No one wants to cause their dentist to lose their license, and those with a legitimate face mask exemption don't want to put themselves at risk by wearing that mask. Your dentist's office has a face mask policy. As with any other face mask policy, you can just learn about the policy and exemptions and see if it fits you.
In the same way that you need never wear a mask to the grocery store to other stores and you need never wear a mask anywhere else in life, there's no reason to wear a mask to the dentist or doctor when you have a legitimate exemption to their rule.
These are steps I would recommend for your dentist's office or doctor's office.