Dr. Mundane is a character who only appears in the episode "The Whole Tooth."
He is an olive-beige fish with a dark green dorsal fin and dark green lips, and wears glasses and a dentist uniform. His eyes are not shown.
He first appears to check on Patrick's teeth. During the check-up, Dr. Mundane notices that Patrick still has a baby tooth. He tells Patrick that the pain he's having is that his adult tooth is trying to push the baby tooth out of its place. In order to help relieve Patrick's pain, he needs to extract the tooth. But Patrick refuses and runs out.
He appears again later on the episode where Dr. Mundane successfully extracts Patrick's last baby tooth.