Subcrestal placement of implant: prosthetic complications?
The installation of implants in the posterior mandible is complicated by the fact that the crest of the lingual cortical plate is higher than the crest of the buccal cortical plate. If you install an implant so that the top of the platform is flush with the buccal crest, the crest of the lingual cortical plate will be above the top of the implant platform. Therefore on the lingual, the implant will be located subcrestally. How do you restore implants installed like this? What kinds of complications should you expect?
12 Comments on Subcrestal placement of implant: prosthetic complications?
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CRS
11/22/2012
I like to use the lingual crest as a guide placing the top of the implant aligned with it. Then I onlay graft some Bio OSS and close primarily. Usually I get some bony overgrowth on the buccal. Usually not a problem if it is just a few milliliters. If you bury an implant subcrestally I see die back to the first thread due to biological width. Good luck!
Tyler
11/23/2012
The simple answer to this question is to plasty your ridge to a flatter profile before inserting the implant. Placement of the implant subcrestally can complicate the restorative phase in that it may be difficult/impossible to get the abutment/impression coping fully seated on the fixture, which will necessitate bone removal (aka unplanned undiscussed second "surgery" = angry patient)
Placement of the implant subcrestally by 1mm to account for "bone loss due to biologic width to the first thread" is simply the result of using a poorly designed system. As a clinician accepting this bone loss as routine to me sounds absurd. You need to use a different system.
Another interesting point is if you have an implant with some buccal dehiscence and you place Bio-Oss around the threads, do you ever get "osseointegration" in that area? Not really important, but interesting from a theoretical point of view.
CRS are you using a membrane? Do you have any experience with re-entry using Bio-Oss around the top of the fixture as far as what it looks like after a few months?
CRS
11/23/2012
Tyler you are correct a better method IS using human allograft with a restorable membrane over the top. I like using the lingual plate as a guide and build up vs flattening the ridge. I use Bio OSS for onlay grafts over intact buccal plate and sinus lifts as a radio graphic marker, it never goes away! Biological width has nothing to do with the system used when it is violated die back occurs. When I was a novice 20 years ago I flattened ridges and buried implants, saw the die back but those implants ate still stable and functioning thank goodness. I use the very sharp pilot burrs now to place the implants regardless of th ridge irregularities. My point is using the lingual plate as a stable reference point is a safe way to determine depth since I work off of a panorex. Thanks for the excellent feedback!
Y
Mike DDS
11/27/2012
I prefer using ankylos implants in the post.mand. I place the implant crestal on the buccal and recontour the ling. bone to allow about 1 mm subcrestal position. The shape of the abutment allows for nice tissue healing and no impingement of the ling bone.
Zaki Kanaan
11/27/2012
CRS, you work off a panorex? Why not CBCT in this region? That would be my choice. You can then plan the case rather than deal with things as you go along. Having taken a scan showing a sloping ridge, I would usually use the Astra Profile implant which works beatifully in these cases...no graft, no membrane, no bone levelling (although I do this occassionally), just simple placement.
CRS
11/28/2012
Dear Zaki, simple straight forward implant cases I use a panorex less radiation for the patient. When warranted I use a cone beam if there is atrophic bone or multiple implants always with a radio graphic stent to exactly correlate where the teeth are to be placed. I see a lot of cone beams referred in to me with no stent which gives no way to correlate at surgery. Also many practioners do not understand how to read the anatomy. I've been reading CT scans since residency and feel that they are extremely valuable but need to be used judiciously. Question do you have a cone beam if so how what do you charge for it and do you use it on every case? I would appreciate the feedback thanks!
DrDolittle2
11/28/2012
contour your ridge before you place the implant..simple!
CRS
11/28/2012
I find that this is not necessary with a sharp pilot at higher rpm to get the osteotomy started. And if you take off too much you radiographic measurement is thrown off. It comes with experience, the leveling off is recommended in the implant manuals without consideration to the bone height. Also remember when the mandible resorbs the lingual plate remains the longest as the palatal of the maxilla does. These are very good reference points, you can add bone on the buccal to compensate for exposed threads. I feel it is important to respect the anatomy and work with it. That said I do use transmucosal Straumann implants which are not buried when I have decent buccal cortex. Thats the trick if the cortex is irregular then primary closure, with grafting and allow time for the implant to heal. Attention to this at placement will save headaches down the line. I don't wnt the patient coming back with a problem and I don't want the restoring doctor to have a problem I find the team approach is best!
Dr. Avi ramavat
11/28/2012
I will remove sharp edges of the lingual cortex first as well diseased bone from buccal cortex, now place the implant 1mm subcrestal or equicrestal or supracrestal buccaly depends up on the available height and if supracresta then graft, if third molar is missing then best to involve same side in to the flap after placement of implant.
Dr. Avi Ramavat
11/28/2012
Just to add in to it autogenous graft from third molar region
Dr. Avi Ramavat
11/28/2012
To add in to it plast of lingual cortex after implant placement as in such situation if you achieve rest of the parameters such as stability, position, removal of diseased bone etc. alteration of soft tissue is also required to reduce the pocket.
Dr. Trely
8/16/2013
Ankylos is a good option with the indication for subcrestal placement. Astra Tech offers a Profile implant for sloped ridges. The actual implant is sloped to match the contour of the bone. I've used this several times with good results but it does require components for impression that are different than standard sized Astra and can be tricky to keep track of the slope at installation the first 1-2 cases. Both implants are owned by Dentsply--our rep let us try both options via trial surgery. Since I was already an Astra user, I use Profile for these cases.
