Radiological prediction of the retention of the lower third molars

Abstract

Objective: To evaluate the validity of the radiological retention coefficient based on linear measurements performed using digital panoramic radiographs as an early prediction index of mandibular third molar eruption/retention status. Methods: This study consists of the analysis by a single operator (S.S.H.) of digital drawings on panoramic radiographs. A total of 328 third lower molars recorded on diagnostic digital orthopantomograms, were used to analyze retromolar space, mesiodistal crown width, and space/width ratio. The radiological retention coefficient was then calculated with these linear measurements. Results: The average age of patients was 23.49 years old for men and 23.89 for women. The frequency of lack of space for the lower third molar eruption was 58%. The frequency of retention of the lower third molar in men is 51%, while in women it reaches 64%. In men the probability of the molar being retained is 95% if the radiological retention coefficient lies between 0.69 and 0.78. In women such probability is 95% if the radiological retention coefficient lies between 0.63 and 0.71. In men the probability of eruption is 95% if the radiological retention coefficient lies between 1.08 and 1.22. In women the probability of eruption is 95% if the radiological retention coefficient lies between 1.06 and 1.19. Conclusions: The radiological retention coefficient is a method with a very high probability of success, for evaluating whether the third lower molar will erupt or be retained.