Your maxillary sinuses are located behind your cheeks and above the upper back teeth. Sinuses are like vacant rooms filled with air. Some of the roots of your natural upper teeth go into the maxillary sinuses. When these teeth are removed, there is usually only a thin floor of bone that separates the maxillary sinus from your mouth. Dental implants need bone in order to hold them in place. When the sinus floor is extremely thin, a dental implant cannot be placed in the bone.
The solution to this problem is a sinus graft or sinus lift (augmentation). Your surgeon will enter the sinus from inside the mouth on the side or the sockets from where the upper teeth were. The sinus lining or membrane is then elevated with special instruments and the bone graft is then inserted between the elevated sinus ling and the bony sinus floor creating more bone height. After 4-6 months, the implants can be placed in the newly regenerated bone.
If there is enough residual upper jaw bone height to stabilize the implant, then implant placement and sinus lift can be performed in one procedure. If there is not enough bone available, you will require two separate procedures.