Friction versus frictionless mechanics during maxillary en-masse retraction in adult patients with Class I bimaxillary dentoalveolar protrusion: a randomized clinical trial.

BACKGROUND: Extraction space closure is a challenging phase during orthodontic treatment that affects not only the total treatment duration but also the whole treatment outcome. OBJECTIVE: To compare the efficiency of friction and frictionless mechanics during en-masse retraction of maxillary anterior teeth in adult patients with bimaxillary dentoalveolar protrusion. TRIAL DESIGN: Two-arm parallel group, single-center randomized clinical trial. MATERIALS AND METHODS: Thirty-two adult patients with bimaxillary protrusion were recruited and randomly allocated to two different retraction mechanics. A friction group, using NiTi coil springs and a frictionless group using closing T-loops for en-masse retraction. Randomization in a 1:1 ratio was generated by Microsoft Excel. The randomization numbers were secured in opaque sealed envelopes for allocation concealment. Retraction started in all patients following first premolars extraction using miniscrews as a source of indirect anchorage. Activation was done on a monthly basis until complete retraction of anterior segment. The rate of retraction, amount of anchorage loss, the dental, and soft tissue changes were analyzed on digital models and lateral cephalograms taken before retraction and after space closure. BLINDING: The outcome assessor was blinded through data concealment during assessment. RESULTS: Two patients were lost to follow up, so 30 patients completed the trial. The rate of anterior segment retraction was 0.88 ±â€…0.66 mm/month in the frictionless group compared to 0.72 ±â€…0.36 mm/month in the friction group which was statistically significant. Anchorage loss of 1.18 ±â€…0.72 mm in the friction group compared to 1.29 ±â€…0.55 mm in the frictionless group with no significant difference. Comparable dental and soft tissue changes following en-masse retraction were reported in both groups, with no statistically significant difference. HARM: one patient complained of soft tissue swelling following miniscrew insertion, but the swelling disappeared after one week of using mouth wash. LIMITATION: The study focused only on the maxillary arch. CONCLUSION: Both mechanics have successfully achieved the required treatment objectives in patients with bimaxillary dentoalveolar protrusion. Frictionless group showed a faster rate of retraction than the friction group, which was statistically but not clinically significant. TRIAL REGISTRATION: Clinicaltrials.gov with the identifier NCT03261024.

Non-compliance treatment in a young adult full-step class II division 2 malocclusion with preadjusted lingual appliance and upper first molars extractions.

This case report describes a complex full-step class II case in a young adult patient treated with lingual straight-wire appliance and upper first molar extraction. As the patient refused a surgical treatment, she was offered the best possible camouflage with the double aim of obtaining an ideal occlusal relationship and maintaining the profile; appropriate biomechanical strategies, including extraction choice and anchorage control during space closure, were needed to achieve the planned results. This case report demonstrates the possibility of successfully resolving severe sagittal discrepancies in an adult patient without surgical treatment by means of a completely invisible non-compliance technique, with the extraction of the most compromised teeth. This report also underlines the need for careful planning during both diagnostic and treatment phases, in order to obtain the best results.

Prospective clinical study of transverse development with orthodontics with self-ligating brackets.

Orthodontics with low friction, low force, passive self-ligating brackets produces alveolar-dental remodeling, resulting in an increase in the transverse diameter of the dental arches, especially in the premolar sector. The aim of this study was to compare the modifications of the transverse diameter in the pre- and post-dental alignment cast models with orthodontics with passive self-ligating brackets in patients with moderate to severe dental discrepancy. The study included 28 patients of both sexes aged 16 to 48 years with dental discrepancies between -6 and -16 mm, treated with self-ligating Damon brackets and thermally activated Nickel- Titanium-Copper arches. With a digital pachymeter, Mitutoyo brand, five measurements were taken per dental arch: distance between canines (C), first premolars (1PM), second premolars (2 PM), first molars (1M) and second molars (2M), before and after orthodontic alignment. The variations were statistically evaluated by Student T Test for paired samples. Average distance between teeth varied with dental alignment in both jaws. The greatest increases in transverse diameter were recorded in the premolar areas. Minor though statistically significant variations also occurred in the 2M of the maxilla and in the C of the mandible In alignment with passive self-ligating brackets, there is an increase in the transverse diameter due to the development of the dental arches, mainly in the premolar sector of both jaws and also at the level of the canines in the mandible.

La ortodoncia con brackets autoligables pasivos, de baja fricción y baja fuerza, produce remodelación alvéolodentaria; con aumento del diámetro transversal de las arcadas, especialmente en el sector de los premolares. El objetivo de este trabajo fue comparar las modificaciones del diámetro transversal en los modelos de yeso pre y post alineación dentaria con ortodoncia con brackets autoligables pasivos en pacientes con discrepancia dentaria moderada a severa. El estudio incluyó 28 pacientes de ambos sexos de entre 16 y 48 años de edad con discrepancia dentaria entre -6 y -16mm, tratados con brackets autoligables sistema Damon y arcos termo activables de Níquel-Titanio-Cobre. Con un paquímetro digital marca Mitutoyo, se tomaron 5 medidas por arcada: distancia entre caninos (C), primeros y segundos premolares (1 PM y 2 PM) y primeros y segundos molares (1M y 2M); pre y post alineación ortodóncica. Las variaciones registradas fueron evaluadas estadísticamente mediante Student T Test para muestras apareadas. La distancia promedio entre dientes varió con la alineación dentaria en ambos maxilares. Los mayores aumentos del diámetro transversal se registraron en las zonas de los premolares. Se produjeron también variaciones menores, aunque estadísticamente significativas, en los 2M del maxilar superior y en los C del maxilar inferior. En la alineación con brackets autoligables pasivos, hay incremento del diámetro transversal por desarrollo de las arcadas, principalmente en el sector premolar de ambos maxilares y en el maxilar inferior también a nivel de los caninos.

Prospective clinical study of transverse development with orthodontics with self-ligating brackets / Estudio clínico prospectivo del desarrollo transversal con ortodoncia con brackets autoligables

ABSTRACT Orthodontics with low friction, low force, passive self-ligating brackets produces alveolar-dental remodeling, resulting in an increase in the transverse diameter of the dental arches, especially in the premolar sector. The aim of this study was to compare the modifications of the transverse diameter in the pre- and post-dental alignment cast models with orthodontics with passive self-ligating brackets in patients with moderate to severe dental discrepancy. The study included 28 patients of both sexes aged 16 to 48 years with dental discrepancies between -6 and -16 mm, treated with self-ligating Damon brackets and thermally activated Nickel- Titanium-Copper arches. With a digital pachymeter, Mitutoyo brand, five measurements were taken per dental arch: distance between canines (C), first premolars (1PM), second premolars (2 PM), first molars (1M) and second molars (2M), before and after orthodontic alignment. The variations were statistically evaluated by Student T Test for paired samples. Average distance between teeth varied with dental alignment in both jaws. The greatest increases in transverse diameter were recorded in the premolar areas. Minor though statistically significant variations also occurred in the 2M of the maxilla and in the C of the mandible In alignment with passive self-ligating brackets, there is an increase in the transverse diameter due to the development of the dental arches, mainly in the premolar sector of both jaws and also at the level of the canines in the mandible.

RESUMEN La ortodoncia con brackets autoligables pasivos, de baja fricción y baja fuerza, produce remodelación alvéolodentaria; con aumento del diámetro transversal de las arcadas, especialmente en el sector de los premolares. El objetivo de este trabajo fue comparar las modificaciones del diámetro transversal en los modelos de yeso pre y post alineación dentaria con ortodoncia con brackets autoligables pasivos en pacientes con discrepancia dentaria moderada a severa. El estudio incluyó 28 pacientes de ambos sexos de entre 16 y 48 años de edad con discrepancia dentaria entre -6 y -16mm, tratados con brackets autoligables sistema Damon y arcos termo activables de Níquel-Titanio-Cobre. Con un paquímetro digital marca Mitutoyo, se tomaron 5 medidas por arcada: distancia entre caninos (C), primeros y segundos premolares (1 PM y 2 PM) y primeros y segundos molares (1M y 2M); pre y post alineación ortodóncica. Las variaciones registradas fueron evaluadas estadísticamente mediante Student T Test para muestras apareadas. La distancia promedio entre dientes varió con la alineación dentaria en ambos maxilares. Los mayores aumentos del diámetro transversal se registraron en las zonas de los premolares. Se produjeron también variaciones menores, aunque estadísticamente significativas, en los 2M del maxilar superior y en los C del maxilar inferior. En la alineación con brackets autoligables pasivos, hay incremento del diámetro transversal por desarrollo de las arcadas, principalmente en el sector premolar de ambos maxilares y en el maxilar inferior también a nivel de los caninos.

Finite element analysis of the effect of power arm locations on tooth movement in extraction space closure with miniscrew anchorage in customized lingual orthodontic treatment.

INTRODUCTION: More patients are choosing customized orthodontic appliances because of their excellent esthetics. It is essential that clinicians understand the biomechanics of the tooth movement tendency in customized lingual orthodontics. This study aimed to evaluate the tooth movement tendency during space closure in maxillary anterior teeth with the use of miniscrew anchorage in customized lingual orthodontics with various power arm locations. METHODS: Three-dimensional finite element models of the maxilla were created with miniscrews and power arms; the positions were varied to change the force directions. A retraction force (1.5 N) was applied from the top of the miniscrews to the selected points on the power arm, and the initial displacements of the reference nodes of the maxillary teeth were analyzed. RESULTS: After applying force in different directions, power arms located at the distal side of the canines led to larger initial lingual crown tipping and occlusal crown extrusion of the maxillary incisors compared with power arms located at the midpoint between the lateral incisors and canines, and caused a decreasing trend of the intercanine width. CONCLUSIONS: In customized lingual orthodontic treatment, power arms located at the distal side of the canines are unfavorable for anterior teeth torque control and intercanine width control. Power arms located at the midpoint between the lateral incisors and canines can get better torque control, but still cannot achieve excepted torque without extra torque control methods, no matter whether its force application point is higher than, lower than, or equal to the level of the top of the miniscrews.

The effect of orthodontic clinical use on the mechanical characteristics of nickel-titanium closed-coil springs.

OBJECTIVE: To examine the effect of clinical use on both force retention and the deactivation of closed-coil nickel-titanium (NiTi) springs in a 16-week trial. METHODS: The force-activation curves for NiTi springs were determined before and after clinical use. The rate of tooth movement and maximum force (MF), hysteresis between activation and deactivation, and mean force of the deactivation plateau (MDF) were examined and correlated as a function of 4, 8, 12 and 16 weeks of clinical use. To recover the force properties, the springs were heat treated at 100°C and the results were compared with the preceding data. RESULTS: A total of 36 springs were analysed. The MF loss after use was 60, 74, 55, and 48 g for the 4-, 8-, 12- and 16-week springs, respectively. Heat treating had little effect on the MF. Clinical use lowered hysteresis by a mean of 180 g*mm compared with the pre-clinical use data, and heat treating increased the hysteresis by a mean of 59 g*mm above the post clinic testing data. The MDF was nominally 100 g less than the MF. Teeth moved approximately 1 mm/month, independent of the force loss. CONCLUSIONS: The loss of MF and the lowering of the MDF was not time dependent. Heat treating can partially recover the mechanical properties of the used springs.

Evaluation of Biomechanical Properties of Four Loops at Different Activation: A Finite Element Method Study.

AIM: The aim of the study was to evaluate the force, moment, and moment/force ratio (M/F) generated by activating T loop, Kalra Simultaneous Intrusion and Retraction (KSIR) loop, Omega loop, and Teardrop loop made of titanium molybdenum alloy (TMA) wire with different preactivation bends at 1, 2, and 4 mm activation. MATERIALS AND METHODS: Finite element method (FEM) models of the four loops were created and different preactivation bends were placed. The loops were then activated and analyzed for force, moment, and M/F ratio using ANSYS software. RESULTS: In loops without preactivation bends, highest force values were generated by Omega loop, whereas T loop had the least force value. The mean value for the M/F in the alpha segment was almost similar. In loops with preactivation bend, the force was highest in Teardrop loop, whereas T loop had the least force value. The mean value for the M/F in the alpha segment was almost similar in all the loops. CONCLUSION: T loop with preactivation bend shows the most favorable properties. CLINICAL SIGNIFICANCE: T loop is comparatively reliable for the frictionless mechanics for the space closure than the other loops evaluated in clinical use.

Canine Retraction Using a Closed Nickel Titanium Coil Spring and an Elastic Module.

OBJECTIVE: To compare the mean change of tooth movement in canine retraction between elastic module and Ni Ti coil spring. STUDY DESIGN: Comparative study. PLACE AND DURATION OF STUDY: Orthodontics Department, Armed Forces Institute of Dentistry, Rawalpindi, from May 2015 to January 2016. METHODOLOGY: Thirty-two patients were inducted. After alignment and extraction of maxillary first premolars, canine retraction was started with closed Ni Ti coil spring on one side of the maxillary arch and with active tie back on the other side. The distance between the lateral incisor and the canine was measured on both sides before starting canine retraction. The same measurements were recorded after four weeks of retraction. The difference between pre and post retraction measurements was recorded. The difference in the rate of canine retraction between both modalities was compared using independent sample t-test. RESULTS: The study included 56% females and 43% males. The mean rate of tooth movement in Ni Ti coil group and in the elastomeric module group was 1.1 mm and 0.7 mm in one month, respectively (p=0.05). CONCLUSION: The rate of tooth movement is more rapid with Ni Ti coil spring than with the elastomeric module.

The T-loop in details.

INTRODUCTION: The T-loop as designed by Burstone is a space closure spring used in the rational application of orthodontic biomechanics. Despite the diversity of studies, there is still no consensus on the optimal parametric characteristics for its conformation. OBJECTIVE: This study aimed at reviewing the literature on the force systems released by different conformations of the T-loop, according to the type of anchorage and the main characteristics and factors that influence them. RESULTS: Comparing the studies, the need for standardization was perceived in the methodology to shape the loops, regarding the variables that influence the force system. Most of the experimental studies with this loop do not report the vertical movement, nor the steps and angles that occur in the brackets. Clinical studies have obtained more variable results in relation to vertical acting forces, considering the influence of chewing. CONCLUSION: There is great potential for future studies with this type of loop, especially using nickel-titanium alloys, in order to achieve a pure translational movement without friction, with optimal and constant levels of force.

Comparative assessment of the efficacy of closed helical loop and T-loop for space closure in lingual orthodontics-a finite element study.

BACKGROUND: Retraction in lingual orthodontics has biomechanical differences when compared to labial orthodontics, which is not yet established. Thus, we have intended to compare the biomechanical characteristics of closed helical loop and T-loop on 1 mm activation with 30° of compensatory curvatures during retraction in lingual orthodontics. METHODS: STb lingual brackets were indirectly bonded to maxillary typhodont model that was scanned to obtain FEM model. Closed helical loop (2 × 7 mm) and T-loop (6 × 2 × 7 mm) of 0.016″ × 0.016″ TMA wire were modeled without preactivation bends. Preactivation bends at 30° were given in the software. Boundary conditions were set. The force (F) and moment (M) of both the loops were determined on 1 mm activation, using ANSYS software. M/F ratio was also calculated for both the loops. RESULTS: T-loop exerted less force, thus increased M/F ratio as compared to closed helical loop on 1 mm activation. CONCLUSIONS: When torque has to be preserved in the anterior segment during retraction in lingual orthodontics, T-loop can be preferred over closed helical loop.

Study Model-based Evaluation of Built-in Tip, Torque, and In-out Characteristics of a Third-generation Preadjusted Edgewise Appliance.

AIM: The aim of the study was to evaluate the clinical effectiveness of MBT™ preadjusted edgewise appliance (PEA) in terms of achieving the optimal expression of its built-in characteristics of tip, torque, and in-out. MATERIALS AND METHODS: Pretreatment and posttreatment study models of 20 subjects who received full fixed appliance treatment involving four first premolar extractions using the MBT™ appliance were measured for tip, torque, and in-out using the method described by Andrews. Treatment changes were analyzed statistically, and the posttreatment measurements were compared with the MBT™ specifications as well as Andrews' values for the above-mentioned parameters. RESULTS: Except for the maxillary canines and second premolars, the built-in tip of MBT™ appliance was nearly fully expressed, though there was some lack of correlation with Andrews' values. Despite the fact that the full amount of torque built into the MBT™ appliance was not expressed, torque measurements for all teeth except the maxillary second premolars and the first molars showed either no statistically significant difference or were significantly higher than Andrews' values for these teeth. In-out readings were lower than both MBT™ and Andrews' values, but the relative order of crown prominences was similar. Conclusion and clinical significance: The MBT™ appliance is thus effective in ensuring a successful treatment result, though individual adjustments may be necessary for optimal tooth positioning at the end of the treatment, as with any preadjusted appliance.

The T-loop in details

ABSTRACT Introduction: The T-loop as designed by Burstone is a space closure spring used in the rational application of orthodontic biomechanics. Despite the diversity of studies, there is still no consensus on the optimal parametric characteristics for its conformation. Objective: This study aimed at reviewing the literature on the force systems released by different conformations of the T-loop, according to the type of anchorage and the main characteristics and factors that influence them. Results: Comparing the studies, the need for standardization was perceived in the methodology to shape the loops, regarding the variables that influence the force system. Most of the experimental studies with this loop do not report the vertical movement, nor the steps and angles that occur in the brackets. Clinical studies have obtained more variable results in relation to vertical acting forces, considering the influence of chewing. Conclusion: There is great potential for future studies with this type of loop, especially using nickel-titanium alloys, in order to achieve a pure translational movement without friction, with optimal and constant levels of force.

RESUMO Introdução: a alça T preconizada por Burstone é um instrumento de fechamento de espaços utilizado na aplicação racional da biomecânica ortodôntica, dentro da técnica do arco segmentado. Apesar da diversidade de estudos, ainda não há consenso quanto às características paramétricas ótimas para a sua conformação. Objetivo: esse estudo teve como objetivo revisar a literatura sobre os sistemas de forças liberados por diferentes conformações da alça T, de acordo com o tipo de ancoragem necessária, salientando suas principais características e os fatores que as influenciam. Resultados: comparando-se os estudos, foi perceptível a necessidade de padronização da metodologia usada para conformar as alças, levando em consideração as variáveis que exercem influência no sistema de forças, de forma a se obter sistemas mais acurados, permitindo a realização de testes mais precisos e uma comparação mais eficaz dos estudos. A maioria dos estudos experimentais com esse tipo de alça não relata a movimentação vertical, nem os degraus e ângulos que ocorrem nos braquetes. Estudos clínicos obtiveram resultados menos rígidos em relação às forças verticais atuantes, levando em consideração a influência da mastigação. Conclusões: há grande potencial para futuros estudos com esse tipo de alça, especialmente utilizando ligas de níquel-titânio, para que se chegue cada vez mais perto de um movimento de translação puro e sem atrito, com níveis de força ótimos e constantes.

Effectiveness of nickel-titanium springs vs elastomeric chains in orthodontic space closure: A systematic review and meta-analysis.

The aim of this study is to explore the effectiveness of nickel titanium closing springs (NiTi-CS) and elastomeric power chains (EPC) in orthodontic space closure and to assess the adverse periodontal effects, cost efficiency and patient-centred outcomes between both of these methods. METHODS: An electronic search of online databases (Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, Scopus, LILACS and Web of Science), reference lists and grey literature as well as hand search were conducted without language restriction up to November/2017. Two authors blindly and in duplicate were involved in study selection, quality assessment and the extraction of data. Only randomized clinical trials (RCTs) were included. The quality of the studies was assessed using the Cochrane Collaboration's risk of bias tool. 95% confidence intervals and mean difference for continuous data were calculated. A meta-analysis that generated a random-effect model for the comparable outcomes was conducted, and heterogeneity was measured using I2 statistic. RESULTS: Of 187 records, 4 RCTs met the criteria and were included in the quantitative synthesis featuring 290 test quadrants. Faster space closure with NiTi-CS was observed with a mean difference of (0.20 mm/month, 95% CI: 0.12 to 0.28). Loss of anchorage appears to be similar within both groups when synthesized qualitatively. With exception to anchorage loss, secondary outcomes could not be investigated in the included trials. CONCLUSIONS: There is a moderate quality of evidence suggesting a faster orthodontic space closure with the NiTi-CS when compared to EPC. A comparable amount of anchorage loss was observed regardless of the utilized method of space closure. Further high-quality RCTs with parallel-groups, reporting on the adverse effects and patient-centred values, are recommended.

Transversal changes, space closure, and efficiency of conventional and self-ligating appliances : A quantitative systematic review.

OBJECTIVE: Self-ligating brackets (SLBs) were compared to conventional brackets (CBs) regarding their effectiveness on transversal changes and space closure, as well as the efficiency of alignment and treatment time. METHODS: All previously published randomized controlled clinical trials (RCTs) dealing with SLBs and CBs were searched via electronic databases, e.g., MEDLINE, Cochrane Central Register of Controlled Trials, EMBASE, World Health Organization International Clinical Trials Registry Platform, Chinese Biomedical Literature Database, and China National Knowledge Infrastructure. In addition, relevant journals were searched manually. Data extraction was performed independently by two reviewers and assessment of the risk of bias was executed using Cochrane Collaboration's tool. Discrepancies were resolved by discussion with a third reviewer. Meta-analyses were conducted using Review Manager (version 5.3). RESULTS: A total of 976 patients in 17 RCTs were included in the study, of which 11 could be produced quantitatively and 2 showed a low risk of bias. Meta-analyses were found to favor CB for mandibular intercanine width expansion, while passive SLBs were more effective in posterior expansion. Moreover, CBs had an apparent advantage during short treatment periods. However, SLBs and CBs did not differ in closing spaces. CONCLUSIONS: Based on current clinical evidence obtained from RCTs, SLBs do not show clinical superiority compared to CBs in expanding transversal dimensions, space closure, or orthodontic efficiency. Further high-level studies involving randomized, controlled, clinical trials are warranted to confirm these results.

Quantification of intrusive/retraction force and moment generated during en-masse retraction of maxillary anterior teeth using mini-implants: A conceptual approach.

OBJECTIVE: 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.

Efficacy of elastic memory chains versus nickel-titanium coil springs in canine retraction: A two-center split-mouth randomized clinical trial.

OBJECTIVE: The use of newly-introduced elastic memory chains (EMCs) in space closure is increasingly gaining popularity. However, no clinical studies have evaluated their efficacy. Therefore, this study was conducted. METHODS: In this two-center split-mouth single-blind randomized controlled trial, 21 jaws were divided into 42 quadrants. The two treatments [canine retraction using EMCs versus nickel-titanium (NiTi) coil springs (as control)] were randomly assigned to two quadrants of each jaw. The premolar space was measured at the baseline, and in the 1st, 2nd, and 3rd months of canine retraction, by a blinded orthodontist. Space closure rates were compared using a paired t-test. RESULTS: The rates of space closure using NiTi springs were 1.93±0.62, 1.71±0.75, and 1.36±0.51mm/month, during the 1st, 2nd, and 3rd months of treatment, respectively. The 3-month average rates of space closure were 1.67±0.39 and 1.89±0.36mm/month in the NiTi and elastic groups, respectively (faster in the elastic group, P=0.022). CONCLUSIONS: The application of elastic memory chains is as effective as NiTi springs.

Stability of beta-titanium T-loop springs preactivated by gradual curvature

ABSTRACT Objective: Evaluate changes in the force system of T-Loop Springs (TLS) preactivated by curvature, due to stress relaxation. Methods: Ninety TLSs measuring 6 x 10 mm, produced out with 0.017 x 0.025-in TMA® wire and preactived by gradual curvature, were randomly distributed into nine groups according to time point of evaluation. Group 1 was tested immediately after spring preactivation and stress relief, by trial activation. The other eight groups were tested after 24, 48 and 72 hours, 1, 2, 4, 8 and 12 weeks, respectively. Using a moment transducer coupled to a digital extensometer indicator adapted to a universal testing machine, the amount of horizontal force, moment and moment-to-force ratios were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation, in an interbracket distance of 23 mm. Results: The horizontal forces decreased gradually among the groups (p< 0.001) and the moments showed a significant and slow decrease over time among the groups (p< 0.001). All groups produced similar M/F ratios (p= 0.532), with no influence of time. Conclusions: The TLSs preactivated by curvature suffered a gradual deformation over time, which affected the force system, specifically the moments, which affected the horizontal forces produced.

RESUMO Objetivo: avaliar as mudanças no sistema de forças das molas T pré-ativadas por curvatura, devido ao alívio de tensão estrutural. Métodos: noventa molas em forma de "T", medindo 6 mm x 10 mm, confeccionadas com fio de beta-titânio TMA® de 0,017" x 0,025" e pré-ativadas por curvatura gradual, foram distribuídas aleatoriamente em nove grupos, de acordo com o momento de avaliação. O Grupo 1 foi testado imediatamente após a pré-ativação da mola e liberação do estresse, por meio de simulação da ativação. Os outros oito grupos foram divididos conforme o intervalo de tempo testado: após 24, 48 e 72 horas; 1, 2, 4, 8 e 12 semanas. Usando um transdutor de momentos acoplado a um indicador digital para extensometria e adaptado a uma máquina universal de ensaios, as magnitudes da força horizontal, do momento e da proporção momento/força (M/F) foram registradas a cada 0,5 mm de desativação a partir da ativação inicial de 5 mm, utilizando-se uma distância interbraquetes de 23 mm. Resultados: as forças horizontais reduziram-se gradualmente nos grupos (p< 0,001) e o momento apresentou uma queda lenta e significativa ao longo do tempo (p< 0,001). Todos os grupos tiveram proporções M/F semelhantes (p= 0,532), não influenciadas pelo período de tempo. Conclusões: as molas pré-ativadas por curvatura gradual sofreram deformação progressiva ao longo do tempo, o que afetou o sistema de forças - especificamente o momento -, alterando as forças horizontais produzidas.