Final answer:
The correct answer is option a. A probe reading of 6 mm measures the distance from the gingival margin to the cementoenamel junction, which indicates the pocket depth around a tooth and is used to assess periodontal health.
Step-by-step explanation:
The measurement of 6 mm when using a probe in dentistry is typically used to assess the health of the periodontium, which includes the gums, periodontal ligament, and bone surrounding the teeth. When a probe is inserted into the gingival crevice, it measures the distance between two specific points within the oral structure. Given the choices provided, a probe reading of 6 mm specifically measures the distance from the gingival margin to the base of the crevice or pocket, which, if there is no recession of the gums, is the cementoenamel junction. Therefore, the correct answer is: (a) Gingival margin to the cementoenamel junction
Gingival margin refers to the top edge of the gum that surrounds the teeth, while the cementoenamel junction (CEJ) is the anatomical point where the enamel covering the crown of the tooth meets the cementum that covers the root. A 6 mm reading is a clinical indicator that there might be periodontal disease, as the normal healthy depth should be between 1 to 3 mm.