Which class of furcation can be detected by probing but does not allow for complete penetration?

The correct choice pertains to Class II furcation involvement. This class is characterized by the presence of horizontal bone loss that creates a furcation defect, which can be detected by probing. While probing can reveal the existence of this defect, it does not permit complete penetration through the furcation due to the depth of the bone loss and the soft tissue attachment remaining at the furcation site.

In Class II furcations, the clinical examination may show a partial involvement, where the probe can enter the furcation area but cannot pass through from one side of the tooth to the other, indicating that some bone remains intact.

This level of furcation involvement is crucial for dental professionals to understand since it influences treatment decisions and prognoses. The other classes of furcation involvement are characterized by different levels of bone loss and probing capabilities. For instance, Class I indicates no significant bone loss that prevents probing; Class III indicates a complete penetrative defect throughout the furcation; and Class IV, similar to Class III, also allows for full penetration but is additionally characterized by gingival recession, enhancing visibility of the furcation.