Three-dimensional repositioning accuracy of semiadjustable articulator cast mounting systems Ming Yi Tan, BDS, a Justina Youlin Ung, BDS, b Ada Hui Yin Low, BDS, c En En Tan, BDS, d and Keson Beng Choon Tan, BDS, MSD e Faculty of Dentistry, National University of Singapore, Singapore; National Healthcare Group, Ministry of Health, Singapore Statement of problem. In spite of its importance in prosthesis precision and quality, the 3-dimensional repositioning accuracy of cast mounting systems has not been reported in detail. Purpose. The purpose of this study was to quantify the 3-dimensional repositioning accuracy of 6 selected cast mounting systems. Five magnetic mounting systems were compared with a conventional screw-on system. Material and methods. Six systems on 3 semiadjustable articulators were evaluated: Denar Mark II with conventional screw- on mounting plates (DENSCR) and magnetic mounting system with converter plates (DENCON); Denar Mark 330 with in- built magnetic mounting system (DENMAG) and disposable mounting plates; and Artex CP with blue (ARTBLU), white (ARTWHI), and black (ARTBLA) magnetic mounting plates. Test casts with 3 high-precision ceramic ball bearings at the mandibular central incisor (Point I) and the right and left second molar (Point R; Point L) positions were mounted on 5 mounting plates (n¼5) for all 6 systems. Each cast was repositioned 10 times by 4 operators in random order. Nine linear (I x, I y, I z ;R x, R y, R z ;L x, L y, L z ) and 3 angular (anteroposterior, mediolateral, twisting) displacements were measured with a coordinate measuring machine. The mean standard deviations of the linear and angular displacements defined repositioning accuracy. Results. Anteroposterior linear repositioning accuracy ranged from 23.8 3.7 mm (DENCON) to 4.9 3.2 mm (DENSCR). Mediolateral linear repositioning accuracy ranged from 46.0 8.0 mm (DENCON) to 3.7 1.5 mm (ART- BLU), and vertical linear repositioning accuracy ranged from 7.2 9.6 mm (DENMAG) to 1.5 0.9 mm (ARTBLU). Anteroposterior angular repositioning accuracy ranged from 0.0084 0.0080 degrees (DENCON) to 0.0020 0.0006 degrees (ARTBLU), and mediolateral angular repositioning accuracy ranged from 0.0120 0.0111 degrees (ARTWHI) to 0.0027 0.0008 degrees (ARTBLU). Twisting angular repositioning accuracy ranged from 0.0419 0.0176 degrees (DENCON) to 0.0042 0.0038 degrees (ARTBLA). One-way ANOVA found significant differences (P<.05) among all systems for I y ,R y ,L x ,L y , and twisting. Conclusions. Generally, vertical linear displacements were less likely to reach the threshold of clinical detectability compared with anteroposterior or mediolateral linear displacements. The overall repositioning accuracy of DENSCR was comparable with 4 magnetic mounting systems (DENMAG, ARTBLU, ARTWHI, ARTBLA). DENCON exhibited the worst repositioning accuracy for I y ,R y ,L x ,L y , and twisting. (J Prosthet Dent 2014;-:---) a Dental Instructor, Faculty of Dentistry, National University of Singapore. b Dental Officer, MOH Holdings, Ministry of Health, Singapore. c Dental Officer, MOH Holdings, Ministry of Health, Singapore. d Dental Officer, MOH Holdings, Ministry of Health, Singapore. e Associate Professor, Faculty of Dentistry, National University of Singapore. Tan et al