The maxillary sinus is an empty cavity that sits above the back teeth of your upper jaw. After the loss of teeth, this cavity can enlarge, leaving less bone to have a dental implant placed to replace the tooth. In such cases, the sinus membrane, which is a paper-thin barrier that protects your sinus cavity, is carefully lifted away and a bone graft is placed and allowed to heal for three to nine months. In many cases, an implant is placed at the same visit. A sinus lift is a relatively comfortable in-office procedure and generally takes no longer than 60 minutes.