| Objective: The mandibular canal contains inferior alveolar nerves and blood vessels.It supplies blood to the mandible and dominates the mandible,lips,teeth and adjacent tissues.Considering the important sensory function of the inferior alveolar nerve,surgeons should try their best not to damage the inferior alveolar neurovascular bundle during the operation in this area,so as to prevent the occurrence of related postoperative complications.Clinical studies have found that there are a variety of anatomical variations in the mandibular canal,which may be affected by many types of jaw lesions,resulting in its displacement.Panoramic radiography,multi-slice spiral CT and conebeam computed tomography are effective imaging methods to evaluate the position of mandibular canal.Among them,cone beam CT is considered to be the most suitable method for mandibular canal detection because of its extremely low ground radiation dose,high spatial resolution,accurate image and powerful 3D application software.In several previous retrospective studies,cone-beam computed tomography was used to determine the location of the mandibular canal in the non-pathological mandible,mainly for the evaluation of the mandibular canal before dental implant planning or third molar surgery.At present,there are few reports on the appearance and displacement of the mandibular canal in the diseased area of the mandible.the common odontogenic jaw cystic lesions in the posterior part of the mandible are odontogenic cyst,odontogenic keratocyst and ameloblastoma.They can show similar imaging features,which are often difficult to distinguish.Although some studies have described the imaging differential diagnosis of three kinds of cystic lesions,these studies mainly focus on atrioventricular characteristics,notch,degree of expansion,root changes and intracapsular density.The relationship between odontogenic cystic lesions of the jaw and the location of the mandibular canal has not been clarified.Therefore,the purpose of this study is to evaluate the mandibular canal visibility and the effect of different cystic lesions on the mandibular canal position by cone beam CT before operation,and to analyze the relationship between the mandibular canal displacement and the disease,so as to provide a reference for preoperative assessment of the risk of lower lip numbness or provide a more intuitive way to visualize the position of the inferior alveolar nerve canal and find new differential factors for surgeons to diagnose and treat it.Methods: The data of 88 patients with odontogenic cyst(dentigerous cyst,DC),odontogenic keratocyst(odontogenic keratocyst,OKC)and ameloblastoma(ameloblastoma,AB)diagnosed pathologically in our hospital from July 2016 to October2020 and their preoperative cone beam CT data were collected.The collected cone beam CT data were imported into e Exam Vision software to reconstruct the mandibular canal in the area of jaw cystic disease.the reconstruction methods included curved surface reconstruction((curver planar reformat,CPR),multiplanar reconstruction((multiple planner reconstruction,MPR)and cross-sectional reconstruction.The imaging features of the mandibular canal(appearance of mandibular canal,visibility score of tube wall,direction of displacement)were retrospectively analyzed.Finally,the CBCT images were inputted into the e Exam Vision software in DICOM format for mandibular canal volume reconstruction(volume rendering,VR)and the relationship between mandibular canal and lesion position was evaluated.The appearance of mandibular canal between CBCT cross-sectional reconstruction and volume 3D reconstruction images was compared with the subjective three-level contrast score system in Srinivasan study.1score indicates that the two images of mandibular canal are similar.2 points show that CBCT cross-sectional images are better than volume 3D reconstruction images,and 3points show that volume 3D reconstruction images are better than cross-sectional images.SPSS21.0 is used to analyze and process the data of this study.Results: A total of 88 patients were included in this study,including 29 cases of dentigerous cysts,30 cases of odontogenic keratocyst and 29 cases of ameloblastoma.The appearance of mandibular canal in all 88 lesions was easily recognizable(23.1%),approximately identifiable(52.3%),unrecognizable(21.6%).The overall appearance rate of mandibular canal observed by CBCT was 78.4%.There was a significant difference in the score of wall visibility between AB group and DC group,but there was no significant difference between the other groups.There was no significant difference in the direction of mandibular canal displacement among the three groups(P > 0.05).The results of CBCT cross-sectional images and volume three-dimensional reconstruction showed that there were 25 patients whose comparison score was 1,the average score of wall visibility in group 1 was 2.27 ±0.22,the comparison score was scored as 2 for 25 patients.The average score of wall visibility in 2 groups was 3.13±0.46,and in 19 patients with comparison score 3,the average score of wall visibility in group 3 was 1.32±0.27.Kruskal-wallis H test showed that there was a significant difference in the score of wall visibility among different contrast groups(P < 0.01).Conclusion: 1.Cone-beam CT can be used to evaluate the mandibular canal in cystic lesion area before operation,and provide reference for surgeons to make treatment plan to avoid the risk of lower lip numbness.2.There is a significant difference in the visibility score between ameloblastoma and dentigerous cyst,that is,the destruction degree of ameloblastoma is much greater than that of dentigerous cyst.This quantitative index once again confirms the biological characteristics of extensive destruction of infiltrative growth bone in ameloblastoma.3.There is no significant difference in the characteristics of mandibular canal displacement among the three kinds of jaw cystic lesions,which can not be used as a factor of differential diagnosis among the three kinds of lesions.4.Volume 3D reconstruction can stereoscopically and intuitively display the spatial relationship between mandibular canal and jaw cystic lesions,especially suitable for observing the displaced mandibular canal with continuous absorption on one side of the canal wall oppressed by cystic lesions.Cross-sectional reconstruction image is better than volume reconstruction in displaying the mandibular canal with no obvious absorption.CBCT cross-sectional images are the basis for the diagnosis of displaced mandibular canal in the area of jaw cystic lesions. |
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