When performing any kind of surgical procedure, a surgeon needs to be familiar with the possible variations in the anatomical configurations of both the mandibular canal and inferior alveolar nerve (IAN) [1,2,3]. This is particularly the case when performing root resections, removing wisdom teeth or harvesting autologous bone grafts.

Different techniques are described for reconstruction of missing areas of bone before or during implant insertion. Autogenous bone, i.e. a block graft, is often used. The block can be obtained intra- or extraorally [4, 5]. Extraoral bone harvesting, e.g. from the hip area (anterior superior iliac crest), requires general anaesthesia, causes higher costs and takes more time. Such a procedure is associated with a hospital stay (often of several days), temporary walking difficulties and an additional scar in the area of bone removal and sometimes with sensory disturbances in the thigh. Intraoral bone harvesting, which can be performed under local anaesthesia, may be suitable for obtaining a graft for localized bone defects [6,7,8,9]. The most common harvesting site is the vestibular retromolar area of the mandible in the area of the external oblique line. Anatomically, the IAN runs significantly close to the vestibular bone surface in the area of the ascending mandibular ramus. This nerve may be exposed during bone harvesting if the external oblique line is less pronounced or the bone block preparation extends below the course of the nerve. The nerve may also be exposed if the distal vertical incision is located in the area of the ascending mandibular ramus, because the IAN runs close to the buccal cortical plate before entering the mandibular body in a lingual direction. Other intraoral harvesting sites for bone blocks are the area of the premolars or the chin [10]. Various methods can be used to remove the graft from the donor region; piezosurgery and use of a trephine drill or a Lindemann drill are particularly worthy of mention. The benefits of such a procedure always have to be weighed up against the risks. Various complications are described in the literature, such as damage to teeth, sensory disturbances in the skin or mucous membrane, excessive keloid formation, postoperative complaints (restricted mouth opening, secondary haemorrhage, swelling and pain) or aesthetic problems (altered profile in the area of the donor region or soft tissue recession) [11,12,13]. Possible damage to the IAN during block harvesting and other procedures that may reach the mandibular canal is a feared complication and is the focus of this paper.