Final answer:
Gingival hyperplasia, a side effect of phenytoin used in epilepsy treatment, refers to the enlargement of the gums. This condition can lead to periodontal issues, and maintaining good oral hygiene is essential.
Step-by-step explanation:
A patient being treated with phenytoin for epilepsy may experience gingival hyperplasia, a condition characterized by the enlargement of the gums. This side effect occurs due to the overgrowth of gum tissue, which can create periodontal issues. Good oral hygiene and regular dental check-ups are important for patients taking phenytoin to manage this side effect.