Preoperative Evaluation of Lingual Cortical Plate Thickness and the Anatomical Relationship of the Lingual Nerve to the Lingual Cortical Plate via 3T MRI Nerve-Bone fusion.

Objectives: To evaluate the reliability of 3 T MRI nerve-bone fusion in assessing the lingual nerve (LN) and its anatomical relationship to the lingual cortical plate prior to the impacted mandibular third molar (IMTM) extraction.

Methods: The MRI nerve and bone sequences used in this study were 3D-T2-weighted fast field echo (3D-T2-FFE) and fast field echo resembling a CT using restricted echo-spacing (FRACTURE), respectively. Both sequences were performed in 25 subjects, and the resulting 3D-T2-FFE/FRACTURE fusion images were assessed by two independent observers. Semi-quantitative analyses included assessments of overall image quality, image artifacts, nerve continuity, and the detectability of five intermediate points (IPs). Quantitative analyses included measurements of the lingual cortical plate thickness (LCPT), vertical distance (V1* and V2*) and the closest horizontal distance (CHD) between the LN and the lingual cortical plate. Reliability was evaluated using weighted Cohen's kappa coefficient (κ), intraclass correlation coefficient (ICC) and Bland-Altman plots. Differences in LCPT between 3D-T2-FFE/FRACTURE fusion images and one-beam computed tomography (CBCT) were compared using independent samples T-tests or Mann-Whitney U tests.

Results: The fusion images demonstrated that the LN continuity score was 3.00 (1.00) (good), with 88% (44/50) of LNs displayed continuously to the IMTM level. Intra-reader agreement for nerve continuity was moderate (κ = 0.527), as was inter-reader agreement (κ = 0.428). The intra-reader and inter-reader agreement for LCPT measurements at the neck, mid-root and apex of the IMTM were all moderate (ICC > 0.60). Intra-reader agreements for V1*, V2* and CHD were moderate to excellent (ICC = 0.904, 0.967 and 0.723, respectively), and inter-reader agreements for V1*, V2* and CHD were also moderate to excellent (ICC = 0.948, 0.941 and 0.623, respectively). The reliability of LCPT measurements between 3D-T2-FFE/FRACTURE fusion and CBCT was moderate (ICC = 0.609-0.796).

Conclusions: The 3D-T2-FFE/FRACTURE fusion technique demonstrated potential feasibility for the identification of the LN and its relationship to the lingual cortical plate, as well as for the measurement of LCPT.

Advances in knowledge: This study has generated a dataset that is capable of simultaneously defining the LN and LCPT.