after i urathaned primered my car i found a couple small dents i need to fill. what do i need to do? sand the urathane primer off in that area?and make the repair or scuff it and fill it. thanks

You may get answers for both ways. I say grind/sand to bare metal in the area of the dent, fill it, sand it, then reprime and block.

The filler will adhere just fine over sanded urethane primers but you may have problems with swelling and shrinkage if the job is rushed. Most polyester glazes and putties work fine over cured primers, maybe they would suit your application if the filling is minimal. When body filler cures some solvents escape/evaporate from the surface, if applied over a primer there is a chance these solvents will be absorbed and later released causing the swelling and shrinkage. One example of filler problems over primer is when a person tries to use filler over self etching type primers that are highly suseptable to solvent absorbtion.