To assess the probing depth on a patient, a periodontal probe is inserted with gentle pressure between the free gingival margin of the gingiva and the tooth surface to the level where the gingiva is attached to the tooth. The depth of penetration directly corresponds with the periodontal probing depth for that area of a tooth. Because a single area may not be representative, six different areas need to be assessed for circumferential evaluation of a tooth. The normal periodontal probing depth is < 1 mm for a cat and 1–3 mm for a dog.