You say he's got a problem; he says there's nothing wrong with brushing every tooth individually 24 times a day. How do you know the difference between nuance and annoyance? These criteria will help you judge whether someone has a personality disorder.
They likely do if their behavior:
Is inflexible, no matter what situation the person is in.
Leads to problems in their work or social life.
Is not part of some other mental disorder.
Is not a direct effect of a medical condition, drug or medication.
As a reminder, always consult your doctor for medical advice and treatment before starting any program.