Associate Professor, Dental Sciences Research Center, Department of Prosthodontics, School of Dentistry, Guilan University of Medical Sciences, Rasht, Iran.
Professor, Dental Sciences Research Center, Department of Maxillofacial Radiology, School of Dentistry, Guilan University of Medical Sciences, Rasht, Iran.
J Prosthet Dent. 2018 Aug;120(2):220-224. doi: 10.1016/j.prosdent.2017.09.006. Epub 2018 Feb 21.
Cement-retained implant-supported restorations have advantages over screw-retained restorations but are difficult to retrieve. Identifying the approximate location of the screw access hole (SAH) may reduce damage to the prosthesis.
The purpose of this in vitro study was to evaluate the ability of cone beam computed tomography (CBCT) imaging to determine the location and direction of SAHs in cement-retained implant prostheses.
Five clear acrylic resin casts were made based on a mandibular model. Several implant osteotomies (n=30) were created on the models with surgical burs, and crowns were made using the standard laboratory method with a transfer coping and the closed tray impression technique. CBCT images from the acrylic resin casts were evaluated by a maxillofacial radiologist who was blind to the locations and angles of the osteotomies. The locations of the access holes were determined on multiplanar reconstruction images and transferred to the clinical crown surface as defined points. Based on cross-sectional images, the predicted angle of the access hole was provided to a prosthodontist who was requested to pierce the crown at the proposed location in the specified direction. If the location and/or direction of the access hole were found, the process was considered successful, as the crown could then be removed from the implant abutment through the SAH. The success rate in the detection of the location and direction of the SAH was calculated, and chi-square and Fisher exact tests were applied for data analysis (α=.05).
According to the results of this study, the success rate of CBCT to define the location of SAHs was 83.3% and 80% to determine the direction. No significant differences were found among the different dental groups in determination of the location (P=.79) or the direction (P=.53) of the SAHs. Most of the failures in determining the location and direction of the access hole in the buccolingual and mesiodistal directions were in the buccal and mesial locations of the SAH. The success rate of using CBCT to determine the location of SAHs in straight abutments was 100%. A significant difference was found between angled and straight abutments (P=.042).
Using CBCT could help determine the direction and location of SAHs in clinical situations.
与螺钉固位修复体相比，黏固式种植体支持修复体具有优势，但难以取出。确定螺钉接入孔（SAH）的大致位置可能会减少对修复体的损坏。
本体外研究的目的是评估锥形束计算机断层扫描（CBCT）成像确定黏固式种植体修复体中 SAH 位置和方向的能力。
根据下颌模型制作了 5 个透明丙烯酸树脂模型。使用外科磨具在模型上进行了几个种植体截骨术（n=30），并使用标准实验室方法，通过转移模板和闭托盘印模技术制作了牙冠。一位颌面放射科医生对丙烯酸树脂模型的 CBCT 图像进行了评估，该医生对截骨术的位置和角度一无所知。通过多平面重建图像确定接入孔的位置，并将其转移到临床牙冠表面作为定义点。根据横截面图像，向一名修复医生提供了接入孔的预测角度，要求该医生在指定位置以指定方向刺穿牙冠。如果找到接入孔的位置和/或方向，则认为该过程是成功的，因为可以通过 SAH 将牙冠从种植体基台移除。计算了检测 SAH 位置和方向的成功率，并应用卡方和 Fisher 精确检验进行数据分析（α=.05）。
根据本研究的结果，CBCT 定义 SAH 位置的成功率为 83.3%，确定方向的成功率为 80%。不同牙科组在确定 SAH 位置（P=.79）或方向（P=.53）方面没有发现显著差异。在颊舌和近远中方向确定接入孔位置和方向的大部分失败发生在 SAH 的颊侧和近中位置。使用 CBCT 确定直基台 SAH 位置的成功率为 100%。在直基台和角度基台之间发现了显著差异（P=.042）。
在临床情况下，使用 CBCT 可以帮助确定 SAH 的方向和位置。
