Effect of the coefficient of friction and tightening speed on the preload induced at the dental implant complex with the finite element method.
BACKGROUND
To prevent screw loosening, a clear understanding of the factors influencing secure preload is necessary.


OBJECTIVE
The purpose of this study was to investigate the effect of coefficient of friction and tightening speed on screw tightening based on energy distribution method with exact geometric modeling and finite element analysis.


METHODS
To simulate the proper boundary conditions of the screw tightening process, the supporting bone of an implant was considered. The exact geometry of the implant complex, including the Straumann dental implant, direct crown attachment, and abutment screw were modeled with Solidworks software. Abutment screw/implant and implant/bone interfaces were designed as spiral thread helixes. The screw-tightening process was simulated with Abaqus software, and to achieve the target torque, an angular displacement was applied to the abutment screw head at different coefficients of friction and tightening speeds. The values of torque, preload, energy distribution, elastic energy, and efficiency were obtained at the target torque of 35 Ncm. Additionally, the torque distribution ratio and preload simulated values were compared to theoretically predicted values.


RESULTS
Upon reducing the coefficient of friction and enhancing the tightening speed, the angle of turn increased at the target torque. As the angle of turn increased, the elastic energy and preload also increased. Additionally, by increasing the coefficient of friction, the frictional dissipation energy increased but the efficiency decreased, whereas the increase in tightening speed insignificantly affected efficiency.


CONCLUSIONS
The results of this study indicate that the coefficient of friction is the most influential factor on efficiency. Increasing the tightening speed lowered the response rate to the frictional resistance, thus diminishing the coefficient of friction and slightly increasing the preload. Increasing the tightening speed has the same result as reducing the coefficient of friction.
Graduate student, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Iran.
Haddad Arabi
HA
Bulaqi
Professor, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Iran.
Mahmoud
M
Mousavi Mashhadi
Associate Professor, Implant Research Center, Department of Prosthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
Farideh
F
Geramipanah
Assistant Professor, Department of Periodontics, School of Dentistry, Qom University of Medical Sciences, Qom, Iran.
Hamed
H
Safari
Associate Professor, Dental Research Center, Department of Periodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Electronic address: mpaknejad@hotmail.com.
Mojgan
M
Paknejad
D000465:Algorithms; D001696:Biomechanical Phenomena; D000069343:Bone-Implant Interface / Q000502:physiology; D003198:Computer Simulation; D003442:Crowns; D059605:Dental Implant-Abutment Design; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D055119:Elastic Modulus; D020342:Finite Element Analysis; D017276:Friction; D006801:Humans; D008334:Mandible / Q000502:physiology; D008422:Materials Testing; D008954:Models, Biological; D012399:Rotation; D013314:Stress, Mechanical; D013997:Time Factors; D019415:Torque
D015921:Dental Implants