40 Clinical evidence and Science Edentulous situation Fixed full-arch restorations on four implants in the mandible Treatment of edentulism with dental implants increases the quality of life and functionality for patients affected. A working group at the Consensus Meeting of the Oral Reconstruction Foundation discussed and issued clinical recommendations for implant-supported full-arch rehabilitations in edentulous patients based on elaborated systematic reviews, e.g. about how to treat an edentulous mandible or maxilla and the influence of material selection and attachment type (Schwarz et al. 2021) (11). Prof. Gerald Krennmair and Dr. Stefan Krennmair from Austria published various papers on the topic of four implants-supported fixed prosthesis in the mandible in edentulous patients which has become the predominant method for fixed rehabilitations. The fixed overdentures were in all cases screw- retained on CAMLOG® SCREW-LINE implants. The common concept of placing four implants in the edentulous mandible is to place the anterior implants in an axial direction and the distal ones tilted. Krennmair et al. 2016 compared with two groups the clinical outcome of only axial implants versus two axial/two distal tilted implants (12). The follow-up of the restorations with cobalt-chromium framework covered three years. The evaluation showed no implant loss nor major prosthetic complications (fractures). The only significant difference found was for plaque index and calculus index when comparing the posterior implants of both groups. All other parameters like bone level change, pocket depth, bleeding index, and gingival index as well as from a complication’s perspective showed no differences and a good clinical outcome for both concepts. In a retrospective review including 38 patients 152 implants were analyzed (Krennmair et al. 2013) (13). After a healing time of 8 to 12 weeks splinted superstructures consisting of cobalt-chromium were fixed to the implants. The survival and success rates on the implant level after a follow-up time of five years were very high with 100% and 98.6%, respectively. The prostheses, however, required more maintenance like repairs, especially of resin teeth fractures and relining of the base. Also, they had to be removed twice during the follow-up time for professional cleaning activities. Another investigation examined the outcome of immediately loaded distally cantilevered fixed mandibular prostheses on four implants (Krennmair et al. 2014) (14). The implants were placed either in fresh extraction sockets or healed sites and immediately restored with a fixed prosthesis. After three months the definitive resin veneered prosthesis with a metal framework was integrated. At two years follow-up no implants were lost. Again, complications were more often found on the prosthetic level. In total, five provisional dentures fractured. No fractures occurred with the definitive prostheses. Interestingly, the implants placed in fresh extraction sockets experienced less bone loss than the implants placed in healed sites. In another prospective study with a follow-up time of five years but with the same design and study procedure, the implants showed still a survival of 100% (Krennmair et al. 2022) (15). The marginal bone level change with the implants placed in fresh extraction sockets, however, was different. The initial bone loss was more pronounced than with the implants placed in healed sites. After the one-year follow-up, the bone loss was again similar and not statistically significant different between the groups. PROSTHETIC RESTORATIONS: SCIENTIFICALLY BASED TREATMENT OPTIONS
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