OBJECTIVE To evaluate the composition, flexural strength and fatigue behaviour of lithium disilicate ceramic (LD) after repeated firings and different staining techniques. METHODS LD discs were fabricated and divided according to number of firing cycles and staining technique: CO - control, discs were crystallized (850°C/10min); SC - single-step characterization - crystallization and staining (applied with a thin brush) were performed in a single step with one firing cycle (850°C/10min); and DC - double-step characterization - crystallization firing cycle was performed first (850°C/10min), followed by staining firing cycle (770°C/90s). Specimens were fired two, four or six times (one crystallization firing cycle and one, three or five staining firing cycles), resulting into 9 groups (n=30): COII, COIV, COVI, SCII, SCIV, SCVI, DCII, DCIV and DCVI. The composition of the specimens was investigated (EDS, XRD, Raman spectroscopy), and the biaxial flexural strength (n=10) and staircase tests (n=20, 5×104 cycles, 5Hz) were performed. Data were subjected to one-way ANOVA and Tukey's test (α=0.05). RESULTS EDS and XRD revealed amorphous content for stained groups. Biaxial flexural strength was not affected by repeated firings in any group, but stained groups presented lower flexural strength than control groups (p=0.001). The fatigue limit results decreased in all groups compared to flexural strength. SC groups showed similar (SCII and SCIV) or even higher fatigue limits (SCVI) than the control groups, and DC showed the lowest fatigue limit values. SEM and Raman suggested that the interfaces between staining and the LD showed only an overlap for the DC groups, whereas for the SC it was suggested an interaction between the stain and the LD. SIGNIFICANCE Repeated firings did not result in decreased lithium disilicate flexural strength.Staining affected flexural strength and also resulted in increased amorphous content in the characterized specimens. Single-step staining resulted in the highest fatigue limit.

中文翻译：

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反复烧成和染色对二硅酸锂的机械性能和组成的影响。

目的评价二硅酸锂陶瓷（LD）经反复烧成和不同染色工艺后的组成，弯曲强度和疲劳行为。方法制作LD光盘，并根据烧成次数和染色技术进行划分：CO-控制，将光盘结晶（850°C / 10min）；SC-一步表征-结晶和染色（用细刷施加）在一个焙烧周期（850°C / 10min）的一步中进行；首先进行DC-双步表征-结晶烧成循环（850℃/ 10min），然后进行染色烧成循环（770℃/ 90s）。将样品烧制两次，四次或六次（一个结晶烧成循环和一个，三个或五个染色烧成循环），分为9组（n = 30）：COII，COIV，COVI，SCII，SCIV，SCVI，DCII，DCIV和DCVI。研究了样品的成分（EDS，XRD，拉曼光谱），并进行了双轴弯曲强度（n = 10）和阶梯测试（n = 20，5×104周期，5Hz）。对数据进行单向方差分析和Tukey检验（α= 0.05）。结果EDS和XRD显示染色组的无定形含量。在任何一组中，重复烧制都不会影响双轴弯曲强度，但是染色组的弯曲强度低于对照组（p = 0.001）。与抗弯强度相比，所有组的疲劳极限结果均降低。与对照组相比，SC组显示出相似的（SCII和SCIV）甚至更高的疲劳极限（SCVI），而DC显示出最低的疲劳极限值。SEM和Raman建议染色和LD之间的界面仅显示DC组的重叠，而对于SC，则建议染色剂和LD之间存在相互作用。意义反复烧制不会导致二硅酸锂的抗弯强度降低，染色会影响抗弯强度，并导致特征样品中的非晶含量增加。单步染色导致最高的疲劳极限。