Comparative Analysis of Screw Loosening With Prefabricated Abutments and Customized CAD/CAM Abutments Janghyun Paek, DMD, MS, PhD,* Yi-Hyung Woo, DMD, MSD, PhD,† Hyeong-Seob Kim, DMD, MSD, PhD,† Ahran Pae, DMD, MSD, PhD,‡ Kwantae Noh, DMD, MSD, PhD,* Hyeonjong Lee, DMD, MSD,§ and Kung-Rock Kwon, DMD, MSD, PhD† C ustomized implant abutments are gaining popularity for optimizing the abutments, by correcting the angle and depth of the implant fixture, as well as the contours of the gingiva. An advantage of a customized abutment is that it can cover an unesthetic margin of the prosthesis by relocating it subgingi- vally. Thus, it can prevent a metal margin showing and a better esthetic result can be obtained. Traditionally, UCLA abut- ments were used to fabricate custom abutments. They are manufactured from a gold platform and a castable sleeve that allows individualizing the shape and the height of each abutment. However, a dis- advantage of a gold cast abutment is its high cost. Today, as the cost of gold has increased, there is greater interest in computer-aided design and manufactur- ing (CAD/CAM) systems for implant- supported prostheses. CAD/CAM tita- nium and zirconia abutments have also been reported to have favorable biocom- patibility. 1 This cutting-edge technology of computer-designed and computer- generated abutments will likely replace traditional implant restorative protocols and fundamentally become the standard for implant dentistry in the foreseeable future. However, studies of the stability of implant abutments are lacking, espe- cially for abutments manufactured using CAD/CAM systems. 2,3 Despite the high clinical success of dental implants, biological and mechan- ical complications still arise. Among mechanical complications, instability of screws, screw loosening, and screw fractures have been reported as common complications. 4–10 The most commonly reported mechanical complication is screw loosening. 9,10 Reasons for screw loosening include fatigue, inadequate tightening torque, settling effects, vibrat- ing micromovements, and excessive bending. Screw loosening can cause fracture of the implant prosthesis and fixtures. Moreover, it can lead to micro- gaps in which microflora can proliferate. This can trigger biological problems, re- sulting in failure of osseointegration. Owing to the fact that a comparative study of the stability of stock abutments versus CAD/CAM titanium custom *Assistant Professor, Department of Prosthodontics, School of Dentistry, KyungHee University, Seoul, South Korea. †Professor, Department of Prosthodontics, School of Dentistry, KyungHee University, Seoul, South Korea. ‡Associate Professor, Department of Prosthodontics, School of Dentistry, KyungHee University, Seoul, South Korea. §Clinical Instructor, Department of Prosthodontics, School of Dentistry, KyungHee University, Seoul, South Korea. Reprint requests and correspondence to: Kung-Rock Kwon, DMD, MSD, PhD, Department of Prosthodontics, School of Dentistry, KyunHee University, 23, Kyungheedae-ro, Dongdaemun-gu, Seoul 130-872, South Korea, Phone: +82-2-9589341, Fax: +82-2-9589349, E-mail: paek217@gmail.com ISSN 1056-6163/16/02506-770 Implant Dentistry Volume 25  Number 6 Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/ID.0000000000000481 Purpose: The aim of this study was to determine the stability of computer-aided design and manufacturing (CAD/CAM) and prefabricated abutment by measur- ing removal torque before and after cyclic loading. Materials and Methods: Three types of fixture and 2 types of abut- ments were used. Removable torque was measured after cyclic loading for 5000 cycles between 25 and 250 N for each group. The same pro- cedure was performed twice. Results: First, removal torque values (Newton centimeter) were measured for stock versus custom abutments as follows: group 1: 27.17 versus 26.67, group 2: 26.27 versus 26.33, and group 3: 37.33 versus 36.67. Second removal torque values (Newton centimeter) were also measured: group 1: 23 versus 23.5, group 2: 22.5 versus 22.33, and group 3: 32.67 versus 32.5. There was no significant difference between the stock and custom abutments in either the first or second removal torque values and also no signifi- cant difference among initial tight- ening torque, first or second removal torque (P . 0.05). Conclusion: With precise con- trol of CAD/CAM abutments, good screw joint stability can be achieved. (Implant Dent 2016;25:770–774) Key Words: stock abutment, joint stability, removal torque, cyclic loading 770 COMPARATIVE ANALYSIS OF SCREW LOOSENING PAEK ET AL Copyright Ó 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.