Influence Of UVAG On The Surface Character And Resin Bond Of Zirconia Ceramic

Currently patient request for more aesthetic and biologically safe restorations have led to an increasing demand for ceramic material.Zirconia ceramic treated with the CAD/CAM system is also widely used to meet this growing demand.One of the present production modes of ziconia ceramic restorations relies upon two-step sintering.A machinable zirconia ceramic block is first manufactured into the magnified shape that the computer has desighed,and is then high temperature sintered.The machining accuracy and mechanical property are influenced by too many procedures required.Another method,which may lead to the abrasion of machining tool and breaking-out of material,is to grind sintered zirconia directly.Nowadays a new method of ultrasonic vibration assisted gringing(UVAG)is proposed to sintered zirconia ceramic machining.This method can hopefully improve working quality,decrease processing time of restorations and reduce abrasion of the machining tool.Therefore it is necessary to explore the particular effects of UVAG on surface character and resin bond strength of zirconia ceramic.Objective:To compare the surface character of zirconia using different surface treatment,in order to summarize the particular effects of UVAG on surface character of zirconia ceramic.Through testing the shear bond strength of zirconia to resin cement using different surface treatments,in order to evaluate Influence of UVAG on resin bond of zirconia ceramic.Methods:55 zirconia ceramic slices were cut from InCorisTZI Zirconia ceramic blocks and sintered as the manufacturer recommendation.The surfaces of the specimens were polished by 280,400,600 grid silicone carbide papers under water cooling.The specimens were then randomly divided into 5 groups based on different treatments(n= 11).group A was left as polished control.Group B was air-particle abraded with 50 ?m alumina particles.Group C was conventionally milled by Ultrasonic 201inear using a diamond grinding tool of normal grain size.Group D was milled using a grinding tool of smaller grain size.Group E was machined using a tool of normal grain size with ultrasonic assistance.After surface treatments,all specimens were cleaned ultrasonically and dried at room temperature.A portable surface roughness measuring gauge was used to record various roughness parameters of the ceramic slices,including arithmetic mean surface roughness(Ra),the point height of irregularities(Rz)and 2-D surface images.The surface topography of one specimen from each group is characterized by scanning electronic microscope(SEM).And edge quality of Group C and E were compared.The surface of 10 specimens from each group was coate with paravia F2.0 resin cement in the limited area.Two prepared resin blocks were pressed on the surface of each specimen slightly.Meanwhile,the bonding cement was polymerized fur 3 minutes with LED light.All the specimens were allowed to stay at room temperature for half an hour and then stored in 37? distilled water for 24 hours.The specimens were fixed on a cylindrical pedestal and the shear bond strengths were test by the universal testing machine.The failure mode of zirconia and resin cement was observed by optical microscope.Statistical analysis was performed using SPSS 18 statistics system.The data of the roughness and the data of shear bond strength of different groups were separately analyzed by one way analysis of variance(ANOVA)and SNK tests for pairwise comparisons among groups(p<0.05).Results:Zirconia specimens using Different treatments differed in numerical value of surface roughness.Compared with polishing procedure,air-abrasion,normal grinding and ultrasonic vibration assisted grinding could significantly increase the surface roughness(p<0.05).While there was no obvious difference of roughness between these three treatment(p>0.05).2-D surface images showed surface characteristics of each group.Group B showed a zigzag line with irregular ups and downs.Images of Group C and D were comparatively regular with that of Group B.Image of Group E was the most regular with similar profile peaks or valleys arranged in order.SEM photographs showed surface characteristics of each group.Zirconia ceramic slice from Group A was relatively smooth with light scratches.Surface topography of Group B was rough and irregular with distinct cracks and grooves.Surface topography of Group C and D showed typical parallel grinding grooves which were shallow compared to Group B.Surface topography of Group E showed many grooves crossed as waves and scattered craters between them.SEM photographs of edges showed the ultrasonic assisted process provide a much better edge quality that only tiny gaps could be found infrequently.Obvious breaking-out of material could be found easily in Group C.After shear bond strength testing,all the failure modes of resin cement to zirconia were failures of cement-zirconia interface.No residual resin cement could be observed on zirconia slices.According to data analysis by SPSS,the differences among the experimental groups were significant(p<0.05).Group B with air-abrasion presented the highest bond strength value.There were no significant differences between the control group and the normal grinding group.However,the specimens treated by ultrasonic vibration assisted grind presented the lowest bond strength value.Conclusions:1.Compared with polishing,Air-abrasion,grinding and UVAG significantly improved the surface roughness of zirconia ceramic.Grinding with diamond tool of larger grain size got higher surface roughness.2.Air-abrasion could remarkably improve the bond strength of resin cement to zirconia.While UVAG significantly had bad effects on the resin bond strength.Air-abrasion after ultrasonic vibration assisted grinding was recommended to enhance the bond between zirconia and resin cement.Normal grinding can not enhance the bonding strength of zirconia so that other assisting surface treatments are needed clinically.