INTRODUCTION T he three-dimensional (3D) application of forces and moments on individual teeth with an orthodontic multibracket appliance results in a complex, statically indeterminate system (Proffit, 2000a; Burstone, 2005). Unexpected and unwanted tooth movement can easily result when an important component of the applied force-moment system is overlooked (Proffit, 2000a). Trauma of dental and periodontal tissues (Proffit, 2000b; Brezniak and Wasserstein, 2002), and possibly pain during orthodontic treatment (Bergius et al., 2000), are correlated with the magnitudes of the load therapeutically exerted on the teeth. Several recent experimental studies in humans revealed that, apart from individual predisposition as a probable main determinant, the application of heavy forces and moments must be regarded as a significant causative factor for root resorption and irreversible loss of dental hard tissue and attachment (Casa et al., 2001; Chan and Darendeliler, 2005). Despite these risks and requirements, objective monitoring of all 6 force and moment components applied to the teeth during orthodontic treatment with fixed appliances remains an unsolved methodological problem. Although several systems have been introduced for the evaluation of force-moment systems in the laboratory (Solonche et al., 1977; Bourauel et al., 1992; Menghi et al., 1999; Gunduz et al., 2003; Wichelhaus et al., 2004), only one apparatus allowing for 3D force and moment measurements in situ, i.e., on the patient, has been realized (Friedrich et al., 1998). The complex configuration of this system (consisting of separable brackets and an extra-orally supported force-moment transducer) is responsible for several significant limitations hampering clinical application: (1) the long time needed for fixation and adjustment, (2) the impossibility for force-moment systems to be determined simultaneously at several teeth, and (3) the limited measurement accuracy associated with the limited rigidity of the system itself and its support by the movable and resilient facial skin. Simpler alternative techniques for force measurements practicable in the orthodontic office (e.g., spring balances) have similar disadvantages. Moreover, they do not allow for multi-dimensional force and moment measurements. Due to the manipulation of the appliance necessary for the measurement—usually the active element (wire, loop, or elastic module) must be uncoupled from the corresponding bracket(s)— measurement bias is relatively high, and the unknown amount of friction between the wire and bracket (normally present in the non-manipulated condition) is often not taken into account (Proffit, 2000a). Previous work in the field of microelectromechanical systems has successfully demonstrated that an encapsulated microelectronic chip equipped with stress sensors can be used for the quantitative determination of externally applied loads (Sweet et al., 1999; Suhling and Jaeger, 2001; Schwizer et al., 2003). Recently, such integrated systems have consisted of multiple diffused silicon resistors distributed over the chip surface (Bartholomeyczik et al. , 2005), each capable of measuring 2 different ABSTRACT Atraumatic, well-directed, and efficient tooth movement is interrelated with the therapeutic application of adequately dimensioned forces and moments in all three dimensions. The lack of appropriate monitoring tools inspired the development of an orthodontic bracket with an integrated microelectronic chip equipped with multiple piezoresistive stress sensors. Such a 'smart bracket' was constructed (scale of 2.5:1) and calibrated. To evaluate how accurately the integrated sensor system allowed for the quantitative determination of three-dimensional force-moment systems externally applied to the bracket, we exerted 396 different force-moment combinations with dimensions within usual therapeutic ranges (± 1.5 N and ± 15 Nmm). Comparison between the externally applied force- moment components and those reconstructed on the basis of the stress sensor signals revealed very good agreement, with standard deviations in the differences of 0.037 N and 0.985 Nmm, respectively. We conclude that our methodological approach is generally suitable for monitoring the relatively low forces and moments exerted on individual teeth with fixed orthodontic appliances. KEY WORDS: smart bracket, intelligent bracket, force control, fixed appliance, microsensor. Received May 16, 2006; Last revision September 29, 2006; Accepted October 5, 2006 A supplemental appendix to this article is published electronically only at http://www.dentalresearch.org. Smart Bracket for Multi-dimensional Force and Moment Measurement B.G. Lapatki 1 *, J. Bartholomeyczik 2 , P. Ruther 2 , I.E. Jonas 1 , and O. Paul 2 1 Department of Orthodontics, School of Dental Medicine, University of Freiburg, Hugstetter Str. 55, D-79106 Freiburg i.Br., Germany; and 2 Department of Microsystems Engineering (IMTEK), University of Freiburg, Germany; *corresponding author, bernd.lapatki@uniklinik-freiburg.de J Dent Res 86(1):73-78, 2007 RESEARCH REPORTS Biomaterials & Bioengineering 73 at UNIV OF MONTANA on April 5, 2015 For personal use only. No other uses without permission. jdr.sagepub.com Downloaded from International and American Associations for Dental Research