烧结次数与氧化锆-饰面瓷双层瓷结构强度及界面显微结构的变化

Influence of firing times on bending strength and microstructure of zirconia/porcelain bilayered dental ceramics

背景:牙科氧化锆修复体为双层瓷结构,在临床应用中经常出现饰面瓷部分折裂剥脱的情况,且临床上有时需要反复的形态和颜色调整,常常需要经过多次烧结或热处理,而多次烧结是否会影响到牙科氧化锆-饰面瓷双层瓷结构的结合强度尚不明确。目的:观察多次烧结后牙科氧化锆/饰面瓷双层瓷结构的力学性能,分析界面及饰面瓷的结构变化对双层瓷结构强度的影响。方法:根据ISO6872牙科陶瓷标准制备KAVO氧化锆/VitaVM9饰面瓷的双层瓷复合结构的三点弯曲样品,氧化锆与饰面瓷的厚度比为1:1。测定经2,4,6,8次烧结后双层瓷的结构强度,并用扫描电镜观察多次烧结后双层瓷结合界面及饰面瓷基质的微观结构,通过X射线衍射分析饰面瓷基质结构的变化,采用热分析仪测定饰面瓷的热膨胀系数变化。结果与结论:氧化锆表面进行多达8次饰面瓷烧结后,氧化锆与饰面瓷的界面结合紧密,但可见界面处及饰面瓷内部白榴石晶体结构发生了明显的变化,晶粒逐渐长大,饰面瓷内的气孔逐渐增多、变大,并向表层移动,热膨胀系数呈现先增大后略降低的改变。多次的牙本质瓷烧结并未影响KAVO氧化锆/VITA-VM9饰面瓷结构的结合强度。说明烧结次数对双层瓷结合界面及饰面瓷内部的晶体结构影响较大,对双层瓷结构的三点弯曲强度无影响。

BACKGROUND：Because dental zirconia restorations require two layers ceramic material,chipping and delamination of veneering porocelain always occur in clinical application,multiple porcelain firing or heat treatment is always needed to adjust the shape and color,however,whether repeated firing could have some effects on the strength of zirconia/porcelain bilayered structure remains unclear.OBJECTIVE：To study the mechanical property of zirconia/porcelain bilayered structure after repeated firing and to observe the microstructure of veneering porcelain and bonding interface of the bilayered complex.METHODS：Bilayered three-point bending strength specimens of KAVO zirconia/Vita VM9 veneering porcelain were made according to ISO6872 standard,the thickness ratio of core to porcelain was 1：1.Specimens were subjected to 2,4,6,8 times of dentine porcelain firing cycles.Three-point bending strength were tested,scanning electron microscopy was used to observe the microstructure characteristics of the interface and porcelain matrix.X-ray diffraction was used to analyze the crystal structure of veneering porcelain,and coefficient of thermal expansion was detected by thermal analyzer.RESULTS AND CONCLUSION：Zirconia surface combined tightly with veneering porcelain interface after multiple firing up to 8 times,the crystal structure of leucite significantly changed at the interface and in the veneering porcelain,the porcelain but looked more porous and pores transferred to the veneer surface with the increasing firing times while the size of crystal phase were increased significantly,transferring to surface layer.The coefficient of thermal expansion was slightly increased,and then decreased at the eighth firing.The bonding strength of KAVO zirconia/Vita VM9 veneering porcelain was nearly identical after multiple dentine firing.There were significant morphological structure changes on the crystal phase in the veneering porcelain after multiple firing,however,three-point bending strength of zirconia/porcelain bilayered structure was not influenced.