Possible Clues:

• Tooth doctors
• Orthodontists, periodontists etc.
• They drill and fill
• They know the drill
• People tend to open up for them, as they are capable of building bridges
• They may bridge the gaps
• These should be able to cap disastrous D in tests
• Hygienists' coworkers
• Canine specialists
• Experts with the ends of 17- and 55-Across and 10- and 24-Down