Objectives The aim was to assess the diagnostic ability of the crown-to-root length ratio of the primary second molar and the position of the corresponding underlying premolar in estimating future anchoring teeth exfoliation during maxillary expansion.Setting and Sample Population Fifty-four subjects (30 females, 24 males; 108 teeth) aged 8.2 +/- 1.0 years that underwent palatal expansion.Methods The upper second premolar position of the corresponding expander anchoring primary molar was determined in relation to the ipsilateral first permanent molar half-pulp chamber (HPC) line on panoramic radiographs. Subjective and objective (based on measurements) assessments of the crown-to-root length ratio of anchoring primary molars were performed. Exfoliation after the expansion was recorded over a retention period of 12 months. All the assessments were performed individually by three examiners at two 3-week-apart sessions, trained and calibrated before enrolment. The intra-/inter-examiner agreements were evaluated, and the diagnostic accuracy of the methods was calculated.Results All methods exhibited almost perfect intra- and at least substantial inter-examiner agreement (Kappa >0.8 and >= 0.63, respectively). Good diagnostic accuracy was seen for the premolar position to the HPC line (0.7-0.8), while the crown-to-root length ratio methods exhibited hardly sufficient accuracy. The diagnostic agreement of the methods was fair.Conclusions 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.
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