An anatomical variation in position of the mental foramen detected by cone-beam computed tomography
rare mental foramen position (posteriorly and almost aligned with the first molar) identified in cone beam computed tomography (CBCT)
clear seeking dental implant treatment
The posterior position of the mental foramen was observed on the left side of the mandible in the 3D and cross-sectional reconstructed images of CBCT. The three-dimensional cropped reconstruction is shown in figure 1. The mental foramen was oval in shape on the left side in region 36. The round foramen observed in region 45 as the common position of the mental foramen. Figure 2 shows serial axial sections with 2-mm slice thickness illustrating the locations of foramina on both sides. Moreover, the bone graft observed on the buccal cortex of the left premolars utilized for ridge augmentation in implant placement. Figure 3 illustrates serial multiplanar sections with a 2-mm slice thickness associated with regions 34-37. An opaque foreign body detected in region 34 suggested root canal overfilling remaining after dental extraction.
Precise knowledge of the mental foramen as a vital anatomic structure is essential before surgical procedures. The position of the mental foramen can vary among individuals. The mental foramen usually lies more coronal than the mandibular canal in the vertical plane. This foramen was identified at an equal distance from either the inferior border of the mandible or the bone crest. However, it might be affected by the amount of crestal bone loss. The mental foramen lies closer to the alveolar crest after dental extraction and alveolar bone resorption. It horizontally lies either between the apices of the first and second premolars or below the second premolar apex and its location varies in vertical and horizontal planes. Race is insignificantly related to the position of the mental foramen. Research on different human races has found the mental foramen to be rarely positioned in line with the mandibular first molar. this abnormal position has been reported in a mere 1-2% of cases. This abnormal position of the mental foramen simplified implant placement in the premolar region. The implant placement of the first molar was, however, more challenging in this case. The mental foramen lies closer to the alveolar crest after dental extraction and alveolar bone resorption. The close proximity of the mental foramen to the alveolar crest in the molar region shown in CBCT required the creation of an adequate space for implant placement by transposing the nerve. Negligence can cause damage to the neurovascular bundle during surgeries. CBCT can help ensure the safety of implant surgeries. Anatomical variations of the mental foramen show the importance of a preoperative radiographic examination. Inexperienced clinicians may misdiagnose the abnormal position of the mental foramen as a radiolucent lesion on X-ray images.
Precise knowledge of the mental foramen as a vital anatomic structure is essential before surgical procedures. CBCT imaging allowed for more accurately locating the mental foramen.