When a probe is perpendicular to the long axis of a tooth, what is it primarily measuring?

When a probe is positioned perpendicular to the long axis of a tooth, it is primarily used to measure furcation involvement. A furcation is the area where the roots of a multirooted tooth diverge. By angling the probe perpendicularly, a clinician can accurately assess the depth of the furcation area, which is crucial for determining the extent of periodontal disease and planning appropriate treatments.

In contrast, attachment levels, periodontal pocket depth, and bite force aren’t primarily assessed through this specific probing technique. Assessing attachment levels and pocket depths typically requires a parallel orientation to the tooth's long axis for accurate measurements along the gingival margin to the base of the pocket. Bite force measurements involve completely different methodologies and tools unrelated to probing around teeth. Thus, the perpendicular approach distinctly applies to evaluating furcations in periodontal assessments.