Evaluation of the Vascular and Neural Elements Located in the Symphyseal Region Before Implant Surgery: a Retrospective Study of Cone Beam Computed Tomography (CBCT) Scans of the Face Performed on Totally Edentulous Patients in the Odontology Department of the Rothschild Hospital

The placement of dental implants in the anterior mandibular region is considered a rather safe and predictable procedure because this region has a limited number of neurovascular elements, a relatively extensive vestibular and lingual cortical bone structure, and dense trabecular bone providing high primary stability and excellent implant survival. However, this anatomical region is not free of risks, some of which are associated with potentially fatal complications (cases of death following a hemorrhagic accident have for example been described). Many clinical cases thus illustrate complications of implant surgery in the symphyseal region such as nerve damage, bone fractures, infections, and bleeding during or after the placement of the dental implant.

Implant surgery can indeed generate nerve damage according to different mechanisms by nerve compression or dilaceration by direct contact of the drill and/or the implant with the nerve compression linked to peri-implant edema or compressed bone debris at the bottom of the drill site.irritation by release of inflammatory mediators from adjacent inflamed or necrotic bone or thermal injury (heating during implant drilling). Nerve injury is clinically manifested by symptoms of varying stage and severity depending on the severity of the injury caused to the nerve. Clinically, nerve damage to the sensory afferents of the NAI can generate sensory dysfunction such as paresthesia (abnormal sensitivity), hypoesthesia (decreased sensitivity), hyperesthesia (increased sensitivity), dysesthesia (unpleasant sensitivity that may result in pain ) or even anesthesia (complete loss of sensitivity) localized to the territory of innervation of the injured nerve. From the epidemiological point of view, the frequency of such complications would be estimated between 0 and 24% for transient lesions and between 0 and 11% for irreversible lesions. Two retrospective studies carried out with more than 1300 patients with iatrogenic lesions of peripheral trigeminal afferents observed that 13% presented with pain following implant surgery.Implant surgery would thus be the second cause of NAI lesions (18%), after wisdom tooth extraction .

In implantology, vascular effraction is most often observed after perforation of the lingual cortex of the symphyseal or posterior regions , the drill causing the tearing of the underlying vascular structures. A fracture of the internal cortex during implant surgical procedures thus increases the risk of bleeding. At the level of the symphyseal region, the lesion of the sublingual artery can for example be responsible for abundant bleeding or intraoperative hemorrhage, and/or hematoma of the floor of the mouth per or postoperative , with a risk of obstruction of the upper digestive airways. From a clinical point of view, it seems very complicated to be able to establish with certainty the origin of bleeding from the floor of the mouth and only endovascular angiography can determine its origin, which complicates the management of this type of complication.

Although the anatomy of the symphyseal region is rather well described in the literature, the data concerning totally edentulous patients remains fragmented. These suggest that the avulsion of the anterior teeth and the bone resorption have an influence on the anatomy of the mandibular region, and of the vascular and nervous elements traveling in the anterior mandibular part. These modifications would be responsible for individual anatomical variations which could constitute unfavorable anatomical conditions with damage to vascular and/or nervous elements during implant surgical procedures.

In order to test this hypothesis, the investigator wish to evaluate the anatomical characteristics of the vascular and nervous elements located in the symphyseal region within a completely edentulous population for which the anatomy has been documented in a three-dimensional way before the placement of dental implants. A better knowledge of the anatomy and anatomical variations affecting the edentulous symphyseal region would allow identification of patients for whom there is a proximity between the implantation sites and the vascular and nervous elements in the edentulous symphyseal zone.