Possible Clues:

• Numbers, at times
• First to fill cavities?
• They look down in the mouth
• ADA members
• They give oral examinations
• They care for teeth
• Drillers and fillers
• Some British rockers need to see them
• They're never afraid to ask someone else to open up, as they tend to spend a lot of time filling in for others!
• Those working on bridges produced foolish dissent over central keystones