Influence Of Porcelain Thickness And Degradation On The Properties Of Zirconia

Purpose:The aim of this study was to evaluate the influence of porcelain thickness and degradation on the mechanical properties of zirconia ceramic by experiments.Material And Methods:4 different brands of zirconia ceramics(Lava Frame,In-ceram,Zenostar,Upcera),were fully sintered according to each manufacture’s recommendations.The fully sintered blocks were cut into the size of 23(Length)x 4(Width)x 0.8 and 1.5(Thickness)approximately.Specimens were artificially aged in distilled water by heat-treatment under 134~oC、0.2 MPa for 10 hours and 20 hours.4brands of zirconia specimens after polished with 1μm diamond suspensions were divided into 24 groups,each group included 6 specimens classified by different porcelain thickness(0.8mm、1.5mm)and aging time 0hours(as control)、10hours and 20hours.In order to induce the phase transformation at the surface.To measure the mechanical property,SEM and X-ray diffraction was used to estimate the relative amount of monoclinic phase of one specimen in each group.In addition,three-point flexure and Vickers hardness tests were used to calculate the mechanical properties of zirconia ceramics.Results:(1)The SEM results suggested with the aging time,the surface defects and micro-cracks of specimen became more obvious,particularly in the 20h group.Compared with 1.5mm group,0.8mm group showed more significant defects and micro-cracks in spite of the aging time.(2)The XRD results revealed an increase in the monoclinic phase fraction in specimens aging with 20 hours compared with 10 hours.Brand VITA:Monoclinic content was 0,11.37%,27.84%in the thickness of 0.8mm group after aging0h,10h,20h,and 0,8.83%,25.16%respectively in thickness of 1.5mm group.Brand LAVA:Monoclinic content was 0,18.97%,32.72%in the thickness of 0.8mm group after aging 0h,10h,20h,and 0,16.96%,29.97%respectively in thickness of 1.5mm group.Brand UPCERA:Monoclinic content was 0,12.71%,29.78%in the thickness of 0.8mm group after aging 0h,10h,20h,and 0,9.84%,27.03%respectively in thickness of 1.5mm group.Brand WIELAND:Monoclinic content was 0,12.81%,28.70%in the thickness of0.8mm group after aging 0h,10h,20h,and 0,9.14%,28.01%respectively in thickness of1.5mm group.(3)The hardness and strength decreased more significantly in specimens aging with 20 hours.In contrast to specimens of 0.8mm thickness,the hardness and strength slightly reduced in specimens of 1.5 thickness.Brand VITA:Bending strength was 1153.33MPa,1116.67MPa,940.89MPa in the thickness of 0.8mm group after aging0h,10h,20h,and 1347.66MPa,1283.59MPa,929.47MPa respectively in thickness of1.5mm group.Brand LAVA:Bending strength was 761.72MPa,757.79MPa,647.23MPa in the thickness of 0.8mm group after aging 0h,10h,20h,and 920.00MPa,838.18MPa,774.27MPa respectively in thickness of 1.5mm group.Brand UPCERA:Bending strength was 1054.69MPa,932.03MPa,844.98MPa in the thickness of 0.8mm group after aging0h,10h,20h,and 1183.33MPa,1085.67MPa,899.41MPa respectively in thickness of1.5mm group.Brand WIELAND:Bending strength was 1042.97MPa,972.03MPa,889.32MPa in the thickness of 0.8mm group after aging 0h,10h,20h,and 1133.33MPa,1023.67MPa,750.05MPa respectively in thickness of 1.5mm group.Conclusions:(1)With the aging time,the micro-cracks on the surface of specimen were more obvious and same to the monoclinic phase.(2)with the aging time,the mechanic-strength and Vickers-hardness of four different brands zirconia were reduced.(3)In terns of the thickness of zirconia,compared with 1.5mm group,0.8mm group showed more significant defects,micro-cracks,monoclinic phrase and stronger mechanic strength in spite of the aging time.