Well

So is that a maybe for the balls orrrr

He is a dentist, obviously he needs to check the balls with his teeth. It's a medical procedure.

This joke is lost, because the picture is of an actual doctor.

Your "instrument" in my mouth then, got it.

Not a good dentist if he doesn't check your ballgums

‘My dentist said “you’re going to feel a tiny prick in your mouth“ and I said “well, then you’d better turn the nitrous up“- Robert Schimmel

Reminds me of that short in The House that has the mouse as the main character haha