Overhangs occur when a filling is not placed flush with the tooth surface.
These extensions create areas that collect plaque bacteria.
The overhanging filling prevents the tooth being cleaned effectively, as it catches the floss, and makes brushing that area almost impossible. This makes a tooth vulnerable to further decay and the gums susceptible to periodontal and gum disease.
Unless it is a temporary filling, you should not finalise your payment until the overhang has been rectified.
Ask your dentist to smooth any sticking-out fillings. If this cannot be done the filling may need to be replaced.