Patient-friendly definition from the DentistsDirectory.org dental glossary.
A periodontal pocket is the space between the tooth root and the inner wall of the gum tissue surrounding it. Even healthy gums have a shallow sulcus (groove) around each tooth — the gum attaches to the tooth just below the visible gum line, creating a natural crevice. Dentists measure the depth of this space during periodontal probing by gently inserting a thin calibrated instrument around the tooth and noting how deeply it slips before reaching the attached tissue. This measurement — done at six points around every tooth — is one of the most important assessments in a dental check-up.
Healthy pocket depths are 1–3 millimetres. At this depth, the gum fits snugly around the tooth, the base of the pocket is accessible to cleaning, and bacterial populations are kept in check by saliva and immune function. When gum disease causes inflammation and the progressive destruction of the periodontal ligament and alveolar bone, the pocket deepens. At 4mm, the pocket is considered borderline; 5–6mm indicates moderate periodontal disease; 7mm or deeper indicates severe disease. Deep pockets are oxygen-poor, difficult to clean, and harbour the most destructive anaerobic bacteria.
Pocket depth is the primary clinical parameter that determines whether gum disease can be managed non-surgically (with scaling and root planing) or requires surgical access to fully debride. Pockets up to 4–5mm can usually be adequately cleaned with deep cleaning (scaling and root planing). Pockets of 6mm or greater often require a surgical flap to be reflected so the root surface can be cleaned under direct vision. After treatment, the goal is to reduce all pockets to 4mm or less, eliminating the anaerobic environment in which the most harmful bacteria thrive.