When a dentist says that " I cannot fix your teeth if you do not open your mouth wide:" He is employing:
Problem ownership.
Voice control
Tolerance.
Flexibility.
Problem ownership:

Negative messages like 'You must sit still'; undermine the rapport between child and dentist. "You" messages carry the implication that the child is wrong.
Instead "I" messages increase the flow of information. Eg: I cannot fix your teeth if you do not open your mouth wide. This is called problem ownership.