Biomechanics of Modified Hawley Appliances For Space Closure

Introduction: The Hawley appliance is used as both a passive retainer and active appliance to achieve minor tooth movements. One such active role has been its use in residual space closures. Several modifications to the Hawley have been devised for this purpose, but have not been compared biomechanically. The purpose of this study was to examine the stresses generated by three modified Hawley appliances in simulated space closing conditions within a photoelastic maxillary arch. Methods: A photoelastic model of a dentulous adult maxilla was fabricated using different teeth and bone simulants. Three modified Hawley appliance designs were fabricated: canine-to-canine labial elastic, full-arch labial bow with C-clasps, conventional Hawley bow with bilateral posterior elastics. The wire diameter effect was evaluated with 0.028, 0.030 and 0.032in diameter stainless steel wires. All components of the appliances without elastics were fitted and observed for passivity and alignment. Wire activated conditions with and without elastics were compared. The photoelastic effects were monitored and recorded photographically in a circular polariscope. Results: The highest stresses upon activation were seen with the canine-to-canine circumferential elastic Hawley appliance. The labial elastic displayed high stress orders concentrated interproximal to the central incisors, while the full-arch bow to C-clasps displayed the lightest observed closing stresses. The 0.028in wire demonstrated the largest difference in arch closure stresses in comparison with and without elastic application. The 0.032in wire generated the highest total arch closure stresses. Conclusion: Elastic activation had the greatest effect with the smaller diameter wire. The full arch bow demonstrated the least closing effects. A modified Hawley design with bilateral posterior closure is offered as a treatment option for space closure. Clinical appliance design is determined by specific patient requirements