Final answer:
To prevent gingival hyperplasia, patients on phenytoin should use a soft toothbrush. Good oral hygiene and regular dental care are crucial to managing this side effect of the medication.
Step-by-step explanation:
The nurse should instruct the patient on phenytoin to use a soft toothbrush to prevent gingival hyperplasia. Phenytoin can cause gum overgrowth, so maintaining good oral hygiene is essential. Using a soft toothbrush can help prevent injury to the gums, which may exacerbate the condition. It's also important that patients continue to floss and attend regular dental check-ups to monitor and manage oral health while on phenytoin therapy.