Pre-cured composite resin cylinders (Filtek Z-250, 3M ESPE, St. Paul, MN, USA) were fabricated in transparent plastic tubes with an inner diameter of 3 mm and a height of 3 mm [12 (link)] using the incremental technique. Each layer of 1 mm thickness was light-cured with a light-curing unit with an intensity output of 1200 mW/cm2 (EliparTM S10, 3M ESPE, St. Paul, MN, USA). The composite resin cylinders were polished with 600-grit silicon carbide papers (Buehler, USA) under water coolant and cleansed ultrasonically in distilled water for 5 min before use.
The 3Y-TZP disks (N = 64) were randomly divided into two groups (n = 32), and the LDGC disks (n = 32) served as positive control. The ceramic disks were processed and bonded according to the following surface treatments:
(1) Group APA+MDP: 3Y-TZP disks were pretreated with APA, as described in 2.1, ultrasonically cleaned with 99.5% ethanol for 3 min then totally dried with oil-free air spray before being bonded with resin cylinders using MDP–containing resin cement (Clearfil SA Luting cement, Kuraray Noritake Dental, Japan) by mixing equal amounts of paste A and paste B of the cement for 10 s. The bonded specimens were kept under a 5N load [31 (link)] for 3 min [32 (link)].
(2) Group GCSD: 3Y-TZP disks pretreated with GCSD were etched with 5% HF (IPS Ceramic Etching Gel, Ivoclar Vivadent IPS, Liechtenstein) for 90 s, thoroughly water-sprayed for 2 minutes, cleansed and then dried with oil-free air spray as mentioned above. They were then applied with silane agent (Monobond N, Ivoclar Vivadent IPS, Liechtenstein), left undisturbed for 60 s and strongly air-dried for 5 s. Finally, they were bonded with resin cylinders using resin cement without MDP (Variolink N, Ivoclar-Vivadent IPS, Liechtenstein) by mixing equal amounts of base and catalyst paste for 10 s. The subsequent bonding procedure was same as that of Group APA+MDP.
(3) Group LDGC: LDGC disks were etched by HF, applied with silane agent and bonded with Variolink N following the procedure of Group GCSD.
A schematic illustration of the materials and methods for bond strength testing is shown inFigure 1 .
The 3Y-TZP disks (N = 64) were randomly divided into two groups (n = 32), and the LDGC disks (n = 32) served as positive control. The ceramic disks were processed and bonded according to the following surface treatments:
(1) Group APA+MDP: 3Y-TZP disks were pretreated with APA, as described in 2.1, ultrasonically cleaned with 99.5% ethanol for 3 min then totally dried with oil-free air spray before being bonded with resin cylinders using MDP–containing resin cement (Clearfil SA Luting cement, Kuraray Noritake Dental, Japan) by mixing equal amounts of paste A and paste B of the cement for 10 s. The bonded specimens were kept under a 5N load [31 (link)] for 3 min [32 (link)].
(2) Group GCSD: 3Y-TZP disks pretreated with GCSD were etched with 5% HF (IPS Ceramic Etching Gel, Ivoclar Vivadent IPS, Liechtenstein) for 90 s, thoroughly water-sprayed for 2 minutes, cleansed and then dried with oil-free air spray as mentioned above. They were then applied with silane agent (Monobond N, Ivoclar Vivadent IPS, Liechtenstein), left undisturbed for 60 s and strongly air-dried for 5 s. Finally, they were bonded with resin cylinders using resin cement without MDP (Variolink N, Ivoclar-Vivadent IPS, Liechtenstein) by mixing equal amounts of base and catalyst paste for 10 s. The subsequent bonding procedure was same as that of Group APA+MDP.
(3) Group LDGC: LDGC disks were etched by HF, applied with silane agent and bonded with Variolink N following the procedure of Group GCSD.
A schematic illustration of the materials and methods for bond strength testing is shown in
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