A common curve ball employees throw when you want to make changes is that they're usually not able to specify. Most people find change hard. Dental employees are no exception. So try this. It usually works quite well:
Employee: Why are you changing everything?
Dentist: What specifically are you referring to?
Dentist: I understand, but let's talk one specific thing you feel I am changing.
Once you get the staff member to give you a specific, discuss it with them. Quite often you will see the objection crumble before your eyes and you can get on with the changes you want to implement.