The most common and serious complications in implantology occur during the surgical procedure. There may be many factors behind the development of these complications, such as inadequate preoperative preparation, implant contamination, overprocessing of the bone, and error in implant orientation .
Preoperative preparation includes a detailed examination of the anatomy of the bone. The submandibular fossa is a commonly encountered and important anatomical structure that should be discovered during this examination. The submandibular fossa is a bony depression located in the posterior part of the mandibular bone, on the medial surface, beneath the mylohyoid line. As the depth of the submandibular fossa increases, the risk of perforation in the lingual cortex, vascular trauma and bleeding during implant surgery increases. The subsequent formation of hematoma, persistent inflammation or infection which may result from the exposed oral environment due to perforations of the lingual oral mucosa, can bring about situations that are difficult to cope with. In daily surgeries, it is thought that the rates of perforation in the lingual cortex are much higher than reported, since most go unnoticed .
Although computed tomography has defined itself as an excellent method for defining the anatomy, anomalies and pathologies of the jaws, the newly introduced CBCT method has become used in dental implant surgery planning . CBCT provides 3-dimensional images for presurgical evaluation but have higher radiation doses then conventional radiography [2, 7].
Panoramic radiographs give information about bone height and bone thickness to some extent, although they only provide two-dimensional information and image distortion, and magnification may occur . However, some authors argue that CT (Computerized tomography) or CBCT are not necessary in all cases, and panoramic radiographs may be preferred . Panoramic radiography is easier to access, have relatively shorter exposure times and a cheaper option and is used frequently for preoperative evaluation; many still evaluate the edentulous site solely on periapical and/or panoramic radiographs [2, 3, 9].
The study by Sumer et al. evaluating the relationship between visibility of the submandibular region on panoramic radiography with the depth of the submandibular fossa could not find any correlation and that panoramic radiographs were not reliable for determination of the depth of the submandibular fossa . Another morphological study on lingual concavities of the mandible as determined by CBCT reported that the deep location of the inferior alveolar nerve close to the basal cortical bone was associated with a deep submandibular fossa. They also mentioned that although panoramic radiographs do not provide data on bucco-lingual bone dimensions, they are reliable in determining the position of the inferior alveolar nerve for dental implant planning . Combining these two conditions, it can be concluded that the deep location of the inferior alveolar nerve on panoramic radiographs may be a marker for a deep submandibular fossa. Based on a similar logic, in the present study, a marker that could explain the depth of the submandibular fossa was searched on panoramic radiography and for this purpose the gonial angle was focused on. The reason for choosing the gonial angle as a marker is its anatomical neighborhood to the submandibular fossa and its easy measurement on panoramic radiographs, if a relationship could be established. However, this relationship could not be established. Establishing this relationship could have been used in dental implant surgery planning and increasing the safety of panoramic radiographs.
Morphological and anatomical changes occur in the mandibular bone depending on age, sex and edentulism. On panoramic radiographs, the differences in the gonial angle caused by the change of these data were investigated by Okşayan et al. and no statistically significant difference was found . Nevertheless, the mean gonial angle measurement was higher in edentulous patients. The present study was conducted on dry mandibles which, data of age, gender and edentulism times were not present. The authors note the absence of these data as limitation of the study and point out that further studies involving these data should be conducted.