Haghi Hamidreza Rajati, Shiehzadeh Masoud, Nakhaei Mohammadreza, Ahrary Fatemeh, Sabzevari Saeid
Department of Prosthetic, Faculty of Dentistry, Dental Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
Department of Prosthetic, Faculty of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
J Indian Prosthodont Soc. 2017 Jan-Mar;17(1):41-47. doi: 10.4103/0972-4052.197937.
A dental impression is a negative imprint of an oral structure that can be used to produce a positive cast of a patient's teeth as a permanent record. The accuracy of the impression affects the accuracy of the cast, and a precise impression is needed in order to create prosthesis with optimal fitting. Minimization of misfit is an important aim in prosthesis science and dental implants. The aim of this study was to evaluate the effects of the materials and techniques used to take an impression on the vertical misfit of implant-supported, screw-retained, three-unit bridges.
The principal model used was an acrylic block with two ITI implants. A 1.5-mm abutment was attached to fixtures with torque of 25 N.cm. A base-metal framework was built on the abutment in the acrylic block. The abutments of the acrylic model were unscrewed and fixture-level impressions were made. The impression techniques included open/closed-tray techniques and the impression materials were polyether and polyvinyl siloxane. Forty acrylic custom trays were built for each impression. The marginal gap in the framework at three points (buccal, lingual, and distal) was measured using an optical microscope with ×250.
It is demonstrated that in all 360 evaluated samples, the mean vertical misfit in polyether samples of molar and premolar teeth was significantly lower than in polyvinyl siloxane ( < 0.001 and = 0.017, respectively) in all three locations of the molar and lingual premolar examined (buccal, lingual, and distal), the mean vertical misfit of the polyether samples was significantly lower than those of polyvinyl siloxane ( < 0.01). On the other hand, although the mean vertical misfit using the open-tray technique in the molar teeth was significantly lower than with the closed-tray method ( = 0.002), no statistical difference was seen between the open-tray and closed-tray technique in general ( = 0.87).
Within the limitations of this study, the following conclusions can be drawn: The impression method had no effect on marginal discrepancy of 3-unit screw retained fixed partial dentures. A higher marginal accuracy was obtained using polyether impression material compared to polyvinyl siloxane.
牙印模是口腔结构的负性印记，可用于制作患者牙齿的正性模型作为永久记录。印模的准确性会影响模型的准确性，为了制作出贴合度最佳的修复体，需要精确的印模。减少不贴合度是修复科学和牙种植领域的一个重要目标。本研究的目的是评估用于取印模的材料和技术对种植体支持的、螺丝固位的三单位桥垂直不贴合度的影响。
主要模型是一个带有两颗ITI种植体的丙烯酸块。一个1.5毫米的基台以25牛·厘米的扭矩连接到种植体上。在丙烯酸块中的基台上构建一个贱金属框架。拧下丙烯酸模型的基台并制作种植体水平印模。印模技术包括开放/封闭托盘技术，印模材料为聚醚和聚乙烯基硅氧烷。为每种印模制作40个定制丙烯酸托盘。使用×250光学显微镜测量框架在三个点（颊侧、舌侧和远中）的边缘间隙。
结果表明，在所有360个评估样本中，在检查的磨牙和舌侧前磨牙的所有三个位置（颊侧、舌侧和远中），聚醚样本中磨牙和前磨牙的平均垂直不贴合度均显著低于聚乙烯基硅氧烷（分别为<0.001和=0.017），聚醚样本的平均垂直不贴合度显著低于聚乙烯基硅氧烷样本（<0.01）。另一方面，虽然磨牙使用开放托盘技术的平均垂直不贴合度显著低于封闭托盘方法（=0.002），但总体上开放托盘和封闭托盘技术之间没有统计学差异（=0.87）。
在本研究的局限性内，可以得出以下结论：印模方法对三单位螺丝固位固定局部义齿的边缘差异没有影响。与聚乙烯基硅氧烷相比，使用聚醚印模材料可获得更高的边缘精度。
