Allahyar Geramy1, Hannaneh Ghadirian. 1. Department of Orthodontics, Dental Research Centre, Tehran University of Medical Sciences, Tehran, Iran. gueramya@yahoo.com
Abstract
BACKGROUND: Methods used to upright lingually tilted mandibular molars frequently result in extrusion and unwanted rotations. AIM: To use the finite element method (FEM) to compare three springs designed to upright a lingually tilted mandibular first molar. METHODS: A 3-D computer model of a lingually tilted mandibular first molar was designed. The FEM was used to compare movement of the molar during uprighting with either a single horizontal helix, an open vertical loop, or a new spring with two vertical helices wound around and perpendicular to the long axis of the archwire. Each spring was assumed to be part of a continuous 0.016 x 0.022 inch stainless steel archwire, and each spring was placed mesial to the buccal tube on the first molar. RESULTS: From the mesial perspective, all designs moved the crown of the lingually tilted molar buccally and the root apex lingually. From the occlusal perspective: the horizontal helix uprighted the molar with a disto-buccal rotation; the open vertical loop uprighted the molar with a mesio-buccal rotation; and the new design uprighted the lingually tilted molar around a mesio-distal axis. CONCLUSION: Using FEM, the most suitable design was a double helix formed around and perpendicular to the long axis of the archwire and sited mesial to the tilted molar. It was the only spring to upright the lingually tilted molar without an unwanted rotation.
BACKGROUND: Methods used to upright lingually tilted mandibular molars frequently result in extrusion and unwanted rotations. AIM: To use the finite element method (FEM) to compare three springs designed to upright a lingually tilted mandibular first molar. METHODS: A 3-D computer model of a lingually tilted mandibular first molar was designed. The FEM was used to compare movement of the molar during uprighting with either a single horizontal helix, an open vertical loop, or a new spring with two vertical helices wound around and perpendicular to the long axis of the archwire. Each spring was assumed to be part of a continuous 0.016 x 0.022 inch stainless steel archwire, and each spring was placed mesial to the buccal tube on the first molar. RESULTS: From the mesial perspective, all designs moved the crown of the lingually tilted molar buccally and the root apex lingually. From the occlusal perspective: the horizontal helix uprighted the molar with a disto-buccal rotation; the open vertical loop uprighted the molar with a mesio-buccal rotation; and the new design uprighted the lingually tilted molar around a mesio-distal axis. CONCLUSION: Using FEM, the most suitable design was a double helix formed around and perpendicular to the long axis of the archwire and sited mesial to the tilted molar. It was the only spring to upright the lingually tilted molar without an unwanted rotation.