Doesn't this really need to be replaced?
A gap may be able to be sealed to prolong the life of the crown and prevent food from getting caught, a ledge should be able to be recontoured so the crown and tooth are flush with eachother. If the gap is too big, you may have to have the crowns redone. These types of issues with crowns (and any kind of tooth restoration for that matter) should be dealt with since they are areas that are more susceptible to the development of decay (cavities).
