Effects Of Polishing On The Retention Strength, Mechanical Interlocking Strength And Bond Strength Of Full Metal Crown

Objective: To evaluate the different strength of bonding and mechanical interlocking of three kinds of luting cements and explore their relating effects by means of observing the change of retention strength of metal full crowns pre- and-post polishing.Material and methods: Freshly extracted human premolars were collected, cleaned and randomly separated into six groups, and prepared teeth with air turbine diamonds points in the condition of water-cooling. A cube of 6×4×3mm~3 was made after such preparation, besides three groups were polished with rubber and the other three groups were not polished, and then made a metal crown for each sample, afterwards three kinds of luting cements Zinc phosphate cement (ZOP), glass ionomer cement(GIC),and resin cement (RC) were selected to bond the metal full crowns to the samples of each group. After thermal cycling between 5℃± 2℃ and 50℃± 2℃ for a total of 1500 cycles and with the speed of 10mm/min in the material mechanics machine the retention strength was performed.Apart from the effect of binding, the effect of bonding was tested. A metal cube of 10 × 10×2 mm~3 was made firstly. Reducing proximal into a plane of 3 × 6mm2.Then felt the plane to the cube with the three kind of luting cements . After thermal cycling between 5℃± 2℃ and 50℃± 2 ℃ for a total of 1500 cycles the bond strength was performed. The occlusion bond strength was performed in the same way. Calculate the mechanical interlocking strength by the expressions bellow: mechanical interlocking strength equal retention strength minor occlusion bond strength and axis bond strength.Statistical analysis was performed with the program SPSS. Results:The retention strength, mechanical interlocking strength and bond strength of ZOP group decreased after polishing , The statistical analysis showed that there has significant difference. There has no obvious change of retention strength of GIC group and RC group. The mechanical interlocking strength is lower and bond strength is higher after polishing of GIC group. There has no obvious change of mechanical interlocking strength and bond strength of RC group. Conclusions:The retention capacities of the complete crowns from the highest to least were: CR > GIC>ZOP. The effects varied with different cements in the retention of complete metal crowns because of the discrepancy in bonding and mechanical interlocking properties.Mechanical interlocking plays a prominent role when ZOP or GIC is used, and the role of bonding is apparent in RC. Polishing has a high effect on ZOP and little affect on GIC and RC.