Statement of problem

Multilayer zirconia blanks comprise material layers with different optical and mechanical properties. Whether positioning within the blank, as well as variation in the sintering procedure, will lead to restorations with different properties is unclear.

Purpose

The purpose of this in vitro study was to test the influence of sintering procedures and positioning in a multilayer blank on the in vitro performance of 3-unit zirconia fixed partial dentures.

Material and methods

Human molars were embedded in acrylic resin and prepared for 3-unit fixed partial dentures. Anatomic contour prostheses were milled from zirconia blanks (ZirCAD Prime 16 mm) in 3 different positions: above (cusp-top at the top of the blank), central (center of the prosthesis in the center of the blank), and bottom (margins at the lower edge of the blank). Sintering time (2:26, 4:25, 9:50 hours:minutes) was varied for the central and bottom prostheses. All prostheses were glazed and adhesively bonded. Thermocycling and mechanical loading was performed at 2×3000×5 °C/55 °C in distilled water for 1.2×10⁶ cycles at a 50-N load. Then, fracture force was determined with a universal testing device by using central loading, a Ø12-mm steel ball, a 1-mm tin foil, and a rate of 1 mm/min. Failure was defined as 10% force drop or acoustic signal (crack). Statistical analysis was performed with 1-way ANOVA and Bonferroni correction (α=.05).

Results

All fixed partial dentures survived thermocycling and mechanical loading. Fracture forces varied between 1002 ±446 N (above; 9:50 hours) and 1760 ±607 N (central; 9:50 hours). The 1-way ANOVA revealed no statistically significant differences (P=.059) among the groups. Individual significant differences (P=.048) were found between prostheses from positions above, 9:50 hours, and central, 9:50 hours. For normal and long sintering times, fracture forces were highest in the central position.

Conclusions

The sintering process and positioning of restorations within a multilayer zirconia blank have little effect on the mechanical properties of the prostheses.

中文翻译：

---

多层氧化锆：毛坯内定位和烧结条件对 3 单元固定局部义齿体外性能的影响

问题陈述

多层氧化锆坯料包括具有不同光学和机械性能的材料层。坯体内的定位以及烧结过程的变化是否会导致具有不同性能的修复体尚不清楚。

目的

这项体外研究的目的是测试烧结程序和在多层空白中的定位对 3 单元氧化锆固定局部义齿的体外性能的影响。

材料与方法

人类磨牙嵌入丙烯酸树脂中，并准备用于 3 单元固定局部义齿。解剖学轮廓假体由氧化锆坯料（ZirCAD Prime 16 毫米）在 3 个不同位置铣削而成：上方（坯料顶部的尖顶）、中央（坯料中心的假体中心）和底部（边缘在空白的下边缘）。中央和底部假体的烧结时间（2:26、4:25、9:50 小时：分钟）不同。所有假体都上釉并粘合。热循环和机械加载在蒸馏水中以 2×3000×5 °C/55 °C 进行 1.2×10 ⁶在 50-N 负载下循环。然后，使用万能试验装置，使用中心载荷、Ø12-mm 钢球、1-mm 锡箔和 1 mm/min 的速率测定断裂力。失效定义为 10% 的力下降或声音信号（裂纹）。使用 1-way ANOVA 和 Bonferroni 校正 (α=.05) 进行统计分析。

结果

所有固定的局部义齿都经受住了热循环和机械负荷。断裂力在 1002 ±446 N（以上；9:50 小时）和 1760 ±607 N（中心；9:50 小时）之间变化。1-way ANOVA 显示各组之间没有统计学上的显着差异 ( P= .059)。在上述位置（9:50 小时）和中心位置（9:50 小时）的假肢之间发现了个体显着差异 ( P= 0.048)。对于正常和较长的烧结时间，中心位置的断裂力最高。

结论

多层氧化锆坯料中修复体的烧结过程和定位对修复体的机械性能几乎没有影响。