Graduate student, Advanced Prosthodontics Residency Program, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, Ohio.
Emeritus Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, Ohio.
J Prosthet Dent. 2022 Sep;128(3):458-466. doi: 10.1016/j.prosdent.2020.12.020. Epub 2021 Feb 19.
The angled screw channel concept has become popular. However, research is lacking as to how reverse torque values of nonaxially tightened implant crowns compare with axially tightened cement-retained crowns restored on angle-correcting abutments when subjected to long-term cyclic loading.
The purpose of this in vitro study was to evaluate the ability of different 25-degree angled screw channel hexalobular systems to apply the target torque value on their screws, the effect of cyclic loading on their reverse torque values, and their survival compared with crowns cemented on conventional 0-degree screw channel abutments.
A total of 28 implants were divided into 4 groups. Twenty-one angled screw channel crowns were fabricated at a 25-degree angle correction by using angled titanium (Ti) bases by 3 manufacturers DY (Dynamic Tibase), DE (AngleBase), and ASC (Angulated Screw Channel) (n=7). The fourth group, UB (Universal Base, Control), had cement-retained crowns with 25-degree custom-milled, angled zirconia abutments that were cemented onto their respective Ti bases (n=7). All implants were embedded in epoxy resin blocks and tightened to manufacturer recommended values: 35 Ncm for ASC, UB, and DE and 25 Ncm for DY. Initial torque values (ITV1) were recorded. After 24 hours, the reverse torque values (24hr-RTV1) were recorded. A new set of screws was then used for each group, and the initial torque values (ITV2) were recorded. Specimens were loaded at 2 Hz for 5 million cycles under a 200-N load, and reverse torque values (RTV2) were recorded. ANOVA (α=.05) was used to compare differences in the means of deviation of initial torque values and means of reverse torque values followed by a Tukey-Kramer post hoc analysis (α=.05). Preload efficiency was calculated for each system (RTV2/ITV2), and a survival analysis was performed by using the Lifetest procedure.
A significant difference in the means of deviation of initial torque values of the groups with 25-degree torque application (DY, DE, and ASC) was found when compared with UB at 0 degrees. ASC and DE had lower initial torque values than UB (P<.001 and P=.003 for ASC ITV1 and ITV2, P<.001 and P=.006 for DE ITV1 and ITV2). A significant difference was found in mean reverse torque values both for after 24 hours and after cyclic loading among all groups (P<.001). A significant difference was found between mean reverse torque values before and after cyclic loading for each group (P<.001). Preload efficiency was 43.8% for DY, 46.8% for DE, 54.2% for ASC, and 48.5% for UB. No significant difference was found in the time-to-failure survival among groups (P>.05).
The hexalobular system of DY delivered comparable initial torque values to its target value at 25 degrees, similar to how UB (control group) delivered at 0 degrees. ASC and DE scored lower initial torque values than their target value compared with UB. The DY abutment, which had a lower manufacturer recommended torque value, had lower reverse torque values compared with those of other groups. Time-to-failure survival of all groups was similar. Fractures at the zirconia to titanium base connection were seen with ASC crowns.
倾斜螺丝通道概念已经流行起来。然而，关于在长期循环加载下，非轴向拧紧的种植体冠与轴向拧紧的、用粘结剂固位的在角度校正基台上的修复体的反向扭矩值如何比较，研究还很缺乏。
本体外研究的目的是评估不同的 25 度倾斜螺丝通道六方系统在其螺丝上施加目标扭矩值的能力、循环加载对其反向扭矩值的影响，以及与传统 0 度螺丝通道基台粘结的冠的存活率。
总共 28 个种植体被分为 4 组。通过 3 个制造商 DY（Dynamic Tibase）、DE（AngleBase）和 ASC（Angulated Screw Channel）制作了 21 个 25 度角度校正的倾斜螺丝通道冠，角度为 25 度（n=7）。第四组，UB（Universal Base，对照），有 25 度定制研磨的、带角度的氧化锆基台的粘结剂固位冠，用粘结剂固位在各自的 Ti 基台上（n=7）。所有种植体都嵌入环氧树脂块中，并拧紧到制造商建议的扭矩值：ASC、UB 和 DE 的扭矩值为 35 Ncm，DY 的扭矩值为 25 Ncm。记录初始扭矩值（ITV1）。24 小时后，记录反向扭矩值（24hr-RTV1）。然后为每个组使用新的一组螺丝，并记录初始扭矩值（ITV2）。在 200-N 负载下以 2 Hz 的频率加载 500 万次循环，记录反向扭矩值（RTV2）。使用方差分析（α=.05）比较初始扭矩值偏差均值和反向扭矩值均值的差异，然后进行 Tukey-Kramer 事后分析（α=.05）。为每个系统计算预载效率（RTV2/ITV2），并使用 Lifetest 程序进行生存分析。
与 0 度的 UB 相比，具有 25 度扭矩应用的组（DY、DE 和 ASC）的初始扭矩值偏差均值有显著差异。ASC 和 DE 的初始扭矩值低于 UB（ASC ITV1 和 ITV2 的 P<.001 和 P=.003，DE ITV1 和 ITV2 的 P<.001 和 P=.006）。所有组的 24 小时后和循环加载后的平均反向扭矩值均有显著差异（P<.001）。每个组的平均反向扭矩值在循环加载前后均有显著差异（P<.001）。DY 的预载效率为 43.8%，DE 的预载效率为 46.8%，ASC 的预载效率为 54.2%，UB 的预载效率为 48.5%。各组的失效时间存活率无显著差异（P>.05）。
DY 的六方系统在 25 度时提供了与目标值相当的初始扭矩值，与 UB（对照组）在 0 度时提供的初始扭矩值相似。与 UB 相比，ASC 和 DE 的初始扭矩值低于其目标值。制造商推荐扭矩值较低的 DY 基台的反向扭矩值低于其他组。所有组的失效时间存活率相似。ASC 冠出现了氧化锆与钛基台连接处的断裂。
