thick enough, this bone can serve as the site for one or more endosteal bladevents. If exceedingly thin, great care must be taken not to perforate or fracture the bony barrier separating the sinus from the oral cavity. Pre-implantation surgical procedures must proceed particularly cautiously. When periodontally involved teeth are to be extracted from shallow bone, it is relatively easy to fracture and tear away bone and soft tissues along with the tooth — thus creating an oral-antral fistula.

Sometimes the bone below the sinus is not intact (photo).

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