What distinguishes a Class 4 furcation from Class 3 furcation?

A Class 4 furcation is distinguished from a Class 3 furcation primarily by its clinical visibility due to the presence of periodontal tissue recession. In a Class 4 furcation, the gingival tissue has receded significantly, allowing for direct visualization of the furcation area. This contrasts with Class 3 furcation, where the furcation is involved but not visible because the gingival tissue remains intact or only minimally recessed.

In clinical practice, being able to see a Class 4 furcation directly provides important diagnostic information about the severity of periodontal disease and the associated loss of attachment. This visibility can help inform treatment plans and predict long-term tooth prognosis.