All teeth within a mouth have a basal health status that is determined by the mouth they are located. We can calculate how much this mouth specific basal health status explain the differences in health status between the teeth.

This is the INTRA-CLASS CORRELATION

I an extreme case all the teeth within a mouth have exactly the same health status and their differences from the population (teeth & mouths) mean are all exactly their mouth difference from the population (teeth & mouths) mean. This would correspond with an ICC=100%

I another opposite extreme case the teeth within a mouth have very large different health status values, and their basal mouth value is identical for all the mouths. This would correspond with an ICC=100%

If the ICC is 50%, one halt of the differences in health status would be explained by the mouths the teeth are located.