Accuracy of implant casts generated with splinted and non-splinted impression techniques for edentulous patients: an optical scanning study

Background: The accuracy of implant casts generated with various impression techniques was mainly investigated in vitro resulting in limited clinical data. Purpose: (1) To compare the three‐dimensional (3‐D) accuracy of splinted and non‐splinted impression techniques to the control casts (verification jigs) that had been used for actual patient treatment; and (2) to determine the maximum level of clinically undetectable misfit. The null hypothesis was that there would be no significant difference in the accuracy of casts generated with different impression techniques. Materials and methods: The implant casts used for the prosthetic rehabilitation of 12 edentulous jaws with CAD/CAM zirconia, implant‐fixed complete dental prosthesis (IFCDP) were included in this study. Intraoral acrylic jigs were used to fabricate index casts. Splinted and non‐splinted, open‐tray techniques were used to generate two casts. Optical scanning acquisition of the x‐coordinates, y‐coordinates and z‐coordinates of the implant positions for each individual cast was performed. The “best fit” algorithm was used with computer software to superimpose the scanning datasets. Group I (n=12) included casts from the splinted impression technique vs. acrylic jig casts, and group II (n=12) included casts from non‐splinted technique vs. jig casts. Results: The paired t‐test and Wilcoxon's signed ranks test were used to compare the 3‐D discrepancies within and between groups I (splinted vs. jig) and II (non‐splinted vs. jig), respectively. Significant difference was found at the x‐axis, y‐axis and 3‐D between groups I and II (P<0.05), but not in the vertical z‐axis (P>0.05). Within subject, global 3‐D discrepancies between groups I and II were significantly different (P<0.05), corroborated by in vivo observations of clinical fit. Implant position in the arch affected the 3‐D accuracy of casts for both anterior and posterior implants (P<0.05). Conclusion: The splinted technique generated more accurate master casts than the non‐splinted technique for one‐piece IFCDPs in edentulous jaws and the null hypothesis was rejected. These clinical implications demonstrate improved accuracy of splinted impression techniques compared with the non‐splinted technique. For the external connection, the implant system used in this study, a 3‐D misfit ranging from 59 to 72 μm, may be considered the maximum discrepancy resulting in an acceptable clinical fit with one‐piece IFCDPs.     

上部结构材料和形态设计对种植支持固定修复体被动适合性的影响

目的 研究氧化锆全瓷和纯钛烤瓷两种上部结构材料及360°颈环设计对计算机辅助设计和制作种植支持固定修复体被动适合性的影响。方法 制作32个弹性模量与牙槽骨相近的环氧树脂块并在每个树脂块上植入两枚种植体,模拟左下颌第二前磨牙至第二磨牙缺失后的种植修复。在每个种植体颈部4个方向上分别粘接应力感应器。制作4组不同材料及形态设计的三单位种植支持固定修复上部结构,每组8个。A组为常规氧化锆全瓷冠组,B组为360°氧化锆颈环基底全瓷冠组,C组为常规纯钛烤瓷冠组,D组为360°纯钛金属颈环基底烤瓷冠组。利用应力感应装置分别测量每颗种植体饰瓷烧结前、后种植体上部结构在粘接时对种植体周围结构引起的应变。结果 饰瓷烧结前,不同的上部结构材料引起种植体周围结构的应变有明显不同,氧化锆组应变较小（P<0.01）,不同形态设计造成应变的差异也有统计学意义,有颈环组应变较小（P<0.01）,上部结构材料与形态设计对种植体周围结构应变的产生存在交互作用,氧化锆有颈环组应变最小（P<0.01）。经饰瓷烧结,各组应变均增加,不同材料对烤瓷前、后应变差异无明显影响（P>0.05）,形态设计对烤瓷前后应变差异的影响有统计学意义,有颈环组差异较小（P<0.01）。结论 氧化锆全瓷比纯钛金属烤瓷修复体具有更好的被动适合性;360°颈环有利于提高种植支持固定修复体被动适合性,并减轻由烧结饰瓷带来的不良影响。     

The effect of framework fabrication technique on the fit accuracy of full arch screw retained implant supported prostheses

PurposeThe purpose of this study was to compare the accuracy of fit of Co-Cr full arch screw-retained implant-supported fixed dental prosthesis fabricated among three different methods: conventional casting, milling, and additive manufacturing technology.Materials and methodsA master model of a completely edentulous mandible with five internal connection implants was utilized. Thirty full arch Co-Cr screw-retained implant-supported frameworks were fabricated by three different methods: conventional casting, milling, and additive manufacturing (AM) technology. The marginal fit was measured using a coordinate measuring machine in x-, y-, and z-axes, as well as the three-dimensional discrepancy. The casting group were measured twice: before the adaptation procedure and again after the adaptation procedure (sectioning and laser welding). For comparisons of marginal fit of frameworks between different groups one-way analysis of variance and Games Howell test was used. Paired t-test was used to compare cast frameworks before and after adaption.ResultsThere were statistically significant differences in marginal fit and width distortion between groups (P <.05). The mean of total distortion of each group was 94.6 µm (SD 50.5 µm) for casting group before adaptation, 92.44 µm (SD 49.6 µm) for casting group after adaptation, 71.4 µm (SD 37.2 µm) for additive manufacturing group, while for the milling group the total distortion was 50.1 µm (SD 27.5 µm).ConclusionFull arch screw-retained implant-supported frameworks fabricated with any of the three fabrication techniques using cobalt-chromium material exhibited acceptable marginal fit. Milling fabrication technique showed the most accurate marginal fit. Adaptation procedure for the cast group has significantly improved the marginal fit.