两种最大载荷值下牙科脆性陶瓷赫兹触压循环疲劳研究

Cyclic fatigue study on brittle dental ceramic by Hertzian's contact under two different maximum loadings

目的比较两种最大载荷值下牙科脆性陶瓷赫兹触压循环疲劳损伤模式。方法应用赫兹触压实验方法对VitamarkⅡ可切削陶瓷标准试件进行循环加载,然后测试加载后的残余3点弯曲强度,观测试件表面及次表面损伤。结果500 N最大载荷下,Vita markⅡ可切削陶瓷低周循环触压疲劳损伤为经典脆性模式,而高周循环下为类塑性模式。200 N最大载荷下则主要表现为以环状裂纹为代表的脆性模式。结论不同最大载荷值下,牙科脆性陶瓷展示不同的触压疲劳模式。即使在相对较小的载荷下,只要达到一定的循环加载周期,牙科脆性陶瓷强度也会显著降低。

Objective To compare with the differences in strength degradation and morphologic damage of brittle dental ceramic after cyclic fatigue with two different maximum loadings. Methods Hertzian contact technique with WC spheres was used to investigate the response of feldspathic dental porcelain to cyclic fatigue. All specimens were fatigued by cyclic loading with two different maximum loadings. Afterwards, the surviving strength was examined by three-point bending test, and the superficial damage was also observed. Results Under 500 N maximum loading,Vita mark Ⅱ machinable dental ceramic showed two different damage modes：classical brittle mode at low cycle and quasi-plastic mode at high cycle. While under 200 N maximum loading, it manifested the brittle mode mainly characteristized by cricoid cracks. Conclusion Brittle dental ceramic showed different cyclic fatigue modes with different maximum loadings. Even though the loading it bore was relatively small, the strength of brittle dental ceramic would dramatically fall off when the cycles of loading reached a certain level.