The Dentist was a dentist who Nathan Explosion had an appointment with. He is now deceased. The cause of death: committed suicide by putting the end of a hunting shotgun to his mouth and firing it.
Nathan was reluctant to have an appointment with him, since hearing that dentists have the highest suicide rate of any career. When he first met him, he decided to do it later. He later visited the dentist, who asked him if he wanted gas or not. Nathan had a good/bad conscience hallucination, with a miniature Murderface telling him not to take the gas, because then the dentist could jack him off once he was unconscious, and a miniature Pickles telling him to take the gas, because he wouldn't feel anything. Nathan went with Murderface and decided not to take the gas. The dentist then drilled a hole onto one of Nathan's teeth, which sent Nathan screaming out of the room.
The dentist later appeared in Dethklok's psychedelic "Hamburger Time" montage, during Nathan's part about him taking the gas and the dentist not wanting to kill himself. Later, he went on a hunting trip with Nathan. After saying that he enjoyed being friends with Nathan, he said "check this out", put the end of his gun in his mouth and committed suicide, to Nathan's horror.
The dentist was shown to be deeply depressed, possibly Melancholia, with incidents only worsening his condition. When Nathan decided to postpone the appointment, the dentist thought he didn't want to be around him, and looked down, sad. There is a poster in his room saying "Hang In There", with a koala hanging on a tree branch. He gives his nurse a note that tells his clients that he is cancelling future appointments, and goes on further to call it a "long note", revealing that the note is in fact almost definitely a suicide note. When asking Nathan about whether he wants gas or not, he says the gas takes the pain away, before realizing that the gas "takes pain away", referring to a method of suicide. The dentist's depression eventually leads him to commit suicide, proving Nathan's initial impression of him to be accurate.