Implant survival

Two of the 27 initially placed implants were lost in the control group (Table 1). Twenty months after placement of the implant-supported crown, one implant (first premolar, regular platform (4.3 mm), length: 13 mm) was lost due to failed osseointegration. No periodontitis or peri-implant marginal bone resorption was obvious at the time of implant removal. A second implant (central incisor, narrow platform (3.75 mm)) was lost during the placement of the final implant crown. For unknown reasons, a minimal rotation of the implant crown occurred several times when the abutment screw was torqued. In the phase of counter-torqueing the abutment screw, the implant loosened and was finally lost. Three months after the implants were lost, sufficient alveolar bone was still present in both patients and new implants were installed without further complications. Consequently, 11 out of 13 implants (85%, 95% CI: 62–104%) survived in the control group, and 14 out of 14 implants survived in the PRF group (100%). There was no statistical difference in implant survival between the groups (p = 0.13).

Implant crown survival

None of the 26 initially placed implant crowns were lost, but one implant and therefore one implant crown was lost after 20 months. Consequently, the definitive implant crown survival was 92% (95% CI: 73–110%) in the control group and 100% in the PRF group. No statistical difference in implant crown survival was seen between the groups (p = 0.28).

Probing depth

At the follow-up, the mean PD in the PRF group was 2.19 (95% CI: 1.95–2.43) mm at implant level with a variation of 1–4 mm at site level. In the control group, the mean PD was 2.13 (95% CI: 1.86–2.41) mm at implant level with a variation of 1–3 mm at site level. The difference between the groups was − 0.06 mm (95% CI: − 0.42–0.30). No statistical difference in PD was seen between the groups (p = 0.74).