Post Graduate Coordinator, Implantology Clinic, Santos Dumont Brazilian Air Force Dental Clinic (OASD), Rio de Janeiro, Rio de Janeiro, Brazil.
Associate Clinical Professor, Department of Prosthodontics, Bauru School of Dentistry, University of São Paulo (USP), Bauru, São Paulo, Brazil.
J Prosthet Dent. 2021 May;125(5):824.e1-824.e8. doi: 10.1016/j.prosdent.2021.01.022. Epub 2021 Mar 26.
Modifications have been made in the microstructure and sintering parameters of monolithic zirconia to improve esthetics qualities and avoid chipping of 2-layer restorations. However, how these modifications affect the physical and mechanical properties of zirconia is unclear.
The purpose of this in vitro study was to compare the influence of different sintering parameters on the microstructure, 4-point flexural strength, density, and grain size of 2 commercially available zirconia advocated for the fabrication of monolithic dental prostheses and 1 commercially available zirconia for use as a core material.
Three presintered blocks (Ceramill Zolid, Prettau, and IPS e.max ZirCAD) were used. Specimens were cut and sintered as per the manufacturer's recommendation or as per a modified heating protocol. Ceramill Zolid (Z1450) was sintered at 1450 °C, Prettau (P1600) was sintered at 1600 °C, and IPS e.max ZirCAD (I1530) was sintered at 1530 °C by following the manufacturer's heating protocol. Groups Ceramill Zolid Z1530 and Z1600 were sintered at temperatures higher than the manufacturer's recommendation. Specimens from each group (n=13) were analyzed with X-ray diffraction (XRD), density calculus, average grain size measurement, and 4-point flexural tests. Data were compared by using ANOVA (α=.05).
XRD analysis showed the presence of a tetragonal metastable phase in all groups before and after sintering. No significant differences were found in relative density values for the 3 Ceramill groups (5.98 g/cm). Groups I1530 (6.03 g/cm) and P1600 (6.03 g/cm) had similar density results greater than 6.00 g/cm. The average grain size of all groups remained lower than 1 μm. P1600 had the highest grain size (0.817 μm), and Z1450 presented the lowest grain size (0.465 μm). P1600 showed the most homogeneous flexural strength and the highest Weibull modulus (m=8.22). Z1530 presented the lowest Weibull modulus (m=4.58). IPS e.max ZirCAD (I1530) had the highest flexural strength (1057.41 ±150.54 MPa), and Ceramill Zolid Z1450 had the lowest (621.01 ±138.08 MPa).
The flexural strength, microstructure, crystal phase, and grain size of the analyzed zirconia varied as per the sintering processing. The IPS e.max ZirCAD had the highest flexural strength (1057.41 ±150.54 MPa), followed by Prettau zirconia (864.18 ±118.21), with a statistically significant difference (P<.05). The Ceramill Zolid zirconia presented the lowest flexural strength, as well as the lowest reliability for all sintering parameters used (Z1450: 621.01 ±138.08 MPa and m=5.42; Z1530: 713.10 ±175.44 MPa and m=4.58; Z1600: 630.15 ±112.08 MPa and m=6.87). At a lower heating rate (8 °C/min), the final density increased and excessive grain growth in group Z1530 was prevented.
为了改善美学质量并避免双层修复体崩瓷，对整体氧化锆的微观结构和烧结参数进行了改进。然而，这些改进如何影响氧化锆的物理和机械性能尚不清楚。
本体外研究的目的是比较不同烧结参数对 2 种市售用于制作整体牙体修复体的氧化锆（Ceramill Zolid、Prettau 和 IPS e.max ZirCAD）和 1 种市售用作核材料的氧化锆的微观结构、4 点弯曲强度、密度和晶粒尺寸的影响。
使用了 3 个预烧块（Ceramill Zolid、Prettau 和 IPS e.max ZirCAD）。根据制造商的建议或修改后的加热方案切割和烧结试件。Ceramill Zolid（Z1450）在 1450°C 下烧结，Prettau（P1600）在 1600°C 下烧结，IPS e.max ZirCAD（I1530）按照制造商的加热方案在 1530°C 下烧结。Z1530 和 Z1600 组的 Ceramill Zolid 烧结温度高于制造商的建议温度。对每组（n=13）的试件进行 X 射线衍射（XRD）分析、密度计算、平均晶粒尺寸测量和 4 点弯曲试验。使用方差分析（α=.05）比较数据。
XRD 分析表明，所有烧结前和烧结后的组均存在四方亚稳相。3 个 Ceramill 组的相对密度值（5.98 g/cm）没有显著差异。组 I1530（6.03 g/cm）和 P1600（6.03 g/cm）的密度结果大于 6.00 g/cm。所有组的平均晶粒尺寸仍低于 1μm。P1600 的晶粒尺寸最大（0.817μm），Z1450 的晶粒尺寸最小（0.465μm）。P1600 显示出最均匀的弯曲强度和最高的威布尔模数（m=8.22）。Z1530 呈现出最低的威布尔模数（m=4.58）。IPS e.max ZirCAD（I1530）具有最高的弯曲强度（1057.41±150.54 MPa），而 Ceramill Zolid Z1450 具有最低的弯曲强度（621.01±138.08 MPa）。
分析的氧化锆的弯曲强度、微观结构、晶体相和晶粒尺寸随烧结工艺而变化。IPS e.max ZirCAD 的弯曲强度最高（1057.41±150.54 MPa），其次是 Prettau 氧化锆（864.18±118.21 MPa），有统计学意义（P<.05）。Ceramill Zolid 氧化锆的弯曲强度最低，所有烧结参数的可靠性也最低（Z1450：621.01±138.08 MPa 和 m=5.42；Z1530：713.10±175.44 MPa 和 m=4.58；Z1600：630.15±112.08 MPa 和 m=6.87）。在较低的加热速率（8°C/min）下，最终密度增加，并防止了组 Z1530 中过度晶粒生长。
