On minimally invasive approaches to sinus lift procedures

Aims: The overall aim of the present thesis was to evaluate implant survival and bone regeneration after minimally invasive sinus lift procedures. Material and methods: In study I, 61 patients were prospectively evaluated 12 to 60 months after two different methods of locally bone harvesting methods adjacent to the maxillary sinus lift procedure. In study II, spherical, hollow, and perforated hydroxyapatite space-maintaining devices (HSMD) with a diameter of 12 mm were manufactured for this pilot study. Three patients with a residual bone height of 1–2 mm and in need of a sinus augmentation procedure prior to implant installation were selected for the study. In study III, 14 consecutive patients in need of maxillary sinus floor augmentation were included. Preoperative CBCT with titanium screwposts as indicators at the intended implant positions was used to visually guide the flapless surgical procedure. Twenty one implants all with a length of 10mm and a diameter of 4.1 and 4.8mm were inserted and followed clinically and with CBCT for 3, 6 and 12 months postoperatively. In study IV, 24 consecutive patients were included and provided with 30 sinus lift procedures. Three procedures for lateral sinus lift were used: Lateral sinus lift with replacement of bone window and without bone graft (BW), lateral sinus lift and covering osteotomy site with a collagen membrane and without bone graft (CM) and lateral sinus lift with autogenous bone graft (ABG). Experimental implants were retrieved after 7 months of healing and analyzed by microcomputed tomography (μCT). Results: In study I the survival rate of implants after a follow-up of 12 to 60 months was 98.8% using locally harvested bone grafts at the site of the maxillary sinus augmentation. There was no significant difference in marginal bone loss on the mesial and distal sides of the implant when baseline to 1-year registration was compared with baseline to final registration. During the same time, graft height decreased significantly on the distal apical side of the implants. A HSMD used in a two stage sinus lift procedure can produce a void for a blood clot and new bone formation and subsequent implant installation (study II). There was minimal marginal bone loss after flapless, CBCT-guided osteotome sinus floor elevation with simultaneous implant installation during the follow-up verified by CBCT. The implants penetrated on average 4.4mm (SD 2.1mm) into the sinus cavity and the mean bone gain was 3mm (SD 2.1mm) (study III). All three methods for lateral sinus lift surgery in study IV were equal when new intra sinus bone formation was compared using data from μCT. Implants apices were seldom covered with bone at the time of retrieval. Conclusions: Bone grafts can be locally harvested at the site of the maxillary sinus augmentation procedure to enable placement, successful healing, and loading of 1 to 3 implants (study I). A HSMD used in sinus lift procedures can produce a void for blood clot and new bone formation and subsequent implant installation (study II). Flapless transalveolar sinus lift procedures guided by preoperative CBCT can successfully be used to enable placement, successful healing and loading of one to three implants in residual bone height of 2.6–8.9mm. There was minimal marginal bone loss during the 3–12 months follow-up (study III). With regards to lateral sinus lift procedure, high degree of bone-to-implant contact was found regardless of the surgical technique utilized. With regards to lateral sinus wall formation only the autogenous Bone Graft (ABG) group consistently regenerated a completely ossified bony wall (study IV).