Читать книгу Management of Complications in Oral and Maxillofacial Surgery - Группа авторов - Страница 86

Planning for implant surgery in locations with anatomical limitations requires meticulous preoperative assessment and planning. Occasionally, complications may happen regardless of preparation and cautious attempts at prevention. In the posterior mandible, for example, care must be taken to plan for the positioning of implants to avoid the inferior alveolar nerve (IAN) within the inferior alveolar canal (IAC). Most authors agree that placing the implant within 2.0 mm of the superior cortex of the IAC may cause a permanent sensory disturbance, and a 2.0 mm margin of safety is generally accepted as the threshold for proximity of the implant to the IAC. It is also critical that the clinician be familiar with the specific implant system used, since some drills have tips that extend (0.5–1.0 mm) beyond the lengths indicated on the drills themselves. There are various potential mechanisms of IAN injury from dental implant placement. Direct IAN damage may be caused by the implant drill itself, with transection or partial transection, due to drill overpenetration. IAN compression may occur from the implant being submerged too apically within the IAC. Also, it is important to consider that thermal injury from bone heat generation near the IAC can cause IAN injury even though the drill or implant has not violated the IAC. This may be prevented by using new sharp drills that cut efficiently, and using the correct implant drill speed to avoid iatrogenic overheating of the bone, since there is no irrigation at the tip of the drill to decrease heat generation. Also, persistent bleeding within the IAC from transection, or partial transection, of the inferior alveolar artery or inferior alveolar vein leading to a “compartment syndrome” with increased intracanal pressure can cause IAN compression. While most other non‐implant‐related nerve injuries (e.g., from third molar removal) result in a decrease in sensation (hypoesthesia or anesthesia), implant‐related injuries (and endodontic‐related injuries) are more likely to result in unpleasant painful sensations (dysesthesia). These implant‐related nerve injuries are also more likely to be permanent, and not amenable to resolution with microneurosurgery, and are managed best with pharmacological therapy (e.g., gabapentin, pregabalin, amitriptyline, baclofen). It should be noted that due to the anatomical location of the IAC/IAN, the two most vulnerable locations for iatrogenic IAN injury are when placing implants in the mandibular second premolar and mandibular second molar regions. Also, immediate implant placement with extractions, as well as tilted implants in the mandible, may increase the risk of nerve injury. In the case where it appears that there is insufficient bone height superior to the IAC on 2D radiography, alternate 3D imaging techniques (CT, CBCT) may be utilized to obtain a more precise measurement of the available bone near the IAC. Of course, if an inadequate height of bone exists, ridge augmentation procedures, or a nerve repositioning procedure (nerve transpositioning or nerve lateralization), may be considered; however, these procedures themselves also have a risk with regard to neurosensory disturbances. Some surgeons would argue that obtaining 3D imaging (CT, CBCT) combined with the use of CAD/CAM fabrication of implant placement surgical guides would eliminate the potential for IAN injury; however, there are no studies that directly compare these groups. One report [20] suggested that iatrogenic displacement of implants in the posterior mandible into the IAC can be attributed in part to the poor quality of the medullary spaces of bone in that anatomical region. It is proposed that the cancellous portion of bone in the posterior mandible is more abundant and less dense than bone in the anterior mandible, and this poor bone density would cause minimal resistance and allow penetration of the cortical bone of the superior aspect of the IAC by an implant. In these cases, the drill tends to “drop” into the medullary space and through the cortical IAC during site preparation, thus rendering the IAN susceptible to damage if the drill is not controlled properly (Figures 3.1 and 3.2). When the implant is placed, there is also less resistance, and the implant may be seated more apically than the prepared osteotomy, even while tightening the healing abutment or cover screw [20]. If there is IAC encroachment on immediate postoperative imaging (Figures 3.3 and 3.4), the surgeon should consider implant removal and delayed replacement, or immediate replacement with a shorter implant, and consider an early referral to a microneurosurgery specialist for evaluation in the event of nonresolving paresthesia or dysesthesia for prompt microneurosurgery. In cases of no IAC encroachment on the postoperative radiograph, methylprednisolone may be prescribed to decrease perineurial edema (e.g., Medrol dose pack), and daily vitamin B12 and nonsteroidal anti‐inflammatory drugs could also be considered to augment spontaneous neurosensory recovery. Furthermore, serial neurosensory testing should be performed, and if no improvement occurs within three months, microneurosurgical exploration and repair should be considered. Early and late dysesthesia should be managed with surgery and medications, respectively. The true incidence of IAN damage during implant placement is unknown, but diligent preoperative planning and meticulous, controlled surgical technique will minimize this complication. Nonetheless, patients should be made aware of the potential for altered sensation as part of the informed consent process (Algorithm 3.1).

Fig. 3.1. Implant displaced in the IAC causing IAN injury.

Fig. 3.2. A closer CBCT view of an implant causing IAN transection.

Fig. 3.3. Implant violation of the superior aspect of the IAC.