Table 2.

Different surface treatment of nine groups before binding.

Groups	Surface Treatment before Bonding
control	no treatment
SB + SL	sandblasting + silane coupling agent *
HF + SL	hydrofluoric acid + silane coupling agent
CAP-He	CAP jet with helium gas
CAP-He + SL	CAP jet with helium gas + silane coupling agent
SB + CAP-He + SL	sandblasting + CAP jet with helium gas + silane coupling agent
CAP-Ar	CAP jet with argon gas
CAP-Ar + SL	CAP jet with argon gas + silane coupling agent
SB + CAP-Ar + SL	sandblasting + CAP jet with argon gas + silane coupling agent

* RelyX ceramic primer (3M ESPE, St. Paul, MN, USA) as silane coupling agent was applied to RNC specimens for 1 min, and dried with oil-free air spray.