Awareness of the anatomy in the anterior region of the mandible is crucial in the field of dental surgery. Wide ranges of operations are performed for example: implants, autogenous chin grafts, and orthognathic surgeries. These surgeries may be accompanied by life-threatening conditions such as hemorrhage, which may lead to airway obstruction and suffocation ending in death [5, 10].
Although there were studies performed on dry mandibles or in vitro concerned with the existence of the lingual foramina, yet the presence of the 3D imaging modalities such as CT and later CBCT improved the understanding of the prevalence, location, and the number of the mandibular lingual foramen in vivo [11, 12].
In this study, CBCT scans were used due to the three-dimensional accuracy in detection of vital anatomical structures, besides its low radiation exposure and simple handling compared to CT scans [6, 10, 13].
The current study showed approximately 99.0% of MLCs within the examined sample presenting the prevalence of MLC, with close proximity to Wang et al. [10] and Zhang et al. [14], who showed a percentage of 97.0%, and 99.3% respectively using CBCT scans with a voxel size comparable to the current study. On the contrary, Scaravilli et al. [15], who used MDCT scans with 1.5 mm slice thickness observed a low prevalence of the canals. Also, the study performed by Yılmaz et al. [8] found 92% of MLC in a sample of 200 patients, and this might be due to a relatively smaller sample size compared to the present study.
Regarding the number of MLC in each examined case, the current findings were consistent with Rosano et al. [4], who recorded that the majority of cases with MLC in a sample of 60 dry mandibles were two canals, followed by the single canals, three canals, and cases with no canals; however, they showed no cases with four canals, and this might be attributed to the use of cadaver study. On the other hand, Kilic et al. [16] and Scaravilli et al. [15], using CT scans, found a high percentage of the single canals with the absence of cases showing four canals in the central incisor region. Also, Kung et al. [17] showed the same results as the aforementioned studies but found two cases with four canals out of 215 patients representing 1.0%.
In the present study, the classification proposed by Wang et al. [10] was used, dividing MLC based on their location regards the genial tubercle as 1.supra-spinosum, 2.intra-spinosum, and 3.infra-spinosum. The MLC was distributed as follows: a high percentage of the median canals (94.33%) were located in the supra-spinosum region, followed by 64.0% canals located in the infra-spinosum, and finally 19.67% canals located in the intra-spinosum region. The current findings were supported by the findings of G. Arun Kumar [18], Zhang et al. [14], and Yılmaz et al. [8], who performed their studies on CBCT scans using i-CAT, Planmeca, and Carestream machines.
Lustig et al. [19], who performed an ultrasound study, showed that the lingual canals with the average arterial diameter of 1.41 ± 0.34 mm may show profound bleeding upon injury, and based on the former study measurements were done on canals with a diameters larger than 1 mm. Regarding the diameter of the MLC, the current results were comparable to Yagmur et al. [20], with a study using spiral and cone beam CT scans, which identified the number of the MLC as 24.4% out of 639 of the studied cases. Also, Wang et al. [10], who identified 24.8% of the MLC out of 101 cases, using the same imaging protocol used in this study. On the other hand, Kung et al. [17] identified the MLC with a percentage higher than the current study showing 37.2% out of 215 cases in the Taiwanese population, with a significant difference between the males and the females which was disagreeing with the current results, and this difference might be related to the different racial type of the sample.
In the study by Wang et al. [10], using CBCT scans of Taiwanese patients, they identified the mean diameter of the (MLC) opening with 1.20 ± 0.25 mm, which was slightly smaller than the present results that showed the mean diameter with 1.68±1.27 mm. Also, the study performed by Moro et al. [21], in Japan, mentioned that the mean diameter of the MLC opening was 1.05±0.59 mm, which was still smaller than the reported measurements.
Regarding the mean diameter of the canal end, the study performed by Ahmed et al. [22], in the Egyptian population using CBCT scans from 50 patients, showed the mean diameter to be 0.5±0.2 mm, with proximity to the present study.
In the implant surgeries, the minimum length used for the fixture is about 6 mm below the crestal bone, with a 2 mm safety margin between the implant and the vital structure to avoid the tendency of bleeding, so a total length of 8 mm is needed for the alveolar crest before performing implant surgery. Alveolar ridge resorption increases after extraction of permanent teeth, so careful evaluation is essential before these kinds of surgeries [5, 19, 20]. Regarding the distance from the canal opening to the alveolar crest, the results of the current study were close to Yagmur et al. [20], who found the distance to be 18.33±5.45 mm in the total of 639 cases and showed a statistically significant difference between the males and the females, this agreement might be due to a large sample size gathered from different demographic areas all over the world including an Arab country. Also, Georges Aoun et al. [23] showed a significant difference in the distance between the lingual foramen and alveolar crest between the male and the female groups, which was similar to the current study. On the other hand, G. Arun Kumar [18] who carried out his study on the South Indian population showed no significant difference between both genders.
Measurements performed from the canal end to the buccal cortical plate were important to avoid any risk of bleeding during chin grafting procedure [21, 22]. Concerning the distance from the end of the canal to the buccal cortical plate, the current results were close to Kung et al. [17], with a distance of 5.44±1.36 mm, but their result showed a statistically significant difference between the female and male groups which was contradictory with the present study.
It was crucial to measure the bone thickness between the MLC and the inferior border of the mandible to exclude the possibility of hemorrhage with orthognathic surgeries [4, 22]. Regarding the distance from the canal opening to the inferior border of the mandible, Wang et al. [10] identified the distance to be 11.50±4.33 mm, which was close to the reported results, with a statistically non-significant difference between the males and the females agreeing with the current results. On the other hand, Rosano et al. [4] and Kung et al. [17] gave the following results: 12.2±3.0 mm and 12.68±3.02 mm respectively, which were slightly larger than the current results.
The current study of the Egyptian sub-population showed some limitations. Although all the measurements were taken with high reliability, the limited number of canals assessed makes further investigations of a larger group necessary which may provide accurate results, besides different demographic areas inside the Arab Republic of Egypt should be included to provide a more representative sample.
