©2016 by Quintessence Publishing Co Inc. 1058 Volume 31, Number 5, 2016 Efect of the Coronal Wall Thickness of Dental Implants on the Screw Joint Stability in the Internal Implant-Abutment Connection Ji-Hye Lee, DDS, PhD 1 /Yoon-Hyuk Huh, DDS, MSD 2 / Chan-Jin Park, DDS, MSD, PhD 3 /Lee-Ra Cho, DDS, MSD, PhD 3 Purpose: To evaluate the effect of implant coronal wall thickness on load-bearing capacity and screw joint stability. Materials and Methods: Experimental implants were customized after investigation of the thinnest coronal wall thickness of commercially available implant systems with a regular platform diameter. Implants with four coronal wall thicknesses (0.2, 0.3, 0.4, and 0.5 mm) were fabricated. Three sets of tests were performed. The irst set was a failure test to evaluate load-bearing capacity and elastic limit. The second and third sets were cyclic and static loading tests. After abutment screw tightening of each implant, vertical cyclic loading of 250 N or static loading from 250 to 800 N was applied. Coronal diameter expansion, axial displacement, and removal torque values of the implants were compared. Repeated measures analysis of variance (ANOVA) was used for statistical analysis (α = .05). Results: Implants with 0.2-mm coronal wall thickness demonstrated signiicantly low load-bearing capacity and elastic limit (both P < .05). These implants also showed signiicantly large coronal diameter expansion and axial displacement after screw tightening (both P < .05). Greater vertical load and thinner coronal wall thickness signiicantly increased coronal diameter expansion of the implant, axial displacement of the abutment, and removal torque loss of the abutment screw (all P < .05). Conclusion: Implant coronal wall thickness of 0.2 mm produces signiicantly inferior load-bearing capacity and screw joint stability. INT J ORAL MAXILLOFAC IMPLANTS 2016;31:1058–1065. doi: 10.11607/jomi.4600 Keywords: axial displacement, coronal wall thickness, internal conical connection, load-bearing capacity, wedge effect F racture failure of implants is catastrophic and irre- versible, and should be prevented. 1 Implant diam- eter has a major impact on the load-bearing capacity to resist fracture failure. 2 Increased implant diameter enhances fatigue fracture resistance with wider stress distribution. 3 The most common cause of implant fracture is biomechanical overload, so an appropri- ate implant diameter should be carefully considered. 4 The risk of fatigue fracture and detrimental efect to crestal bone in small-diameter implants has been documented. 5,6 However, the distinction between diferent implant- abutment connection types should also be considered in the load-bearing capacity of the implant-abutment complex. Unlike the external butt joint, the internal conical connection (ICC) type has a thin-walled cylin- drical conical connection inside of the implant. The cor- onal third of this implant reportedly yields the highest stress levels on the internal connection. 7 Thus, special care should be taken to avoid excessive deformation of thin-walled implants. A comparison of the critical failure of various commercially available implants con- cluded that the reduced coronal wall thickness area of some internal connection systems could become the weakest link. 8 Coronal wall thickness reduction after implantoplasty or implant collar preparation decreases the bending moment or fracture strength of the im- plant-abutment complex. 9,10 Due to the diferent con- nection dimensions, results from previous studies have not been instructive concerning the critical coronal wall thickness necessary to prevent implant fracture. 9,11 Elastic or plastic deformation of an implant caused by the wedge efect must be considered. ICC induces high compressive force between an abutment and 1 Clinical Instructor, Department of Prosthodontics and Research Institute of Oral Science, Gangneung-Wonju National University, Gangneung, South Korea; Department of Dentistry, Uijeongbu St. Mary’s Hospital, Catholic University of Korea, Uijeongbu, South Korea. 2 Assistant Professor, Department of Prosthodontics and Research Institute of Oral Science, Gangneung-Wonju National University, Gangneung, South Korea. 3 Professor, Department of Prosthodontics and Research Institute of Oral Science, Gangneung-Wonju National University, Gangneung, South Korea. Correspondence to: Prof Lee-Ra Cho, Department of Prosthodontics and Research Institute of Oral Science, Gangneung-Wonju National University, Gangneung, Korea. Fax: +82 33 640 3103. Email: lila@gwnu.ac.kr © 2016 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.