| Objectives:This study compared the difference in tensile bond strength and shear bond strength between the composite resin and cast Ni-Cr disk when different physical retention struction were used to make the laboratory specimen. Methods:the adhesive systems tested were solidex light-cured hard composite resins.The microbeads used were spherical and had a diameter of 0.18 millimeter,which were filtered through a sieve to ensure a uniform size . The size of the collected beads were randomly verified with a x40 power microscope。Ninety-six wax cylindrical-shaped patterns were formed in an addition mold with the following dimensions: disk 4 millimeter thick and 8 millimeter in diameter ,which were divided into two groups,one group owns 60 patterns for tensile bond strength test ,the other group owns 36 patterns for tensile bond strength test.The tensile wax specimens were prepared and randomly and equally divided into five subgroups ,each containing 12 patterns(including the full retention bead group,semi-retention bead group, particle-roughened surface group,one third group, blank control group).The other thirty-six wax specimens were also randomly and equally divided into three subgroup,each also containing 12 patterns( including full retention bead group, semi-retention bead group,blank control group). A thin layer of adhesive was painted with a sable brush on the ground surface of each wax pattern. An even distribution of closely packed microbeads on the ground surface of wax pattern must be obtained.Excess microbeads collected at the periphery or overlapped on the wax pattern were removed and x40 power microscope to ensure a single uniform layer of microbeads.Twelve wax specimens were randomly closed from the others wax patterns ,which were roughed surface by NaCl particle( ≥99.5%).Twenty-four specimens were randomly prepared for shear bond strength group.A thin layer of adhesive was painted with a sable brush on the side of each specimen.An even distribution of closely packed microbeads must also be obtained. Excess microbeads collected at the periphery or overlapped on the side of wax specimen were removed under x40 power microscope to ensure a single uniform layer of microbeads.Others were regarded as blank control group.All specimens were invested and were cast with centrifugal casting machine. Each metal disk was sandblasted with 120μm aluminum oxide at 0.15MPa of air pressure,and was sandblasted again with 100μm aluminum oxide at 600KPa of air pressure after steam cleaned.The cast disk was examined under the microscope at x40 magnification to rule out any surface porosities.The retention bead was abrased 0.09 millimeter by precision machine tool in the semi-retention bead group,and was abrased0.12millimeter by precision machine tool in the one third retention bead group. The metal surface was treated with metal photo primer by a sable brush.The solidex composite resin was light-cured polymerized on the metal(wave length range of 320~520nm). All groups of specimens were tested after 24 hour immersion in distilled water at a 37 ℃temperature,2000cycles at 4~60℃. A universal testing machine was used to measure the tensile bond strength and the shear bond strength of the specimens at a cross head speed of 0.5mm/min.The rupture peak load was used to calculate the tensile bond strength and shear bond strength by the formula σ=F/S.Fractured specimens were examined by using stereomicroscope. The numeric results obtained were statistically assessed with SPSS software(Release version 12.0). The difference in tensile bond strengths and shear bond strengths were evaluated by use of one-way analysis of variance(ANOVA),followed by linear contrasts between systems at α=0.05. Results:The results showed that the strongest mean tensile bond strengths was obtained with the full retention bead group(6.57±0.18MPa), followed by the semi-retention bead group (6.20 ±0.35MPa),the particle-roughened surface group(5.91±0.55MPa),the one third retention bead group(2.93 ±0.43MPa),the poorest bond strengths group was observed for blank control group(2.18 ±0.47MPa).The linear contrast showed no significant difference between the mean tensile bond strengths of the semi-retention group and the particle-roughened surfacegroup.(p>0.05)There are ,however, a significant different when the mean tensile bond strength of the full retention bead group and semi-retention bead group;(p<0.05)The mean shear bead strengths of all test groups to blank control group were significantly different(p<0.01).For the mean shear bond strength ,the highest group was obtained for the full-retention bead(9.94 ±0.31MPa),followed by the semi-retention bead (9.47 ±0.61MPa),the blank control group (2.12 ±0.42).There are a sighificant different when the mean shear bond strength of the full retention bead group was compared with the semi-retention bead group and blank control group(p<0.05).Viewed with the microscope at x40 magnification ,all of the composite resin-bonded disks showed a complex fracture pattern at the surface of between resin and Ni-Cr alloy.In the periphery the fracture plane was seen on the top of the microbeads ,with resin tags remaining in the undercuts under the stereomicroscope at 10x10 magnification. Conclusion:Within the limitation of this in vitro study,the full retention bead groups should considerably higher tensile bond strength and shear bond strength than other groups.No statistical significant different was found in the mean tensile bond strength of the semi-retention bead groups(6.20MPa) and particle-roughened surface groups(5.91MPa).There was statistical difference when semi-retention bead groups was compared with one third retention bead (p>0.05).The result demonstrated that different physical retention struction on the surface of Ni-Cr alloy could be a factor in affecting the bond strength in the metal-resin interface.They also affectedthe bond strength between the composite resin and cast Ni-Cr alloy. |
PDF Full Text Request