Efficacy of CBCT for assessment of impacted mandibular third molars: a review - based on a hierarchical model of evidence

Abstract

A radiographic examination of mandibular third molars is meant to support the surgeon in establishing a treatment plan. For years panoramic (PAN) imaging has been the first choice method; however, where an overprojection is observed between the third molar and the mandibular canal and when specific signs suggest a close contact between the molar and the canal, CBCT may be indicated. The present review provides an evaluation of the efficacy of CBCT for assessment of mandibular third molars using a six-tiered hierarchical model by Fryback and Thornbury in 1991. Levels 1-3 include studies on low evidence levels mainly regarding the technical capabilities of a radiographic method and the diagnostic accuracy of the related images. Levels 4-6 include studies on a higher level of evidence and assess the diagnostic impact of a radiographic method on the treatment of the patient in addition to the outcome for the patient and society including cost calculations. Only very few high-evidence studies on the efficacy of CBCT for radiographic examination of mandibular third molars exist and, in conclusion, periapical or PAN examination is sufficient in most cases before removal of mandibular third molars. However, CBCT may be suggested when one or more signs for a close contact between the tooth and the canal are present in the two-dimensional image-if it is believed that CBCT will change the treatment or the treatment outcome for the patient. Further research on high-evidence levels is needed.

Keywords: cone beam computed tomography; molar; radiography; third.

Figure 1

(a) Segmented panoramic image of the two mandibular third molars. Interruption of the upper radiopaque borders of the canal is present in both sides. (b) Axial and coronal views of the right mandibular third molar showing no bony separation between the roots of the third molar and the mandibular canal. Arrows indicate the mandibular canal. (c) Axial and coronal views of the left mandibular third molar showing no bony separation between the roots of the third molar and the mandibular canal. Arrows indicate the mandibular canal.

Figure 2

(a) Example of a right mandibular third molar for which the treatment was changed from surgical removal to coronectomy after CBCT images were available. A, stereo-scanogram; B, CBCT axial view; C, CBCT coronal view. Arrows indicate the mandibular canal. (b) Example of a left mandibular third molar for which the treatment was changed from coronectomy to surgical removal after CBCT images were available. A, stereo-scanogram; B, CBCT axial view; C, CBCT coronal view. Arrows indicate the mandibular canal.