Is there a Federal or state requirement for the minimum size for a driver's side external rear view mirror? Motorcycle and racing mirrors get pretty small but dental mirrors/inspection mirrors would be really small.
Inspection mirror at least have an adjustable ball for aiming.
I can't say for sure on the Federal level, but I know that in Oregon at least, the requirement for rear view is fairly vague and open. Essentially it boils down to unobstructed view to the rear of 'x' number of feet. The Oregon statute says nothing about what type of mirror or where they must be mounted. Other states obviously will have different interpretations. Look it up in the vehicle equipment code for your state to be sure.