RESEARCH AND EDUCATION Clinician-generated torque on abutment screws using different hand screwdrivers Marzieh Alikhasi, DDS, MS, a Mahmoud Kazemi, DDS, MS, b Hamid Jalali, DDS, MS, c Shervin Hashemzadeh, DDS, d Hamide Dodangeh, DDS, e and Burak Yilmaz, DDS, PhD f The use of dental implants has become increasingly popular for replacing missing teeth because they can maintain natural appearance 1 and long- term stability and durability. 2,3 However, implants do have some disadvantages, such as screw loosening, screw frac- ture, and abutment frac- ture. 2,4-6 Screw loosening is one of the most common prosthetic complications and could lead to bacterial leakage in the implant assemblies 7,8 and periimplant soft tissue inflammation. 9 The generated load placed upon the abutment by screw tightening is called preload. When the separating forces on implant assemblies exceed the generated preload, screw loosening occurs. 10-12 There- fore, the preload should be adequate to provide resis- tance for the assemblies against the separating forces exerted in the oral environment. 13,14 However, preload values should not exceed the yield strength of the screws to prevent the permanent deformation or fracture of the screws. 15,16 Therefore, the application of the proper Presented at the 93th General Session of the International Association of Dental Research/American Association of Dental Research/Canadian Association of Dental Research, Boston, Mass, March 2015. a Associate Professor, Dental Research Center, Department of Prosthodontics, Tehran University of Medical Sciences, Tehran, Iran. b Assistant Professor, Department of Prosthodontics, Tehran University of Medical Sciences, Tehran, Iran. c Assistant Professor, Department of Prosthodontics, Tehran University of Medical Sciences, Tehran, Iran. d Visiting Scholar, Division of Restorative Sciences and Prosthodontics, The Ohio State University College of Dentistry, Columbus, Ohio. e Dentist, Dental Research Center, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. f Associate Professor, Division of Restorative Sciences and Prosthodontics, The Ohio State University College of Dentistry, Columbus, Ohio. ABSTRACT Statement of problem. Many clinicians use hand screwdrivers to tighten prosthetic and abutment screws. The impact of the screwdriver type, the location of the implant, and the sex of the prac- titioner on the generated torque is not well understood. Purpose. The purpose of this in vitro study was to compare the torque generated by different hand screwdrivers when used in the anterior and posterior regions and to evaluate the correlation between the applied torque and the sex and body mass index (BMI) of the practitioner. Material and methods. A mandibular typodont with anterior and posterior implants was mounted in a mannequin head. Fifty clinicians (6 prosthodontists, 8 graduate prosthodontic students, and 36 dental students) used their maximum force to tighten the abutment screws in the anterior and posterior regions, using 3 different hand screwdrivers, with handles of different shapes and sizes (small, medium, and large). The torque values generated were measured using torque meters connected to the implants. The generated torque, sex, age, height, and weight were also recorded for each clinician. A generalized linear model was used to find correlations between the different factors and the generated torque (a=.05). Results. Significant differences were observed among the applied torque values when different screwdrivers were used (P<.001). Higher torque values were generated in the anterior region than in the posterior region (P<.001). The interaction of the sex and BMI of the participants significantly affected the generated torque values (P=.044). Conclusions. The type of screwdriver and location of the implant affected the generated torque. Torque values generated by the large screwdriver were higher than those of small and medium screwdrivers. Higher torque was applied in the anterior region. (J Prosthet Dent 2017;-:---) THE JOURNAL OF PROSTHETIC DENTISTRY 1