Predicting lower third molar eruption on panoramic radiographs after cephalometric comparison of profile and panoramic radiographs.

Previous studies have suggested methods for predicting third molar tooth eruption radiographically. Still, this prediction is associated with uncertainty. The aim of the present study was to elucidate the association between cephalometric measurements on profile and panoramic radiographs and to find a simple and reliable method for predicting the eruption of the mandibular third molar by measurements on panoramic radiographs. The material consisted of profile and panoramic radiographs, taken before orthodontic treatment, of 30 males and 23 females (median age 22, range 18-48 years), with no known diseases. Cephalometric measurements on panoramic and profile radiographs were performed and compared, i.e. the size of the gonial angle and sagittal distance from the alveolar margin between the mandibular central incisors to the anterior border of the mandibular ramus. Furthermore, the mesiodistal width of the second molar was measured. Statistical methods included analysis of method error. The probability of eruption was modelled using logistic regression analysis. Correlation was observed between all measurements on profile and panoramic radiographs. The skeletal variable expressing the length from the ramus to the incisors (olr-id) showed a statistically significant correlation. By combining this length with the mesiodistal width of the lower second molar, the prediction of eruption of the lower third molar was strengthened. A new formula for calculating the probability of eruption of the mandibular third molar was made and a graph constructed for easy assessment. In conclusion, a simple method for predicting the eruption of the third molar is presented.