Prognosis of third molar eruption.

This study was designed to find a threshold value for an increased probability of upper and lower third molar eruption measured on rotational tomograms compared with lateral cephalometric radiographs. Twenty-seven patients had been followed over a 7-year period. Space available in the retromolar region had been measured at mean ages of 13, 16, and 20 years. At early ages, patients with erupted third molars had significantly more space available in the retromolar region. More wisdom teeth had erupted with a space/width ratio > or = 1 measured on rational tomograms and a distance of 25 mm or more on lateral cephalometric radiographs. There was a strong correlation between rotational tomograms and lateral cephalometric radiograph measurements as well as good reliability and reproducibility compared with study casts.