What defines a class IV furcation?

A class IV furcation is characterized by being clinically visible with recession, along with the probing instrument passing completely through the furcation area. This definition indicates that there is significant bone loss and periodontal attachment loss surrounding the furcation area, which exposes it to direct visibility. The presence of clinical recession also signals advanced periodontal disease, as the gum tissue has significantly receded, making the furcation accessible for probing and visualization.

This stage in furcation involvement indicates a more severe periodontal condition, where the structural integrity of the tooth is compromised. It differs from class III, where the furcation may be probed but is not visible due to the presence of soft tissue over the area.