Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Univ Estadual Paulista (UNESP), Sao Paulo, Brazil.
J Prosthodont. 2011 Oct;20(7):523-7. doi: 10.1111/j.1532-849X.2011.00753.x. Epub 2011 Aug 31.
The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.
Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 μm, 100 μm, and 200 μm in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2×10(4) , 5×10(4) , and 1×10(6) cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two-way ANOVA and Tukey's test (p < 0.05).
Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05).
Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.
本研究旨在评估机械循环和不同不匹配水平对单种植体支持修复体固位螺钉维氏显微硬度的影响。
预加工 UCLA 基台用钴铬合金铸造以获得 48 个牙冠，分为 4 组（n = 12）。组 A（对照组）无不匹配，组 B、C 和 D 分别有单侧 50μm、100μm 和 200μm 的不匹配。牙冠用钛固位螺钉（扭矩 30 N/cm）拧到外六方种植体上，然后将这些牙冠套装进行三种不同的机械循环周期：2×10(4)、5×10(4)和 1×10(6)循环。在每个循环周期前后测量螺钉的显微硬度值。数据采用双因素方差分析和 Tukey 检验（p < 0.05）进行评估。
无论循环周期和组如何，机械循环都会降低固位螺钉的显微硬度值。在组 A、B 和 C 中，初始显微硬度值与最终显微硬度值有统计学差异（p < 0.05）。组间初始螺钉显微硬度值无统计学差异（p > 0.05）；然而，在机械循环后对各组进行比较时，组 B 和 D 之间存在统计学差异（p < 0.05）。
机械循环降低了所有组固位螺钉的维氏显微硬度值。不匹配程度最高的牙冠具有最高的维氏显微硬度值。
