Introduction
Nutrient canals (NCs) contain blood vessels and nerves and most commonly occur in the anterior mandible [1,2]. NCs are derived from the incisive branch of the inferior neurovascular bundles, which supply teeth and gingival tissues of the anterior mandible [3,4]. NCs are visible in approximately 5%–40% of periapical radiographs [5] and 94.3% of computed tomography (CT) imaging [6]. Damage to NCs during surgery can result in hemorrhage or postoperative paresthesia of the associated region. This has been reported in dental implant treatment [6], tooth extraction [6], and fracture of the anterior mandibular region [7–9]. Several studies have reported certain imaging findings associated with NCs in adults observed on periapical radiographs, cone beam CT (CBCT), and helical CT [10–12] and children [10]. CBCT has a lower radiation dose than multidetector low computed tomography [13], which is beneficial for patients. However, the literature regarding normal CBCT findings of anterior mandibular NCs in pediatric patients is insufficient.
Better knowledge of NCs on CBCT would allow better clinical management of mandibular fractures, tooth extraction, or other dental surgeries of the anterior mandible, particularly in pediatric patients. The purpose of this study was to assess the normal imaging findings of mandibular NCs using CBCT images, including canal prevalence, number, and size.
Materials and Methods
This retrospective study was approved by the Ethics Committee on Epidemiological Studies at Kagoshima University (200239Epi ver.1).
Patients
Patients who underwent CBCT imaging for the evaluation of maxillary and mandibular diseases as outpatients at Kagoshima University Hospital (Kagoshima, Japan) between April 2018 and November 2020 were enrolled. Data from patients younger than 18 years with mandibular CBCT images were included in the retrospective analysis. Patients were excluded if the images included tumors and cysts in the mandible, had poor or absent mandibular visualization, or contained metal artifacts precluding visualization of the mandible.
Imaging protocol
CBCT images were obtained using a 3D Accutimo F17+ Promax 3D (Morita, Tokyo, Japan) CBCT unit, which automatically sets the appropriate exposure parameters for each patient with the following parameters: tube voltage, 90 Kv; tube current, 7 mA. The exposure volume was set to 30 mm in diameter and 60 mm in height, and the voxel size was 0.2 × 0.2 × 0.2 mm. The acquired images were processed using the Anatomage software (Santa Clara, CA).
Image analysis
Initially, NCs running through the lingual cortical bone of the anterior mandible to the alveolar process were located on CBCT axial images. Parameters, including canal prevalence, number, and size (mesial-distal and buccal-lingual diameters), were measured on CBCT axial images (Fig. 1). We have used 21.3-inch light-emitting diode monitor (EIZO; Ishikawa, Japan) under dim lighting condition. All radiologists viewed the images 1.5 feet from the monitor.
All images were retrospectively evaluated by two oral and maxillofacial radiologists with >10 years of experience. Prior to the study, 20 CBCT images that were not included in this study were used for observer calibration. They independently observed CBCT axial images on the monitor. After an interval of 2 weeks, the presence or absence of NCs, number, and diameter of the NCs were evaluated in 30 randomly selected patients to statistically evaluate intra- and inter-observer reliability.
Statistical analyses
The significance of gender-related differences in the mean number of NCs was statistically evaluated using the Mann-Whitney U test and the Steel-Dwass test. The significance of age-related differences in size was evaluated using the Pearson product-moment correlation coefficient. A p-value less than 0.05 was set to indicate statistical significance. Intra- and inter-observer reliability was evaluated using the intraclass correlation coefficient (ICC). Statistical tests were performed using the SPSS software version 20 for Windows (SPSS, Chicago, IL).
Results
Patient characteristics
During the observation period, 500 patients were evaluated with maxillary and mandibular CBCT images. Of these, images from 340 consecutive pediatric patients were included in our analysis: 202 males and 138 females. Age ranged from 3-18 years [mean 10.4; standard deviation (SD), 3.3]. The number of patients in each age group is shown in Table 1.
Intra and inter observer reliability
Intra-observer reliabilities for the presence or absence of NC were 0.9 and 0.87, respectively.
The intra-observer reliabilities for the number of NCs between the two radiologists were 0.81 and 0.80. The intra-observer reliabilities for the size of the NCs between the two radiologists were 0.77 and 0.79. The inter-observer reliability was 0.83.
Prevalence, number, and size
Canal prevalence
Of the 340 cases, 280 (82.4%) had NCs in the anterior region of the mandible.
The mean number of NCs in the anterior mandible
The mean number of NCs in males ranged from 0 to 1.88, with a mean of 1.39. The mean number of NCs in females ranged from 1.11 to 2, with a mean of 1.49. The mean number of NCs (total and by age) was analyzed for sex-specific differences (Table 1). The mean number of NCs (total and by age) was analyzed for age-related differences. No significant age- or sex-related differences were observed in the mean number of NCs (Fig. 2).
Size of the NCs
In total, 279 NCs in males and 205 NCs in females were analyzed for NC size (Fig. 3). The mesial-distal diameters of NCs (mean ± SD, 0.67 ± 0.19 mm; range, 0.2-1.21 mm) and buccal-lingual diameters (mean ± SD, 0.61 ± 0.19 mm; range, 0.15-1.6 mm) of NCs in males are shown in Figure 3a and b. The mesial-distal (mean ± SD, 0.62 ± 0.19 mm; range, 0.26-1.15 mm) and buccal-lingual diameters (mean ± SD, 0.57 ± 0.17 mm; range, 0.13-1.1 mm) of NCs in females are shown in Figure 3c and d. There were no significant age-related differences in the size of NCs between males and females.
Table 1.
The mean number of NCs (by age and total) for gender specific differences.
| Male | Female | ||||||
|---|---|---|---|---|---|---|---|
| Mean | SD | The number of patients | Mean | SD | The number of patients | p values | |
| 3 years | 0 | - | 0 | 2 | 0.83 | 1 | - |
| 4 years | 0.8 | 0.83 | 5 | 2 | - | 2 | 0.12 |
| 5 years | 0.8 | 1.1 | 5 | 1.2 | 1.1 | 5 | 0.55 |
| 6 years | 1.67 | 0.52 | 6 | 1.75 | 0.5 | 4 | 0.79 |
| 7 years | 0.96 | 0.92 | 26 | 1.14 | 1.07 | 7 | 0.65 |
| 8 years | 1.53 | 0.81 | 26 | 1.25 | 0.75 | 12 | 0.29 |
| 9 years | 1.35 | 1.35 | 23 | 1.11 | 0.69 | 17 | 0.28 |
| 10 years | 1.31 | 0.71 | 41 | 1.5 | 1.04 | 30 | 0.62 |
| 11 years | 1.58 | 0.9 | 19 | 1.62 | 0.76 | 13 | 1 |
| 12 years | 1.5 | 1.02 | 14 | 1.53 | 0.63 | 15 | 1 |
| 13 years | 1.22 | 0.58 | 3 | 2 | - | 1 | 0.32 |
| 14 years | 1.7 | 0.67 | 10 | 1.33 | 1.63 | 6 | 0.41 |
| 15 years | 1.67 | 0.87 | 9 | 1.86 | 0.38 | 7 | 0.65 |
| 16 years | 1.75 | 0.5 | 4 | 2 | 0 | 9 | 0.13 |
| 17 years | 1.88 | 0.35 | 8 | 1.67 | 0.58 | 3 | 0.44 |
| 18 years | 1.67 | 0.58 | 3 | 1.5 | 0.55 | 6 | 0.65 |
| Total | 1.39 | 0.84 | 202 | 1.49 | 0.84 | 138 | 0.43 |
Figure 1.
CBCT axial images of NCs in the anterior mandible in 10-year-old male patients. NCs (a, white arrows) appear between the central and lateral incisors. Figure 1b shows the measurement of the buccal-lingual diameter (b, vertical white double arrow) and mesial-distal diameter of the NCs (b, horizontal white double arrow) on an axial CBCT image.
Discussion
NCs are derived from the incisive branch of the mandibular canal, supplying teeth and gingival tissue in the anterior region of the mandible [2]. NCs have also been called inter dental canals, circulatory canals, vascular canals, or inter dental canals [2]. Gupta et al. [10] reported that NCs have a wide age distribution ranging from 11 to 70 years, and is commonly seen in both males and females. They concluded that a significant correlation was observed between sex and NCs, whereas no significant correlation existed between age and the presence of NCs. Our results showed no sex or age-related differences, which is in accordance with Gupta et al. [10].
Figure 2.
The mean number of NCs for age related differences. There were no significant age-related differences in the mean number of NCs.
Figure 3.
Size of the NCs. The mesial-distal diameters of the NCs (Fig. 3a) and buccal-lingual diameters (Fig. 3b) of the NCs in males. Mesial-distal (Fig. 3c) and buccal-lingual diameters (Fig. 3d) of the NCs in females. There were no significant age-related differences in the size of the NCs between males and females.
Ogawa et al. [11] investigated 105 patients aged >20 years and concluded that the identification of NCs on CBCT images may be useful during the harvesting of bone blocks or placement of endosseous implants in the anterior region of the mandible. de Oliveira Júnior et al. [12] analyzed Brazilians aged 25–75 years using CT and concluded that morphometric findings may help clarify the detailed anatomy of the mandibular canal and its topographical relationships for the planning of dental implantation. Damage to the NC region may cause sensory abnormalities or act as a potentially fatal source of major bleeding [10–12]. In pediatric patients, a fracture of the mandibular anterior region [7–9] may cause damage to the NC, and can result in severe hemorrhage.
Our results showed that 82.4% of the patients had NCs in the anterior region of the mandible. Kawashima et al. [6] reported anterior mandibular NCs in 94.3%, which was higher than the prevalence in our study. We believe that this difference may be characteristic findings of pediatric patients.
No significant age- or sex-related differences were observed in the mean number of NCs. Gupta et al. [10] reported that NCs are commonly observed in females and males. Kawashima et al. [6] reported no sex-related difference in the mean number of NCs between males and females. Gupta et al. [10] showed that a significant correlation was seen between sex and NCs, whereas no significant correlation existed between age and the number of NCs. The mean number of NCs does not change with age or gender in pediatrics because of their role in supplying nutrients to the anterior region of the mandible; they are necessary at all ages and thus do not significantly fluctuate throughout aging. However, the mean number of NCs was smaller than that reported previously. We believe that this difference was due to the age distribution of the patients in each study. Further research is necessary to verify these results.
Our results revealed that the size of the NCs varied from 0.13 to 1.21 mm and the mean diameter of the NCs varied from 0.57 to 0.67 mm. Kawashima et al. [6] reported that the size of the NCs between the central and lateral incisors varied from 0.4 to 1.8 mm and the mean diameter of the NCs varied from 0.9 from 1.0 mm. Our results showed that the mean diameter of the NCs was narrower than that reported previously. We believe that these results may be due to body size differences as previous studies included adults, and our study population was children. There were no significant age-related differences in the mean size of NCs in our study. We believe that the size of NCs does not change throughout childhood and adolescence.
This study had some limitations. It was a retrospective study. Additionally, there were varying numbers of patients in each age group, which may have affected the results. Therefore, additional studies are required to verify these findings.
Conclusion
This is the first study to describe the normal CBCT findings of anterior mandibular NCs in pediatric patients. Using CBCT images, we showed that there are no sex or age-related differences in the prevalence, number, or size of anterior mandibular NCs in pediatric patients. Although CBCT is safer, clinicians should choose an appropriate imaging modality based on specific cases. However, normal NC findings on CBCT can lead to better preoperative awareness and reduce complications in pediatric patients.
Declaration of competing interest
The authors declare no conflicts of interest directly relevant to the content of this article.
