The loss of natural teeth inevitably leads to the loss of supporting bone. Unfortunately, this results in some negative consequences such as; a decrease of bone volume and density, a lack of lip support, and a residual ridge, which is more difficult to restore.
Implant supported restorations are often the treatment of choice when re-establishing; function, aesthetics, contour, comfort, phonetics and health. However, with a lack of supporting bone structure, the practitioner would be forced to place the implants in an unfavorable position. This would affect the biomechanics, lip support, and future retention of the implants.
To avoid all of these problems, the implant dentist should first perform an autogenous bone graft. This article presents the case of a 40-year-old male patient with a division C-W ridge in the maxillary central positions where the implants were to be placed (#11 & #21). The patient’s goal was to have two implant-supported crowns that look natural.
His treatment would consist of three-tiered approach: an autogenous onlay graft, implant placement, and prosthetic completion with abutments and crowns after the appropriate healing periods.
The residual ridge was extremely deficient in bone both vertically and horizontally. The patient had already undergone three symphysis graft procedures interspersed with four to six month healing periods at another office. The end results were anything but satisfactory. The initial surgeon then referred the patient to our office for treatment and to correct the problem.
A new symphysis graft was performed at our office (Figs. 1-35).
DISCUSSION
After the teeth in the premaxillary region are extracted, the thin labial plate of bone resorbs very rapidly. The ‘new buccal plate of bone’ is really the palatal bony wall of the extraction socket. The average size of a maxillary central incisor is between 5.7 and 6.3mm. The average loss of lip support in the first 12 to 18 months would be 6 to 7mm. This is definitely an indication for a bone graft prior to implant placement. The residual bone presents a ‘one walled bony defect’, and the most predictable way to restore bone volume is with an autogenous onlay graft.
Many donor sites have been used in the past for grafting resorbed edentulous ridges prior to implant placement. The use of intra-oral donor sites has many advantages over extra-oral donor sites (when their use is possible). There is considerably less morbidity, they have a less invasive technique, there is no need for general anesthesia and hospitalization, there are no visible scars, it takes less time to recover, and we certainly end up with a better quality of bone for grafting.
For the premaxilla, the two most common donor sites available for use in block grafting are the ramus and the symphysis. Both have a very high success rate. The ramus graft has the advantage of length with the average harvested block being 45 x 12 x 5mm compared to the symphysis block which averages 33 x 12 x 8mm.
The main advantage of the ramus graft is that by using both sides of the mandible, the entire premaxilla can be grafted. So for a completely edentulous maxilla, this graft should be considered first. However, the ramus graft only has an average thickness of 5mm compared to the 8mm average of the symphysis. Since we are looking for an average of 7mm to regain the lost support in the premaxilla, and since we only have to graft a partially edentulous arch, the symphysis graft is considered the treatment of choice in this case. In partially edentulous cases, the adjacent teeth do not allow compromise in terms of volume, lip support, and esthetics.
After using these grafts for almost two decades, ‘horizontal’ bone grafting can be accomplished with approximately a 98 percent success rate. This percentage drops dramatically when we try to gain ‘vertical’ height with onlay grafting. The success rate for gaining 1-2 mm vertically is around 90 percent. The rate drops to around 78 percent if you are trying to gain 3 mm, and drops to under 50 percent if you try to gain more than 3 mm of bone. There is shrinkage of the soft tissues during the healing period, which creates pressure on the graft. This is considered one of the reasons for graft failure.
CONCLUSION
Today it seems that the distraction osteogenesis technique is gaining in popularity and has produced some tremendous results in gaining vertical bone height. It has been used in orthopedics for almost 20 years, but has only been used with predictable results in implant dentistry for the last four to five years. The concept of distraction osteogenesis is to mobilize a section of bone in the ridge, while maintaining vascularization of the block through the attached soft tissues. With the distraction device, the mobile block of bone is distracted from the host bone very slowly while new bone forms behind the slowly moving block. This technique allows vertical bone augmentation predictably for up to 10 to 14mm. The soft tissues grow with the distraction and follow the block down without creating any pressures on the newly forming bone–and there is no shrinkage.
Dr. Yvan Poitras is Founder and Director of the Canadian Implant Institute (Recognized provider ADA CERP), which provides training in both surgical and prosthetic aspects of implantology. He divides his time between his private practice limited to implantology, teaching and international lectures. He is affiliated with the research group in Biomechanics/Biomaterials at l’cole Polytechnique de Montral.
Oral Health welcomes this original article.
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