Abstract
This retrospective study evaluated the presence, location, and diameter of the mandibular lingual canals in a Taiwanese population using cone beam computed tomography (CBCT), to help improve the safety of mandibular surgical procedures. A total of 101 patients (46 men and 55 women), with a mean age of 55 years, were enrolled. Cross-sectional CBCT images of the mandible were used to define the orifice and diameter of each lingual canal detected. The relevance of all data for both sexes was assessed and analyzed statistically using non-paired t -tests. The canals were categorized as median (MLC) and lateral lingual canals (LLC) based on the position of the mandible. The midline of the symphysis showed the highest frequency of lingual canals (97.0%), and all patients exhibited at least one lingual perforating bone canal in the mandible. The lingual canal diameter ranged from 0.25 to 1.90 mm (mean 0.61 mm) in the midline region and from 0.25 to 1.60 mm (mean 0.58 mm) in the lateral region. Significant differences in diameter were observed between the sexes in the MLC and LLC groups (men > women). The results suggest that mandibular lingual vascular canals are common and detected regularly using CBCT.
Various surgical procedures are performed in the anterior region of the mandible, and such surgeries are often considered simple and safe. However, relevant safety recommendations are not based on knowledge of the position or the course of related anatomical landmarks. The use of implants and grafts for mandibular rehabilitation has also increased the incidence of postoperative complaints. Previous studies on both haemorrhagic and neurosensory complications in the anterior mandible have demonstrated that the presence of neurovascular structures should be assessed carefully prior to performing mandibular surgery. A study of the literature for the period 1986–2010 identified 19 reported cases of life-threatening bleeding associated with dental implants. All of these cases occurred in the interforaminal region, particularly in the canine region (10 of 19) ; the resolution of haemorrhage generally required a surgical intervention for ligation of the bleeding vessel and evacuation of the haematoma.
Most cadaver studies have described the median lingual canal (MLC) as a perforating branch of the sublingual artery, and in previous anatomical studies, investigators have focused on its presence, location, and diameter. However, only a few studies have focused on the lateral lingual canal (LLC). To reduce the probability of a fatal complication, further anatomical study of the MLC and LLC with regard to the larger-diameter canals should be emphasized. In the current study, the presence and location of the mandibular lingual canals and larger-diameter vessels in the lingual surface of the mandible were investigated.
The conventional, two-dimensional pre-surgical assessment using panoramic and peri-apical radiographs, often fails to show these structures. Cone beam computed tomography (CBCT) has proved to be an excellent procedure for characterizing the anatomy and dental-related abnormalities of the jaw. Routine CBCT examinations are performed widely before endosseous dental implant surgery. The bony canals in the lingual surface of the mandible can be observed clearly from the multiple perspectives of the CBCT images ( Figs. 1 and 2 ).
The objectives of this retrospective study were to evaluate the presence, location, and diameter of the MLCs and LLCs in CBCT images obtained from the Taiwanese population, with particular focus on the larger-diameter canals. The results are discussed in the context of a comprehensive literature review.
Materials and methods
Dental CBCT scans of the mandible were recorded for radiographic diagnosis or pre-implantation evaluation in the dental department of the study hospital between 2009 and 2013. All patients aged ≥18 years were included in this study; those with an edentulous ridge or a bone pathology in the mandibular region were excluded. All CBCT images were obtained using a standard protocol (i-CAT Cone Beam 3D Dental Imaging System; Imaging Sciences International, Hatfield, PA, USA). The acquisition parameters were as follows: pixel size 0.25 mm, slice thickness 0.25 mm, tube voltage 120 kVp, tube current 36.12 mA/s, and acquisition period 40 s. Reformatted cross-sectional images were obtained using the dental CT software (i-CAT 3D Dental Imaging System) and presented as real-size images through a thin-film transistor monitor with a high resolution of 1600 × 1200. All of the data were analyzed retrospectively.
A total of 101 subjects were collected through random sampling; 46 were men and 55 were women, and their average age was 55 years (range 27–77 years). Cross-sectional CBCT images of the mandible were used to define the orifice and diameter of each lingual canal detected. The MLC group was further categorized into three regional subgroups: supra-spinosum, inter-spinosum, and infra-spinosum. The LLC group was also categorized into three regional subgroups: molar, premolar, and incisor–canine region (except for the midline region). In addition, the mandibular height in the midline region (AB), the distance from the lower border of the mandible to the most convex point of the mental spine (BD), and the distance from the lower border of the mandible to the upper margin of the lingual canals (BC) were measured ( Figs. 3 and 4 ). The lingual canals with a diameter of ≥1 mm were recorded and evaluated.
The relevance of all data for both sexes was assessed and analyzed statistically using non-paired t -tests. A P -value of <0.05 was considered statistically significant.
Results
The canals were categorized into two groups: MLC and LLC. The midline of the symphysis exhibited the highest frequency of lingual canals (97.0%), and all of the patients examined showed at least one lingual perforating bone canal in the mandible. The AB and BD measurements ranged from 23.25 to 38.25 mm (mean ± standard deviation 31.08 ± 2.97 mm) and from 7.25 to 21.25 mm (mean 11.75 ± 1.71 mm), respectively.
In the MLC group, 204 lingual canals were detected in the 101 study subjects, with 0–4 branches (mean 2.01 ± 0.83) detected for each patient. Moreover, 44 mandibles (43.6%) exhibited two branches, 28 mandibles (27.7%) exhibited three branches, and 24 mandibles (23.8%) exhibited only a single branch at the lingual side of the mandibular midline. Furthermore, only two mandibles (2.0%) showed four branches at the mandibular midline ( Table 1 ).
| MLC (%) | LLC (%) | |
|---|---|---|
| No canal | 3 (3.0) | 1 (1.0) |
| 1 canal | 24 (23.8) | 9 (8.9) |
| 2 canals | 44 (43.6) | 30 (29.7) |
| 3 canals | 28 (27.7) | 25 (24.8) |
| 4 canals | 2 (2.0) | 27 (26.7) |
| 5 canals | 0 (0) | 7 (6.9) |
| 6 canals | 0 (0) | 2 (2.0) |
| Total | 101 (100) | 101 (100) |
The MLC diameter ranged from 0.25 to 1.90 mm (mean 0.61 ± 0.33 mm). The mean diameters among the supra-spinosum, inter-spinosum, and infra-spinosum subgroups were 0.71 ± 0.36 mm, 0.75 ± 0.43 mm, and 0.49 ± 0.34 mm, respectively. The BC measurements ranged from 1.5 to 25.25 mm (mean 10.2 ± 5.24 mm). The mean distance of BC among the supra-spinosum, inter-spinosum, and infra-spinosum subgroups were 15.02 ± 2.05 mm, 12.28 ± 1.99 mm, and 5.25 ± 2.68 mm, respectively. The other parameters evaluated for these three subgroups are presented in Table 2 .
| Measurement | MLC | MLC | ||
|---|---|---|---|---|
| Supra-spinosum | Inter-spinosum | Infra-spinosum | ||
| Frequency (%) | 97.0 (98/101) | 85.1 (86/101) a | 18.8 (19/101) | 72.3 (73/101) b |
| Occurrence rate (%) | – | 44.1 (90/204) | 9.3 (19/204) | 46.6 (95/204) |
| Mean diameter (mm) | 0.61 ± 0.33 | 0.71 ± 0.36 | 0.75 ± 0.43 | 0.49 ± 0.34 |
| Range (mm) | 0.25–1.90 | 0.25–1.90 | 0.25–1.75 | 0.25–1.27 |
| Mean distance of BC c (mm) | 10.2 ± 5.24 | 15.02 ± 2.05 | 12.28 ± 1.99 | 5.25 ± 2.68 |
| Range (mm) | 1.50–25.25 | 11.75–25.25 | 8.50–15.75 | 1.50–12.75 |
a Four of the 101 subjects (4.0%) had two supra-spinosum MLCs.
b Twenty-two of the 101 subjects (21.8%) had two infra-spinosum MLCs.
c BC: the distance from the lower border of the mandible to the upper margin of the lingual canal.
In the LLC group, 299 lingual canals were detected in the 101 subjects (right side n = 145, left side n = 154), with 0–6 branches (mean 2.95 ± 1.21) detected for each patient ( Table 1 ). The incisor–canine region exhibited the highest occurrence rate of LLC (223/299, 74.6%), whereas the molar region showed the lowest occurrence rate (17/299, 5.7%).
The LLC diameter was slightly smaller than the MLC diameter, with a diameter of 0.25–1.60 mm (mean 0.58 ± 0.30 mm). The BC measurements ranged from 0.5 to 35.25 mm (mean 20.72 ± 10.39 mm). The data of the three LLC subgroups are presented in Table 3 .
| Measurement | LLC | LLC (right side n = 145, left side n = 154) | ||
|---|---|---|---|---|
| Incisor–canine | Premolar | Molar | ||
| Frequency (%) | 99.0 (100/101) | 93.1 (94/101) | 41.6 (42/101) | 14.9 (15/101) |
| Occurrence rate (%) | – | 74.6 (223/299) | 19.7 (59/299) | 5.7 (17/299) |
| Mean diameter (mm) | 0.58 ± 0.30 | 0.56 ± 0.29 | 0.66 ± 0.30 | 0.60 ± 0.37 |
| Range (mm) | 0.25–1.60 | 0.25–1.46 | 0.25–1.60 | 0.25–1.50 |
| Mean distance of BC a (mm) | 20.72 ± 10.39 | 24.33 ± 8.99 | 9.50 ± 5.79 | 10.31 ± 4.36 |
| Range (mm) | 0.25–35.25 | 0.50–35.25 | 0.75–28.00 | 3.00–18.25 |
a BC: the distance from the lower border of the mandible to the upper margin of the lingual canal.
In this study, the occurrence rate of larger canals (those with a diameter ≥1 mm) was 13.2% (27/204) in the MLC group and 13.4% (40/299) in the LLC group ( Tables 4 and 5 ). In the MLC group, the inter-spinosum region exhibited the highest occurrence rate of larger canals (31.6%, 6/19); the mean diameter of these larger canals was 1.25 ± 0.29 mm, and the mean distance of BC was 12.21 ± 1.55 mm. By contrast, in the LLC group, the premolar region showed the highest occurrence rate of larger canals (22.0%, 13/59), with a mean diameter of 1.12 ± 0.17 mm and mean distance of BC of 7.69 ± 1.29 mm.
| Measurement | MLC ≥1 mm | MLC ≥1 mm | ||
|---|---|---|---|---|
| Supra-spinosum | Inter-spinosum | Infra-spinosum | ||
| Frequency (%) | 24.8 (25/101) | 11.9 (12/101) | 5.9 (6/101) | 8.9 (9/101) |
| Occurrence rate (%) | 13.2 (27/204) | 13.3 (12/90) | 31.6 (6/19) | 9.5 (9/95) |
| Mean diameter (mm) | 1.20 ± 0.25 | 1.21 ± 0.28 | 1.25 ± 0.29 | 1.15 ± 0.12 |
| Range (mm) | 1.00–1.90 | 1.00–1.90 | 1.00–1.75 | 1.00–1.27 |
| Mean distance of BC a (mm) | 11.50 ± 4.33 | 14.79 ± 1.54 | 12.21 ± 1.55 | 6.64 ± 3.62 |
| Range (mm) | 2.25–17.75 | 11.75–17.75 | 9.50–14.25 | 2.75–12.75 |
a BC: the distance from the lower border of the mandible to the upper margin of the lingual canal.
| Measurement | LLC ≥1 mm | LLC ≥1 mm | ||
|---|---|---|---|---|
| Incisor–canine | Premolar | Molar | ||
| Frequency (%) | 31.7 (32/101) | 21.8 (22/101) | 10.9 (11/101) | 3.0 (3/101) |
| Occurrence rate (%) | 13.4 (40/299) | 10.8 (24/223) | 22.0 (13/59) | 17.6 (3/17) |
| Mean diameter (mm) | 1.16 ± 0.15 | 1.18 ± 0.12 | 1.12 ± 0.17 | 1.25 ± 0.20 |
| Range (mm) | 1.00–1.60 | 1.00–1.46 | 1.00–1.60 | 1.00–1.50 |
| Mean distance of BC a (mm) | 19.81 ± 11.01 | 26.83 ± 7.29 | 7.69 ± 1.29 | 8.25 ± 1.34 |
| Range (mm) | 6.25–34.50 | 8.25–34.50 | 6.25–10.00 | 6.50–9.75 |
a BC: the distance from the lower border of the mandible to the upper margin of the lingual canal.
Table 6 presents the correlation between the aforementioned measurements and patient sex. In the MLC group, a statistically significant difference between men and women was observed for the lingual canal diameter (men > women, P -value = 0.034), but no correlation was observed among the three subgroups. In the LLC group, a statistically significant sex difference was observed for the lingual canal diameter (men > women, P -value = 0.002), but no correlation was observed for the molar region subgroup. Moreover, men exhibited a significantly longer distance of BC in the supra-spinosum ( P -value = 0.0005) and incisor–canine ( P -value = 0.027) regions. Furthermore, the AB and BD measurements indicated a significant correlation with sex (men > women), with respective P -values of 0.005 and 0.043.
