Efficiency and side effects of a novel method for maxillary central root torque (a horizontal box loop of round wire) in comparison with the conventional rectangular wire: A finite element study

Biomechanical effects of a new crimpable gate spring combined with conventional rectangular archwires for torque adjustment of individual anterior teeth : A comparative finite element study

OBJECTIVE

Precise root torque adjustment of anterior teeth is indispensable for optimizing dental esthetics and occlusal stability in orthodontics. The efficiency of traditional rectangular archwire manipulation within bracket slots seems to be limited. The crimpable gate spring, a novel device, has emerged as a promising alternative. Yet, there is a paucity of guidelines for its optimal clinical application. This study used finite element analysis (FEA) to investigate the biomechanical impact of the gate spring on torque adjustment of individual anterior teeth and to elucidate the most effective application strategy.

METHODS

A FEA model was constructed by a maxillary central incisor affixed with an edgewise bracket featuring a 0.022 × 0.028 inch (in) slot. A range of stainless steel rectangular archwires, in conjunction with a gate spring, were modeled and simulated within the bracket slots. A control group utilized a conventional rectangular wire devoid of a gate spring. Palatal root moments were standardized to 9, 18, and 36 Nmm for both experimental and control groups.

RESULTS

The gate spring significantly amplified palatal root movement, notably with the 0.019 × 0.025 in archwire. However, this was accompanied by an increase in stress on the tooth and periodontal ligament, particularly in the cervical regions. The synergistic use of a 0.019 × 0.025 in rectangular archwire with a gate spring in a 0.022 × 0.028 in bracket slot was identified as most efficacious for torque control of individual anterior teeth.

CONCLUSIONS

The gate spring is a viable auxiliary device for enhancing torque adjustment on individual teeth. However, caution is advised as excessive initial stress may concentrate in the cervical and apical regions of the periodontal ligament and tooth.

Effects of Rigid and Nonrigid Connections between the Miniscrew and Anchorage Tooth on Dynamics, Efficacy, and Adverse Effects of Maxillary Second Molar Protraction: A Finite Element Analysis

Introduction

Direct, rigid indirect, and nonrigid indirect absolute anchorages using temporary anchorage devices (TADs, mini-implants/miniscrews) can provide promising opportunities for challenging, yet common, orthodontic tooth movements such as molar protraction. Rigid rectangular wire and ligature wire are the most common methods of attaching a tooth to a miniscrew in indirect anchorages. We aimed to provide a comparison of the rigidity of the connecting wire in terms of stress on the miniscrew, the anchorage loss, and the risk of root resorption using finite element analysis (FEA).

Methods

The maxillary right second molar was protracted into the proximal space at a 150 g load (1) using direct absolute anchorage with a tapered miniscrew implanted between the premolar roots and using indirect absolute anchorage with the second premolar reinforced by the miniscrew through (2) a rigid stainless steel (SS) wire or (3) a nonrigid SS ligature wire (4) at different elastic moduli. Stresses and displacements of 4 models' elements were measured. The risk of external root resorption was evaluated.

Results

Connecting the tooth to the miniscrew using rigid full-size wire (model 2) compared to ligature (model 3) can give better control of the anchorage (using the ligature wire, the anchorage loss is 1.5 times larger than the rectangular wire) and may reduce the risk of root resorption of the anchorage unit. However, the risk of miniscrew failure increases with a rigid connection, although it is still lower than with direct anchorage. The miniscrew stress when using a ligature is approximately 30% of the rigid model using the rectangular wire. The miniscrew stress using the rectangular wire is approximately 82.4% of the miniscrew stress in the direct model. Parametric analysis shows that the higher the elastic modulus of the miniscrew-tooth connecting wire in the indirect anchorage, the less the anchorage loss/palatal rotation of the premolars/and the risk of root resorption of the anchorage teeth and instead the stress on the miniscrew increases.

Conclusions

Direct anchorage (followed by rigid indirect anchorage but not nonrigid) might be recommended when the premolars should not be moved or premolar root resorption is a concern. Miniscrew loosening risk might be the highest in direct anchorage and lowest in nonrigid indirect anchorage (which might be recommended for poor bone densities).

Dynamics, Efficacies, and Adverse Effects of Maxillary Full-Arch Intrusion Using Temporary Anchorage Devices (Miniscrews): A Finite Element Analysis

Introduction

Absolute anchorages obtained from temporary anchorage devices (TADs, miniscrews) considerably facilitate dental movements and make some very difficult movements such as full-arch intrusions possible. Despite the significance of assessing strategies to fully intrude the arch using mini-implants, there is no study in this regard except a few case reports. Therefore, we simulated/tested 4 scenarios.

Methods

Four maxilla models were created with different miniscrews/appliances: (1) two miniscrews were placed distal to laterals and one in the mid sagittal region. (2) Two mini-implants were inserted in mesial of canines and 2 others between bilateral first and second molars, plus another TAD in the midpalatal area, plus a transpalatal arch (TPA). (3) Two mini-implants were inserted between bilateral canines and first premolars and 2 others between bilateral first and second molars + TPA. (4) Two mini-implants were installed between lateral-and-canine and 2 miniscrews between second premolars and first molars + TPA. Intrusive forces (80 g anterior, 150 g posterior) were exerted using stainless-steel coil springs. Stresses/displacements were measured. Risk of external root resorption was evaluated.

Results

The highest amounts of incisor/molar intrusion were seen in model 1. Model 2 had fewer intrusions, but its control over undesired movements was greater. Model 4 drastically reduced molar intrusion and considerably increased premolar intrusion. Overall amounts of intrusion were highest in the first 2 models, marking them as proper candidates for cases needing greater intrusion extents. Model 2 may be useful when miniscrew loosening/failure is a concern, while model 1 is recommended when fewer miniscrews are allowed. Overall, the highest and lowest root resorptions might occur in models 1 and 4, respectively.

Conclusions

Each model showed certain efficacies/drawbacks and thus is recommended for a particular set of cases. Therefore, depending on the diagnosis and treatment plan, one or more of these scenarios might be desirable.

A Comparison of the Ligation Torque Expression of a Ribbonwise Bracket-Archwire Combination and a Conventional Combination: A Primary Study

OBJECTIVE

To assess the effect of the third-order mechanics of a new ribbonwise bracket-archwire combination using an orthodontic torque simulator. Material and Methods. An orthodontic torque simulator was used to measure the third-order moment of a maxillary central incisor as it changed from a neutral position to a 40° rotation in 1° increment. A new ribbonwise bracket (Xinya, China) was compared with a conventional ligation bracket (American Orthodontic, U.S.A.). The effects of different archwire sizes (i.e., 0.017″ × 0.025″ and 0.019″ × 0.025″) and materials (i.e., nickel-titanium, titanium-molybdenum alloy, and stainless steel) were analyzed. Paired sample t-tests were conducted to compare the moments between the two bracket types corresponding to each of the archwires. The effects of the stiffness of the bracket-archwire complexes were also assessed.

RESULTS

Statistically significant differences (P=0.05) between the moments from the two brackets were found. The ribbonwise bracket-archwire complex generated larger moments when the rotation angle was lower than 30°. The ribbonwise brackets produced moments that could reach a threshold of 5 Nmm more quickly as the angle was increased. The higher the stiffness of the complex, the larger the moment.

CONCLUSION

The ribbonwise bracket-archwire complex reached the moment threshold limits earlier than the conventional complex. When the rotation angle is less than 30°, the ribbonwise bracket-archwire complex generated a greater torque moment in comparison with the conventional complex.