The mobility of a tooth is a critical diagnostic and prognostic tool. The degree of normal physiological movement is limited to the width and elasticity of the periodontal ligament. Abnormal, or pathological, movement increases with loss of supporting tissues (alveolar bone, periodontal ligament) or following trauma. The degree of movement can be classified as follows:
- Stage 0 (M0) – Physiologic mobility up to 0.2 mm.
- Stage 1 (M1) – mobility is increased in any direction other than axial over a distance of more than 0.2 mm and up to 0.5 mm.
- Stage 2 (M2) – the mobility is increased in any direction other than axial over a distance of more than 0.5 mm and up to 1.0 mm.
- Stage 3 (M3) – the mobility is increased in any direction than axial over a distance exceeding 1.0 mm or any axial movement.