Clearfil ceramic primer

The composite material was applied to the specimens in Groups A2, B2, C2, D2, and E2. The groups were treated first with silane for 60 s. Clearfil Ceramic Primer and Clearfil SE BOND primer, mixed one to one according to the manufacturer’s instructions (Kuraray Medical Inc., Japan), were applied to the remaining specimens of Groups A, B, C, D, and E. After application of Clearfil Ceramic Primer and Clearfil SE BOND primer mixture, Clearfil SE BOND (Kuraray Medical Inc., Japan) was applied and polymerized for 40 s. A 2 mm thick composite (Kuraray Esthetic Majesty, Kuraray Medical Inc., Japan) was applied to each sample surface with reference to the 2 mm high silicone matrix that was formed. After the matrix was removed, each sample was polymerized for another 20 s on each surface.

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.

The materials used in this study are presented in Figure 1. The experimental flowable resin composites were developed in collaboration with Tokuyama Dental, Tokyo, Japan. Nine experimental flowable resin composites consisting of different sizes and loadings of spherical fillers were used. The size and loading of the spherical filler in each group is shown in Figure 2. The experimental flowable resin composites used in this study are shown in Figure 3. A bonding agent (Bond Force, Tokuyama Dental Corp., Tokyo, Japan) and a ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake Dental Inc., Tokyo, Japan) were used for bonding between a ceramic cavity and experimental flowable resin composites.