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  • Title: Evaluation of the success rate of cone beam computed tomography in determining the location and direction of screw access holes in cement-retained implant-supported prostheses: An in vitro study.
    Author: Neshandar Asli H, Dalili Kajan Z, Gholizade F.
    Journal: J Prosthet Dent; 2018 Aug; 120(2):220-224. PubMed ID: 29475756.
    Abstract:
    STATEMENT OF PROBLEM: 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. PURPOSE: 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. MATERIAL AND METHODS: 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). RESULTS: 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). CONCLUSIONS: Using CBCT could help determine the direction and location of SAHs in clinical situations.
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