Final answer:
The correct answer is 'OD. se cepilla' (He brushes).
Step-by-step explanation:
The correct answer is OD. se cepilla (He brushes).
In the given sentence, the verb 'cepilla' is conjugated in the third person singular form, which agrees with the subject 'el dentista' (the dentist).
Since 'el dentista' is a male singular noun, the reflexive pronoun 'se' is used to indicate that the subject is performing the action on themselves.
Learn more about Verb conjugation in Spanish