Assessing the Interdimensional Fit of Archwire-Bracket Slot Engagement Using Microcomputed Tomography

Abstract

Edgewise orthodontic brackets are designed with a geometric three-dimensional prescription that allows for specific angulation, inclination, and in-out positioning of individual teeth when a rectangular archwire is engaged and ligated into the bracket’s slot. A precise archwire-bracket slot fit is necessary to produce these prescribed tooth movements. As a result, any discrepancy in bracket slot size, archwire dimension, or bracket configuration diminishes tooth movement position accuracy. The objective is to develop a novel microcomputed tomography approach to examine and more accurately measure the interdimensional fit of archwire-bracket slot engagement. .022x028 inch self-ligating Empower® orthodontic brackets were obtained from American Orthodontics. Self-ligating refers to the manner with which the archwire is retained by the bracket. The Empower® system incorporates a clip into the bracket construction that, when closed, retains an archwire. Using TransbondTM XT light cure adhesive by 3M Unitek, these brackets were bonded to a stone model representing the maxillary left quadrant. A .017x.025 inch nickel-titanium archwire was engaged in the bracket slots. The sample was scanned using microcomputed tomography. Three-dimensional reconstruction, reorientation, and volumetric analyses were completed using the accompanying microcomputed tomography software. The archwire-bracket slot interdimensional fit measurements showed poor interaction between the archwire and bracket slot. All archwire-bracket slot pairs were significantly different from the standard (P<0.05) with excessive remaining space after engagement. The majority of archwire-bracket slot pairs were significantly different from each other (P<0.05). The potential clinical significance of these findings involves incomplete expression of the prescribed tooth movements incorporated into orthodontic brackets. The poor interdimensional fit of the archwire in the bracket slot inhibits the attainment of appropriate tooth angulation, inclination, and in-out positioning. The improved understanding of archwire-bracket slot interaction provided by this study can lead to better, more efficient treatment outcomes.