The upper back jaw loses bone height fast after an extraction, and a sinus lift rebuilds it so an implant has something solid to hold on to.
The maxillary sinus sits directly above your upper molars, separated from them by a floor of bone that is often only two or three millimetres thick. Once a molar is extracted the ridge resorbs from above while the sinus quietly expands downwards, and within a year the remaining height can fall below five millimetres. A standard implant needs roughly eight to ten millimetres of anchorage, which is why a three-dimensional CBCT scan, not a panoramic X-ray, decides this question.
With five to eight millimetres of bone left, the sinus floor can be tapped upwards through the implant socket itself. The membrane is raised three or four millimetres, graft granules are packed underneath and the implant goes in during the same appointment. Below four or five millimetres we open a small window in the side wall instead, lift the membrane under direct vision, fill the space and let it mature before any implant is placed.
The granules are usually processed bovine bone mineral, treated until no protein remains, often mixed with your own bone chips collected during drilling. It behaves as a scaffold rather than a filler: over six to nine months your body grows vessels and new bone into the spaces and replaces most of the granules. A resorbable collagen membrane holds everything in position while that happens, so the implant finally sits in remodelled bone of your own.
A crestal lift changes nothing about your schedule, because the lift and the implant happen in one sitting. A lateral window means two trips: surgery now, implants six to nine months later, crowns a few months after that. Any clinic promising fixed teeth in a single week over three millimetres of bone is either skipping the graft or placing short implants without saying so. We would rather quote two trips and lose the booking.
A lateral window gives swelling and a feeling of pressure for three to four days, closer to a wisdom tooth extraction than to a filling. The rules that matter are no nose blowing, no straws and no flying for a week, because pressure is what disturbs a healing membrane.
Small perforations are common and are patched with a collagen membrane in the same session. A large tear means we close, wait a few months and repeat the lift. A surgeon who tells you this on the day it happens is behaving correctly; one who never mentions it is not.