A 3-D view of the maxilla, indicating the bony area behind which the maxillary sinus cavity is
A projected CT slice through the maxillary sinus at the level of the back teeth
The cross-sectional CT scan slice from the picture on the left. Notice that the red double arrows indicate only about 3-4mm of bone - not enough to place a dental implant
The maxillary sinus is the largest of the sinus cavities we have in the upper jaw or maxilla. It is located just to the inside of the bone in the upper cheek area, as indicated in the image above. The maxillary sinus starts out as a small air cavity in children and then expands and gets bigger as we grow older. Once teeth are missing in the back areas of the upper jaw, the sinuses will expand even further down towards the jaw ridge from the inside of the jaw bone.
When the above image is tilted "downward", so that you can get a sectioned view from the top, you can clearly see the right and left maxillary sinuses in the upper jaw. Notice how large these cavities can become when all the teeth are gone. The sinus cavity is lined with a membrane.
This membrane is unique in that it is histologically actually a "bilaminar" membrane, with cilitated columnar epithelial cells oriented towards the inside of the cavity and a periosteum-type layer oriented towards the bony side of the cavity. This makes the membrane actually quite resilient and fairly easy to manipulate.
When there is not enough bone height from the top of the jaw ridge, as it is shown in the cross-sectional CT scan slice in the image above, then a sinus augmentation or sinus lift procedure is indicated. These two terms are often used interchangeably, but they are actually two very distinct procedures, achieving the same result.
A sinus augmentation procedure is what is shown on the images to the left. Here the tissues are reflected somewhat above the root tip level of the the teeth and a "window" is cut to access the sinus cavity. As you can see on the left, the window is first outlined and then infractured. After that the sinus membrane is carefully curetted and detached from the floor of the sinus and lifted "upwards" as can be seen in the middle picture. Once the lift is sufficiently high, a bone graft is placed underneath the sinus membrane, in order to keep it in "tented up" in this position. With this we have effectively "raised" the floor of the sinus in that portion. Typically the bone graft matures within the following six to twelve months enough to where the dental implants can be placed into the grafted sinus space.
A sinus lift, on the other hand is a much simpler procedure. A sinus lift is usually performed right through the hole, which is prepared for the dental implant (this procedure is not shown here). This usually means that the implant is placed at the same time of the lift (which is most often not the case with the augmentation procedure). A sinus lift is also usually performed when the "lift amount" needed is not as big.
Sinus Augmentation Procedure
