Experimental Study On Wear Performance Of Dental CAD/CAM Zirconia And Lithium Disilicate Glass-Ceramic

AIM:This study was based on the theory of three stages of mechanical friction（“running-in stage”,“stable wear stage”and“severe wear stage”）to perform in-vitro wear tests to investigate CAD/CAM zirconia ceramics,lithium disilicate glass ceramics,and bovine tooth enamel or its own counterparts.The law of wear behavior over time provides experimental reference data for understanding the wear properties of dental ceramic restoration materials,guiding the selection of clinical porcelain restoration materials,protecting natural teeth,and improving the performance of dental ceramic materials.METHOD:1.Study on dynamic wear behavior of CAD/CAM zirconia ceramics and bovine tooth enamel pair:A zirconia ceramic cylinder with a length of 10 mm and a diameter of 3mm was used as the upper grinding head,and a bovine tooth enamel with a thickness of 3mm and a diameter of 20 mm.The next test piece was randomly grouped and matched to form nine pairs of friction pairs.Using a friction and wear machine,1.44 million cycles of abrasion experiments were performed under conditions of artificial saliva,room temperature environment,10 N load,rotation speed 100 r/min,radius of gyration 2.5 mm,and uniform circular motion.20 cycle nodes are selected throughout the wear cycle,and the wear loss of the upper and lower test pieces at each node is measured with a three-dimensional profile meter and the corresponding wear curve is plotted.According to the obtained wear stage,three-dimensional profile instrument and scanning electron microscope observation are used to explor wear surface roughness and micro-morphology of each wear stage.2.Study on dynamic wear behavior of CAD/CAM lithium silicate glass-ceramics and bovine tooth enamel pairs:A 10 mm long,3 mm diameter lithium disilicate glass ceramic cylinder was used as the upper grinding head,with a thickness of 3,diameter of 20 mm bovine tooth enamel specimens were randomly divided into pairs to form 9 pairs of friction pairs.Using a friction and wear machine,1.44 million cycles of abrasion experiments were performed under conditions of artificial saliva,room temperature environment,10 N load,rotation speed 100 r/min,radius of gyration 2.5 mm,and uniform circular motion.20 cycle nodes are selected throughout the wear cycle,and the wear loss of the upper and lower test pieces at each node is measured with a three-dimensional profile meter and the corresponding wear curve is plotted.According to the obtained wear stage,three-dimensional profile instrument and scanning electron microscope observation are used explor wear surface roughness and micro-morphology of each wear stage.3.Study on the dynamic wear behavior of CAD/CAM zirconia ceramics with their own pairs:9 zirconia ceramic cylinders with a length of 10 mm and a diameter of 3 mm are used as the top grinding head and 9 zirconias with a thickness of 3 mm and a diameter of 20 mm.The ceramic test pieces were randomly grouped and matched to form nine pairs of friction pairs.Using a friction and wear machine,1.28 million cycles of wear experiments were performed under conditions of artificial saliva,room temperature environment,50 N load,rotation speed 100 r/min,radius of gyration 2.5 mm,and uniform circular motion.Select 10 loop nodes throughout the wear cycle,measure the wear loss of the upper specimen at each node with a 3D profile meter and draw the corresponding wear curve;according to the resulting wear stage,observe the wear using 3D profiler and SEM Stage wear surface roughness and microtopography changes.4.Study on the dynamic wear behavior of CAD/CAM lithium silicate glass ceramics with their own pairs:Nine 10 mm long,3 mm diameter lithium disilicate glass ceramic cylinders were used as the top grinding head,and with 9 thicknesses of 3 mm and diameter of 20 mm lithium disilicate glass ceramic samples were randomly grouped to form nine pairs of friction pairs.Using a friction and wear tester,1.28 million cycles of wear experiments were performed under conditions of artificial saliva,room temperature environment,50 N load,rotation speed 100 r/min,radius of gyration 2.5 mm,and uniform circular motion.10 cycle nodes were selected throughout the wear cycle,the wear loss of the upper test piece at each node was measured with a 3D profile meter,and the wear curve was plotted.According to the obtained wear stage,the wear surface roughness and microtopography changes of wear stages were observed with a three-dimensional profiler and a scanning electron microscope.RESULT:1.When zirconium oxide ceramics wear with bovine tooth enamel,the“running-in stage”of zirconia ceramic is 0²40,000 cycles,the wear rate was greater[（0.89².39）×10^-3mm³/10⁴ cycles],the wear amount was 33.88×10^-33 mm³ and the roughness Sa was 0.1625μm（initial 0.1048μm）.From the 240,000 cycles into the“stable wear stage”,the wear rate decreased[（0.06⁰.59）×10^-33 mm³/10⁴ cycles],the wear amount was 31.27×10^-33 mm³,and the roughness Sa was 0.1492μm.The running-in stage of the bovine tooth enamel paired with zirconia ceramic is0-160,000 cycles,the wear rate was larger[（0.08⁰.15）mm³/10⁴ cycles],the wear amount was 1.69 mm³,and the roughness Sa was 0.1415μm（the initial value was 0.1041μm）.Entering into the stable wear stage after 160,000 cycles,the wear rate decreased[（0.02⁰.04）mm³/10⁴ cycles],the wear amount was 3.61 mm³,and the roughness Sa was0.1325μm.The micro-morphology showed that the wear surface morphology of zirconia ceramics does not change significantly in different stages of wear.When the bovine tooth enamel wears out during the running-in stage,the wear scars on the wear surface are small and dense,and the roughness was relatively large.In the stable wear stage,wear surface was observed relatively flat.2.When the lithium disilicate ceramic was worn with the bovine tooth enamel pair,the running-in stage of the lithium disilicate ceramic is 0²40,000 cycles,and the wear rate was relatively large[（1.09¹3.59）×10^-33 mm³/10⁴ cycles],the wear amount was108.69×10^-33 mm³,and the roughness Sa was 0.3799μm（initial 0.1030μm）.From the240,000 cycles into the stable wear stage,the wear rate decreased[（0.10⁰.78）×10^-3mm³/10⁴ cycles],the wear amount was 49.64×10^-33 mm³,and the roughness Sa was 0.2913μm.The matched bovine tooth enamel running-in stage is from 0 to 160,000 cycles,with a higher wear rate[（0.08⁰.25）mm³/10⁴ cycles],a wear amount of 2.42 mm³,and a roughness Sa of 0.4149μm（initial 0.1084μm）.After 160,000 cycles,entering the stable wear stage,the wear rate decreased[（0.02⁰.07）mm³/10⁴ cycles],the wear amount was4.74 mm³,and the roughness Sa was 0.3409μm.The microscopic appearance showed that the wear surface of the lithium disilicate ceramic was wide,and the wear scar was dense in the running-in stage,the furrow was shallow,and the wear surface was relatively flat in the stable wear stage;the wear surface of the bovine tooth enamel appeared a large amount of intensive wear scars and the integrity of the surface was destroyed during the running-in stage,the wear scars become shallow and cracks appear on the wear surface during the stable wear stage.3.The wear curves of the zirconia ceramics paired with themselves showed three characteristic wear stages,which can be divided into:running-in stage（0³20,000 cycles）,stable wear stage（320,000⁸00,000 cycles）,and severe wear stage（800,000¹,280,000cycles）.Among them,the wear rate during the running-in stage was relatively large[（0.00164⁰.00336）mm³/10⁴ cycles],the wear amount was 0.0759 mm³,the roughness Sa was 0.3791μm（initial was 0.1905μm）;and the wear rate decreases during the steady wear stage[（0.00017⁰.00038）mm³/10⁴ cycles],wear amount was 0.0146mm³,roughness Sa was 0.2774μm;wear rate during in severe wear stage increased again[（0.00202⁰.00252）mm³/10⁴ cycles],wear amount was 0.1059mm³,roughness Sa was0.4399μm.Micro-morphological changes:During the running-in stage,wear scars on the wear surface were small and dense;when the wear stage was stable,the wear surface was relatively flat with respect to the running-in stage;after entering the severe wear stage,a large number of cracks could be seen on the wear surface.4.The wear curve of the lithium disilicate ceramic paired with itself showed two characteristic wear stages:running-in stage（0⁸0,000 cycles）and stable wear stage（80,000¹,280,000 cycles）.Among them,the wear rate during the running-in stage was relatively large（0.0793 mm³/10⁴ cycles）,the wear amount was 0.6344 mm³,the roughness Sa was 0.4772μm（initial 0.2027μm）;and the wear rate decreased during the stable wear stage[（0.00426⁰.02716）mm³/10⁴ cycles],the wear amount was 1.2062 mm³,and the roughness Sa was 0.3600μm.Microscopic topography changes:From the running-in stage to the stable wear stage,the plough-like wear marks on the worn surface gradually become sparse and shallow from the dense deep.CONCLUSION:1.When paired with bovine enamel,the wear dynamic derivation law of two distinct stages（"running-in stage"and"stable wear stage"）that the wear behavior of zirconia ceramics,lithium disilicate ceramics,and matched bovine tooth enamel exhibited shows that its wear behavior is in line with the tribological dynamic wear law.2.The wear amount of zirconia ceramics is lower than that of lithium disilicate ceramics when used with bovine tooth enamel,and the zirconia ceramics are smaller than the lithium disilicate ceramics in the paired pairs of enamel wears,indicating that the zirconia ceramics wear performance is better than lithium disilicate ceramics.3.When the zirconia ceramic and the lithium disilicate ceramic matched themselves,the wear behavior of the zirconia ceramic exhibits three characteristic wear stages（"running-in stage","stable wear stage"and"severe wear stage"）,and the wear behavior of lithium disilicate ceramic exhibits two characteristic wear stages（“running-in stage”and“stable wear stage”）,indicating that the wear behavior of the zirconia ceramic and the lithium disilicate ceramic both conform to the tribological dynamic wear law.4.When the zirconia ceramics and lithium disilicate ceramics matched themselves,the wear of the zirconia ceramics is smaller than that of the lithium disilicate ceramics,suggesting that the wear between the zirconia ceramic restorations is smaller than that between the lithium disilicate ceramic restorations.