| Objective:To study the effect of Er:YAG laser surface treatment with different output energy and pulse width on the bonding strength of zirconia ceramic-resin cement in vitro.Methods:88 specimens(specification:10.0mm x 10.0mm x 3.0mm)of zirconia ceramic slice made by CAD/CAM were polished with 400#,600#,800#water sand paper in turn.They were randomly divided into 11 groups(n=8)according to the random digital table method.Sandblasting group(SB group):sandblasting with 110 ?m alumina particles;laser etching group(E1-E9 group):E1-E3 groups with output energy of 100mJ and pulse width of SSP/MSP/SP,respectively.The output energy of E4-E6 groups were 200mJ,the pulse width of SSP/MSP/SP,E7-E9 groups were 300mJ,and the pulse width of SSP/MSP/SP;control group(group C):without any treatment.The surface roughness of all samples was measured,then one sample was randomly selected from each group and the surface morphology was observed by scanning electron microscope(SEM).A total of 77 resin columns(4 mm in diameter,3 mm in height)were made from polyethylene tubes.The resin column was bonded with Panavia F cement to the surface treated with zirconia.The adhesive samples were stored in water bath at 37? for 24 hours and embedded in self-condensing resin.The embedded samples were fixed to a universal material tester under shear loading at a constant speed of 0.5mm/min.The maximum load values of the interface fracture between porcelain and cement were recorded and the shear strength values were calculated before the oxidized specimens were bonded.The fracture patterns of each sample were observed under stereoscopic microscope.Single factor analysis of variance(one-way ANOVA)was performed on the experimental data by using SPSS 21.0 statistical software,and multiple comparisons were performed between groups of LSD test lines(test level a = 0.05).Results1.Surface roughness measurement:Ra value of the control group was the lowest,which was(0.691±0.131)?m.The Ra values of sandblasting and the laser etching group were higher than that of the control group,and the differences were statistically significant(P<0.05).The results of pairwise comparison of Ra values between the experimental groups showed that the Ra values of E3,E6 and E9 groups were lower than those of sandblasting group,and the difference had statistical significance(P<0.05),while there was no significant difference between the other laser groups and sandblasting group;2.SEM observation:the surface of Zirconia sample in the control group was flat and a small number of shallow scratches were observed,and the surface of the sand blasting group showed a shallow pit-like rough surface.The surface of each group of laser etching samples showed different degree of crystal dissolution and rough surface.No obvious material defects or cracks were found in each experimental group.3.Shear strength:the shear strength of the control group was the lowest,which was(3.634±1.182)MPa;.The shear strength of the laser etching group was higher than that of the control group,and the difference was statistically significant(P<0.05).There was no significant difference in shear strength between laser treatment group and sand blasting group except E3 group(P>0.05).When the laser energy was the same,the shear strength values of all SSP/MSP/SP groups showed that SSP group>MSP group>SP group,that is,shear strength decreased with the increase of pulse width,but there was no significant difference(P>0.05).The different energy groups(100mJ,200mJ,300mJ)showed that:300mJ group>200mJ group>100mJ group,that is,shear strength value increased with the increase of energy,while the laser pulse width was the same,the shear strength values of different energy groups(100mJ,200mJ,300mJ)showed a tendency to increase with the increase of energy.But there was no significant difference(P>0.05).4.Fracture mode:the interface failure was mainly in the control group,the mixed failure was the main fracture mode in sand blasting and laser etching groups,and the interface failure was followed by the interface failure in the control group.Conclusions1.Er:YAG laser etching and sandblasting can increase the surface roughness of the oxide and change its appearance.2.Er:YAG laser etching can improve the bonding strength between the resin cement and zirconia,which can be considered as a pre-treatment method for zirconia bonding.3.Er:YAG laser treatment with higher energy and shorter pulse width may achieve a similar effect as the sandblasting treatment. |
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