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Pre-operative radiographic evaluation of lower third molars with computed tomography

¹ Department of Radiology, Sunderby Hospital, SE-971 80, Luleå, Sweden; ² Department of Maxillofacial Surgery, Sunderby Hospital, SE-971 80 Luleå, Sweden

*Correspondence to: Anders Öhman, Department of Radiology, Sunderby Hospital, SE-971 80 Luleå, Sweden; E-mail: anders.ohman{at}nll.se

Received 29 October 2004; revised 12 April 2005; accepted 12 May 2005

Objectives: To report radiographic findings of examinations with computed tomography (CT) of impacted lower third molars with an intimate relation to the mandibular canal and to investigate how findings of a dark band across the roots of the lower third molar on panoramic views correspond to the CT findings.

Methods: CT images of 90 lower third molars (64 patients, mean age 34.6 years) in which plain radiography was insufficient to allow determination of the precise anatomical relations were reviewed retrospectively. Panoramic views of 88 teeth existed; these images were interpreted independent of the CT examinations with respect to presence of a dark band across the roots.

Results: In 31% of the CT images, the course of the mandibular canal was buccal, in 33% lingual, in 26% inferior, and in 10% inter-radicular. The tooth was in contact with the mandibular canal in 94% and with the lingual cortex in 86%. In 23%, grooving of the root by the canal was judged to be present. In 63% of the cases where a dark band across the roots was observed on panoramic radiographs, CT revealed grooving of the root.

Conclusions: Pre-operative CT of lower third molars is motivated in selected cases when plain radiography is inconclusive. The finding of a dark band across the roots on panoramic radiographs is an indicator of grooving of the tooth by the canal and justifies a pre-operative CT examination. The absence of dark bands on panoramic views does not exclude grooving of the roots.

Keywords: computed tomography; inferior alveolar nerve; radiography; third molar

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