Quantitative histopathologic assessment of developing phenytoin‐induced gingival overgrowth in the cat

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Abstract
Phenytoin (Dilantin) induces gingival overgrowth characterized by an accumulation of connective tissue. The cell-to-matrix ratio in the mature lesion is normal, yet there must be more fibroblasts per oral cavity if there is excessive tissue mass. Using a mongrel cat model system, the early, developing phenytoin-induced lesion was studied by quantitating fibroblasts per unit of tissue in papilla biopsies collected over a 3-mo. period of daily drug administration. At 6 and 8 wk, the number of fibroblasts per unit of tissue increased dramatically. By 3 mo., as the lesions matured, the fibroblast-to-matrix ratio returned to normal. The drug probably interacts with resident gingival fibroblasts, causes them to proliferate and thus induces a true, but transient, hypercellularity. Cell division then appears to slow or cease and rapid production of connective tissue matrix ensues, returning the cell-to-matrix ratio to normal.