Arch dimension changes with a passive self-ligating system

Abstract

Recently, self-ligating brackets have gained popularity among clinicians around the world (Pandis et al., 2010, Berger, 2008). A passive self-ligating system utilizes a passive self-ligating slot, which is supposed to allow a low friction tooth movement environment (Harradine, 2008). The combination of thin super-elastic copper-nickel-titanium wires and 'low-friction systems' is claimed to be advantageous when leveling crowded dental arches (Tecco et al., 2009, Cattaneo et al., 2011). Some passive self-ligating systems even claim that there is less need for tooth extraction when using their system (Ormco, 2013, Scott et al., 2008). This raises the question of whether passive self-ligating systems achieve their results at the expense of overexpanded dental arches, which requires lifelong retention due to questionable stability. The aim of this study was to evaluate the arch dimension changes that occur after treatment with a 0,022" slot passive self-ligating system, and to compare the results with those obtained after treatment with a 0,018" slot conventional bracket system. Existing pre- and post treatment records of 31 anonymous patients (15 patients treated with passive self-ligating system, and 16 patients treated with a conventional bracket system) from a private orthodontic practice were subjected to examination and measurement. Dental casts were measured using a digital caliper up to a hundredth of a millimeter for changes in: intercanine-, interpremolar- and intermolar widths. Arch length was measured on a photocopied image (scale of 1:1) of the occlusal surfaces of the dental casts using the digital caliper. Results were compared between both the passive self-ligating system and conventional bracket system groups. The results indicated statistically significant increase for nearly all measured dimensions between pre- and posttreatment measurements within each group. Only the maxillary arch length in the passive self-ligating group, and both the maxillary- and mandibular arch lengths in the conventional bracket system group did not show statistically significant increase. When comparing the arch dimension changes between the two groups (after baseline correction), it was found that the passive self-ligating system showed statistically significantly more expansion than the conventional bracket system in the following dimensions: maxillary second interpremolar width, maxillary intermolar width, maxillary arch length, and mandibular intermolar width. Since preservation of original archform is important for posttreatment stability, and since overexpansion of dental arches are more prone to relapse (de la Cruz et al., 1995, Nojima et al., 2001), the cases treated with the passive self-ligating system might be more prone to relapse. However, no long-term studies on stability of passive self-ligating appliance systems are available at the present time. Until then, their implications on long-term stability will remain largely unknown. Further studies to investigate the arch dimension changes between a 0,022: slot passive self-ligating appliance system and a 0,022" slot conventional appliance system are recommended to evaluate whether similar trends between the two groups exist. Also, further research on long-term stability of passive self-ligating appliance systems are recommended.