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

February 27, 2014 Michael Fetner

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.

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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Prospective study with a 2-year follow-up on immediate implant loading in the edentulous mandible with a definitive restoration using intra-oral welding.

February 5, 2014 Michael Fetner

Image 1:  Intraoral welding abutments placed.Image 2 and 3:  Bar bent and welded to abutments — Image 1: Intraoral welding abutments placed.
Image 2 and 3: Bar bent and welded to abutments

Implant retained full arch prostheses have come a long way. Studies have shown that just two implants are capable of retaining a removable denture on the mandible. Some patients would like something more stable that is not removable. A fixed hybrid denture is usually fabricated with some kind of metal bar by a lab. This type of prostheses requires multiple appointments with the dentist to try it in several times to make sure that the fit of the bar and prosthesis matches the mouth. This is an expensive and time consuming process.

In Italy, progress is being made on a procedure that would simplify the metal bar-making process for a fixed denture. They are calling the process intramural welding and seems to be a very promising idea.

This technique was originally published in 2006 by this same author. Intraoral welding is performed once the implants are placed. In this study, four implants are placed intra-foraminally. A special intraoral welding abutment is placed and a metal bar bent to closely approximate all abutments. The bar is then welded to the abutments with a special instrument, that heats, then cools the metal, in a fraction of a second. Once the bar is welded then the abutments and bar are taken out of the mouth, opaqued, and fitted with an acrylic denture. The whole prosthesis can be fabricated and delivered the same day. Because the bar is welded in the mouth with the abutments in place, passive fit is ensured with minimal time and money spent in the process.

In this report, 80 implants were placed and they found a 100% survival rate after 2 years. Only one patient reported and prosthesis problem, which was an incisal fracture that was easily repaired. Survival of implants does not necessarily mean that the implants were successful. The authors looked at bone levels which can give a good indication of success rate, as stable bone levels usually indicate healthy esthetic implants. Average bone levels remained stable through the length of the observation period.

Take home: Intraoral welding can significantly reduce the time, money, and inconvenience of making a bar-implant retained fixed prostheses. This study only looked at mandibular full arch cases, but there is no reason why it could not be applied to upper prostheses as well. It would also be interesting to use these bars with an acrylic restoration for 3-5 unit, acrylic, fixed prostheses that would not include the entire arch. This would be a low cost way to replace many teeth.

A Comparison of Narrow Diameter Ti-Zr Implants To Convention Ti Implants

January 15, 2014 Michael Fetner

Straumann funds a lot of research for their implants. So it's no surprise that they will have a lot to show for their new titanium-zirconium alloy, known as roxolid in the vernacular. The idea behind this Ti-Zr alloy is that it is stronger, allowing a smaller diameter implant to be created with a chance for fracture. This is great for areas such as the maxillary lateral or mandibular incisor, but can it be used to replace a larger size tooth that just has limited horizontal bone? This randomized controlled study aims to find any differences between a standard 4.1mm titanium implant and the 3.3mm Ti-Zr implant.

Method and Materials: 40 implants were randomized into two groups of 20 for implant placement into anterior or premolar sites. A two stage approach was used (erring on the side of caution, don't want to have a failure for company). Temp placed at 3 months and final restoration at 6 months post implant placement. Patients were followed up for one year.

Results: Surprise, surprise, no statistically significant difference between the groups at all. No difference in bone level, success, bone grafting, etc. Wouldn't expect an implant company to want you to stop buying one of their implants to start buying another one. But realistically, there is no statistically significant difference because they are both good implants and they work.

Some interesting results, though not significant, was the surgery time was shorter in the smaller implants (less drills), and surgeons preferred these implants more than the conventional size. This is surprising because both size implants required the same amount of bone grafting at implant placement. I have a feeling the smaller size has more bone around it when placed even when bone grafting is necessary, thus giving the surgeon some peace of mind.

My thoughts: Many implant companies have a really small implant. If you look at the connection of these implants you will invariably see a really small band of titanium holding the implant together, and that should scare you. This study had only one year of follow up. In a prosthetic complication timeline, one year is nothing. If this Ti-Zr alloy can really prevent prosthetic complications in a small implant than it really is an intriguing product.

Another advantage to smaller implants is: esthetics. As long as they are placed in a way to allow for good esthetic emergence, they allow for greater bone and papilla thickness on either side of the implant, thus allowing fuller and more esthetic papillas.

If this implant can stand the test of time, it may be the best little implant on the market.

Benic G, Galucci G, Mokti M, Hammerle C, Weber HP, and Jung R: Titanium-zirconium narrow diameter versus titanium regular diameter implants for anterior and premolar single crowns: 1-year results of a randomized controlled clinical study. J Clin Periodontol 2013; dii: 10.1111/jcpe.12156

The effects of mechanical instruments on contaminated titanium dental implant surfaces: a systematic review.

January 8, 2014 Michael Fetner

Treating contaminated dental implants is going to be an increasingly common treatment modality dentists offer in the future. Currently, there is little research to show what is the best treatment for the implant that has been exposed to the oral environment. In my experience, these contaminated implants can lose bone fast, sometimes faster than periodontitis patients.

This systematic review looks at 14 studies comparing means to clean contaminated titanium implants. The most common ways to clean the contaminated surfaces were: air-abrasives, plastic and metal tipped ultrasonics, metal hand scalers, and titanium brushes. Keep in mind that all of these studies are in vitro.

Some take homes from the various studies:

Air abrasives with sodium bicarbonate powder is capable of removing all viable cells.
No real difference in effectiveness of plastic covered or metal ultrasonic tips
Ultrasonic scalers show a significant decrease in biofilm covered areas
Steel/carbon curette seems to be the least effective means of cleaning a titanium surface
Rotating titanium brush shows a significant decrease in residual biofilm areas

My personal take-home from all these studies is that air abrasion, titanium brush, and ultrasonics are effective at cleaning titanium surfaces IN VITRO. IN VIVO, may be a different experience. Peri-implantitis usually creates a circumferential defect that tapers toward the implant as it moves apically. This creates a difficult lesion to gain access to and clean properly, even when properly flapped.

My guess is that the titanium brush and ultrasonic will be the easiest to use under surgical conditions and the air abrasive will be the least convenient due to the grit and mess in a flapped surgical site.

The authors conclude that there is still a lot of work needed in this area. I agree

Louropoulou A, Slot DE, Van der Weijden F. The effects of mechanical instruments on contaminated titanium dental implant surfaces: a systemic review. Clin. Oral Impl. Res. 00, 2013, 1-12

Immediate Implant Placement in Molar Sites

November 22, 2013 Michael Fetner

I recently saw Paul Fugazzotto speak at the American Academy of Periodontology anual meeting in Philadelphia. Paul is an excellent speaker and a big proponent of immediately placed molar implants. I believe he even said that 95% of the time, he will place an immediate implant post molar extraction! I thought his would be a good opportunity to look at his papers on the subject.

The first paper describes his immediate implant technique in mandibular molars with 341 implants placed and the second paper describes the technique in maxillary molars with 391 implants placed. Both papers were written in 2008 and published in Journal of Periodontology.

First, let's start with the technique:

1) The molar is extracted in an attempt to retain as much interradicular bone as possible. If bone has to be removed then an immediate implant is aborted.

2) Pilot drill is started at an angle for stability and then brought up to the proper angle. Up to a 2.2mm twist drill is used

3) Osteotomes are used to widen the osteotomy sequentially until the proper width and depth for implant placement

4) Implant is placed to the the most coronal bone level of the interradicular bone.

5) If the surrounding horizontal defect remaining was >3mm the site is grafted with a membrane. If the defect is <3mm the site is left to heal. Primary closure was obtained on all implants and they were exposed 3-6 months post op.

6) The implant is allowed to heal and is restored normally.

Results: In the mandible, two implants failed with 339 remaining in function for up to 6 years. In the maxilla, two implants were also lost with 389 remaining in function. This gives a survival rate of 99.1% and 99.5%, respectively. Success rates were not given in the study.

Take home: The pros of this procedure are shorter wait time for final prosthesis 6 months down to 3 as long as they are uncovered in 3 months. Shorter wait time is better for the referring dentist, and the patient. In the hands of Dr. Fugazzotto, there does not seem to be any difference in the survivability of the implants placed with this technique.

The cons of the procedure is that it seems very technique sensitive. To make the proper osteotomy in the interradicular bone can be difficult. Maintaining proper angulation can be difficult with immediate implants. Obtaining primary closure following an extraction involves large flap advancement which can be difficult to obtain and will lead to a decrease in keratinized gingiva.

I think that it is a very interesting technique and should be considered in the appropriate circumstances.

Sources:

Fugazzotto PA: Implant placement at the time of maxillary molar extraction: treatment protocols and report of results. J Periodontol 2008;79:216-223

Fugazzotto PA: Implant placement at the time of mandibular molar extraction: description of technique and preliminary results of 341 cases. J Periodontol 2008; 79: 737-747