Objective

To investigate the intraoral development and kinetics of low-temperature degradation (LTD) in second-generation 3 mol.% yttria-doped tetragonal zirconia polycrystal (3Y-TZP) monolithic prostheses, as well as the influence of masticatory mechanical stress and glaze layer on it.

Methods

A total of 101 posterior tooth elements were included in a prospective clinical study, which included ex vivo LTD monitoring (at baseline, 6 months, 1 year, and 2 years) using Raman spectroscopy (n = 2640 monoclinic phase measurement points per evaluation time) and SEM. Four types of areas (1–2 mm² surface, 6 on molars, and 4 on premolars) were analyzed on each element surface: occlusal, axial, glazed, or unglazed. Raman depth mapping and high-resolution SEM were performed on the selected samples.

Results

LTD developed in 3Y-TZP monolithic restorations 6 months after intraoral placement and progressed with time. After two years, the tetragonal-to-monoclinic transformation was non-uniform, with the presence of localized clusters of transformed grains. In axial areas, the grain aspect was typical of the classical nucleation-growth process reported for LTD, which progresses from the surface to a depth of several tens of microns. However, in occlusal areas, tribological stress generated surface crushing and grain pull-out from the clusters, which induced an underestimation of the aging process when the evaluation was limited to monoclinic phase quantification. Glazing cannot be considered a protection against LTD.

Significance

If LTD occurs in dental prostheses in the same way as in orthopedic prostheses, its clinical impact is unknown and needs to be further studied.

中文翻译：

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单片氧化锆假牙的口腔内低温降解：前瞻性临床研究的结果，体外监测

客观的

研究第二代 3 mol.% 氧化钇掺杂四方氧化锆多晶 (3Y-TZP) 整体修复体的口腔内发展和低温降解 (LTD) 动力学，以及咀嚼机械应力和釉层对它。

方法

一项前瞻性临床研究共包括 101 个后牙元素，其中包括使用拉曼光谱进行离体LTD 监测（基线、6 个月、1 年和 2 年）（每个评估时间 n = 2640 个单斜相测量点）和扫描电镜。在每个元件表面上分析了四种类型的区域（1-2 mm ²表面，6 个在臼齿上，4 个在前磨牙上）：咬合面、轴向、釉面或未釉面。对选定的样品进行拉曼深度映射和高分辨率 SEM。

结果

LTD 在口内放置 6 个月后在 3Y-TZP 整体修复中发展，并随着时间的推移而进展。两年后，四方到单斜的转变是不均匀的，存在局部的转变颗粒簇。在轴向区域，晶粒方面是 LTD 报道的经典成核生长过程的典型特征，从表面发展到几十微米的深度。然而，在咬合区域，摩擦应力会产生表面压碎和颗粒从簇中拉出，当评估仅限于单斜相量化时，这会导致对老化过程的低估。玻璃不能被视为对 LTD 的保护。

意义

如果 LTD 以与矫形假体相同的方式出现在假牙中，其临床影响尚不清楚，需要进一步研究。