Objective

This study evaluated the effect of dwell time (conventional or extended) and cooling protocol (fast or slow) of self-glaze firings on the mechanical (flexural strength and crack propagation) and optical (color and translucency) properties of a porcelain-veneered zirconia system.

Methods

Bilayer disc-shaped samples were prepared (Vita VM9 + In-Ceram YZ) and divided according to the final thermal treatment: glaze firing followed by slow cooling (furnace opening at 200 °C) (G-S) or fast cooling (furnace opening at 600 °C) (G-F, manufacturer-recommended protocol), extended glaze firing (15 min of dwell time) followed by slow cooling (EG-S) or fast cooling (EG-F), or no thermal treatment (CTRL). Porcelain roughness (Ra and Rz) was measured before and after glaze firings. Color (ΔE₀₀) and translucency (TP₀₀) alteration were also evaluated. Flexural strength was measured with the piston-on-three-ball test and crack propagation analysis was performed after Vickers indentations. Complementary analyzes of crystalline phase and scanning electron microscopy were carried out.

Results

Significant effect of dwell time was observed, with extended glaze leading to higher flexural strength and shorter crack lengths. Cracks of EG groups were observed to end in clusters of crystals. Color and translucency changed below perceptibility thresholds. All treatments led to a smoother surface and EG groups reached the lowest Rz values. An extra SiO₂ peak was revealed in control and EG groups. No effect of cooling protocol was found.

Significance

Extended glaze firing was able to improve the resistance to crack initiation and propagation of porcelain-veneered zirconia without clinically perceptible changes in optical properties.

中文翻译：

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瓷贴面氧化锆的延长釉烧：对机械和光学行为的影响

客观的

本研究评估了自釉烧制的停留时间（传统或延长）和冷却方案（快或慢）对瓷贴面氧化锆的机械（弯曲强度和裂纹扩展）和光学（颜色和半透明度）性能的影响系统。

方法

制备双层圆盘形样品 (Vita VM9 + In-Ceram YZ) 并根据最终热处理进行划分：釉烧后缓慢冷却（200 °C 开炉）（GS）或快速冷却（600 °C 开炉） °C）（GF，制造商推荐的协议），延长釉料烧制（15 分钟的停留时间），然后缓慢冷却 (EG-S) 或快速冷却 (EG-F)，或不进行热处理 (CTRL)。在釉料烧制之前和之后测量瓷器的粗糙度（Ra 和 Rz）。还评估了颜色（ΔE ₀₀）和半透明度（TP _{00 ）变化。}弯曲强度用活塞-三球试验测量，裂纹扩展分析在维氏压痕后进行。进行了结晶相和扫描电子显微镜的补充分析。

结果

观察到停留时间的显着影响，延长釉料导致更高的抗弯强度和更短的裂纹长度。观察到EG基团的裂纹以晶体簇结束。颜色和半透明度更改为低于可感知阈值。所有处理都导致表面更光滑，EG 组达到最低的 Rz 值。在对照组和EG组中显示出额外的SiO _2峰。没有发现冷却协议的影响。

意义

延长釉料烧制能够提高瓷贴面氧化锆的抗裂纹萌生和扩展能力，而光学性能没有临床可察觉的变化。