The effect of platform switching on stress distribution in implants and periimplant bone studied by nonlinear finite element analysis Siyu Liu, MDS,a Chunbo Tang, DDS, PhD,b Jinhua Yu, DDS, PhD,c Wenyong Dai, MDS,d Yidong Bao, EngD, PhD,e and Dan Hu, MEngf Affiliated Hospital of Stomatology, Nanjing Medical University, Nanjing, Jiangsu, China; College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China Statement of problem. It is unknown whether dental implant systems with a platform-switched configuration have better periimplant bone stress distribution and lead to less periimplant bone level changes. Purpose. The purpose of this study was to quantitatively investigate interfacial stress and stress distribution in implant bone in 2 implant abutment designs (platform-switched design and conventional diameter matching) by using a nonlinear finite element analysis method. Material and methods. A finite element simulation study was applied to 2 commercially available dental implant systems: the Ankylos implant system with a reduced-diameter abutment (platform-switched implant) and the Anthogyr implant system with an abutment of the same diameter (regular platform implant). These 2 dental implant systems were positioned in a bone block, which was constructed based on a cross-sectional image of a human mandible in the molar region. In simulation, a single vertical load of 50 N, 100 N, or 150 N and horizontal loads of 50 N and 100 N were applied to the occlusal surface of the abutment. Results. The finite element analysis found that the Ankylos implant system has a higher maximum von Mises stress in the implant abutment connection section and a lower maximum von Mises stress in the periimplant bone. The opposite results were found in the Anthogyr implant system. Conclusions. Lower stress levels in the periimplant bone with a more uniform stress distribution were found for the Ankylos implant system with a platform-switched configuration. Although relatively higher stress was found in the abutment, premature implant failure is not anticipated because of the high strength of titanium alloy. (J Prosthet Dent 2014;-:---)

Clinical Implications The stress distributions at the implant/abutment connection and in the periimplant region are dominated by the structural characteristics of the connection interface. This study found that platform-switched implants had more advantage in periimplant bone resorption than regular platform implants.

This work was supported by the Medical Science Foundation of Health Department (contract No. H201034); the Six Talent Summit Foundation of Jiangsu Province, China (contract No. 2010-WS081); the Science and Technology Support Program of Jiangsu Province (grant No. BE2011778); and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD, No. 2014-37). a

Postgraduate student, Institute of Stomatology, Nanjing Medical University. Assistant Professor, Department of Dental Implantology, Affiliated Hospital of Stomatology, Nanjing Medical University. c Assistant Professor, Department of Endodontology, Affiliated Hospital of Stomatology, Nanjing Medical University. d Postgraduate student, Institute of Stomatology, Nanjing Medical University. e Assistant Professor, College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics. f Postgraduate student, College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics. b

Liu et al

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Volume The close relationship between the implant and the periimplant bone is the essence of osseointegration. Periimplant bone resorption is a major factor leading to implant failure.1,2 Resorption usually starts from the collar of the implant and extends to the first screw thread of the implant body or to the initial contact region where the implant meets the bone.3-6 The preservation of periimplant bone is essential to ensure the sustainability and reliability of implant loading, and attention to this issue has increased since Lazzara et al7 first reported on platform-switching methodology. Platform switching uses an abutment with a smaller diameter than the dental implant. This specific design shifts the perimeter of the implant/abutment

1 of B, b, d,

junction inward and converges the edge of the implant/abutment connecting surface toward the central axis of the implant.7 A platform-switched implant is also known to reduce the stress concentration in the periimplant bone.8-10 A recent study found that platformswitched implants had the least reduction in periimplant bone height and soft tissue level loss.11,12 However, a high periimplant bone level alteration was also reported in this type of implant system, which may be attributed to the diameter mismatch of the implant and abutment.13-15 The clinical data of platformswitched implants16-18 indicate that the periimplant bone loss varies between 0.05 and 1.4 mm in the first year after loading, which is less than that of

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diameter-matched implants. Fickl et al19 evaluated 89 dental implants in 36 patients and found that the implants with a platform-switched configuration (n¼75) exhibited significantly less bone loss than the platform-matched implants (n¼14), both at the time of inserting the definitive prosthesis (0.30 0.07 mm versus 0.68 0.17 mm; P