The mental foramen is a well-known cranial anatomical structure located bilaterally on the mandible along the buccal cortical plate. It is located approximately between the roots of the premolars in the anteroposterior dimension, and its superior inferior level varies over the alveolar height in each individual. The location of the mental foramen is critical when planning surgical interventions in the area. The accessory mental foramen can be well detected in the three-dimensional (3D) imaging method, especially in 3D images. It can still be appreciated in two-dimensional (2D) imaging modalities such as panoramic images; However, sometimes it can be confused with periapical pathology, especially in cases where caries is present. The 3D imaging modality plays an important role in determining this anatomical difference, and therefore, it is important to evaluate any surgical site in three dimensions prior to surgical intervention.
The mental foramen is located bilaterally on the mandible along the buccal cortical plate. It is located approximately between the roots of the premolars in the anteroposterior dimension, and its superior inferior level varies over the alveolar elevation in each individual [1-3]. The mental foramen is generally a single entity located on each side of the mandible and is the anterior border of the mandibular canal. It conveys the terminal branch of the inferior alveolar nerve, the mental nerve, and its corresponding vessels, the mental artery and mental vein . The mental nerve supplies the lower lip, buccal mucosa, and ventral chin skin to the foramen .
The location of the mental foramen is critical when planning surgical interventions in the area. In cases of implantation planning, a site for the mental foramen is essential, especially when there is resorption of the alveolar septum, which may result in a higher site for the foramen. In cases where osteotomy is planned in the area, it is critical to evaluate the position of the foramen to avoid injuries of the nervous system within the foramen.
The extra mental hole can be well detected in the 3D imaging method, especially in three-dimensional (3D) volume images. It can be appreciated in two-dimensional (2D) imaging modalities such as panoramic images; However, sometimes it can be confused with periapical pathology, especially in cases where there is caries in the teeth .
In our case report, we present a unique case of a triangular foramen foramen, which was discovered incidentally when evaluating cone beam computed tomography (CBCT) for implant planning in the region.
The CBCT scan of a 76-year-old male patient was sent for radiographic assessment of implant planning at the 19th tooth superposition. The CBCT scan had a limited field of view extending from teeth 18–20. A CBCT scan was acquired using a Carestream (Canada) CS9600 with a voxel size resolution of 0.1 mm.
Initial evaluation of the macro-anatomy was performed using 3D volumetric reconstruction, which showed three mental holes in the recaptured part of the left body of the mandible (Fig. 1). CBCT scan was further evaluated in coronal, axial and sagittal cross-sections; These planar reconstructions showed multiple well-defined oval openings on the buccal cortical lamina in continuation of the inferior alveolar duct. These cross-sections were then analyzed in several serial cross-sections for the detailed proximity of these multiple holes (illustrations). 2–3).
The three holes were placed apically on the root of the 20 tooth a few millimeters apart (Fig 1). The superior foramen was approximately 1.63 mm in the anteroposterior direction, the intermediate foramen was 3.27 mm in the anteroposterior direction, and the inferior foramen was 3.20 mm in the anteroposterior direction (Fig.). 4).
Additional 2D radiographs, such as panoramic and periapical radiographs, that were available in the patient’s record were evaluated for comparison; These multiple holes were not appreciated on the two-dimensional radiographs (Fig 5).
Several studies have been published in the literature demonstrating the existence of the extra mental foramen [5-8]. This accessory mental foramen has been coined by many different terms in the literature, such as additional mental foramen, multiple mental foramen, bifurcated or double mental foramen, or even triple mental foramen. [4,8-10]. A comprehensive 3D evaluation of important anatomical structures is important whenever any surgical intervention is planned in the area to avoid injury to these structures and subsequent potential complications.
The presence of accessory mental foramen is rare, with its prevalence in the literature showing a varied presentation; It is said to be between 5% and 30%. [11-15].
Although two-dimensional radiographs play a major role in the initial survey of the area of interest, they lack the actual perception of proximity as well as the true identification of the entity in the area. In our case, the multiple left-sided mental foramen was not visualized in the panoramic radiograph. Because the mental foramen may be oblique, it may not be clearly visualized due to overlaying of normal bony trabeculae or distortion of structures due to technical errors . CBCT imaging was able to provide the exact location of all holes and is essential for optimal planning of implant placement in this region.
The risk of nervous system injury in the mental foramen may be related not only to surgical procedures but also to endodontic treatment in the area. [17-18]. CBCT evaluation of the area may be considered in cases where anatomical divergence is suspected, either from two-dimensional radiographs or in cases with a high potential for anatomical divergence. In the present case, because it was a field-of-view-limited CBCT scan, we were unable to assess the contralateral side for the presence of any accessory mental foramen. In this case, there is an increased possibility of additional perforation on the right side, and a CT scan should be taken into account when planning any surgical intervention in the area. The risk of neurovascular injury can also be associated with the anesthesia procedure with local anesthesia administered to the area .
In our case report, the presence of three mental holes may complicate implantation surgery if not properly identified. The proximity of these holes to the implant site played an important role in treatment planning, particularly in choosing the size and angle of the implant placement.
3D imaging modalities play an important role in determining this anatomical difference. Optimal imaging and correct recognition of this anatomical difference will provide correct diagnosis of additive mental foramen and prevent inappropriate patient care. In order to avoid any complications of paresthesia and bleeding, it is necessary to obtain a CBCT scan and check for additional perforation during implant placement, apical surgery, or reconstructive surgery in that area.