Optimal loading conditions for controlled movement of anterior teeth in sliding mechanics

Abstract

Objective: To determine optimal loading conditions such as height of retraction force on the power arm and its position on the archwire in sliding mechanics. Materials and Methods: A 3D finite element method (FEM) was used to simulate en masse anterior teeth retraction in sliding mechanics. The degree of labiolingual tipping of the maxillary central incisor was calculated when the retraction force was applied to different heights of a power arm set mesial or distal to the canine. Results: When the power arm was placed mesial to the canine, at the level of 0 mm (bracket slot level), uncontrolled lingual crown tipping of the incisor was observed and the anterior segment of the archwire was deformed downward. At a power arm height of 5.5 mm, bodily movement was produced and the archwire was less deformed. When the power arm height exceeded 5.5 mm, the anterior segment of the archwire was raised upward and lingual root tipping occurred. When the power arm was placed distal to the canine, lingual crown tipping was observed up to a level of 11.2 mm. Conclusions: Placement of the power arm of an archwire between the lateral incisor and canine enables orthodontists to maintain better control of the anterior teeth in sliding mechanics. Both the biomechanical principles associated with the tooth's center of resistance and the deformation of the archwire should be taken into consideration for predicting and planning orthodontic tooth movement.

Apical root resorption in patients treated with en-masse retraction using skeletal anchorage system versus conventional method

“…Elastomerics were not used as a mean of retraction because they give an excessive initial force and they deformed permanently when exposed to oral environment due to absorption of saliva and water leading to stress relaxation of elastomerics [25].A power arm was placed on an archwire between the lateral incisor and canine to maintain better control of the anterior teeth during retraction (26) .…”

Effect of gable bend incorporated into loop mechanics on anterior tooth movement: Comparative study between en masse retraction and two-step retraction

“…The CT images were saved and converted to a 3D FE model using FE analysis pre-and postprocessor software (Patran 2013 64 bit, MSC Software Corp, Los Angeles, CA, USA). The details of the procedure have been described in previous articles [10,11]. Each 3D FE model for periodontal ligament (PDL), alveolar bone, bracket, and archwire were separately constructed using the same software.…”

Biomechanics of incisor retraction with mini-implant anchorage

“…For example, if the power arm can be made long and rigid to extend to the C RES of the tooth, M F can be entirely eliminated, as the applied force will pass through the C RES (Moment5Applied force6distance from the C RES ). Based on theoretical calculations, in vitro and in vivo experiments, and with certain assumptions, we have proposed a model (Figure 4), which describes various types of tooth movement, depending upon the line of force application and by the location of the tooth centre of rotation as a rotation axis (Kojima et al, 2012;Kojima and Fukui, 2014;Sia et al, 2009;Tanne et al, 1988;Tominaga et al, 2009). Figure 4 shows the centre of rotation for every level of force.…”

“…It is well known that space closure is a dynamic process and things change as teeth move. Considerable research in this area has provided us with a more detailed representation of the incisor movement and its effect on the entire dentition (Barlow and Kula, 2008;Josell et al, 1997;Kojima and Fukui, 2010;Kojima et al, 2012;Kojima and Fukui, 2014;Moore and Waters, 1993;Sia et al, 2009;Tominaga et al, 2009) Based on the evidence gathered from this pool of research, we have further refined the mechanical model of incisor retraction with MIs. Essentially, incisor retraction can be divided into four phases ( Figure 6):…”

“…This force produces a moment (M F ) acting at the C RES of the incisor segment, causing it to tip as it is being distalized. Since there is some degree of play between the archwire and the bracket slot at this stage, the tooth is free to tip in the mesio-distal direction in an uncontrolled manner, creating a centre of rotation (C ROT ) slightly apical to the C RES (Kojima et al, 2012;Kojima and Fukui, 2014;Sia et al, 2009;Tominaga et al, 2009) (Figure 4). This can also be referred to as the 'unsteady state' of incisor retraction, characterized by uncontrolled tipping.…”