QUESTION:
I’ve got a case to restore the lower right posterior quadrant with mini dental implants and a fixed bridge. Previously, I extracted #29 (failed bridge abutment) and grafted the site.
The CT Scan and case work up was in consultation with Vinny @ evolution lab. The only available quality (D2/D3) bone was just distal to #28; the bone mesial to the molar was poor D4 or worse according to Houndsfield values.
So, the original plan was a bicuspid or small molar in the #29/30 area and leaving open space between the implant retained tooth and the remaining molar.
But here’s what happened at fixture placement: the first (most mesial of the two implants and directly next to #28) went fairly well, final torque value @30Ncm+, but the most distal implant had to be placed a bit more distally than expected because there was no resistance or stability at the pre-surgically planned location. Final torque value at the improvised location was @20Ncm+.
So. now the patient is still hoping for a fixed restoration but I think the A-P spread is too long for just the two minis: (#29 mini = 2.1 dia.x 10mmL and #30 mini = 2.4 dia. max. x 10mmL).
Would you please share your thoughts on what options I might consider at this point, I would very much appreciate your time and input. Currently, she is wearing temporary caps and assuming integration, I plan to wait four months to proceed.
I’ve enclosed a photo and x-ray images.
Best regards.
Dr. S.R.
ANSWER:
Firstly, It looks as the the grafted site has filled in nicely so good job on the socket preservation! it’s an easy skill that I sometimes teach in my mini dental implant CE courses. With mini implants, even a good plan needs to be modified to achieve a successful outcome in some cases. One thing we don’t want to do though is let good information make us second guess ourselves.
For example, you are one of the sophisticated dentists who is exposed to CBCT scans for MDI work. We know that mini implants need to be placed in solid, D1-D2 bone for the most part. When we evaluate CBCT scans with Houndsfield values we can trick ourselves into thinking the bone is not good for implants. Here’s how: If we evaluate only a small point in the medullary cavity we can easily find a HU value below 100. Maybe even a large portion of the space represents as a lower value. This may lead us to believe that we are dealing with D3-D4 bone. But we must remember that an implant has width and length and that point evaluation is an incorrect method of density determination. Even if an area seems dark with little tubercular bone, we must appreciate that the cortices contribute significantly to the stability of the implant. In other words, a more ideal evaluation method would be to plan the implant in 3D and evaluate all the bone touching the implant and associate HU values.
The other problem is HU values are not completely reliable with Cone Beam. Additionally, The MDI insertion protocal calls for a self tapping auto advance in unprepped bone. This can add to the stability of the implant regardless of the HU values. In the end, You may choose to stick with your plan and try to place the MDI before you modify location based on the CBCT.
Your strategy for waiting 4 months is a good one here, but I’d like to see the entire space between the premolar and molar filled instead of leaving a space. You may decide here to adjust the occlusion so there is very little occlusion in centric and absolutely no contact in excursive movements. The space isn’t too big but the distribution of mdis is not ideal. None-the-less, I believe if the implants are stable after 3 months and the occlusion is adjusted appropriately the case will be successful. You can always add another mini implant distally if you are concerned. I might go this route.
Hope this helps.
Dr. Ben Oppenheimer
