Reassessing the center of resistance in maxillary central incisors for clinical application

The center of resistance (CR) allows orthodontists to predict tooth movement (TM) in response to therapeutic load application. However, previously reported CR locations vary immensely, questioning the reliability of commonly used mean values. This study quantifies CR variability in maxillary central incisors relative to anatomical variables to improve the reliability and individualization of CR assessment. CR locations were determined from volumetric scans of 30 teeth using nonlinear finite element analysis under clinically relevant loads. Results for various labiolingual crown inclinations (-45°-30°), expressed as vertical distance to the orthodontic bracket and relative to root height, were analyzed and compared with literature, considering load direction and methodology employed. Morphological and load variables were correlated with CR locations via linear regression, and predictor importance was assessed. The mean vertical CR-to-bracket-center distance was 9.1 mm in Andrews' anatomical orientation. Thirty-degree retroclination (vertical tooth long axis) and proclination yielded 11.6 mm and 4.3 mm, respectively. Morphology-driven 95 % variability was consistently around 4.4 mm. Relative to root height, CR locations were highly reference-dependent, averaging 44-55 % from the mesiodistal alveolar margin and -15-40 % from the labial margin, over the inclination range. Vertical tooth height was the dominant predictor, explaining 93 % of CR variability. Further accounting for labiolingual crown inclination reduced the 95 % prediction interval half-width to 1 mm. A reliable CR description requires a well-defined reference frame and is best normalized by vertical tooth length. Including inclination and TM direction as predictors enables sufficiently accurate CR estimates for advanced computer-aided treatment planning and simulation.