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.

T HE diagnosis and treatment of third molars often have been cited as being special problems to the oral surgeon and orthodontist, but the relationship of the third molars and their extraction to gingival changes, loss of bone, development of periodontal pockets, and exposure of the cementum on the distal of the second molars has received very little attention. Most of the studies of the status of the third molar have been directed towards classification of impactions, surgical procedures for their removal, their effect upon the development and treatment of malocclusion, their relationship to resorption and repair of the roots of the second molars, and their relation to cysts, pericornal infection, Vincent's infection, cellulitis, and caries. 1,2,3,4 Indications for the prophylactic removal of third molars are usually related to possible spread of infection, fractures, cystic degeneration, possibility of poor healing in older individuals, and treatment of malocclusion. 5,6,7 Although Robb 8 pointed out some of the problems related to the presence of impacted third molars and the periodontal complications following their removal, no intensive investigation of periodontal problems has been reported. Thus the importance of third molars to the investing and supporting structures of the second molar and the periodontal indications and contraindications for the removal of third molars has been largely overlooked. The objectives of this study were to determine the effect of the extraction of third molars on the periodontal structures distal to the second molars; the indications and contraindications for extraction of third molars relative to possible periodontal complications; and possible means of minimizing periodontal complications following the removal of third molars.

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