Accuracy in the Diagnosis of the Mental Nerve Loop: A Comparative Study Between Panoramic Radiography and Cone Beam Computed Tomography

Abstract

SUMMARY: Dental implant and chin osteotomy are executed on the mandible body and the mental nerve is an important anatomical limit. The aim of this research was to know the position of the mental nerve loop comparing result in panoramic radiography and cone beam computed tomography. We analyzed 94 hemimandibles and the patient sample comprised female and male subjects of ages ranging from 18 to 52 years (mean age, 35 years) selected randomly from the database of patients at the Division of Oral Radiology at Piracicaba Dental School State University of Campinas; the anterior loop (AL) of the mental nerve was evaluated regarding the presence or absence, which was classified as rectilinear or curvilinear and measurement of its length was obtained. The observations were made in the digital panoramic radiography (PR) and the cone beam computed tomography (CBCT) according to a routine technique. The frequencies of the AL identified through PR and CBCT were different: in PR the loop was identified in 42.6% of cases, and only 12.8% were bilateral. In contrast, the AL was detected in 29.8% of the samples using CBCT, with 6.4% being bilateral; Statistical comparison between PR and CBCT showed that the PR led to false-positive diagnosis of the AL in this sample. According to the results of this study, the frequency of AL is low. Thus, it can be assumed that it is not a common condition in this population.

Panoramic radiographs underestimate extensions of the anterior loop and mandibular incisive canal

“…Our results were indicative of considerable anatomical variability, as distances from the mental foramen reached up to 20 mm (2.0 cm). Couto-Filho et al, 26 evaluating only the anterior loop, obtained mesial measures of the mental foramen similar to those obtained this study. This variability could be related to the incisive canal, a structure not evaluated in the previous study by Couto-Filho et al 26 Due to these discrepancies, it is recommended that all surgical cases involving the anterior mandible be assessed individually rather than relying on averages.…”

“…Previous studies have shown that the interpretation of 2-D images has limitations and often results in false negatives and false positives, as well as misestimating anterior loop extension. 2 3 22 26 The presence of the anterior loop was overestimated by as much as 40% in PAN images in a previous study, in which false positives were determined by dissection of the radiographed anatomical specimens. 2 Image overlapping and the degree of corticalization of the bony canals are factors that may affect the visualization of structures such as the anterior loop and incisive canal.…”

“…Previous anatomical studies in cadavers and anatomical specimens reported the prevalence of the anterior loop to range from 10% to 62.7%. 2 3 4 5 8 25 26 Kieser et al's study 27 did not show the measurable anterior loop that would have any significant impact on treatment planning for implants in the anterior mandible. Benninger et al 8 considered the anterior loop to be an anomaly, rather than an anatomical finding.…”

“…Depending on the reference plane adopted, the distances from the mental foramen are different. Uchida et al 5 6 used only the lower border of the mandible as the reference, while de Oliveira-Santos et al 9 and Couto-Filho et al 26 used two references: the lower border of the mandible (measurements performed in CBCTp) and the occlusal plane, which could be more representative of the field of vision of the surgeon during the implant placement procedure (for CBCTcs).…”

Assessment of the anterior loop of mental nerve in an Iranian population using cone beam computed tomography scan

“…Studies have shown that panoramic radiography is not sufficient for presurgical implant planning in the mental region and may need to be supplemented with other modalities such as CT for better visualization of the area. [ 2 13 14 ] The CT and CBCT allow three-dimensional imaging without magnification and distortion. Of these, CBCT has the advantage of providing high-quality images with less radiation dose than CT.[ 4 7 10 ]…”