Three different oral and maxillofacial surgeons performed the sinus lift procedure with an external approach according to comparable surgical standards and inserted all implants examined in this study in a submerged protocol with uncovering after 3–4 months due to the manufacturer’s surgical recommendations. Specifically, a total of 35 external sinus floor elevations were performed through a bone window in the facial aspect of the maxillary sinus. The internal sinus lift approach was applied once. In four patients, sinus floor elevation was accompanied with a LeFort I osteotomy or in one case with a reconstruction of the maxilla after tumor surgery. Preexisting defects were assumed due to trauma or previous surgical interventions in three operation sites.

For sinus floor augmentation including defects of less than 2 cm³, bone filter material and bone substitute [13, 14] were applied. If the defect exceeded 2 cm³, only autologous bone was used.

Perforations up to a diameter of 5 mm in size were covered with a BioGide membrane (Geistlich, Wolhusen, Switzerland), and perforations beyond a diameter of 5 mm up to 10 mm were additionally stitched with resorbable sutures (Vicryl 6-0, Ethicon, Norderstedt, Germany) while larger defects led to termination of the procedure. Only in exceptional cases were perforations left untreated or sealed with fibrin glue.

Implants were either placed in a one-stage procedure accompanied with the sinus floor elevation or in a two-stage procedure if primary stability might not be achieved due to the bone being present.

Patients received antibacterial mouth rinse, systemic antibiotics, nose drops, and inhalants from 7 to 10 days beginning directly after the operation. Sutures were removed 7 to 10 days after the surgical procedure. All patients were instructed how to maintain appropriate oral hygiene directly after surgical intervention and were re-instructed after the uncovering procedure and during recall sessions. Patients were further asked to join for regular recall examinations after prosthodontic rehabilitation and thereafter each year. Six months after sinus floor elevation, panoramic radiographs were made.