminal part, more rarely it may instead produce an intramurally growing ameloblastic fibroma, which may call for more radical surgery. It occurs mainly in patients between 10 and 29 years of age. 3. A unilocular cyst with extensive luminal as well as mural ameloblastomalike proliferations of epithelium. The C.O.C. may be located outside or inside the bone according to the location of the source of odontogenic epithelium, from which it develops. The neoplasm shows an entirely different structure. It consists of ameloblastoma-like strands and islands of odontogenic epithelium growing infiltratively in a mature connective tissue. Varying amounts of ghost cells are seen in the epithelium and varying amounts of dentinoid is formed in contact with the odontogenic epithelium. The term "Dentinogenic ghost cell tumour" is suggested for this lesion. It is possible that it occurs predominantly in the later part of life. It occurs as an extraosseous as well as an intraosseous lesion. Recurrence has been observed following cystectomy.