Twenty-five PICN crowns (Vita Enamic, Vita Zahnfabrik, Bad Säckingen, Germany) for premolars were produced using CAD/CAM technology and polished with the Vita Enamic Polishing Set Technical (Vita Zahnfabrik) as recommended by the manufacturer. All crowns were bonded to identical one-piece zirconia testing implants. The implants were turned from pre-sintered zirconia blocks (VITA In-Ceram® 2000 YZ–55, VITA Zahnfabrik) by the faculty of physics and geosciences at the University of Leipzig. Subsequently, the implants were sintered in a dental laboratory. The abutment had a cone angle of 3 °, while the length of the implant totaled up to 21.5 mm. The abutment length was 6 mm. The thread was conceived schematically.

Twenty of the specimens belonged to the experimental group (n = 20) and underwent mechanical loading and wear behavior tests, whereas five of the specimens (n = 5) only underwent the pull-off tests.

Five specimens fit into the chewing simulator which is why five specimens were prepared at a time. Therefore, four rounds of CS were performed.

All steps of the bonding procedure followed the manufacturer’s instructions: the bonding surface of the crown was degreased with alcohol and conditioned with 5 % hydrofluoric acid gel for 60 s (Vita Ceramics Etch, Vita Zahnfabrik). The hydrofluoric acid gel was removed with water spray and the bonding surface was dried for 20 s. Conditioning of the bonding surface of the implant was ensured by sandblasting with aluminum oxide (Al₂O₃) 110 μm at 1 bar and cleaning with alcohol. After that, a bonding agent (Scotchbond Universal, 3M ESPE, St. Paul, MN, USA) was applied to the surfaces to bond the crown and the implant and both dried with air. The crowns were adhesively bonded (RelyX™ Ultimate, 3M ESPE) to the one-piece zirconia implants. Photopolymerization of the luting agent was carried out by a dental curing light for 40 s on each surface.

All specimens were embedded in acrylic resin (Technovit 4000, Heraeus Kulzer GmbH, Wehrheim, Germany) with a parallelometer for the exact vertical orientation. Epoxy was prepared according to manufacturer’s data, and the specimens were embedded directly into the sample holder of the chewing simulator. Figure 1 shows a luted crown on an embedded implant ready for CS.