Paula Vitor G, Lorenzoni Fabio C, Bonfante Estevam A, Silva Nelson R F A, Thompson Van P, Bonfante Gerson
Department of Prosthodontics, University of São Paulo - Bauru College of Dentistry, Bauru, SP, Brazil.
Department of Prosthodontics, UNIGRAN University, Dourados, MS, Brazil.
Dent Mater. 2015 Feb;31(2):77-87. doi: 10.1016/j.dental.2014.10.005. Epub 2014 Nov 22.
To compare the fatigue life and damage modes of zirconia crowns fabricated with and without framework design modification when porcelain veneered using a fast or slow cooling protocol.
Composite resin replicas of a first molar full crown preparation were fabricated. Zirconia copings were milled as conventional (0.5mm even thickness, Zr-C, n=20,) or modified (lingual margin of 1.0mm thickness, 2.0mm height connected to two proximal struts of 3.5mm height, Zr-M, n=20). These groups were subdivided (n=10 each) according to the veneer cooling protocol employed: fast cooling (Zr-CFast and Zr-MFast) and slow cooling (Zr-CSlow and Zr-MSlow). Crowns were cemented and fatigued for 10(6) cycles in water. The number of cycles to failure was recorded and used to determine the interval databased 2-parameter probability Weibull distribution parameter Beta (β) and characteristic life value Eta (η).
2-parameter Weibull calculation presented β=5.53 and β=4.38 for Zr-MFast and Zr-CFast, respectively. Slow cooled crowns did not fail by completion of 10(6) cycles, thereby Weibayes calculation was applied. Increased fatigue life was observed for slow cooled crowns compared to fast cooled ones. Groups Zr-MFast and Zr-MSlow presented no statistical difference. Porcelain cohesive fractures were mainly observed in fast cooled groups. Slow cooled crowns presented in some instances inner cone cracks not reaching the zirconia/veneer interface.
Improved fatigue life in tandem with the absence of porcelain fractures were observed in slow cooled crowns, regardless of framework design. Crowns fast cooled chiefly failed by porcelain cohesive fractures.
比较采用快速或慢速冷却方案进行瓷贴面时，有无框架设计改进所制作的氧化锆全冠的疲劳寿命和损坏模式。
制作第一磨牙全冠预备体的复合树脂复制体。按常规方法（均匀厚度0.5mm，Zr-C，n = 20）或改进方法（舌侧边缘厚度1.0mm，高度2.0mm连接至两个高度3.5mm的邻面支柱，Zr-M，n = 20）研磨氧化锆内冠。根据所采用的贴面冷却方案将这些组再细分（每组n = 10）：快速冷却（Zr-CFast和Zr-MFast）和慢速冷却（Zr-CSlow和Zr-MSlow）。全冠粘结后在水中进行10⁶次循环疲劳试验。记录失效循环次数，并用于确定基于区间数据的双参数概率威布尔分布参数β和特征寿命值η。
双参数威布尔计算得出，Zr-MFast和Zr-CFast的β分别为5.53和4.38。慢速冷却的全冠在10⁶次循环完成前未失效，因此应用了威贝斯计算。与快速冷却的全冠相比，慢速冷却的全冠疲劳寿命增加。Zr-MFast组和Zr-MSlow组之间无统计学差异。瓷粘结性骨折主要出现在快速冷却组。慢速冷却的全冠在某些情况下出现未到达氧化锆/贴面界面的内锥裂纹。
无论框架设计如何，慢速冷却的全冠均观察到疲劳寿命提高且无瓷骨折。快速冷却的全冠主要因瓷粘结性骨折而失效。
