What characterizes a grade III furcation involvement?

A grade III furcation involvement is characterized by the complete loss of interradicular bone between the roots of a multirooted tooth. In this situation, there is a radiographic evidence of the furcation involvement, indicating a significant periodontal disease process where the bone loss is extensive enough that the furcation area can be probed and feels open without any obstruction. This means that there is a separation between the roots, making it possible for periodontal instruments to pass through the furcation.

The complete absence of interradicular bone signifies a severe form of periodontal disease, suggesting that the tooth may have compromised support and is at a higher risk of mobility or even loss if not properly managed. Recognizing this condition is critical for treatment planning and prognosis evaluation.

The other options hint at varying degrees of periodontal disease but do not accurately describe the characteristic features of grade III furcation involvement. Partial destruction of interradicular bone would correspond more to grade II furcation involvement, while apical recession of gingival tissue is a common finding but not specifically related to the degree of furcation involvement. The visibility of the furcation opening refers to a clinical finding but does not define the complete destruction of bone that is requisite for grade III classification.