Is MRI a viable alternative to CT/CBCT to identify the course of the inferior alveolar nerve in relation to the roots of the third molars?

Florian Beck,Stephanie Austermann,Christian Ulm,Andrea Toelly,Stefan Lettner,Kristina Bertl,André Gahleitner

doi:10.1007/s00784-020-03716-4

Florian Beck, Stephanie Austermann + Show 5 more

Open Access

https://doi.org/10.1007/s00784-020-03716-4

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Abstract

ObjectivesTo assess the reliability of judging the spatial relation between the inferior alveolar nerve (IAN) and mandibular third molar (MTM) based on MRI or CT/CBCT images.MethodsAltogether, CT/CBCT and MRI images of 87 MTMs were examined twice by 3 examiners with different degrees of experience. The course of the IAN in relation to the MTM, the presence/absence of a direct contact between IAN and MTM, and the presence of accessory IAN were determined.ResultsThe IAN was in > 40% of the cases judged as inferior, while an interradicular position was diagnosed in < 5% of the cases. The overall agreement was good (κ = 0.72) and any disagreement between the imaging modalities was primarily among the adjacent regions, i.e., buccal/lingual/interradicular vs. inferior. CT/CBCT judgements presented a very good agreement for the inter- and intrarater comparison (κ > 0.80), while MRI judgements showed a slightly lower, but good agreement (κ = 0.74). A direct contact between IAN and MTM was diagnosed in about 65%, but in almost 20% a disagreement between the judgements based on MRI and CT/CBCT was present resulting in a moderate overall agreement (κ = 0.60). The agreement between the judgements based on MRI and CT/CBCT appeared independent of the examiner’s experience and accessory IAN were described in 10 cases in MRI compared to 3 cases in CT/CBCT images.ConclusionsA good inter- and intrarater agreement has been observed for the assessment of the spatial relation between the IAN and MTM based on MRI images. Further, MRI images might provide advantages in the detection of accessory IAN compared to CT/CBCT.Clinical relevanceMRI appears as viable alternative to CT/CBCT for preoperative assessment of the IAN in relation to the MTM.

Highlights

The inferior alveolar nerve (IAN) is next to the lingual nerve, one of the most endangered anatomical structures during the surgical removal of mandibular third molars (MTM)
The aim of this study was to assess the reliability of judging the spatial relation between IAN/mandibular canal (MC) and the roots of the MTM based on orthoradial slices of magnetic resonance imaging (MRI) or CT/CBCT images
Nineteen participants contributed with CBCT images of a single MTM, while in 34 participants, both MTM were examined by CT; the MTM distribution left to right was 39 to 48

Summary

Introduction

The inferior alveolar nerve (IAN) is next to the lingual nerve, one of the most endangered anatomical structures during the surgical removal of mandibular third molars (MTM). The probability of IAN impairment after MTM removal depends on the spatial relation between the mandibular canal (MC) and the MTM [2] and lack of a bony MC wall increases the risk of IAN impairment [3]. CT/CBCT diagnostics relies on the presence of a bony MC wall for locating the IAN. A histomorphometric analysis indicated that the integrity of the MC wall is dependent on the quality/density of the surrounding trabecular bone [6], which explains that in approximately every fifth patient the IAN/MC appears difficult to be identified based on CBCT images [7]

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