Panel 1: We start off with Elly wearing her pink smock looking at what Lynn thinks a dental chart looks like as she tells John, who's in the background holding Lynn's idea of a dental X-ray, "This is going to be fun--I haven't assisted you in years."
Panel 2: As she passes him a tray of dental instruments, she gushes "You were just out of dental school---doesn't this bring back fond memories?"
Panel 3: Her smile is erased and replaced by the Bug-Eyed Glare of Existential Horror after he says, with chin in hand, "Sure! That was when I still enjoyed working."
Summary: Years of dealing with misshapen people with odd surnames seems to have killed whatever enthusiasm John might have had for his chosen profession; he can now only console himself by belittling his wife and messing with her head.