In the standard mobility classification, which class describes a tooth that moves more than 2 mm in any direction?

• A. Class I mobility
• B. Class II mobility
• C. Class III mobility
• D. Class IV mobility

Answer: (C)

Mobility classification assesses how far a tooth can move in its socket, reflecting the amount of periodontal support remaining. Up to about one millimeter of horizontal movement in any direction is considered mild mobility. If the tooth moves more than one millimeter but less than two millimeters, that’s moderate mobility. When movement exceeds two millimeters in any direction, or the tooth can be depressed in the socket, this is severe mobility. Thus, a tooth that moves more than two millimeters in any direction falls into the third class of mobility. In some systems there are other designations for extreme cases, but the standard interpretation of more than two millimeters is third class.