Buzz I never have to put my hands into anyone's mouth. A couple of fingers perhaps. Trust me when I say females clearly prefer doctors with small hands. There are more internal examination procedures done by an OB/GYN. I don't have to turn a babies head or do a internal exam by with multiple fingers or more. I use mirrors a lot to retract a cheek or tongue. I grip instruments which I move into the mouth which gives me four to five inches extra reach. Your dentist hand size does not mean you have to open extra wide so he can get his mitts into your mouth.
And hand strength is very important when it comes time to remove difficult teeth. Leverage, skill and force is still required to do that job. After tens of thousands of teeth I can get just about any tooth out with ease and as much patient comfort as possible. I've seen dentist who were rough as a rasp doing that job and they all tended to be small and weak or just stupid. It takes a gradual force, increased and decreased over time to allow the bone to stretch and relax so the tooth can be removed. The weaker ones just apply max force right away and if it breaks off, which they do too often that way, the patient is not going to enjoy the next half hour.