When English professors get flummoxed, they turn to meaningless idioms. I can't criticize Ian in this case, however; true, cars do not have teeth, but teeth do not have skin. Thus, his usage is as correct as any. Wait a minute... his lips have grown so full and pouty... perhaps that is what he's referring to.
Now that we know there was no accident, we understand why Joe Giella used "SCREECH" instead of "CRASH" in Thursday's strip. But what was with the white flash that seemed to indicate impact? Perhaps it was a marshmallow blast that cushioned the blow. Perhaps it was his car's teeth skin.