The patient was treated for recurrent failure of her fixed dental prosthesis over several years. She was very upset with her situation because she works as a sales assistant in a department store and relies on impeccable function and aesthetics of her dentition.  The female patient was 61 years old when she presented at our clinic. She was a non-smoker in very good general health and did not take any medication. However, she felt anxious about dental treatment in general.  Coauthor: Patrick Zimmermann, Dental Technician, from Zahnmanufaktur, Bern, Switzerland.

Initial situation

There were no signs or history of temporomandibular disorders, and mouth opening was normal at 43mm. Thus, the access to the oral cavity was adequate, and even the posterior sites could be reached without restriction. There were no signs of abnormal occlusal activity such as bruxism. Intraorally, the patient presented with failing dentition in the upper jaw. Over the course of the last few years several tooth-borne fixed dental prostheses had failed. At the time of the first consultation she wore a provisional overdenture that covered the roots of teeth UR3, UR2, UR1, UL1 and UL2. The molar UL6 was also present. All the remaining tooth structures in the maxilla were largely affected by caries and heavily restored. In the lower jaw an intact dental arch from LL5 to LR5 was present. The periodontal condition was healthy, with no signs of inflammation and probing depths < 3mm. Functionally, the patient was satisfied with the shortened dental arch.  The aesthetic assessment showed a round, symmetrical face with evenly distributed facial compartments. The patient had a medium to high lip line and exposed some mucosa in the upper anterior region when smiling without the provisional prostheses. The buccal corridor was narrow and the gaps in the lower molar region were barely visible.

Treatment planning

The patient’s expectations were realistic and comprehensible; her wish was to be able to participate in the activities of daily living without constantly worrying about her dental condition. The removal of all remaining roots and teeth from the maxillary jaw was indicated. As the patient was already accustomed to wearing a removable dental prosthesis (RDP), the provision of an overdenture with horseshoe design retained by four unsplinted attachments on four implants was proposed to the patient. From the prosthodontic standpoint, there were several considerations that led to this proposal. The patient presented a medium to high smile line and exposed the transition area between the prosthesis and mucosa when she smiled. This can occur especially in fresh extraction sites and indicates that the atrophy of the alveolar bone is not very pronounced (Tallgren 1972). Thus, it seemed easier to restore aesthetics with a buccal flange of an overdenture. An unsplinted, very small stud-type attachment was also indicated because of the restricted vertical space. An RDP retained by a milled bar needs a minimum height of 12-14 mm and can severely interfere with phonetics. The Novaloc® stud-type attachment however demands very little space, since the female part is only 2.3mm high and 5.5mm in diameter. Thus, the Novaloc® attachment is one of the smallest  suitable attachments available on the market. Consequently, the anterior third of the maxilla (phonation zone) can be designed functionally (Clark et al.2006 20). Although some expert opinions demand the primary splinting of implants in the maxilla, no clear evidence exists in the literature demonstrating a higher survival rate for splinted implants (Schimmel et al. 2014). However, Cordaro et al. demonstrated a very high success rate for overdentures retained by four unsplinted stud-type attachments in the maxilla on narrow-diameter titanium-zirconium (Ti-Zr) implants (Cordaro et al. 2013 110). For a maxillary overdenture, a minimum number of four implants is advisable (Schley et al. 2013).  From a surgical point of view, the patient presented with very narrow alveolar crests, especially in the posterior regions. In the premolar region the width of the alveolar crest was only 2-3 mm. In the maxillary molar region the width of the crest was sufficient for implant placement, although the bone height in the region was very limited at just 1 mm.  The treatment plan was designed to provide the patient with a maxillary overdenture retained by four unsplinted Novaloc® attachments on four tissue-level TiZr implants. Therefore, the following treatment sequence was planned: 1. Extraction of the remaining roots and teeth in the maxilla, followed by a minimum healing phase of eight weeks. 2. Sinus floor elevation on both sides and guided bone regeneration in the canine regions, followed by a minimum healing phase of 6 months. 3. Placement of implants in the regions UR6/5, UR3, UL3, UL5/6. 4. Fabrication of the overdenture, starting three months after implant placement (conventional loading protocol). Taking all information into consideration, the current case was classified as “Complex” in the normative ITI SAC classification with low additional complexity/risk based on modifiers. The patient consented to the treatment plan after discussion of the alternatives and options. In comparison to fixed implant-supported prostheses, an implant overdenture also has advantages in terms of simplified hygiene and facilitated replacement of oral tissue (Feine et al. 1994).

Surgical procedure

The teeth and roots in the upper jaw were extracted in toto, and the existing denture was relined with tissue conditioner. After a sufficient healing time, the oral surgeon performed the augmentation procedures under local anesthesia. A ridge incision in the region UR7 to UL7 with two distal reliefs in the vestibule was performed. The mucoperiosteal flap was carefully raised, and bone chips were harvested with a bone scraper. The maxillary sinuses on both sides were opened with lateral windows, and the augmentation was performed with the bone graft mixed with bone xenograft in the ratio 1:1. In the canine regions the buccal cortical bone was perforated, and the bone graft was applied laterally and covered with a collagen membrane. After perforation of the periosteum the margins of the flap were fixed with simple interrupted sutures using Seralon® (5-0). The post-operative medication included ibuprofen 600mg and Aziclav 2x1gram/day and disinfectant mouthwash. After a sufficient healing time the implants (all Straumann, SP, 4.1mm, RN, SLAactive, TiZr, 10mm) were placed in the regions UR6, UR3, UL3, UL6 with good primary stability. A smaller bony defect in the UR3 region was covered with a mixture of bone chips and bone xenograft. The flap was sutured to allow for transgingival healing of the implants with adequate healing caps. Post-operative medication included ibuprofen 600mg, Aziclav 2x1gram/day and disinfectant mouthwash. After eight weeks healing time the implants showed high ISQ-values: UR6 (75), UR3 (77), UL3 (84), UL6 (86) and the oral surgeon referred the patient back to the prosthodontist for the reconstructive phase (Figs. 1-2).

Prosthetic procedure

An indirect prosthetic workflow was chosen. Accordingly, the correct height of the abutments was chosen with single-use try-in abutments. They click into the implant connection, and vertical marks allow for easy identification of the correct abutment (Fig. 3). It is strongly advisable to select the abutments clinically and not subsequently on the master cast. The height of the abutments was chosen to fulfill two requirements: First, the housing of the matrices should not touch the peri-implant mucosa to avoid trauma to the sensitive tissues. Therefore, the shoulder of the abutment should be placed at least 1mm above the mucosa (Fig. 4). The second consideration for the height selection comprises the path of insertion of the overdenture. In order to avoid interferences, the uppermost platforms of the abutments in one jaw should form an even plane, which ideally is parallel to the occlusal plane (Fig. 5). The technician provided special trays on the basis of preliminary alginate impressions. The impression posts were screwed in and their seating was carefully verified (Fig. 6). Subsequently, the impression was taken using the high-precision viscoelastic impression material Identium® (Kettenbach GmbH, Germany), which is a Vinylsiloxanether® (Fig. 7). The master cast was produced in a class IV stone that carried the appropriate implant analogs. On this master cast the occlusal wax rim was produced with already incorporated female parts to ensure maximum stability of the base plate. The anterior teeth were chosen from the Candulor NFC+® line (Candulor, Switzerland), form no. 660, shade M3, using the Candulor Alameter and Papillameter for determining the length of the upper lip and the anterior teeth. The Candulor Bonartic II TCR M3/06 were chosen as posteriors. The technician provided the set-up, and the patient consented to finalize the overdenture. In the lab, a reinforcement framework made out of PEEK (Peek Juvora by Amann Girrbach) was milled, and the PEEK housings of the Novaloc® attachment systems were bonded into this framework. The wax design of the overdenture was transformed into PMMA using the PMMA Candulor no. 34 and the Candulor Aesthetic blue colors 34, 53, 55 and 57. On delivery, the Novaloc® abutments were screwed into the implants and torqued with 35Ncm (Fig. 8), and the denture was fitted.

Final result

The overdenture was finished with individualized pink resin on the PEEK framework in a horseshoe design with open palate. It was shaped with individual palatal rugae and incisive papilla to match the patient’s anatomy and to allow for correct phonetics and easy adaptation to the new intra-oral situation (Fig. 9). A light retention was chosen for the denture with the white Novaloc® PEEK retention inserts (Fig. 10), with approximately 750 grams of retention force. This retentive force was largely sufficient, as the overdenture was retained by four attachments. The patient was extremely pleased with the treatment and the outcome. Much to her surprise, the surgery only caused her little discomfort. The prosthetic treatment was straightforward with a functionally and aesthetically pleasing outcome (Fig. 11). After many years of suffering the patient was finally able to smile again (Fig. 12).

Conclusion

In conclusion, an RDP in the upper jaw can be retained by four unsplinted attachments, but the implants should be large and strong enough for this indication. Therefore, a possible recommendation is to use implants at least 10mm long made from a reliable alloy like TiZr. The Novaloc® abutments are sufficiently small to ensure a denture design that respects phonetics and aesthetics. The stud-type attachments in general are widely applicable clinically as long as both the female and male parts show favorable wear behavior. The new coating on the Novaloc® abutment shows consistent in-vitro results, and the PEEK matrices may also prove to be more wear-resistant than inserts made from polyethylene. Further in-vitro and in-vivo investigations of the promising attachment systems may confirm these initial positive clinical experiences.