Existing studies have proved that the MC, mental foramen, and lingual canal are anatomical structures that should be carefully evaluated before oral treatments, such as mandible surgeries, root canal treatments, apical surgeries, and tooth extractions. In this retrospective study, we aimed to further improve the understanding of the important anatomical structures in the mandible by jointly studying the MC, MF, LCS, and BCAT.

Previous autopsy and CBCT studies have demonstrated that mandibular incisor tubes occur commonly; however, most extend between the first premolars and fangs and rarely reach the area below the central incisors [7, 8]. This occurs owing to the large difference in the position of the third molar within the mandible. Therefore, this study measured the MC and its extension, from the second molar region to the cusp area. Additionally, the anatomical parameters of the MC recorded the observation angle in the long axis of the tooth, and this angle is more conducive to measuring the distance between the MC and the tooth root. Mardinger et al. reported that the diameter range of the mandibular incisor tube was 0.48–2.9 mm. When the tube wall was unclear, the measurement data on the mandibular duct and its extension pipe were recorded as 0 in this study; therefore, the diameter of the head and tail directions of the tube in the cusp area were as follows: 0–2.34 mm on the right and 0–1.54 mm on the left, where the minimum recorded values were 0.45 mm and 0.55 mm on the right and left, respectively. The diameter range was 0.45–2.34 mm, which is close to the measurements reported by Mardinger. According to Hur et al. [9], the diameter in the first and second molars were 3.31 ± 0.8 and 3.1 ± 0.6 mm (range 2.1, 4.9 mm, and 2.4, 4.3 mm), respectively. In this study, the diameter in the first and second molars on the right was 2.40 ± 0.45 mm and 2.70 ± 0.55 mm, respectively, and 2.51 ± 0.44 mm and 2.69 ± 0.48 mm, respectively on the left.

Mandibular lingual foramen anomalies can lead to the death of the patient. Katakami et al. [6] reported the anastomosis rate of the lower lingual canal and MC and its extension canals, such as the mental foramen and anterior ring, as follows: the anastomosis rate of the first premolar (1/155) and second premolar (24/155), the first molar (5/155), the third molar (1/155), and no anastomosis of the lingual canal with the MC was observed in the rest of the teeth. According to the corresponding tooth position of the LCS opening in each tooth position recorded on the mandible, there were anastomotic central incisors (1/229), canines (1/229), first premolars (2/229), second premolars (17/229), first molars (35/229), and second molars (2/229), and no anastomosis was observed for the rest of the teeth. Additionally, this study found that the anastomosis of the LCS and the MC can be tracked more easily and accurately through the method illustrated in Fig. 4. Therefore, we can quickly and accurately observe the opening position and anastomotic position of LCS and MC when we use the conventional method to observe the distribution of the LCS, as illustrated in Fig. 4, and further avoid the LCS damage to the side tubes.

According to the observation of this experimental group, the BCAT is a common anatomical structure in the mandible; however, there are few CBCT imaging studies on the BCAT. In this study, the MC and its surrounding canals were determined. Simultaneously, to verify our ideas, we observed the BCAT from multiple angles through DVR and 3D layers and adjusted the viewing angle to verify the root canal and the authenticity of the presence of the BCAT. From Table 4, it can be observed that the BACT not only has a high occurrence rate in the canine area, premolar area, and molar areas but also connects with the MC. Owing to the differences in viewing angles at the 3D and DVR levels, the connection recorded in this test is direct or has obvious evidence of a connection. Wilbrand et al. [10] and Lindgre et al. [11] reported that calcium hydroxide enters the MC during root canal treatment, and a series of reactions lead to skin damage. Among them, the root tip of the former affected tooth has a significant distance from the MC. Hur et al. [9] reported that the MC has branches connected with the roots of the mandibular teeth. We previously suspected that the subapical bone canal may be the branch of the MC going to the apex of the tooth root; however, some of the BACT have a larger diameter, and the BACT is connected to the root tip of the tooth but not to the MC. The connection rate of pipes did not exceed 53%, without sufficient evidence to prove the appeal conjecture. Further research with imaging equipment such as magnetic resonance imaging, which facilitates visualization of soft tissues, may be required.

In this study, CBCT was utilized to examine the anatomical structure of the mandible from various angles. This approach enhanced our understanding of the mandibular anatomy. Additionally, it revealed the significance of unconventional observation methods in identifying frequently overlooked structures. The findings of this experiment emphasize the need for careful observation and identification of the MC and LCS prior to mandibular surgery, implant surgery, and root canal treatment. Moreover, the discovery of BACT holds promise in advancing our comprehension of the mandibular canal. This knowledge can potentially contribute to the development of AI-assisted diagnosis for jaw anatomy in the future.