Al Jabbari Youssef S, Fournelle Raymond, Ziebert Gerald, Toth Jeffrey, Iacopino Anthony M
Department of Prosthodontic Dental Sciences, King Saud University College of Dentistry, Riyadh, Saudi Arabia.
J Prosthodont. 2008 Apr;17(3):168-80. doi: 10.1111/j.1532-849X.2007.00265.x. Epub 2007 Nov 15.
The general aim of this study and those presented in Parts 2-4 of this series was to characterize the structure, properties, wear, and fracture of prosthetic retaining screws in fixed detachable hybrid prostheses after long-term use in vivo. This part of the overall investigation addresses whether there are differences in thread wear between the screws closest to the fulcrum and those that are farthest from the fulcrum in fixed detachable hybrid prostheses.
The total number of prosthetic retaining screws used in this study was 100 (10 new and 90 used). New screws (controls) from Nobel Biocare (NB) were divided into Group 1 (slotted) and Group 2 (hexed). Ninety used screws (in service 18-120 months) were retrieved from fixed detachable hybrid prostheses in 18 patients (5 screws from each patient, 60 from NB and 30 from Sterngold). The used screws were divided into 18 groups. Additionally, each group was subdivided into A and B categories. Category A contained the middle three prosthetic screws, which were considered the farthest screws from the fulcrum line. Category B contained the most posterior two screws, which were considered the screws closest to the fulcrum line. All 100 screws were subjected to thorough, nondestructive testing.
Light and scanning electron microscopic examination of all used screws for each group revealed surface deterioration of the active profile of the screw threads consistent with adhesive wear. The observed thread profile deterioration ranged from mild to severe. The wear was aggressive enough to cause galling, which led to thinning of the threads and, in severe cases, to knife-edges at thread crests. In ten groups, the most anterior three screws exhibited more wear than the most posterior two screws. In addition to thread wear, severe plastic deformation was detected on the bottom part of each screw for three groups, and a long external longitudinal crack was detected in one screw of Group 2.
The findings of this study and those presented in Parts 2-4 demonstrate that different retaining screws from the same manufacturer and/or from different manufacturers have different geometrical design, microstructures, major alloy constituents, and microhardness, and that these differences influence their preload and fractured load values. In this part of the overall investigation, the occurrence of galling as a result of wear involving prosthetic retaining screws appears to be an inevitable and unavoidable consequence of long-term use in vivo in fixed detachable hybrid prostheses regardless of the intended/original preload value. The galling rate is greater on the middle three screws compared to the most posterior two screws in fixed detachable hybrid prostheses. The wear pattern is consistent with an adhesive wear mechanism; however, this study does not provide enough data to support a definitive analysis.
本研究以及本系列第2 - 4部分中所呈现研究的总体目标是，描述固定可拆混合式修复体中修复固位螺钉在长期体内使用后的结构、性能、磨损及断裂情况。整体研究的这一部分探讨了在固定可拆混合式修复体中，最靠近支点的螺钉与离支点最远的螺钉在螺纹磨损方面是否存在差异。
本研究中使用的修复固位螺钉总数为100颗（10颗新的和90颗使用过的）。诺贝尔生物公司（NB）的新螺钉（对照组）分为第1组（开槽的）和第2组（内六角的）。从18例患者的固定可拆混合式修复体中取出90颗使用过的螺钉（使用时间为18 - 120个月）（每位患者5颗螺钉，60颗来自NB，30颗来自施特恩戈尔德）。使用过的螺钉分为18组。此外，每组又细分为A和B两类。A类包含中间的三颗修复螺钉，被认为是离支点线最远的螺钉。B类包含最后面的两颗螺钉，被认为是最靠近支点线的螺钉。所有100颗螺钉都接受了全面的无损检测。
对每组所有使用过的螺钉进行光学显微镜和扫描电子显微镜检查，发现螺钉螺纹有效轮廓表面出现与粘着磨损一致的劣化。观察到的螺纹轮廓劣化程度从轻度到重度不等。磨损严重到足以导致擦伤，进而导致螺纹变薄，在严重情况下，螺纹顶部会形成刀刃状。在十组中，最前面的三颗螺钉比最后面的两颗螺钉磨损更严重。除了螺纹磨损外，在三组螺钉的每颗螺钉底部都检测到严重的塑性变形，在第2组的一颗螺钉中检测到一条长的外部纵向裂纹。
本研究以及第2 - 4部分中所呈现研究的结果表明，来自同一制造商和/或不同制造商的不同固位螺钉具有不同的几何设计、微观结构、主要合金成分和显微硬度，并且这些差异会影响它们的预紧力和断裂载荷值。在整体研究的这一部分中，因修复固位螺钉磨损导致的擦伤现象，似乎是固定可拆混合式修复体在体内长期使用不可避免的结果，无论预期/原始预紧力值如何。在固定可拆混合式修复体中，中间三颗螺钉的擦伤率比最后面两颗螺钉更高。磨损模式与粘着磨损机制一致；然而，本研究没有提供足够的数据来支持确定性分析。
