59 Maxillary implant overdentures: four or two implants implant location from both a surgical and prosthodontic perspective. Regarding the experimental group, the implants were planned in the canine to lateral incisor region, enabling the connection of both implants by using a bar attachment system. The implants for the control group were planned in the first premolar to lateral incisor region. The implant positions were transferred to surgical template using computer software (3-Matic Medical 11.0; Materialise, Leuven, Belgium). To ensure optimal stability, the template was bone supported and extended into the nasal aperture15. All the participants were treated by the same oral and maxillofacial surgeon (GMR). All the implants (NobelActive NP 3.5mm, Nobel Biocare AB, Gothenburg, Sweden) were placed at crestal bone level using a surgical template and consecutive diameter drill sleeves, following the manufacturer’s instructions. Small bone dehiscences were covered with intra-orally harvested bone and a resorbable membrane (Bio-Gide®, Geistlich Pharma North America Inc., Princeton, USA). After placement, the flap was primarily closed using non-resorbable sutures, following a two stage submerged procedure and a conventional loading protocol. All the participants received antibiotics (500mg Clamoxyl, GlaxoSmithKline, Utrecht, the Netherlands) for seven days, three times daily, and a mouth wash containing 0.2% chlorhexidine (Corsodyl, GlaxoSmithKline, Utrecht, The Netherlands). All the participants were instructed not to wear their conventional denture until suture removal. After two weeks, the sutures were removed and the conventional denture was relined (Soft-Liner, GC, Leuven, Belgium). After three months of osseointegration the implants were provided with healing abutments during second-stage surgery, enabling the prosthodontic procedure. Prosthodontic procedure Preliminary impressions were made using stock metal trays (Schreinemakers; Clan Dental Products, Maarheeze, the Netherlands) and alginate (Cavex CA 37; Cavex Holland BV, Haarlem, the Netherlands), enabling the dental technician to produce individual impression trays (Lightplast base plates; Dreve Dentamid GmbH, Unna, Germany). The rims of the individual trays were relined using wax-based material (Iso Functional; GC Europe A.G., Leuven, Belgium). After placing screw-retained impression copings the final impressions were made with a polyether impression material (Impregum F; 3M ESPE, St. Paul, MN, USA). Vertical and intermaxillary relations were verified using wax rims and a pin registration device mounted on an individual record base (Lightplast base plates; Dreve Dentamid GmbH, Unna, Germany). Next, the wax rims were replaced by acrylic resin teeth (Ivoclar SR Orthotyp DCL and Ivoclar VivodentPE, Ivoclar Vivadent AG, Schaan, Liechtenstein), providing a trial arrangement following a bilateral balanced occlusion concept. Finally, the overdenture was provided with a virtually designed, 3D printed cobalt chromium reinforcement (Proscan, Zonhoven, Belgium) with point-lasered gold retentive clips (Cendres+Metaux, Biel/Bienne, Switzerland). Both groups’ participants received milled ovoid titanium bars or ‘Dolder bars’ with distal extensions. In the experimental group, the overdenture was attached to a single bar using 3 to 5 clips, dependent on the shape of the bar (Fig 4.2). In the control group, the overdenture was attached to one or two bars using 4 to 6 clips dependent on the shape of the bar(s) (Fig 4.3). All the participants received oral hygiene instructions and routine maintenance appointments. All the prosthodontic procedures were accomplished by one prosthodontists (HJAM). 4
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