What is referred to as a four-sided (circumferential) defect?

A four-sided (circumferential) defect is characterized by its complete around the affected area, making it distinct from other types of defects. The term "moat" refers to this specific configuration, as it implies a surrounding area that is lower or deficient in tissue, similar to how a moat encircles a castle. This circumferential nature encompasses all sides, indicating that the defect is not limited to just one or two surfaces of the tooth or surrounding tissue, but rather is fully encircled, resembling a moat that surrounds a fortified structure.

In contrast, a crater typically refers to a more localized destruction and is often limited to the apical area of a tissue. A trench suggests a long, narrow opening or cut, emphasizing a particular orientation rather than a full circumferential involvement. Class II furcation relates specifically to the area between the roots of multi-rooted teeth, addressing interradicular bone loss, but does not denote a fully surrounding defect. Thus, the designation of a "moat" accurately reflects the four-sided nature of the defect in question.