I wonder if quick checkups are any less profitable per unit time than doing fillings. Not much in the way of materials required, and you can get a good throughput, with each visit likely to be of predictable duration.
(My teeth are in good shape, and my average dentist visit takes all of 15 minutes: check teeth for basic soundness, scrape off tartar, remove tea stains from upper incisors. Still costs me £55.)
There is also orthodontic work.