Phenytoin-induced gingival overgrowth in rats infected with Streptococcus sobrinus 6715

Inbred Fischer rats were fed a high sucrose diet (No. 2000) containing phenytoin (5,5-diphenyl-hydantoin) for 52 days, which produced serum and salivary PHT levels of 13-14 and 2.6-2.7 micrograms/ml, respectively. Gingival overgrowth was induced in the molar region of all PHT-treated rats but was more severe in Streptococcus sobrinus 6715-infected rats than in non-infected rats, which had lower plaque scores. No significant overgrowth was found in rats infected with Strep. sobrinus and fed the same diet without PHT. Thus dental plaque accumulation enhanced, but was not essential for the development of the PHT-induced gingival overgrowth. Histological examination showed that the density of fibroblasts and connective tissue fibres was similar in all groups. This experimental model could serve as a useful means of understanding the pathogenesis of PHT-induced gingival overgrowth.