What characterizes a class III furcation?

A class III furcation is characterized by the probe passing completely through the furcation area to the other side of the tooth. This indicates that there is significant loss of attachment surrounding the multirooted tooth, allowing the probe to navigate through the furcation without obstruction. This condition reflects advanced periodontal disease, resulting in the separation of the roots within the furcation area, allowing for direct access between the periodontal pockets on either side of the tooth.

In contrast, in a class I furcation, the probe can enter the furcation but not pass through, while in a class II furcation, there is partial penetration but not complete access. A class III furcation presents a much more severe condition. Radiographically, class III may show significant radiolucency due to the loss of alveolar bone, but it is not limited to only slight radiolucency, which makes that option incorrect. The option suggesting that it can be felt but cannot be measured refers more closely to class II or class I conditions, where some attachment loss is present, but not enough to allow full probe passage, which is characteristic of class III.