(Strip Number 6684, Original Publication Date, 25 September 1983)
Panel 1: We start things off with John injuring his hand while working on a dental mold.
Panel 2: Just then, a man who I'll call Kresge Savomart peers in from the doorway and asks John if he bit himself.
Panel 3: It appears that Mister Savomart is here for his check-up; that's because he tells John that he looks a little down in the mouth and asks if he had another tough day at the orifice. John laughs at his 'joke'.
Panel 4: John continues to laugh when the man says that he hears that John has a lot of pull in town, ain't it the tooth.
Panel 5: As John continues looking a ungifted horse's hind end in the mouth, the man sings the song "Fillings/nothing more than fillings....."
Panel 6: John even laughs when the man says 'just a little tongue in cheek' just before he's told to rinse and spit.
Panel 7: Now that the appointment is over, the man thanks John, hopes he didn't needle John too much and says that he's going back to the old grind.
Panel 8: After he leaves, Jean asks John how he can listen to all of those old jokes.
Panel 9: Simple. He uses the same old laugh.
Summary: My guess is that this is less about Rod's practice and more about how uncomfortable Lynn is when she's not dominating the conversation.