According to the Osteology Consensus Conference, the mean ridge reduction after tooth extraction is 3.8 mm horizontally and 1.24 mm vertically.1,2 What are the reasons for bone resorption following tooth extraction? First we have to be clear that it is the bone of the alveolar process that is mainly resorbed. The remaining jaw, the basal bone, is resorbed to a lesser extent.4
Bone loss in posterior and anterior sites
The extent of bone loss varies according to the site and the patient. Our studies show that net loss of bone is greater in the posterior than the anterior regions. Fortunately, the posterior sites contain so much bone that resorption is often not a major clinical problem.
On the other hand, due to the limited amount of anterior bone, the loss of less bone in the anterior region can be problematic. As alluded to above, facial bone walls are very thin and often lost completely after a tooth has been extracted. Accordingly, the net bone loss is lowest in the incisor region, but the percentage of bone reduction is the highest.
Lack of bone vs. lack of volume
There is another phenomenon to be considered. Despite alveolar process and basal bone reduction, there is more bone after tooth extraction than before – because new bone is formed in the space previously occupied by the root.
Thus, frequently we will have bone enough to hold an implant, especially a narrow diameter implant. But to restore a tooth with implants, not only is bone necessary but also ridge volume to provide the mucosa profile for esthetics. Now, if we have enough bone for placing the implant but not enough volume, in reality we don’t necessarily need more bone but any graft that could provide volume, whether it is a gingival graft, a soft-tissue matrix, a bone substitute or anything that is compatible and stable.
Less volume loss with Ridge Preservation
Ridge Preservation prevents volume loss after tooth extraction, but not always 100 percent.4 Results depend, again, on the tooth region and the patient. We have recently shown that, for the vast majority of patients, preserving ridge dimension provides enough bone tissue to place an implant in a proper three-dimensional orientation and with an ideal amount of bone surrounding the implant.5 Animal studies have shown that in extraction sockets Geistlich Bio-Oss® Collagen supports new bone formation, particularly in the cortical region, and contributes to ridge profile preservation.6,7 Given these studies, we can assume that Ridge Preservation modifies bone modelling and alleviates buccal bone loss.8
How long does Ridge Preservation last?
Many studies on Ridge Preservation are limited to a six-month observation period. There is, however, reason to believe that extraction sockets filled with Geistlich Bio-Oss® continue to be stable much longer. Long-term studies measuring lateral augmentations9 and sinus floor elevations10 have revealed that, if there is no loss caused by inflammation, Geistlich Bio-Oss® preserves ridge volume long term. Further extraction socket studies would, however, be helpful in confirming this assumption.