Sometimes it's not what you say its how you say it.
Most dentists I know, feel like they know their stuff. They know what causes cavities and gum disease and how to perform the procedures needed to help their patients. What some lack is how to effectively communicate their knowledge in a way that will be well received by their patients. Often its not what they say it is how they say it that can limit their effectiveness. Telling patients they should crown a tooth, or they should come in more often for cleanings or do a better job with their home care should not be expressed in a way that will make their patient feel defensive or resentful. A perfect example is the hygiene "nazi" who admonishes their patients to do a better job and has an angry tone when telling their patient this. A better way of communicating the same thing would be letting the patient know how "concerned" we are and helping them understand why it is so important for them to do better ( and how expensive to fix problems will be avoided if they can...