Effects of Skeletally Supported Anterior en Masse Retraction with Varied Lever Arm Lengths and Locations in Lingual Orthodontic Treatment: A 3D Finite Element Study

Abstract

Objective. This study is aimed at analyzing different points of force application during miniscrew supported en masse retraction of the anterior maxillary teeth to identify the best line of action of force in lingual orthodontic treatment. Materials and Methods. Three-dimensional (3D) finite element models were created to stimulate en masse retraction with different heights and positions of the miniscrew and lever arm to change the force application points; a 150 g retraction force was applied from the miniscrew to the lever arms, and the initial tooth displacements were analyzed. Results. Lingual crown tipping and occlusal crown extrusion were seen at all heights and positions of the miniscrew and lever arm, but when the miniscrew height was at 8 mm and the power arm was located between the lateral incisors and canines, these tipping patterns were less than those obtained with a 4.5 mm high miniscrew and a lever arm located distal to the canines. Conclusion. All miniscrew heights and lever arm positions showed initial lingual crown tipping and labial root tipping with occlusal crown extrusion. However, the 8 mm miniscrew height and the lever arm located between the lateral incisor and canine showed fewer amounts of these tipping patterns than a 4.5 mm miniscrew height and lever arm located distal to the canines. Therefore, this could be the preferred point of force application during en masse retraction in lingual treatment with additional torque control methods.

The Influence of Heights of Power Arm for Controlled Anterior Teeth Movement in Sliding Mechanics: A 3D FEM Study

“…Lee predicted that a pressure range of 150-260 gm/cm2 would be necessary to achieve optimal tooth growth. Ruenpol et al [ 9 ] used 200gm of power for withdrawal in their study and obtained development similar to the outcome of our present research. As shown in a study by Ren et al, it is impossible to identify an edge for force extent that would influence orthodontic tooth movement, as demonstrated in a study published in the Journal of Dental Research [ 11 ].…”

“…Sliding mechanics is the commonly used mechanics for space closing after premolar extraction. Orthodontic mini-implants are used as a skeletal anchorage, which provides absolute stability to the segments by providing resistance toward undesirable reactionary tooth movements [ 9 ]. An 8-mm distance from the gingival margin was chosen for the placement of mini-implants in this study, which was shown to be appropriate for passing of force vector to the center of resistance.…”

“…Ghannam et al [ 8 ] observed fewer tipping moments when the implant was placed 8mm from arch wire than when it was placed at 4.5mm height. In the present study, the mini-implant was placed 8mm from the gingival margin because it made the force vector pass as close to the center resistance which brings a bodily retraction, and also placing coronal to this height might result in perforation of PDL, sinus or root damage [ 9 ].…”

Digital lingual appliance combined with micro-screws for the treatment of a skeletal bimaxillary protrusion and ‘gummy’ smile

“…16 Since the patient had a bimaxillary protrusion with a hyperdivergent facial pattern, it was essential to close the extraction space using the micro-screws to maintain anchorage and vertical control. 6,11 Ghannam et al reported that an 8 mm micro-screw produced less incisor tipping than a 4.5 mm microscrew, 17 which mirrors the present case. Two microscrews were also bilaterally placed in the maxillary palatal alveolar bone between the first and second molars at a position of 8 mm gingival to the arch wire for maximal en-masse retraction of the anterior teeth.…”

Biomechanical analysis of maxillary anterior teeth movements during different retracting methods with a lever arm miniscrew system in double‐slot lingual brackets: A finite element method study

“…4 Generally, lever arms are located between lateral incisors and canines; miniscrews are located between the first molar and second premolar and first and second molars. [5][6][7] This lever arm and miniscrew system can effectively provide additional skeletal anchorage and minimize the bowing effect both vertically and transversally. [8][9][10] However, due to the mushroomshaped lingual archwire, an increasing trend of the inter-canine width is observed during retraction.…”