What does a 'grade III mobile' status indicate for a lower second tooth?

A 'grade III mobile' status signifies significant mobility in the tooth, specifically indicating that there is both vertical movement and a considerable amount of horizontal movement. This grade typically suggests that the tooth is highly compromised due to periodontal issues, which may be resulting in the loss of support structures.

In this context, vertical tooth movement points to the fact that the tooth can not only be moved in a side-to-side motion but can also be displaced in an upward and downward motion, indicating a severe degree of instability. This classification is crucial for dental professionals to assess the prognosis of the tooth and to determine appropriate treatment options.

The other choices indicate differing levels or types of mobility that do not fully capture the extent of movement associated with a grade III designation, particularly the absence of severe vertical movement or specific measurements of side-to-side motion.