Abstract
ABSTRACTObjective: The aim of the present study was to clarify the biomechanics of en-masse retraction of the upper anterior teeth and attempt to quantify the different forces and moments generated using mini-implants and to calculate the amount of applied force optimal for en-masse intrusion and retraction using mini-implants. Methods: The optimum force required for en-masse intrusion and retraction can be calculated by using simple mathematical formulae. Depending on the position of the mini-implant and the relationship of the attachment to the center of resistance of the anterior segment, different clinical outcomes are encountered. Using certain mathematical formulae, accurate measurements of the magnitude of force and moment generated on the teeth can be calculated for each clinical outcome. Results: Optimum force for en-masse intrusion and retraction of maxillary anterior teeth is 212 grams per side. Force applied at an angle of 5o to 16o from the occlusal plane produce intrusive and retraction force components that are within the physiologic limit. Conclusion: Different clinical outcomes are encountered depending on the position of the mini-implant and the length of the attachment. It is possible to calculate the forces and moments generated for any given magnitude of applied force. The orthodontist can apply the basic biomechanical principles mentioned in this study to calculate the forces and moments for different hypothetical clinical scenarios.
Highlights
Space closure with mini-implant anchorage usually involves application of force by means of closed coil spring or elastic traction from the mini-implant placed between the maxillary second premolar and maxillary first molar, bilaterally[1,2,3,4,5,6,7], to an attachment placed between the lateral incisor and canine, on a continuous archwire (Fig 1)
The amount of 212 grams is the optimum force required for en-masse intrusion and retraction of anterior teeth using mini-implants
A residual moment of 309 g was produced when an optimum force of 212 g was applied at 16° to the occlusal plane when the attachment was placed between the lateral incisor and canine
Summary
Space closure with mini-implant anchorage usually involves application of force by means of closed coil spring or elastic traction from the mini-implant placed between the maxillary second premolar and maxillary first molar, bilaterally[1,2,3,4,5,6,7], to an attachment placed between the lateral incisor and canine, on a continuous archwire (Fig 1) This usually results in the application of a diagonal vector of force on the maxillary anterior teeth of both sides. This applied diagonal force vector can be resolved into an intrusive and retraction component, and its magnitude depends on the direction of applied force, in relation to the occlusal plane This direction of applied force is determined by the length of the attachment and the height of the mini-implant from the base archwire (Fig 2). The aim of this paper is: 1. To calculate the magnitude of optimum force required for en-masse retraction using mini-implants
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