Smartcem 2

To protect the Vickers indentations from contamination, they were covered with Mylar tape. The ceramic surface was pretreated with hydrofluoric acid (Ultradent Porcelain Etch, Ultradent Products, Inc., St. Louis, USA) and silane coupling agents (CLEARFIL CERAMIC PRIMER, Kuraray, Tokyo, Japan, or Monobond Plus, Ivoclar Vivadent, Schaan, Liechtenstein) strictly following the manufacturers’ recommendation (Fig. 1). The holes were then filled with increments of the nine self-adhesive resin composite cements ((1) G-CEM, GC Europe, Leuven, Belgium; (2) iCEM, Kulzer, Hanau, Germany; (3) Bifix SE, VOCO, Cuxhaven, Germany; (4) Maxcem Elite, Kerr, Orange, USA; (5) PANAVIA SA, Kuraray; (6) SoloCem, Coltene/Whaledent, Altstätten, Switzerland; (7) SmartCem 2, Dentsply Sirona, Konstanz, Germany; (8) SpeedCEM, Ivoclar Vivadent; (9) RelyX Unicem 2, 3M, Seefeld, Germany) or the glass ionomer cement (control group; Ketac Cem, 3M, Seefeld, Germany; n = 13 per subgroup). Specimens were covered with Mylar tape before curing of the self-adhesive resin composite cements was performed using a LED polymerization device with wavelengths between 430 and 480 nm (Elipar S10, 3M) for 60 s. The glass ionomer cement was self-cured. After polymerization, specimens were stored for 10 min before a repeated measurement of the crack length was performed.

All preparation walls were cleaned with pumice, and inlay restorations were ultrasonically cleaned in distilled water for 10 min and then air-dried. Inlays were luted with self-adhesive dual-cure resin cement (SmartCem2, Dentsply, Konstanz, Germany) (Figure 2). The cement was mixed with the manufacturer’s dispenser and applied to the cavity walls. Then, the restoration was positioned into the cavity by using a custom-made tip in a universal machine (Shimadzu, Tokyo, Japan) for standardization of cementation procedures. Excess cement was removed, then light curing (Elipar) was applied for 20 s through the proximal, lingual, buccal, and occlusal enamel walls recommended by the manufacturer, and kept under 50 N of static load for 6 min (total curing time). Finishing was performed with finishing diamonds (Prisma) and polishing disks (SofLex Pop-on, 3M ESPE, St Paul, USA).