This study should evaluate the influence of extended firing on the dimension, optical properties and flexural strength of a fully crystalized zirconia-reinforced lithium-silicate ceramic (ZLS) for single tooth restorations.

Methods

150 ZLS (Celtra Duo) and 30 lithium disilicate (LDS, IPS e.max CAD) specimens (17 × 4 × 1 mm) were milled in a standard device (Cerec MC XL). The ZLS specimens were distributed equally to five experimental groups (polished, standard firing [IFU], and three extended firings). LDS acted as a control group. The extended firings of ZLS addressed the first glaze firing (EF1) as well as the subsequent glaze firing (EF2) by a controlled overheating of +15 °C during the holding time. Color was measured with a digital spectrophotometer (Shadepilot), and dimensions with a digital calliper, before and after firing. A color change of ΔE ≥1.5 and a volume change of ±0.5% was regarded as clinical relevant.

All specimens underwent a three-point-bending test to calculate flexural strength and Weibull statistics.

Results

The color change after firing of ZLS (ΔE value; mean = 1.06; SD = 0.53) exceeded the perceptible threshold of ΔE ≥1.5 in 20% of IFU (mean = 1.18) and EF1+2 (mean = 0.95), 23% of EF1 (mean = 1.11), and 10% of EF2 (mean = 0.99) specimens with no statistical difference between the experimental groups. In 80% of IFU, 63% of EF2, 56% of EF1, and 33% of EF1+2 vol. change after firing exceeded ±0.5%. Characteristic Weibull strength σ₀ and modulus m of polished ZLS specimen was affected by firing in IFU (σ₀ = 314.35 MPa; m = 5.81), EF1 (σ₀ = 324.68 MPa; m = 5.67), EF2 (σ₀ = 326.4 MPa; m = 7.24), and EF1+2 (σ₀ = 357.15 MPa, m = 3.69). LDS revealed σ₀ = 405.7 MPa; m = 8.04, and polished ZLS σ₀ = 219.3 MPa; m = 8.9 with statistical significant difference of the flexural strength between all fired ZLS experimental groups towards “as polished” as well as LDS.

Conclusion

Firing of ZLS led to changes in dimensions, color, and Weibull modulus. Firing increases flexural strength, but minimal temperature extension also increases materials inhomogeneity and risk of failure. The findings call for further investigations towards firing behavior of ZLS and its clinical relevance for restorations.

中文翻译：

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最小扩展烧成对结晶的氧化锆增强硅酸锂玻璃陶瓷的尺寸，光学和机械性能的影响。

这项研究应评估长时间烧制对用于单齿修复的全结晶氧化锆增强硅酸锂陶瓷（ZLS）的尺寸，光学性能和抗弯强度的影响。

方法

在标准设备（Cerec MC XL）中研磨150个ZLS（Celtra Duo）和30个二硅酸锂（LDS，IPS e.max CAD）（17×4×1 mm）标本。ZLS标本平均分配到五个实验组（抛光，标准射击[IFU]和三个扩展射击）。LDS充当对照组。ZLS的延长烧成通过在保持时间内控制+15°C的过热来解决第一个釉料烧成（EF1）和随后的釉料烧成（EF2）的问题。在焙烧之前和之后，使用数字分光光度计（Shadepilot）测量颜色，并使用数字游标卡尺测量尺寸。ΔE≥1.5的颜色变化和±0.5％的体积变化被认为与临床有关。

所有样本均经过三点弯曲测试，以计算抗弯强度和威布尔统计量。

结果

ZLS发射后的颜色变化（ΔE值；平均值= 1.06； SD = 0.53）在20％的IFU（平均值= 1.18）和EF1 + 2（平均值= 0.95），23％的IFU中超过了ΔE≥1.5的可感知阈值。 EF1（平均值= 1.11）和EF2（平均值= 0.99）标本的10％，实验组之间无统计学差异。在80％的IFU，63％的EF2、56％的EF1和33％的EF1 + 2 vol。烧成后的变化超过±0.5％。特性威布尔强度σ ₀和模量米抛光ZLS试样受到影响通过在IFU烧成（σ ₀  = 314.35兆帕;米 = 5.81），EF1（σ ₀  = 324.68兆帕;米 = 5.67），EF2（σ ₀  = 326.4兆帕;米 = 7.24），和EF1 + 2（σ ₀ ＝ 357.15MPa，m  ＝ 3.69）。LDS揭示σ ₀  = 405.7兆帕; 米 = 8.04，和抛光ZLSσ ₀  = 219.3兆帕; m  = 8.9，在所有经焙烧的ZLS实验组之间，抗“抛光”和LDS的抗弯强度具有统计显着性差异。

结论

ZLS的烧结导致尺寸，颜色和威布尔模量发生变化。焙烧可提高抗弯强度，但最小的温度范围也会增加材料的不均匀性和失效风险。该发现需要对ZLS的发射行为及其与修复体的临床相关性进行进一步研究。