Objective:The aim of this study was to experimentally evaluate the influence of porcelain thickness and LTD on dental Y-TZP by experiments.Materials and.Methods:Thin discs of Y-TZP from 4 manufactures were fully sintered according to each manufacture's recommendations then the fully sintered blocks were prepared in 23mm (length) × 4mm (width) × 0.8mm/1.5mm (thickness).The Experimental specimens were artificially aged at standard autoclave sterilization conditions,134℃ at 0.2 MPa for 10h and 20h,and finally grounded and polished.Tetragonal to monoclinic transformation was measured by using X-ray diffraction (XRD) for all groups.Flexural strength was measured in 3-point bending and Vickers-hardness for all groups.Specimens surfaces were examined by scanning electron microscopy (SEM).Results:The microstructure investigation 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.The mean flexural strength of Vita In-ceram YZ 0.8mm without aging was 1153.33MPa.When applied LTD for 10h or 20h the flexural strength dropped to 1116.67MPa and 940.89MPa.However,at the thickness of 1.5mm,without aging was1347.66MPa,LTD tests for 10h and 20h the flexural strength decreased to 1283.59MPa and 929.47MPa.Conclusions:The flexural strengths of all 4 Y-TZP materials were decrease with the decrease of the thickness,there are notable contribution to further studies.Moreover,hydrothermal aging of Y-TZP can cause significant transformation from tetragonal to monoclinic crystal structure,which also results in a statistically significant decrease in the flexural strength of Y-TZP.%目的:评价不同厚度的氧化锆材料在不同老化时间情况下,其微观结构及机械性能的变化,初步分析其老化规律,为临床上氧化锆全瓷材料应用提供数据参考.方法:分别将4种不同品牌氧化锆按照制造商要求进行预烧结,接着将氧化锆试件根据实验要求备至2种不同厚度(0.8mm及1.5mm)后采用6μm金刚砂进行抛光,保证氧化锆试件两个表面平整且均无划痕,再置于高温高压灭菌锅内分别进行10h、20h人工低温老化处理,最终把4种氧化锆品牌按照不同切割厚度(0.8、1.5mm)、老化时间(0h、10h或20h)分成24组,每组6个样本,共计试件144块,并对其进行微观结构及力学性能进行检测.结果:微观检测结果提示老化时间越长,试件表面缺陷和晶粒尺寸更加明显.再者,相比厚度1.5mm组,较薄的0.8mm组无论在老化10h、20h组其晶粒尺寸和微裂纹皆更明显.力学性能检测以VITA品牌为例,VITA 0.8mm对照组老化前三点抗弯强度1153.33MPa;低温老化10h、20h后强度分别为1116.67MPa,940.89MPa.VITA 1.5mm对照组三点抗弯强度1347.66MPa;低温老化10h、20h后强度分别为1283.59MPa and 929.47MPa.结论:4种品牌氧化锆力学强度皆随着试件厚度降低,老化时间的延长而减弱.氧化锆全瓷材料在水热低温环境下其内部晶粒结构会由稳定的四方相向单斜相发生转变,引起其晶粒尺寸增大,表面缺陷增加最终导致材料机械强度下降,当氧化锆材料越薄对低温老化越敏感,晶相转变易往内部发展,进而导致材料老化速度加快.
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