Radiographic examination of mandibular third molars

A radiographic examination is meant to support the clinical examination of mandibular third molars aiding the surgeon to establish a treatment plan. When deciding on which radiographic method to use, the ALARA-principle should always be kept in mind, and for most general dental practitioners a periapical examination is the only available method in the clinic. Studies have shown however that in around 25 % of the cases, it is impossible to obtain a sufficient periapical image; therefore panoramic imaging is the state-of-the-art method where this unit is available. In cases of over-projection between the third molar and the mandibular canal in the panoramic image and specific signs that a close contact exists between the molar and the mandibular canal, an additional 3D radiographic examination (CBCT) may be indicated to explore if there is direct contact between the third molar and the mandibular canal indicated by no bony separation between these structures. A direct contact as seen in CBCT-sections has been shown to be the most important factor with an impact on deciding on performing a coronectomy instead of removing the whole tooth. Studies, where the full tooth was removed seem to indicate, that the use of CBCT does not change the outcome for the patient with regard to sensory disturbances to the inferior alveolar nerve and moreover, the costs and the radiation burden to the patient are higher for CBCT than for conventional 2D methods.

In conclusion, periapical or panoramic imaging is sufficient in most cases before removal of mandibular third molars, but CBCT may be suggested when one or more signs for a close contact between the tooth and the canal are present in the 2D conventional image – if it is believed that CBCT will change the treatment or the treatment outcome for the patient.