Diagnostic ability of the primary second molar crown-to-root length ratio and the corresponding underlying premolar position in estimating future expander anchoring teeth exfoliation.

When primary molars are considered as anchoring teeth for maxillary expansion, the premolar position in relation to the HPC line appears to be the most valid and reliable method for predicting their stability. Despite high repeatability values, the crown-to-root length ratio needs a cut-off point re-definition to increase its predicting ability.