2. 1. Materials and Methods
Table (1) show materials used in this study.
Materials used in this study were:
1) Yttria- partially stabilized tetragonal zirconia ceramic blocks for CAD/CAM.
2) Luting cements (adhesive& Self-adhesive resin cements);
Adhesive resin cement (VITA ADIVA® F-CEM).
Self-adhesive resin cement (Calibra®Universal).
Conditioning Materials:
1) EDTA.
2) Polyacrylic Acid.
3) Self etch adhesive primer.
Table (1): The materials used in the study
Material type
|
Product name
|
Manufacturer
|
Lot number
|
Chemical Composition
|
Yttria- partially stabilized tetragonal zirconia ceramic blocks for CAD/CAM
|
IPSe.maX®ZirCAD
|
Ivoclar Vivadent, Schaan, Liechtenstein
|
W89510
|
ZrO2 + HfO2 + Y2O3: > 99.0
Y2O3: 4.5 – 5.6
HfO2: ≤ 5
Al2O3: ≤ 0.5
Other oxides: ≤ 1
|
50 µm Al2O3 for sandblasting
|
SHERA ALUMINIUM OXID 50 µm
|
SHERA
Werkstoff- Technologie, Germany
|
1799872
|
99.7% aluminum oxide
|
EDTA for dentin conditioning
|
MD-ChelCream
|
META® BIOMED,
Korea
|
2003201
|
K2H2EDTA,Ca(Cl)2,KOH
MD-Chelcream 7.0g (5.4ml) x 2
|
PolyAcrylicAcid for dentin conditioning
|
DENTIN CONDITIONER
|
GC,Tokyo,
Japan
|
1905301
|
10%polyacrylicacid(23.8 ml)
|
Self etch Adhesive
|
Optibond TMXTR
|
Kerr Italy
|
|
Primer bottle +
Adhesive bottle
|
Adhesive resin cement
|
VITA ADIVA® F-CEM
|
VITA
Zahnfabrik,
Germany
|
E72001839
|
Bis-GMA-based resins,catalysts,stabilizers,pigments,inorganic filler particles
|
Self adhesive resin cement
|
Calibra®Universal
|
Dentsply Sirona
|
00027156
|
Urethane Dimethacrylate resins,Barium boron FluoroAluminoSilicate Glass,organic Peroxide Initiator,Camphorquinone Photoinitiator,Accelerators,UV Stabilizer
|
Self-curing acrylic resin
|
Acrostone Cold Cure
|
Acrostone, Egypt
|
Missed
|
Powder: PMMA, Benzoyl peroxide, Pigments (1%)
|
|
|
|
Liquid: MMA,
Ethylene glycol, Dimethacrylate (10%), Hydroquinone (>1%)
|
2.2. Methods:
2.2.1. Teeth collection:
This study was approved by Ethical committee at Faulty of Dentistry, Mansoura University (No. M04150620). The informed consent form from the patients that their teeth were used in this study was waived by the same ethical committee. Sixty-four freshly extracted human mandibular first molars free of caries and cracks were collected for this study from outpatient dental clinic, in oral surgery department at Faculty of Dentistry, Mansoura university. These teeth were extracted due to periodontal disease. Teeth were cleaned by hand scaling and stored in a 0.1% chloramine solution throughout the course of the study.
2.2.2. Zirconia discs preparation:
A total of sixty-four zirconia discs of monolithic Y-TZP ceramic with the dimensions of 8 mm diameter and 3 mm thickness were fabricated using CAD/CAM technology. The zirconia discs were dry milled from zirconia blank IPS e.maX®ZirCAD (MO 2) Blank (Ivoclar Vivadent, Schaan, Liechtenstein) by using ceramill® Motion 2 CAD/CAM machine (Amann Girrbach, Austria).
2.2.3. Surface treatment of zirconia specimens:
Zirconia discs were randomized and divided according to the type of surface treatment of dentin into 4 main groups (n=16). The bonding surfaces of zirconia discs were sandblasted using 50 μm Al2O3 particles (SHERA Werkstoff-Technologie, Germany) under a pressure of 2 bars for 15 seconds with 10 mm distance perpendicular to discs bonding surfaces using Renfert Basic sandblaster (Renfert, Germany).
Zirconia discs were ultrasonically cleaned for 5 min in 95% alcohol and air dried.
2.2.4. Extracted teeth preparation:
Molars were mounted in plastic rings with chemical cured acrylic resin and were prepared by exposing flat coronal dentin surfaces by removing the occlusal enamel and superficial dentin with a low-speed, water-cooled diamond saw (PICO155).
Dentin surfaces were abraded with #600 grit silicon carbide paper under running water to create standardized smear layers.
Finally, all prepared molars were ultrasonically cleaned in distilled water for 5 min.
The prepared molars were then divided into 4 main groups (n=16) according to dentin surface treatment, as following:
Group "1": Dentin surface was left as cutted.
Group "2": Dentin surface was treated with Ethylene diamine tetra acetic acid (EDTA gel) by manual application on the cutted dentin surface for 30 seconds. Then, dentin surface was rinsed thoroughly with water. Finally, it was dried by blotting with a cotton pellet and gently blowing with an air syringe.
Group "3": Dentin surface was treated with Polyacrylic Acid dentin conditioner by applying to the bonding surfaces for 20 seconds using a sponge according to manufacturer instructions. Then, dentin surface was rinsed thoroughly with water. Finally, it was dried by blotting with a cotton pellet and gently blowing with an air syringe.
Group "4": Dentin surface was treated with self-etch adhesive according to manufacturer instructions. OptiBond XTR primer was applied to dentin surface for 20 seconds using scrubbing motion followed by air thin with medium air pressure for 5 seconds. OptiBond XTR adhesive was then applied to dentin surface for 15 seconds using light brushing motion followed by air thin with medium air pressure and then strong air for at least 5 seconds. Finally, light curing for 10 seconds was accomplished.
2.2.5. Bonding of specimens:
Each main group was subdivided into 2 sub-groups (n=8) according to type of resin cement used. The bonding of previously treated zirconia discs to treated dentin surfaces was performed according to manufacture instructions for each luting cement.
Subgroup (A): adhesive resin cement (VITA ADIVA® F-CEM).
Subgroup (B): self-adhesive resin cement (Calibra®Universal).
As follow:
Zirconia discs were secured to a specially designed device with lever system to deliver a constant load of 5 Kg on the dentin/zirconia discs assembly during cementation.
Each luting cement was automixed according to the manufacturer instructions and applied through the disposable automix tip on the bonding surface of the secured zirconia discs.
Zirconia discs were placed onto the conditioned dentin surface after cement application. The constant load (5 Kg) was applied on the dentin/zirconia discs assembly. Excess resin cement was removed with a micro brush then curing was done using (liteQ LD- 107, MONITEX, Taiwan) from four directions for 40 seconds. The bonded assembly was kept for 5 minutes under the static load.
2.3. Artificial aging
To simulate clinical condition, one hour after cementation, all specimens were stored in water bath at 37⁰C for 6 months followed by thermocycling for 10000 cycles using thermocycling device (Julabo®FT200, Germany) Each thermal cycle consisted of 5⁰C cold bath for 1 min and 55⁰C hot bath for 1 min with a dwell time of 30 seconds. Finally, specimens were air dried prior to shear bond strength testing.
2.4. Shear bond strength measurement:
Shear bond strength test was performed using Bluehill Lite Software from Instron(R). All specimens were mounted horizontally and individually on a computer-controlled testing machine (Model 3345; Instron Industrial products, Norwood, USA) with 5 KN loadcell. Computer software (Bluehill Lite; Instron Instruments) was used for data recording.
Shear force was applied using compressive load applied at dentin surface/zirconia disc interfaces. A chisel shaped mono-bevelled metallic rod attached to the movable upper compartment of testing machine was used for applying shear force at cross-head speed of 1mm/min. The required load for debonding was recorded in Newton. The bond strength was expressed in Mpa by dividing the load at failure by the bonded surface area.
2.5. Failure analysis:
The debonded specimens were examined using binocular optical microscope to determine the mode of failure. The recorded failure patterns were one of the three following types:
- Adhesive failure pattern.
- Cohesive failure pattern.
- Mixed failure pattern.
2.6. Scanning Electron Microscope (SEM):
Each examined specimen was sputter coated with gold using (K550X Sputter Coater, England) followed by SEM of the surface topography of each specimen. SEM examination of representative specimens figures (1-8) of each failure pattern was done under (×500 magnification) using Scanning Electron Microscope (Quanta 250-FEG, FEI, Netherlands).
2.7. Statistical analysis:
The SPSS statistical package for social science version 22 (SPSS Inc., Chicago, IL, USA) was used for data analysis. Kolmogorov Smirnov and Shapiro-Wilk tests were used to test the normality of the shear stress values. The data was parametric and normally distributed. Descriptive statistics were performed in terms of mean, median, standard deviation, range, minimum, maximum. Two-way ANOVA was used to test significant difference in shear stress between groups and between surface treatments followed by Tukey post hoc test for correction of p value resulted from multiple comparisons. P was considered significant if < 0.05 at confidence interval 95%.