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

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.

Dual-section versus conventional archwire for en-masse retraction of anterior teeth with direct skeletal anchorage: a finite element analysis

Background The aim of this study is to compare the biomechanical effects of the conventional 0.019 × 0.025-in stainless steel archwire with the dual-section archwire when en-masse retraction is performed with sliding mechanics and skeletal anchorage. Methods Models of maxillary dentition equipped with the 0.019 × 0.025-in archwire and the dual-section archwire, whose anterior portion is 0.021 × 0.025-in and posterior portion is 0.018 × 0.025-in were constructed. Then, long-term tooth movement during en-masse retraction was simulated using the finite element method. Power arms of 8, 10, 12 and 14 mm length were employed to control anterior torque, and retraction forces of 2 N were applied with a direct skeletal anchorage. Results For achieving bodily movement of the incisors, power arms longer than 14 mm were required for the 0.019 × 0.025-in archwire, while between 8 and 10 mm for the dual-section archwire. The longer the power arms, the greater the counter-clockwise rotation of the occlusal plane was produced. Frictional resistance generated between the archwire and brackets and tubes on the posterior teeth was smaller than 5% of the retraction force of 2 N. Conclusions The use of dual-section archwire might bring some biomechanical advantages as it allows to apply retraction force at a considerable lower height, and with a reduced occlusal plane rotation, compared to the conventional archwire. Clinical studies are needed to confirm the present results.

Evaluation of Angular Changes of Canine in En Masse Retraction of Maxillary Anterior Teeth Using Power Arm and Titanium Mini-Implant - A Split Mouth Randomised Control Study

BACKGROUND This study was conducted to determine angular changes of maxillary canine in en masse retraction of anterior teeth in a new modified power arm with a conventional intraoral anchorage unit compared to a mini-implant anchorage in the first premolar extraction case. We wanted to compare angular changes of maxillary canine between modified conventional anchorage with a power arm and titanium mini-implant anchorage in en masse retraction. METHODS A total of 15 participants requiring maxillary first premolar extraction was selected for this study. In each participant, the en mass retraction was carried out with miniimplants on one side & modified conventional anchorage with a power arm on the other side. The choice of mode of retraction on the right and the left side was done based on the coin flip method. Angular position of the maxillary canine was evaluated on orthopantomogram (OPG) & diagnostic cast. RESULTS A mean disto-palatal rotation observed post retraction was of 9° on the conventional anchorage side & 9.86° on the mini-implant anchorage side. A mean difference in maxillary canine angulations post retraction was 1.13° on the conventional anchorage side and 0.93° on the mini-implant side. An increase in angle suggested the tipping of canine teeth. The difference was very small which was not statistically & clinically significant. CONCLUSIONS There was no difference in the type of tooth movement during retraction by miniimplant and power arm suggesting minimal variation in teeth movement in the anterior region. So, the choice mainly depends on the type of the anchorage required in the given clinical situation. KEY WORDS Anchorage, Mini-Implant, Power Arm, Type of Tooth Movement