Al Jabbari Youssef, Fournelle Raymond, Ziebert Gerald, Toth Jeffrey, Iacopino Anthony
Division of Prosthodontics, Marquette University School of Dentistry, Milwaukee, WI 53233, USA.
J Prosthodont. 2008 Apr;17(3):181-91. doi: 10.1111/j.1532-849X.2007.00271.x. Epub 2007 Nov 28.
This study involved testing and analyzing multiple retrieved prosthetic retaining screws after long-term use in vivo to: (1) detect manufacturing defects that could affect in-service behavior; (2) characterize the microstructure and alloy composition; and (3) further characterize the wear mechanism of the screw threads.
Two new (control) screws from Nobel Biocare (NB) and 18 used (in service 18-120 months) retaining screws [12 from NB and 6 from Sterngold (SG)] were: (1) metallographically examined by light microscopy and scanning electron microscopy (SEM) to determine the microstructure; (2) analyzed by energy dispersive X-ray (EDX) microanalysis to determine the qualitative and semiquantitative average alloy and individual phase compositions; and (3) tested for Vickers microhardness.
Examination of polished longitudinal sections of the screws using light microscopy revealed a significant defect in only one Group 4 screw. No significant defects in any other screws were observed. The defect was considered a "seam" originating as a "hot tear" during original casting solidification of the alloy. Additionally, the examination of longitudinal sections of the screws revealed a uniform homogeneous microstructure in some groups, while in other groups the sections exhibited rows of second phase particles. The screws for some groups demonstrated severe deformation of the lower threads and the bottom part of the screw leading to the formation of crevices and grooves. Some NB screws were comprised of Au-based alloy with Pt, Cu, and Ag as alloy elements, while others (Groups 4 and 19) were Pd-based with Ga, Cu, and Au alloy elements. The microstructure was homogeneous with fine or equiaxed grains for all groups except Group 4, which appeared inhomogeneous with anomalous grains. SG screws demonstrated a typical dendritic structure and were Au-based alloy with Cu and Ag alloy elements. There were differences in the microhardness of gold alloy screws from NB and SG as well as palladium alloy screws from NB.
Significant differences within NB retaining screws and between NB and SG screws were found for microstructure, major alloy constituents, and microhardness.
本研究对多枚长期体内使用后取出的修复固位螺钉进行测试和分析，以：（1）检测可能影响使用性能的制造缺陷；（2）表征微观结构和合金成分；（3）进一步表征螺纹的磨损机制。
两枚来自诺贝尔生物保健公司（NB）的新（对照）螺钉和18枚使用过的（使用18 - 120个月）固位螺钉[12枚来自NB，6枚来自施特恩戈尔德公司（SG）]进行了以下操作：（1）通过光学显微镜和扫描电子显微镜（SEM）进行金相检查以确定微观结构；（2）通过能量色散X射线（EDX）微分析进行分析以确定定性和半定量的平均合金及各相成分；（3）测试维氏显微硬度。
使用光学显微镜检查螺钉的抛光纵向截面时，仅在一枚4组螺钉中发现明显缺陷。其他螺钉未观察到明显缺陷。该缺陷被认为是合金原始铸造凝固过程中产生的“热裂”导致的“接缝”。此外，对螺钉纵向截面的检查显示，一些组呈现均匀的微观结构，而其他组的截面则呈现出一排排的第二相颗粒。一些组的螺钉下部螺纹和螺钉底部出现严重变形，导致形成缝隙和凹槽。一些NB螺钉由含Pt、Cu和Ag作为合金元素的金基合金组成，而其他螺钉（4组和19组）则是含Ga、Cu和Au合金元素的钯基合金。除4组呈现不均匀的异常晶粒外，所有组的微观结构均为均匀的细晶粒或等轴晶粒。SG螺钉呈现典型的树枝状结构，是含Cu和Ag合金元素的金基合金。NB和SG的金合金螺钉以及NB的钯合金螺钉在显微硬度上存在差异。
在NB固位螺钉内部以及NB和SG螺钉之间，在微观结构、主要合金成分和显微硬度方面发现了显著差异。
