PDR or paintless dent removal, simply put, is a highly skilled process of shrinking the stretched metal (the dent) with many connected pushes using specially made rods. The art of paintless dent repair lies in the technician's ability to make these pushes without marking or damaging the paint while shrinking the metal. Inferiorly trained or inexperienced techician's tell-tale mark is what we like to refer to as "chocolate-chip-cookies" or many bumps or pick marks made from pushing too hard on the panel's underside. Crease dents are more difficult than door dings and depending on the sharpness, are some of the most difficult types of dent repair in general. Large dent repair requires an understanding of metal theory and how the panels are manufactured (down to how the sheet metal was made). Always ask for examples of large dent repair before and after photos as well as if the company offers a guarantee on their work before going forth in choosing a company to perform large dent repairs.