CBCT Shows Anterior Loop up 14mm to the Mental Foramen: Is it Crucial to Avoid This?

Dr. S asks:

I have an edentulous case that I have treatment planed for 4 regular platform dental implants in the anterior mandible to support a fixed prosthesis. However the CBCT shows that there is a clear anterior loop that tracks up to 14mm anterior to the mental foramen. This leaves just enough room to place the 4 implants with the recommended 3-4mm interproximally. The problem is that if I allow 14mm each side then I will only have enough space to place 2 regular platform implants inter-foraminally rather than the 4 I intended. Is it crucial that I avoid the whole anterior loop? Or can I just allow say 8-10mm and then place the implant without risking paraesthesia? Does anyone have any experience with this?

*CBCT slices attached 14mm anterior to mental foramen.

42 thoughts on “CBCT Shows Anterior Loop up 14mm to the Mental Foramen: Is it Crucial to Avoid This?

  1. Don’t drill into the loop. Consider an overdenture w two implants or placing the two other implants somewhere else.

  2. Whilst damaging the the “loop” is not good , this is just the anterior branch which supplied the teeth that are now absent so no issue . You will often see this on scans.
    Peter

  3. This is often misinterpreted as a “anterior loop” of the mental nerve, but as dr. Fairbairn says it’s more likely a anterior or the incisive branch of inferior alveolar nerve.

  4. Is it crucial to avoid this? I love your question. It made me laugh after a long day.My advice, get a good implant book and improve your knowledge. Hopefully your next question may have some though to it.
    I don’t want to discourage you, keep on doing what you want to do, just get some basic knowledge.
    For future reference: stay away from anything with a name( mand canal,floor of the nose, mental foramen, anterior loop, submandibular fossa)use the 2mm rule.

  5. One option is to consider very short implants (5.0, 6.5 mm) above the nerve. Another is to widen the ridges, ant. or post., using two step ridge splits with the same short implant bodies. This leaves a 6-8 mm wide ridge crest covered with attached tissue.

    John

  6. if you have a cbct, realize that you can look at the patients anatomy in 3 dimensions. no, it is not a good idea to put an implant into a vascular structure. and although as some of the other folk pointed out you are probably looking at the incisive bundle, it can pose a bleeding hazard also. so take the cbct and look at it in all dimensions, and see if there are 4 sites where you can place a fixture. sometimes we need to place them lateral to a neurovascular bundle. if you are not comfortable doing this, find someone who is. edentulous cases can be tricky, as you have no existing landmarks to go by.

    gary

  7. The cadaver studies looking for the anterior loop of the IAN do not find it more than 5 mm anterior to the M.F. The structure seen on the cbct is the incisal nerve. The occasional symptom after damage to this structure is numbness under the chin. Advise the patient of this when discussing the risks and alternatives.

  8. Dr. Garcia, I believe there are numerous books out there to improve one’s basic COURTEOUSNESS. In addition, please re-read the Comment Guidelines below.

  9. Dr. S thank you for posting your case and asking questions. There usually are great comments once you filter out the finger waggers. It is a foregone conclusion that we all should seek continually seek training and read instructive manuals. Statements like these don’t answer your questions.
    In my training we were instructed to find the canal and measure 7mm anterior. Discuss alternative tx options if you feel you are encroaching anatomy. Some patients move forward even when informed of the risk. There is no such thing as a stupid question. Just stupid people who won’t ask questions.

  10. Dr. S
    Thank you for posting.I’ve treated similar & more complex anterior loop situations. A pre-op radiographic stent with opaque markers at the planned positions, 2mm. from vital structures, will assist you in construction of the surgical stent. Save your diagnostic stent CBCT. Better safe than litigation.

  11. go ahead with Sx, BUT…be PREPARED!

    Occassionaly you will get blood spurting up and keep your calm. You might initally think that you have a lingual perforation. It will stop and implant placement will keep it stopped.

    I see these anterior branches more and more with my Kodak 9000 CBCT. Theyu usually don’t show on 2D Panx.

    Bill I.

  12. “Is it crucial to avoid this ?” Is this a serious question ? I have to say that I agree with Dr. Garcia’s comments. No finger waggering here. Please remeber the Hypocratic oath “at first do no harm”. While there are no stupid questions when asked in the correct setting, but going online to learn how to do surgery is indeed inappropriate and bad for dentistry’s image in general. I have seen too many patients harm. Please, get some appropriate training in an appropriate setting. If your patients only knew…

  13. See here we go. So much is lost communicating in a forum. One cannot hear voice inflections, intonations or see body language. So alot if comments are misread an misinterpreted. No one stated, and and I wager noone would anyone agree that online learning supplant live instruction. I guess you should list your c.v. before venturing out here with a question.
    Happy Thanksgiving to all of my colleagues who celebrate the holiday. We all have something for which to be grateful. I for one will enjoy some time out of the office with family and friends.

  14. I for one have learned some valuable information from this discussion, so I thank you, Dr. S for posting it. I might also suggest to some of the posters that if you don’t have anything constructive to say, then you might consider abiding by the guideline that “Speech is Silver, but Silence is Golden” Thank you.

  15. We all have something to learn from each other. But if you go on a website to learn that it is generally not consider a good idea to place an implant into a neurovascular structure, there is something terribly wrong. For all those shameless doctors defending this practice, next time one of you or your loved ones need surgery, just imagine your surgeon going online to learn very basic anatomy and instructions before performing it on you !!

  16. We really don’t know anything , unless we look at the entire scan.it would be a pretty interesting anomaly to see a 14 mm loop. Like the” boy” said , it’s probably the incisive branch. This is routinely sacrificed, with little or no sequalie. Most suggest, it regenerates spontaneously. Would image fiber type ratio is different than main branch. The Scrooge is back! You really should know the answer to this question! Bv

  17. A good recent study of several hundred cadavers, prooves that the “anterior loop”, rarely occurs. I will concur. I personally looked at 100 of my own patients after reading article in JOMS , last year and rarely found any anterior loop. Bv

  18. I love it! Put 10 dentist in a room get 15 opinions! Some rude ones that aren’t really needed. Thanks for the posting. Don’t see a real consensus but I for one would avoid vital structures for a number of reasons, some listed, and I could think of a dozen more. No need to cowboy up here, but don’t be disturbed by crotchety commentary, keep learning ANYWHERE you can. Good luck!

  19. Dr. Pawl. , if you need a consensus, then I’m going to suggest you ” hit the books”. The fact that this is the portion of the scan that is presented , makes me think that there maybe a misunderstanding of the anatomy or the scan. Bv

  20. Only one patient reported numbness in mental area after 2 implants placed anterior to MF. Patient recovered completely after 2 weeks. Never had any bleeding complication. Placed aprox 200 implants anterior to MF.

  21. Dont , drill into the vital structure , go for a short implant as advised earlier by some dentist above or use NP implant or you have enough space on the side tilt the implant and use angle implant ( this needs skill) , so if possible do that other wise go for 2 implants and denture.

  22. Its controversial that the ant loop is mental n or incisive.I would suggest not to take a chance and rather consider doing an All on 4 in ur case.

  23. The appropriate cbct scan ,obtained with a scanner that has a small enough focal spot, will give you some definitive information. Send the scan to a radiologist or show it to a colleque that does a lot of them . If there is a 14 mm anterior loop, get someone to publish it. There are scenarios with bifid main branches, bifid lingual nerves and mental nerves with branches that range from 2 to 7, In my brief experience . So, nothing is impossible. If you think it’s a larger than average diameter structure stay away from it. If there is any doubt, there will be less of one postop. Bv

  24. Dr. S,
    Would you like to be the patient of a neurosurgeon/cardiac surgeon etc. who is asking online how to perform surgery?

  25. before CBCT we didn’t mind the incisive bundle and got paresthesia and ‘meteorotropism’ every now and then. Today we can see all the structures we routinely violated (nerve, lingual fossa, buccal undercuts…). I haven’t changed much in my ways, except in the presence of perforating vessels. But what will the judge say if you obtain a neuralgia by willingly severing the incisive bundle?

  26. A great tip is to check out article on the subject in Clin Oral Impl Res by Apostolakis and Brown from 2011. Article recommended by BV is also a good read!

    SG – read your own post and take notice.

  27. Omsjaw, get ready to get some whimpy responses, but couldn’t have said it better. Is this forum set up to teach the simplest fundamentals, or is it a platform for seasoned doctors to have intelligent discussions?? Happy tgiving , bv

  28. You may consider placing the implants slightly tipped with the apex of the implant passing lingual to that canal. I would use a 3D scan generated surgical guide, bone supported which works best for me. Then you could get a longer implant. Should work fine.

  29. While I continue to giggle at the thought of some of the responses, I continue to see the words, vital or vascular. The 3rd branch of the fifth cranial nerve is far from a structure needed to sustain life and while it always has a vascular component, that is not what should concern us. Everytime I do a nerve lateraliztion , the blood vessels are sacrificed. Attention to detail is important, even if we are just kicking around ideas. Reference is important, when we consider relative science. Hey resident, you can’t enjoy any old holidays. You need to be ” in house”. Don’t you have something to read? Bv

  30. OMS resident: Was there something that I wrote that disturbed you?? Please be a little more direct. Thank you.
    SG

  31. Based on what I see, this is the terminal branch of the inferior alveolar nerve which supplies the lower incisor teeth. The lower lip receives its sensory innervation from the mental branch. You are able to implant past the terminal branch in the incisor region without problem. However damage to the mental branch including the anterior loop, will create paresthesia in the lip. In most CBCT scans, the anatomy is clearly shown, including the anterior loop which is usually very short and is nothing more than the main part of the inferior alveolar nerve curving up and outward to exit the mental foraman as the mental nerve.

  32. Gary , I feel like I have a fair vocabulary , but you got me with that one. Please read almost every description of the 5th cranial nerve lateraliztion. They call for incision of the incisive branch, almost every time. When you do one , or watch one , you will see that mobilization is impossible, with that branch in tact. Bv

  33. BV – you got me! I was just being polite.. Where do you think I am? I “live” in my scrubs and the OMS reference guide is my “pillow” (but there’s no time for sleeping)…

  34. This anatomy is clearly the incisive canal. Two thirds of the IAN exits at the mental foramen while one third continues to course through the symphysis and anastomoses at the midline. There is no such thing as the “anterior loop”. This is an misnomer created when clinicans were looking at panorex films and saw what appeared to be an anterior extension which ended, on average, 7mm anterior to the foramen. This error was created because the incisive branch courses from the buccal side of the mandible to the lingual cortex as it travels anteriorly. It will seem to disappear because of the change of density of the midline at mid-symphysis. However, if you take high resolution CBCT imaging, you will be able to track the entire length of this neurovascular bundle. If you transect this structure when teeth are still present, you will devascularize the teeth anterior to the resected segment. If, however, the ridge is totally edentulous, there is less concern. The real considerations are: 1. What is the density of bone anteriorly? If it is D1, elimination of the blood supply raises the chance of pathologic fracture. Larger medullary spaces have other collateral blood supply. 2. If you are relatively close to the mental foramen, you run the risk of Wallerian degeneration of the proximal segment of this branch, resulting in dysesthesia, most commonly manifested as a burning sensation. However, you will generally not get a sensory deficit, or parasthesia, as few branches of this anterior nerve supply the lip or chin. The only exception is when there is a branch at the cuspid position called the superior genial nuerovascular bundle. You will get a slight deficit in the chin area but not the lip.
    Next month, our paper on maxillofacial anatomy in anterior mandible will be published in the AAID Journal of Oral Implantology. It will clearly show all of the important anatomy in the intra-foramenal zone, including the incisive canal, mylohyoid branch, lingual/sub-lingual arteries, sub-mental artery, and superior genial foramen. We will no longer be able to classify this anatomical area as the “zone of safety”. There are serious anatomical considerations here that all implantologists need to be aware of and then treated appropriately.
    RJM

  35. Wow! so many opinions. Anatomical anomolies do exist so without having the the entire scan to look at it would be riskey to advise you to place these implants in this area. There is no shame in referring the case for implant placement when we are unsure of the surgical risk to our patient. Look at the scan together with your surgeon and learn from it, there is most likely no 14mm loop. BUT. If you have any doubt as to potential harm that may result to a patient do not do the surgery. Please do not blindly follow the advise to go ahead with this implant placement. I have seen (cadaver) the nerve curve ahead and then back to the foramen, but only a few mm. It does happen.

  36. I recently placed an implant in the #28 position where the tooth which had a 12mm long root was extracted and a 14mm implant placed immediately.the patient had an anterior loop which was 3 to 4mm anterior to the foramen.what was interesting about this case was that everything the good doctor has noted above occurred as soon as I drilled into the anterior loop.first there was good amount of bleeding which stopped as soon as the implant was placed.second, in the post op appointment the patient reported slight numbness of her lower anterior teeth mainly tooth #’s 25,26,27.third,the numbness lasted one month after which the patient reported completely gone.this has happened on several cases of anterior loop violations,however this is not to say they will all react the same way postop,it’s just my experience after doing over 2000 cases.I hope that this was helpfull,after all I don’t think all the implant books in the world can replace your experience hands on and surgical protocols which are sound and not reckless.

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