Third molar maturity index reliably classifies 18-year age threshold across five populations

The third molar maturity index (I3M) on panoramic radiographs showed excellent discrimination for classifying age ≥18 vs. <18 years across five populations (AUC 0.917–0.942). Optimal cutoff values varied from 0.126 (Croatia) to 0.223 (China), and machine learning with leave-one-…

• I3M is the ratio of open apical width to tooth length of the mandibular third molar; both teeth 38 and 48 were measured on orthopantomograms from 3000 individuals aged 13–22 years across Brazil, China, Croatia, Portugal, and Sweden.
• Population was an independent predictor of 18-year classification; significant intra-population sex differences were found in three populations, with females showing higher I3M values.
• When ethnic background is unknown, the authors recommend a conservative threshold of 0.10–0.15 to minimize misclassification of minors.

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