The AAP definition of tooth mobility is “The movement of a tooth in its socket resulting from an applied force”.
Class 0
Normal (physiologic) movement when force is applied.
Class I
Mobility greater than physiologic.
Class II
Tooth can be moved up to 1mm or more in a lateral direction (buccolingual or mesiodistal).
Inability to depress the tooth in a vertical direction (apicocoronal).
Class III
Tooth can be moved 1mm or more in a lateral direction (buccolingual or mesiodistal).
Ability to depress the tooth in a vertical direction (apicocoronal).