Κωνσταντίνος Τσιχλάκης, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, Ε.Κ.Π.Α
Δήμος Καλύβας, Αναπληρωτής Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, Ε.Κ.Π.Α
Ευάγγελος Παπαδάκης, Επίκουρος Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, Ε.Κ.Π.Α
Purpose: The purpose of the present study was to investigate the radiographic location and course of Mandibular Canal (MC), in relation to the cortices of the mandible (buccal and lingual cortical plates and inferior border of the mandible) using Cone Beam Computed Tomography (CBCT). In addition, the study describes the variations in the relative course of MC and the association of MC with the patient's sex and the side of the mandible (right ang left).
Materials and Methods: A retrospective study was performed using the CBCT mandibular image records of 111 dental Greek patients (52 males and 59 females) at the Department of Oral Diagnosis and Radiology, School of Dentistry, National and Kapodistrian University of Athens. The sample of the study was selected after the application of inclusion and exclusion criteria in the CBCT of year 2017. Specifically, CBCT with artifacts that affected diagnostic quality and patients who had maxillofacial deformities, any pathologic conditions or any previous manipulation which could alter the position of MC or tooth position including impactions, were excluded. Radiographically there was completely bilaterally corticated MC. The CBCT examinations were conducted using a Newtom VGI (QR, Verona, Italy) with a field of view 12x8 cm, 110 kV and exposure time 3.6s. The CBCT scans were analyzed by one experienced Oral Radiologist, who repeated CBCT measurements after a 2-months interval. The CBCT images were analysed with built-in software (NNT 7,2,0), with an EIZO FlexScan MX210 screen and with resolution 1600×1200 of pixels in a darkroom. During the secondary reconstruction procedure, the orientation of the resulting axial sections was determined to be parallel to the occlusal plane of the mandibular teeth. The location of MC was evaluated in 4 different regions. The first cross-sectional image (point P1) was selected at 10 mm distal to the mental foramen and intervals of 10 mm, respectively, points P2, P3 and P4 were selected for examination. Three measurements were made at each cross-sectional image. The distances from the MC to the: 1) buccal cortical plate (distance B), 2) lingual cortical plate (distance L) and 3) inferior border (distance I) of the mandible were measured. The data were analyzed with the Minitab 16 and the tables were created with MS Excel 2016. Descriptive of parameters were given as Mean ± Standard Deviation (SD). The observation quality control was performed using the Cohen's Kappa Coefficient statistical test. The significance of differences between comparable measurements was tested for females and males, for left and right sides by using t-test. Probabilities≤0.05 were accepted as significant.
Results: The study sample consisted of 111 patient CBCT scans (52 males and 59 females). The mean age of the patients was 54.9 (S.D: 14.7), with ages ranging from 20-84 years. The observer repeated CBCT measurements after a 2-months interval and the intraobserver coefficient (Cohen’s Kappa>0.80) suggesting excellent intraobserver agreement. In the molar region the distance from the MC to the buccal cortical plate from the anterior positions to the posterior positions, initially increased until position 20 mm distal to the mental foramen and then decreased. The MC was situated closer to the lingual cortical plate in the molar region. The distance from the MC to the inferior border of the mandible from the anterior positions to the posterior positions, initially decreased until position 20 mm distal to the mental foramen and then increased. Furthermore, its mean vertical position from the inferior border of the mandible was 8,04mm for men and 7,48 mm for women. There was no statistically significant difference in the distances from MC to the cortices of the mandible between right and left side of the mandible. Comparing distance measurements of MC to the buccal cortical plate and inferior border of the mandible, were greater in males than females in all cross-sectional images, but only for certain cross-sectional images were statistically significant differences. Generally, a greater distance of MC to the lingual cortical plate was noticed in females compared to males, for six of eight cross-sectional images, but differences were not statistically significant.
Discussion-Conclusions: The distance of MC to the buccal cortical plate was significantly greater in males than females for 2 cross-sectional images (10 mm distal to the mental foramen on the right-side of mandible and 20 mm distal to the mental foramen on the left side of mandible). Similarly, the distance of MC to the buccal cortical plate was significantly greater in males than females for 3 cross-sectional images (10 mm distal to the mental foramen on the right and left side of mandible and 20 mm distal to the mental foramen on the left side of mandible). Regarding the comparable measurements for left and right sides of the mandible, it was found that the corresponding mean values of the measurements were similar, and thus, the course of MC was symmetrical between right and left side of the mandible. The distance from the MC to the buccal cortical plate was greater at position 20 mm distal to the mental foramen, which is considered the safest position to place the vertical buccal cut of the sagittal ramus split osteotomy. In the buccolingual dimension, the MC was situated closer to the lingual cortical plate in the molar region and it was positioned with approximately 3/5 of the available bone buccal to the MC. In the vertical dimension, from posterior to anterior positions the MC travelled downward until the position 20 mm distal to the mental foramen (region between first and second molar), where it ascended to reach the mental foramen at the premolar region. Its mean vertical position from the inferior border of the mandible was 8,04 mm for men and 7,48 mm for females in the molar region. The ‘’Standard’’ Imaging modalities, chosen for the radiographic determination of the MC, should provide the required diagnostic information with the least radiation exposure to the patient. In selected cases where conventional radiographs fail to provide the information required, CBCT should de indicated. This study confirms the variations in the relative position and course of the MC along the body of the mandible. Precise preoperative assessment of the location of MC by using CBCT scans is critical for surgical procedures in the posterior mandible when there is risk of injury to the MC. The contribution of the CBCT information enables the surgeon for efficient and accurate surgical planning and encountering an intraoperative complication.
Mandibular canal, Cone beam computed tomography, Inferior alveolar nerve, Course