Dental magnetic resonance imaging: study of impacted mandibular third molars

To assess the usefulness of MRI in the evaluation of the relationships between the mandibular canal and impacted mandibular third molars.

29 young patients from our hospital dental service, all with a unilateral impacted mandibular third molar, were investigated with MR and the anatomical details were evaluated in three dimensions by two MR-experienced radiologists from our radiology division. MR images were obtained by using a 1.0 T Siemens Magnetom Expert unit with a radiofrequency (RF) head coil. T(1) weighted axial oblique images and proton density-weighted sagittal/coronal oblique images were acquired in order to evaluate the anatomical details in the three dimensions.

In all of the cases it was possible to evaluate the depth of the third molar in the alveolar bone, its inclination towards the occlusal plane and the relationships with the mandibular canal, but in 2 of 29 cases it was not possible to distinguish the mandibular canal from the third molar because of magnetic susceptibility artefacts.

Owing to the possibility of inferior alveolar nerve injury during oral surgery, where dental panoramic radiography is not sufficient to demonstrate the relationships between mandibular third molar teeth and the mandibular canal, a dental CT scan is often needed; however, in young patients, to avoid high levels of radiation dose, MRI of the jaw may be useful.