Final answer:
The term for excess restorative material extending beyond the cavity margin is known as an overhang.
Step-by-step explanation:
The term for excess restorative material that extends beyond the cavity margin is called overhang. This happens when the material used to fill the cavity is not properly contoured and extends beyond the natural borders of the tooth. An overhang can trap food and bacteria, leading to potential new cavities or gum disease. It is important for dental professionals to carefully shape and polish restorative materials to prevent this issue.