22 Chapter 2 Surgical procedure All the participants received four maxillary implants (Nobel Active Narrow Platform ⌀ 3.5 mm, Nobel Biocare AB, Gothenburg, Sweden), guided by a surgical stent at crestal bone level in predefined positions (anterior implants in the central/lateral incisor region, posterior implants in the cuspid/first bicuspid region) via a two-stage surgical protocol. Incidental bone dehiscence was covered with a mixture of maxillary tuberosity bone and organic bovine bone (Bio-Oss, Geistlich Pharma AG, Wolhusen, Switzerland) and a resorbable membrane (Bio-Gide, Geistlich Pharma AG). In case of partial extension into the anterior region of the sinus, sinus floor elevation surgery was performed using the lateral window technique11 with bone harvested from the tuberosity and mixed with organic bovine bone. The lateral window was covered by a resorbable collagen membrane. If not already present, the participants simultaneously received two mandibular implants (Nobel Replace Select TC, Nobel Biocare AB). All the participants received antibiotic prophylaxis before the surgery (Amoxicillin, 3000mg, one hour preoperatively), and then continued afterwards with antibiotics (amoxicillin, 500mg, three times daily, seven days) and an additional 0.2% chlorhexidine mouth rinse (Corsodyl, GlaxoSmithKline). The participants were instructed not to wear their conventional prosthesis for two weeks. Thereafter, the prosthesis was adjusted with a resilient lining material (Soft liner; GC Corp., Tokyo, Japan). After a 3-month osseointegration period, second stage surgery was performed by placing healing abutments and a standard prosthetic procedure was initiated. Prosthodontic procedure The solitary attachment group’s final superstructure consisted of an overdenture with a built-in cobalt chromium reinforcement structure with Locator® denture caps and nylon Locator® males which were connected to four Locator® attachments (DIT-USA, Scottsdale, Arizona, USA; Fig. 2.2). The study’s participants were initially provided with pink inserts (13.4 N; medium force), providing possibilities to strengthen or loosen the retention force. Regarding the bar group, the final superstructure consisted of an overdenture with gold retentive clips (Cendres+Metaux, Biel/Bienne, Switzerland) that were point-lasered to a virtually designed, 3D-printed cobalt chromium reinforcement (Proscan, Zonhoven, Belgium), attached to a virtually designed, milled ovoid titanium bar with distal extensions (Proscan, Zonhoven, Belgium) which were screw-retained to multi-unit abutments (Nobel Biocare AB) (Fig. 2.3). The overdenture was attached to the two bars with three retentive clips per bar. Both groups’ overdentures were designed without palatal coverage of the maxilla. Most participants simultaneously received a mandibular IOD. In case the participant’s current IOD was adequate, no new IOD was made. The participants were instructed in hygiene procedures associated with the overdentures and superstructures, and routine maintenance appointments were scheduled.
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