Which class of furcation indicates a larger radiolucency that is clinically visible?

A Class IV furcation is characterized by a more severe and extensive involvement of the inter-dental area, resulting in a larger radiolucency that can be observed clinically. This class indicates that the furcation is not only involved but is also clinically visible through direct observation, meaning that there is a significant degree of bone loss and that the furcation area can be probed or assessed visually.

In contrast, lower classes such as I and II represent less severe involvement, with Class I indicating the initial stages of furcation involvement with no clinical visibility, and Class II demonstrating some degree of attachment loss but still not being fully visible from a clinical standpoint. Class III furcation may be visible radiographically but generally is not considered to have the same degree of clinical visibility as Class IV, where the bone is so destroyed that both the furcation and the underlying bone destruction are evident.