Tooth mobility is the detectable movement of a tooth within its socket when lateral or axial forces are applied — a clinical sign that ranges from physiologic micromovement to pathologic loosening requiring intervention. While every tooth has a slight, natural degree of mobility due to the cushioning properties of the periodontal ligament, abnormal mobility signals that the supporting structures have been significantly compromised.

Grading Tooth Mobility

Clinicians commonly use the Miller Mobility Index to classify tooth mobility on a standardized scale:

• Grade 0: Physiologic mobility only — barely perceptible movement of less than 0.2 mm.
• Grade I: Slight mobility, with detectable horizontal movement up to 1 mm.
• Grade II: Moderate mobility, with horizontal movement greater than 1 mm but no vertical displacement.
• Grade III: Severe mobility, with movement in both horizontal and vertical (apical) directions.

Common Causes

Elevated tooth mobility most often reflects destruction of the alveolar bone and connective tissue that anchor the tooth in its socket. Leading causes include:

• Advanced periodontitis, in which chronic inflammation degrades bone and ligament support
• Occlusal trauma or bruxism, placing excessive repetitive force on the periodontal ligament
• Periapical infection or abscess eroding surrounding bone
• Systemic conditions such as osteoporosis or uncontrolled diabetes that weaken bone density
• Orthodontic treatment, which intentionally produces temporary, controlled mobility as teeth are repositioned

Clinical Significance and Management

Tooth mobility is a reliable proxy for the degree of periodontal destruction. A tooth exhibiting Grade II or III mobility generally indicates significant attachment loss and warrants a thorough periodontal evaluation, including radiographic assessment of crestal bone levels. When mobility co-exists with furcation involvement — where the space between diverging roots becomes exposed — the long-term prognosis for that tooth becomes considerably more guarded.

Treatment targets the underlying cause. Controlling active periodontal disease through scaling, root planing, and surgical intervention can halt further bone loss and sometimes reduce mobility. Occlusal adjustment may relieve traumatic forces, and splinting mobile teeth to adjacent stable teeth can provide symptomatic relief, though neither approach substitutes for addressing the primary etiology.

Documenting tooth mobility at every recall appointment gives clinicians an objective, reproducible measure of periodontal stability, making it an essential element of any thorough oral examination.