Oral hygiene is of utmost importance. Most dreaded complication after valve replacement is infective endocarditis and the most common source for the same is through oral route. That is why you have been advocated for thorough cleaning. But again, there shouldn't be any bleeding. If there is any bleed, it can be a nidus for infection and progress to endocarditis.
Next Steps
would advice to brush the teeth regularly twice a day. any abnormal bleeding, visit the dentist for definitive treatment.