Loss of maxillary posterior alveolar bone resulting in the need for sinus augmentation is common and it often occurs rapidly after extraction. To better understand the problem and find a solution, we will look at the factors that contribute to maxillary posterior alveolar bone resorption. The following case illustrates the problem:
Four months after extraction and grafting, the site was reentered with no bone formation. Only granulation tissue was present. At this time, the granulation tissue was removed and grafted with an allograft. Note that there is persistent pathology remaining in the sinus with a thickened sinus membrane.
Four months after grafting with an allograft and 8 months after extraction, bone formation is still questionable and sinus pathology is still present. There is ongoing resorption of the floor of the sinus. When comparing the 4-month CT scan to the 8-month CT scan, it appears that approximately two millimeters of bone have been resorbed on the floor of the sinus.
To understand the reasons for these failures, we will start with a discussion on how bone grows in a socket and then discuss what can interfere with that process. All sockets fill with bone starting at the apex. The reason is simple: that is where the most regenerative cells are located. There a very few regenerative cells in interradicular and interseptal bone when compared to the mass of bone usually located at the apex of a tooth. Bone formation begins at the apex and proceeds gradually to the crest. The last area to mineralize is the crest and this process you can see in a previous article, “Watching Bone Grow“.
With this understanding, look at the preop radiograph. With pneumatization of the sinus, there is virtually no bone around the apex of the tooth. In addition, there is very little interradicular or interseptal bone present. This factor alone would slow and compromise the regenerative process. Fewer regenerative cells equals slower the regeneration but that is not the reason for failure at this site.
In addition to the lack of regenerative cells, the minimal bone that is present at the apex is covered by an inflamed sinus membrane. A bone physiology fact is that inflammation/infection = bone resorption, and normal bone will never grow in an inflammatory environment.
In this case, we are starting with a minimal number of regenerative cells in an inflammatory environment and no bone will grow in this situation. Four months after extraction, the sinus inflammation is still present as evidenced by the thickened sinus membrane. No bone will grow in proximity to this sinus pathology. After 8 months, the sinus pathology is still present as evidenced by the persistent thickening of the sinus membrane. Even without infection, the sinus pathology immediately adjacent to the socket is close enough to prevent mineralization.
Tooth extraction often occurs because the tooth is the nidus of the infection. It is assumed that when the nidus of the infection is removed, the bone will heal. Consequentially, many dentists will not prescribe antibiotics or will prescribe a minimal amount of antibiotics when doing extractions. In this case, a single dose of antibiotics was administered at the time of extraction. A single dose of antibiotics may be effective to prevent cellulitis, but it is not likely to eradicate the offending bacteria. While this is often adequate for extraction where the tooth is removed and no pathology is present, when sinus pathology is present a much more aggressive antibiotic dosing is required.
In our clinic, when sinus pathology is present, the sinus pathology is attacked prior to tooth removal. When sinus pathology is present, our routine is to prescribe Augmentin 500 mg tid for 3 days prior to extraction and 7 days post extraction. This aggressive antibiotic protocol has shown to be effective in providing a non-inflammatory environment in the extraction socket when sinus pathology is associated with the tooth being extracted. The preop dosing will significantly reduce bacterial load and inflammation, but of course alone will not control the sinus pathology. When the tooth is removed and the nidus of the infection is gone, the post operative antibiotics will eliminate the bacteria and its associated inflammation.
With a better understanding of how sinus pathology compromises alveolar regeneration, we can significantly reduce post operative complications and most importantly produce alveolar bone that does not require sinus augmentation for implant placement. Future posts will outline additional successes and failures of bone regeneration when sinus pathology is present in order explore how to best handle these complex cases.