Injury of the inferior alveolar nerve during implant placement: a literature review

Damaging the inferior alveolar nerve is one of the biggest fears of any dentist that places implants, and for good reason.  The inferior alveolar nerve is a large branch of the trigeminal nerve.  It supplies the mandibular premolar and molar teeth with their associated gingiva.  It then splits into the mental nerve to provides sensation to the lower lip, mental area, and the incisive nerve to provide sensation for the anterior mandible and teeth.  This is a very important nerve for the human experience.  Drinking, kissing, talking, and anything else one does with their mouth is effected.  This paper reviews the literature to show how IAN damage occurs and how to treat it.

I want to stick to the injuries caused by the implant drill and not via anesthetic injection.  The implant drill can cause the most severe nerve damage.

The image on the below shows the type of IAN injuries that can occur during implant placement.  Not all are direct drilling of the nerve.  Sometimes just getting the drill near the nerve can cause damage.

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The review gives a couple of words that help describe the type of injury that occurred to the nerve.  Neuropraxia, is a a nonpermanent damage to conduction or demyelination of the nerve.  It will usually recover fully in less than a month.  Axonotmesis, includes damage to all parts of the nerve except the endoneurium.  It can have a full recovery to an incomplete recovery if a neuroma forms.  Neurotmesis, is a complete severing of the nerve with a possible combination of other types of injury.  This would never fully recover without intervention.

Prevention:  The best way to prevent this type of injury is good planning.  A CT scan to show 3D location of the nerve with digital placement of the implant will allow the surgeon to know exactly the limits of the anatomy.  When approaching the area of the nerve, it is important to use less pressure on the drill, and slower RPMs at larger drill sizes.  Even with this step, sometimes an experienced clinician may accidentally "slip" into, or around, the nerve space.  

Management:  Once a nerve is suspected to have an injury, a CT scan should be taken to determine if the surgical area did in fact, approach the nerve.  If an implant is near, or in the nerve canal, it should be removed immediately and no material should be placed in the osteotomy as it heals.  Mechanoceptive tests, using a sharp object on the skin of the affected area, should be used to draw the area where the patient has a lack of sensation or pain.  This area should be photographed every week, to observe if symptoms are improving.  NSAIDs and corticosteroids have shown to help with symptoms.  If the nerve shows signs of improvement, it may be a neuropraxia and no more treatment is necessary.  If neurotmesis is suspected, then the patient should be referred to a microneurosurgeon for nerve repair.  Around 50% of patients with microsurgical nerve repair have significantly improved nerve function.

Conclusion:  Inferior alveolar nerve damage is a very serious complication of implant placement.  Careful planning and proper diagnostics should be employed to avoid it at all cost. If you have any suspicion that nerve injury did occur, proper management should be employed immediately.  

Juodzbalys G, Wang HL, Sabalys G.  Injury of the Inferior Alveolar Nerve during Implant Placement: A Literature Review.  J Oral Maxillofac Res 2011 (Jan-Mar);2(1):e1

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