August 1, 2014
by Dr. Blake Nicolucci, BSc, DDS
When there is little or no bone in the posterior maxilla, the tendency for implant dentists is to use smaller implants to avoid the maxillary sinus. In all honesty, this contradicts the laws of nature, which illustrate that the posterior maxilla has the lowest bone density of both the maxilla and the mandible. Obviously the lower density of the bone in the posterior maxilla creates an environment where the bone/implant interface will have a lower percentage than say the anterior mandible which, generally has the highest density of bone in the maxilla and mandible. The higher density of the mandible means a greater bone/implant contact due to the higher amount of cortical bone and thicker trebeculation. It is obviously much easier to place ‘more implants’ and ‘longer implants’ in an area with few anatomical complications, and this is generally what implant dentists do. This is, of course, the reverse of what should happen. The posterior maxilla, with its lower density bone, should get a greater number of implants to increase the bone/implant contact area. The other parameter to take into consideration is the increased biting forces in the posterior (which can reach up to five times the force in the anterior mandible).
FIGURE 10. A tear in the Schneiderian membrane necessitated the use of a stiff long lasting barrier (Neomem Collagen Membrane — Citagenix Inc. in Laval, QC, Canada) on the superior aspect of the membrane to act as a repair of the membrane tear (against which the grafting material will be placed).
FIGURE 14. Autogenous bone harvested from the tuberosity and from the site of the impacted wisdom tooth is then cut into small pieces to be placed on the inferior aspect of the compartment, against the host bone which used to be the floor of the sinus.
FIGURE 18. A second more malleable barrier (Bio-guide resorbable bilayer collagen membrane — Osteohealth Co. — Division of Luitpold Pharmaceuticals Inc., New York) is draped over both the grafted socket and the window that was produced to give access to the sinus.
FIGURE 20. The same process is started on the second quadrant. There is no impacted wisdom tooth to deal with in this area which will make the surgery much neater, and the same process is completed as was performed in the first quadrant.
If there is insufficient bone to place ‘normal’ length implants in the posterior maxilla, then bone volume in this area should be generated so that ‘standard’ implant lengths can be used and the bone/implant surface area can be increased. This will also create a surgical situation which will allow ‘more’ implants to be used — again countering the increased forces of mastication in this particular area. This is where the ‘Sinus Augmentation’ comes into play.
FIGURE 21. Both sides have been sutured closed with tensionless interrupted sutures. These sites must be left for a minimum of nine months for the allograft to be converted into a decent quality autogenous bone for implant placement.
FIGURE 22. Panorex radiograph showing the amount of bone we are expecting to regenerate as a result of the double sinus augmentations. The dense HA on the top of the graft helps us visualize the amount of graft that was placed.
FIGURE 25. (Left) Occlusal (mirror) view showing positions of implants in both first and second quadrants and also the amount of bone regenerated on the lateral walls in both quadrants. The restoration of tooth #24 will be completed before placement of the implant crowns on the implants.
FIGURE 30. The Impression transfer copings are then placed for a final impression and fabrication of two two-unit bridges as final prosthesis. Joining the crowns gives mutual support to each implant and lessens the chance of overload on one individual implant.
FIGURE 31. I like to use custom cast abutments when possible. The draw created on each abutment is more exacting from the laboratory and the crown margins are much easier and cleaner radiographically.
The following case shows a bilateral sinus elevation procedure, followed by implant placement and is followed through to conclusion with the prosthetics in place. What I would like the reader to do is to come away from this article with a new perspective on the importance of increasing the implant surface area to bone contact in the posterior maxilla, and how increased bone/implant contact in the posterior maxilla will increase the success rates long-term. OH
Dr. Nicolucci is president of the Canadian Society of Oral Implantology and is Oral Health’s editorial board member for Implantology.
Oral Health welcomes this origial article.