Abstract. A total of 279 cases of reactive lesions of the gingiva have been subdivided into three groups: pyogenic granuloma/gingival fibromatoid lesions, peripheral giant cell granuloma and peripheral ossifying fibroma. Age, sex and and site distribution are similar for pyogenic granuloma/ gingival fibromatoid lesions and peripheral giant cell granuloma; namely, comparable bimodal age peaks occur, women are affected more often, and a predilection exists for the anterior segment of the dental arch. Although peripheral ossifying fibromas also have the same sex and site predilection, incidence occurs as a single age peak in the second decade with a continuous decline thereafter. Clinical and histopathologic features invite speculation that all three lesions represent varied histologic responses to irritation.

Within the conditions of the experimental design, this study has provided laboratory evidence that microorganisms were necessary for the occurrence of inflammatory periodontal disease. Furthermore, this investigation has shown that the presence of both local irritation and microorganisms was necessary to produce periodontal inflammation. However, neither factor alone was capable of producing the inflammation. The results of this study have shown that a type of dental calculus may be formed in the absence of microorganisms. However, the same results have demonstrated that the presence of microorganisms greatly facilitates the formation of calculus. The presence of polymorphonuclear leukocytes in the gingival crevices and tissues could not be explained on the basis of bacteria and/or irritation. It was postulated that these cells are a normal component of the gingival tissues of these animals and that their presence does not constitute a pathologic process. The findings of the present study were considered with those of other studies. From this comparison it was suggested that differences in animal species and strains should be considered when evaluations and extrapolations of experimental results are made.

An aggressive form of odontogenic cyst known as the keratocyst has been reviewed with a report on the findings of 70 new instances. Recurrence after 2 years of followup was found to be 20%. From both a review of the literature and original cases, carcinomatous and ameloblastomatous transformation in odontogenic keratocysts seems to be an extremely rare phenomenon. Alternatively, epidermoid carcinoma and mucoepidermoid carcinoma arising centrally within the jaws are often associated with other types of dental cysts. Review of 36 instances of central epidermoid carcinoma has disclosed that 75% were associated with a cyst lining; the 2‐year survival rate was found to be 53%. Central mucoepidermoid carcinoma was associated with a dental cyst or impacted tooth in 48% of the cases, and enjoyed a 100% 2‐year and 5‐year survival; however, 2 patients were recorded alive with disease at 4 months and 10 years, whereas another patient succumbed to disease 14 years post‐operatively.

4hxtract. A tolal of 841 reviewed cases and 75 reported cases ol' fibro-osseous lesions of the jaws, excluding (he giant cell group, are analyzed willi regard lo elinical. radiographic, and hislologic features. Precise criteria for Ihe differential diagnosis of fibrous dysplasia, ossifying fibroma, gigantiform cemenloma, chronie diffuse selerosing osteomyelitis, foeal sclerosing osteomyelitis, and periapical cementoma have been ptese/ited with emphasis on radiographic and behavioral features.

Verrucous‐type oral tumors have been reviewed. This variety of epidermoid carcinoma of the oral cavity presents as a warty growth in patients who have a history of chewing tobacco and poor oral hygiene. They are slow‐growing, locally invasive, and do not metastasize to lymph nodes in our experience. In five of these patients, the microscopic pattern was that of a well‐differentiated squamous cell carcinoma. The others presented the classical histologic pattern of verrucous carcinoma. No difference was found in the behavior of these two groups. Three cases developed anaplastic transformation after irradiation and surgery. A change in the clinical behavior of the tumor was observed in these patients and all three died. There is some possibility that ionizing radiations could be the trigger mechanism in this transformation. The authors feel that surgery is the treatment of choice in early or easily resectable lesions. It would appear unnecessary to perform neck dissection in these patients. Radiation therapy should be used in advanced verrucal‐type lesions in which surgical resection is difficult or not feasible. These patients require frequent and careful observation. The authors believe that this entity deserves further investigation.