Dear friends, in the next few minutes we will discuss some implications of implant dentistry in the posterior maxilla. As we have seen previously, the extraction of teeth is a catalyst to a chain reaction that leads to compromise of the alveolar bone and the soft tissues. In the case of the posterior maxilla, we have two different phenomena which together can significantly reduce the availability of bone for dental implants. The first, is the reduction of the height and width of the alveolar ridge which occurs normally after every extraction. The second, is what we call the pneumatisation of the sinus. Pneumatisation is one of the funny Greek words that is easier to understand than to actually pronounce. In Greek, it means to "pump air" into something, to inflate. And exactly this is how it looks like sometimes, the sinus cavity expands as if a balloon is actually inflated inside. Is there a balloon in the sinus? Not really, but then again I like the idea! Let's try to imagine a bit of the anatomy. Sinus is lined with a very thin membrane, the sinus mucosa or Schneiderian membrane. And just like a balloon this membrane has only one opening at the highest point, the Ostium, where it communicates with the nose. If you think about it, the sinus is under mild but constant pressure changes as long as you live. Every breath you take in, creates negative pressure in the sinus cavity and every time you breathe out, the pressure becomes positive. If the sinus membrane wasn't firmly attached on the bone what we could see with every breath would resemble the idea of the balloon. And if you prefer the real thing to the animations, take a look at this clip. The membrane detached from the sinus walls during augmentation surgery as it moves following the breathing of the patient. This is actually an elderly patient with a thick fibrous membrane. Sometimes the move can be much more spectacular, especially in younger patients with thinner and more sensitive membranes, as in this case. So maybe the balloon metaphor might be not so far from the reality after all! The dynamics of the anatomy might give you a good idea of the complexity of this area when it comes to implant surgery. The constant pressure changes transferred to the mechanosensitive bone through the sinus membrane might contribute to the gradual expansion of the sinus after teeth are lost. Regardless of the cause, a recent radiographic study estimated that approximately 60% of the bone loss height is attributed to the marginal alveolar ridge reduction, while about 35% is due to the sinus pneumatisation. This means that we often have to augment both the sinus as well as the alveolar ridge, in order to place the implants in the proper prosthetic position. Does the extent of the pneumatisation correlate with the amount of the missing teeth? A clear answer to this is not easy based on the existing research. In one of our three dimensional radiographic studies we found that the bucco-lingual width of the residual alveolar ridge was related to the presence or absence of adjacent teeth, but not the height. A good predictor of reduced bone height appeared to be periodontal bone loss at the existing teeth and evidence of abnormal lining of the sinus membrane. Often, we will see that the presence of a single posterior tooth appears to prevent major sinus expansion, but other times, even the loss of one single tooth can provoke a significant downgrowth of the sinus. What appears to be significant predictive factor is the relation of the roots of the posterior teeth to the actual floor of the sinus and this is something that is not easy to evaluate on the basis of two-dimensional radiographs. Very often, the apical portion of the roots of the molars are in very close proximity or even intermingled with the sinus floor. In such cases, extraction of the teeth can actually lead to much faster pneumatisation of the sinus. Consequently, in order to address the challenges of this compromised anatomy, sinus floor elevation and sinus augmentation procedures have been proposed with the most established being the Transalveolar or Osteotome technique and the Lateral window sinus floor elevation. Each of these approaches will have many modifications and also specific indications and contraindications. In general, 8 mm or more of bone height should be enough for the placement of an implant without engaging the sinus. Cases where we have 6 to 7 mm combined with a flat sinus floor are well indicated for the Osteotome technique. Similarly, we can treat cases with 4 to 5 mm and a flat sinus floor with osteotome, only here, often a grafting material is recommended. Cases with an oblique sinus floor or with less than 4 mm of residual bone height are typically treated with the lateral window approach. In the case of the lateral window, implants can be placed simultaneously with the sinus elevation if the residual bone height is enough to offer primary stability. Otherwise, a two-stage procedure is followed and implants are placed six to nine months after the sinus augmentation.
