A Radiographic Evaluation Of The Anterior Loop Of Mental Nerve:Comparision Between Panoramic Radiography And Cone Beam Computed Tomography

Objective:This study used digital panoramic radiography(PR) and cone beam computed tomography(CBCT) to identify the prevalence,position,visibility and the length of the anterior loop of mental nerve;Evaluate the difference between these two radiographic methods in clinical application.This would be useful to operate safely in the most distal area of the interforaminal region.Methods:Retrospective study were taken in radiographic images of mandibles of 231 patients randomly selected from those who both took panoramic and CBCT radiography at the hospital of Stomatology of Nanchang University or West China Hospital of stomatology of Sichuan University.Patients should meet the following inclusion criteria: adults(older than 18); panoramic and CBCT radiography were both taken;the images were distinct. 113 patients were male and 118 were female patients. Mean age was 40.97(range 18 to 85) years, grouping as 18~44、45~59、60~74、75~89 years. 90 patients were partially edentulous and 8 patients were edentulous. The interforaminal region of 231 patients,462 hemimandibles were evaluated on the prevalence,positon,visibility and the length of the anterior loop of mental nerve.All analysis and measurements were conducted by a dentist experienced in oral radiology.2 weeks later 25% samples randomly selected from those the anterior loop was existing in,mesasurement of the anterior loop of mental nerve was repeated to evaluate the intra-observer reproducibility for PR and CBCT. A descriptive and comparative analysis was performed. Chi-square tests and Nonparametric tests were used to examine the difference between genders,the left and right sides of the mandibles, different age groups,and different status of dentition, respectively.A Pvalue of less than 0.05 was considered statistically significant. Results:1.231 patients(462 samples)were included. The results of Kappa statistics showed 0.418 、0.660(P<0.05) reproducibility for PR and CBCT, respectively.2.An AL was identified in 65.15 %(301/462)of PR and 80.09%(370/462) of CBCT,statistical difference were shown between PR and CBCT(P<0.05).There were no statistical significance in genders,left and right sides of the mandibles and the different status of dentition(P>0.05),but the prevalence in different age groups show statistical difference(P<0.05).3.The position of AL relative to whole dentition most located at the apical region between the first and second premolar,90.94% in PR and 86.72% in CBCT. Statistical difference were not shown between PR and CBCT(P > 0.05). There were no statistical significance in genders,left and right sides of the mandibles, different age groups and different status of dentition(P>0.05).4.According to the creteria of visibility of AL,6.97% was wholly visible(scored 3),51.83% more than 1/2 was visible(scored 2),and 41.20% less than 1/2 was visible(scored 1) in PR;But in CBCT, 70.54% was wholly visible,25.68% more than 1/2 was visible,and only 3.78%% less than 1/2 was visible, statistical difference were shown between PR and CBCT(P<0.05). There were no statistical significance in left and right sides of the mandibles, different age groups and different status of dentition(P>0.05).But statistical difference were shown in genders of visibility of AL on PR(P<0.05).5.The mean length of AL for PR was 2.78±1.04 mm,ranging from 0.98 to 7.32mm;95.68%(288/301) were less than 5mm.And the mean length of AL was 2.98±1.24 mm on CBCT,ranging from 1 to 7 mm;96.49%(357/370)were less than 5mm. Significant difference were not shown between PR and CBCT(P>0.05). There were no statistical significance in left and right sides of the mandibles, different age groups(P>0.05).But statistical difference were shown in defferent age groups(P<0.05).And also statistical difference were shown in genders on the PR(P<0.05). Conclusions:1.It is better to evaluate the prevalence,visibility and to measure the length of AL on CBCT than PR,but CBCT didn’t show advantages on the identifying of the positon of AL.2.Identifying a fixed distance msially from the mental foramen generally as a safe distance should not be recommended for the operation in the interforaminal region,each pre-operative radiographic evaluation should be independent;But when the mental foramen and AL can not be identified,we should operate at least 5mm mesially from the mental foramen to avoid the complications mostly encountered.3.Considering the complexity of the structure in the interforaminal region and that two dimensional imaging provides less accurate and reliable information regarding AL, a CBCT scan could be recommended when planning implant placement in the interforaminal region.