Effect Of Bond Strength Between Alloy With Different Surface Roughness Used To PFM And Dentin

Objective:To compare the bond strength between Ni-Cr alloy, Titanium alloy, Co-Cr alloy with different surface roughness and dentin respectively.Methods:The Ni-Cr alloy, Titanium alloy, Co-Cr alloy were collected for the experiment. Every kind of them was 30 pieces and they were randomly devided into 6 groups,5 samples for each group. All groups of specimens were rubbed separately with 60,80,100,150,240,320 grit silicon carbide sand paper, then surface routhness of each group was measured. The occlusal surfaces of 90 freshly extracted human molars were flattened to expose an adequate area of lower dentin. Followed by wet-grinding on a series of Si-C sand paper from number 320,400,600 grit to produce the dentin bonding surface, then divided randomly into 18 groups. Each alloy and dentin specimens were bonded with Ketac TM Cem Easymix GIC bonding system. All bonded specimens were stored in 37℃distilled water for 24 hours, and tested under microtensile loading until fracture on the universal testing machine. The bond strength of each group was analyzed by using SPSS13.0 Microsoft ANOVA test. The differences among mean values were compared by Student-Newman-Keuls multiple comparison test. Take Co-Cr alloy specimens for example, the fractured surface of alloy were observed with scanning electron microscope.Results:①In Ni-Cr alloy groups, ANOVA detected statistically significant differences between sub-groups (F=8.837, P<0.001). The post SNK-q test showed that,the bond strengths of 150 grit group were significantly higher than other groups (p<0.05). In other groups, the bond strengths between 240 grit and 320 grit groups were statistically different (p<0.05).②In Ti alloy groups, ANOVA detected statistically significant differences between sub-groups (F=26.501, P<0.001). The post SNK-q test showed that,the bond strengths of 80 grit and 320grit groups were significantly different to other groups (p<0.05). In other groups, the bond strengths among 60 grit,150 grit and 240grit groups were statistically different (p<0.05).There were no statistically differences among 100grit,150grit and 240grit groups (p=0.267>0.05).③In Co-Cr alloy groups, ANOVA detected statistically significant differences between sub-groups (F=3.849, P=0.011<0.05). The post SNK-q test showed that,the bond strengths of 150 grit group were significantly higher than other groups (p<0.05). There were no statistically difference among other groups (p=0.628>0.05).⑤Broken surface of alloy specimens in this group were observed with scanning electron microscope showing the sectional surfaces with different surface roughness were different.④The bond strength between alloy and dentin was affected not only by surface roughness of alloy (F=14.048, p<0.001),but also by the kinds of alloy (F=61.127, p<0.001);The interaction of the two factors can affect the result too (F=10.322, p<0.001).Conclusions:①, The surface roughness could affect the bond strength between alloy and dentin.②, The bond strength between different alloys and dentin was different.③, Ni-Cr alloy and Co-Cr alloy rubbed with 150 grit Si-C sand paper, separately with 2.14±0.25μm and 2.05±0.18μm surface roughness(Ra) bonded to dentin showed the maximum bond strength. Ti-alloy rubbed with 80 grit Si-C sand paper, with-2.69±0.32μm surface roughness(Ra) bonded to dentin showed the maximum bond strength.