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.
The sinus lift procedure is a simpler procedure than the sinus augmentation procedure, because it is performed right through the same hole which is prepared for the implant fixture. It is therefore often a less traumatic procedure than the sinus augmentation. On the other hand this procedure is often reserved for minimal elevations, although new hand instruments and piezoelectric instruments have recently been developed, which allow for much more aggressive lifts.
The procedure is typically started by preparing the hole for the dental implant fixture, either with rotary drills or bone expanders. Once the diameter of the hole is close to that of the implant fixture and the length of the hole is to within 1or 2 mm of the floor of the sinus (see images to the left), osteotomes are being used to start the lifting procedure.
A little bit of bone graft or collagen is placed into the hole and the osteotome is inserted all the way into the implant hole. Now, with very light tapping onto the osteotome with a surgical mallet (basically a fancy name for a surgical hammer), the osteotome is "pushed" further up towards the floor of the sinus. Eventually, the floor of the sinus will "break", but the membrane, which lines the inside of the sinus stays intact.
What happens next will largely be determined by the amount of lift that is needed. For a small lift, the osteotome can be pushed in further with continued action of the mallot until a maximum lift distance of 3-4mm is reached. For a larger lift, different hand instruments or piezoelectric instruments need to be used, in order to carefully detach the membrane around the implant hole.
Once the membrane has been loosened enough, more bone graft can be used to "push" the membrane up further and thus increase the lift distance. Once the final lift distance has been reached, the dental implant can be placed into the prepared hole, as can be seen on the image on the left.
One of the disadvantages of this procedure is that one does not have a direct visual contact to the membrane. This is only the case with a sinus augmentation.
