Labial and Mental Foramina of the Mandible: A Cone Beam Computed Tomography Study

Complications associated with symphyseal bone grafts include intraoperative bleeding, wound dehiscence, mental nerve injury, pulp canal obliteration, and a loss of pulp sensitivity in the anterior lower teeth [2,3]. To avoid these complications, total knowledge of the bone anatomy is a must [4]. Before any surgical procedures in the mandibular premolar area, the anatomy of the mental foramen (MF) and canal, as well as the presence of accessory mental foramina (AMF) should carefully be investigated [5].


INTRODUCTION
Many complications are associated with surgical interventions in the anterior region of the mandible. Sensory disturbances of the mental nerve after dental implant placement have been reported. Loss of lip sensation may further be complicated by lip biting, impaired speech, and diminished salivary retention, which have a significant impact on patient's lifestyle [1].
Complications associated with symphyseal bone grafts include intraoperative bleeding, wound dehiscence, mental nerve injury, pulp canal obliteration, and a loss of pulp sensitivity in the anterior lower teeth [2,3]. To avoid these complications, total knowledge of the bone anatomy is a must [4]. Before any surgical procedures in the mandibular premolar area, the anatomy of the mental foramen (MF) and canal, as well as the presence of accessory mental foramina (AMF) should carefully be investigated [5].
CBCT is used for diagnostic purposes in oral and maxillofacial surgery and endodontics, particularly for its low cost, easy accessibility and low radiation [6,7]. It was considered to have better accuracy and diagnostic value than periapical films in the detection of interradicular periodontal bone defects [8]. Detailed information was obtained about dentoalveolar structures with CBCT [9]. CBCT is capable of providing submillimetre resolution in images with short scanning time [10]. Cone beam computed tomography (CBCT) was used for investigating structures inside bone without dissection. The lingual foramina and canals are from the structures studied by 2 DOI: https://doi.org/10.35702/dent.10001 many investigators [11,12].
Many foramina are present on the lingual aspect of the anterior mandible which may have variations in number and position. It is typically visualized as a single round radiolucent canal with a well-defined opaque border [11,13]. Actually, blood vessels and nerves running through these lingual canals often generate anastomosis with neurovascular structures from the mandibular canal and its branches [14].
The median perforating canal (MPC) of the mandible is the canal connecting the median lingual foramen (MLF) and the labial foramen (LaF) [15]. It was previously concluded that the MPC of the mandible, rarely found in humans, is seen in all specimens in Macaca fascicularis because they have no mental protuberance [16]. A high prevalence of these structures was found in many reports [11,12,17,18].
The labial extensions of the lingual foramina and canals were studied by many investigators [17,19]. CT images were used for the identification of the intrabony canals and for the localization of canalicular communications connecting the labial and lingual mandibular plates. These communications mainly appeared as a crossing of the lateral lingual with the incisive canal, but also as an extension of the median lingual canal to the labial plate [19]. MPC was reported in one cadaveric study of the human mandible [15].
The MF as an important mandibular anatomical landmark is located bilaterally. Its location, size, and shape have been studied by many investigators [20][21][22]. In the current literature AMF, mandibular incisive canal, and buccal foramina (BF) are frequently documented in various species and ancient skulls in addition to living subjects [23][24][25]. CBCT analysis for labial and buccal mandibular foramina, however, has not been widely evaluated or used in clinical dentistry yet. The term labial foramen is not used up till now for describing foramina on the labial surface of anterior mandible. The term additional foramina is used by some investigators in describing foramina on the labial and lingual surface of anterior mandible [25]. There is a need to establish a well-defined profile for the anatomical characteristics of labial foramina in CBCT. Therefore, the aim of this study was to assess the occurrence and anatomical features of mental, accessory mental and labial foramina and their bony canals in inter foraminal region of the mandible using CBCT.

RESULTS
A total of 390 foramina on the outer side of the mandible were recorded from coronal, sagittal, and axial planes of 104 CBCT scans. These foramina were assigned into 3 main categories mental, accessory mental, and labial foramina (Table 1).
Mental foramina were found to be present in both sides of the mandible in all studied scans (100%). Seventy three patients (70%) showed at least one more foramen other than the bilateral mental foramina. were found to be smaller than mental foramina (Figure 1).

Variations in size of accessory mental foramina and location in
relation to mental foramina could be seen in many cases. Nine cases showed bilateral accessory mental foramina and those were seen in coronal (Figure 2), axial (Figure 3), and sagittal planes according to their locations.       include the MF, the AMF, and LaF or buccal foramina [31][32][33].
In this study, identified defects of the buccal cortical plate were classified as MF, AMF and LaF. At least one MF was found in both sides in all the studied scans (100%). These results are in agreement with many previous studies [5,34,35]. We considered AMF as a foramen connecting with mandibular canal and smaller than MF. In our sample of Egyptian cases, there was a relatively high incidence of AMF. Knowledge of the anatomical variations of neurovascular canals is necessary to preserve these structures during surgical procedures of mandible and preventing complications. To the best of our knowledge, this study was the first to investigate the radiographic anatomy of labial foramina of the anterior mandible in Egyptian population.

CONCLUSION
The results of this study showed that mandibular labial foramina and bony canals are frequently present in mandibles with wide variations in CBCT. In the lateral to symphysis, the incidence of foramina was the highest in this region.
The prevalence of accessory mental foramina in Egyptian population is relatively high. These findings should be considered in diagnosis and planning for anesthesia and surgery in the lower anterior region to prevent possible complications. A preoperative thorough investigation of the symphyseal and parasymphyseal regions using CBCT is highly recommended when targeting surgical interventions in these areas.