Force-deflection properties of superelastic nickel-titanium archwires

Expression of artefacts from different orthodontic brackets and wires in cone beam computed tomography scans-an in vitro study

OBJECTIVES

To investigate artefacts produced by different orthodontic brackets and wires in cone-beam computed tomography (CBCT) scans.

MATERIALS AND METHODS

Two dental arches were made using extracted human teeth and plaster. Three pairs of acetate plates containing different brackets - metallic, ceramic, and self-ligating ceramic with NiTi clip - along with a control plate (i.e., without brackets) were prepared. Wire changes (NiTi and steel) were made during CBCT acquisitions, performed with a fixed exposure protocol. Axial slices were selected for mean gray values and standard deviation measurement in three regions of interest (buccal, lingual, and tooth). Noise and contrast-to-noise ratio (CNR) were calculated and compared among the different brackets and wires by ANOVA with a significance level of 5%.

RESULTS

Overall, the buccal and tooth region were mostly affected by the metallic and self-ligating brackets, showing higher noise, and lower CNR (p < 0.05). On the other hand, less impact of ceramic brackets in the image quality was observed (p ≥ 0.05). The lingual region did not show expressive differences among the brackets and wire combinations (p ≥ 0.05). The presence of wire associated with the brackets did not worsen image quality (p ≥ 0.05).

CONCLUSIONS

In conclusion, metallic and self-ligating brackets have greater artefact expression than ceramic brackets. The wire did not influence image quality.

CLINICAL RELEVANCE

One should pay attention to the type of brackets when requesting a CBCT scan during treatment, as metallic and self-ligating brackets may express greater artefacts than ceramic brackets.

Deflection of tandem archwire in a specific self-ligating metal bracket system: an in vitro study

The aim of this study was to quantify the force exerted by tandem archwires in a specific system of passive self-ligating bracket. Forty-eight thermo-activated nickel-titanium orthodontic archwires were separated into four groups (n = 12): G1 - two .014" + .014" round archwires; G2 - two .014" + .016" round archwires; G3 - .014" x .025" rectangular archwire; and. G4 - .016" x .022" rectangular archwire. Brackets were fixed onto teeth 1.5 to 2.5 using a device that represented the upper teeth, maintaining an interbracket distance of 6.0 mm. The deflection tests were performed using the structure representative of tooth 1.1 as support on the Instron testing machine at a speed of 2.0 mm/min. The archwires were evaluated at deflections of 0.5 mm, 1.0 mm, and 1.5 mm. The data were analyzed by a generalized linear model, considering values at different deflections as repeated measurements in the same experimental unit (α = 0.5%). At 0.5 mm, higher forces were observed in G2 and G3, which did not differ significantly (p > 0.05). The lowest force was observed in G4 (p < 0.05). At 1.0 mm and 1.5 mm, the highest force was observed in G3, followed by G4 and G2 (p < 0.05). The lowest force was observed in G1 (p < 0.05). In general, tandem archwires (same or different calibers) in a specific passive self-ligating bracket exerted lower force when compared with rectangular archwires.

EVALUATION AND COMPARISON OF LOAD DEFLECTION RATE OF FOUR INITIAL ORTHODONTIC ARCH WIRES: AN IN VITRO STUDY

Aim: The aim of this study was to evaluate the load-deflection rate of four different types of archwires used in initial stage of orthodontic treatment. Materials and methods: A modified three-point bending test was performed on the sample of 60 wires of superelastic Nickel Titanium(NiTi), everwhite esthetic NiTi, thermal NiTi and multistranded coaxial stainless steel (15 each). The load exerted by each of the wire was measured at the deflections of 2 mm and 4mm, subsequent unloading process at 37°C temperature. Results: Comparison of mean load-deflection values revealed that thermal NiTi wires had lowest value at both 2 and 4mm deflection when compared to other three wires which was statistically significant(p=0.009).  Superelastic and esthetic NiTi showed similar values of load deflection ratios at both the deflections where as co-axial wire showed 1.89N at 2mm and 5.22N at 4mm deflection. Conclusion: The heat-activated NiTi wires are acceptable in severe crowding and periodontally compromised patients. Multistranded co-axial wire is acceptable when we need minimal alignment; whereas esthetic NiTi wires can replace superelastic Niti based on patient’s need.

In vitro comparison of the mechanical behaviour of archwires after computer-assisted and conventional bracket positioning protocols

INTRODUCTION

The mechanical properties of orthodontic archwires can be defined using experimental setups incorporating brackets that provide conditions closer to those encountered in vivo. We aimed to compare a methodology based on computer-aided design with the gold standard protocol, performed when brackets are engaged to a full-size archwire to test the behaviour of wires in this condition.

METHODS

Three models simulating a dental arch with an orthodontic fixed appliance (0.018-inch aesthetic conventional brackets) were designed. The brackets were positioned with a stainless-steel full-size wire on the first two models, with different interbracket distances. The setup 3, based on a computer-assisted design, allowed individualized placement of each bracket. Mean forces recorded and standard deviation were compared for a 0.016×0.022-inch copper-nickel-titanium wire deflected until 2mm.

RESULTS

The inter-bracelet distances do not cause a statistical difference in the average maximum force recorded (12.6N and 11.4N; P=0.081) whereas the behaviour of the wires is affected. With setup 3, the recorded efforts (mean value: 8N) are statistically lower than with setup 1 and 2 respectively (P=0.018; P=0.012).

CONCLUSION

An individualization of the housings by CAD-CAM dedicated to each bracket optimizes their placement. In our test conditions, the mechanical behaviour of the wires is more influenced by the positioning methods of the brackets than by the value of the interbracket distance. In perspective, our innovative methodology can be extended to other types of brackets.

Effectiveness of two thermal activated orthodontic archwire sequences based on transition temperature range during alignment: A randomized non-controlled comparative study

INTRODUCTION

It has been suggested that heat-activated NiTi archwires (HANT) speed up crowding alleviation. HANT wires are available with different austenite finish temperatures.

OBJECTIVE

The aim of the present study was to compare the effectiveness of two alignment sequences using thermally activated archwires with different austenite activation temperatures for the correction of mandibular anterior crowding.

MATERIAL AND METHODS

The following NiTi archwire sequence was used for both groups: 0.012 in (conventional NiTi), 0.018 in (heat-activated NiTi archwires), 0.016×0.022 in (heat-activated NiTi archwires) and 0.019×0.025 in (conventional NiTi). The conventional NiTi used for both groups belongs to the same commercial brand. Two different austenite activation temperatures (35°C and 37°C) were used for the heat-activated archwires. The primary outcome was the degree of crowding correction measured on study models. The secondary outcome was crowding survival time over a six-month period. This RTC included fifty-four patients that were randomly allocated to the two different archwire sequences. A Mann-Whitney test was used to compare the groups regarding crowding alleviation. A survival curve was created using the Kaplan-Meier method to illustrate the reduction of crowding over time. A Mantel-Cox log-rank test was used to compare survival times (until correction of crowding).

RESULTS

No differences in crowding alleviation were identified between both groups (log-rank test; P=0.77).

CONCLUSIONS

The two alignment sequences with different thermal activated archwires at 35°C and 37°C achieved similar clinical results during the correction of mandibular anterior crowding.

DSC analysis and evaluation of forces released on deactivation of 0.40-mm (0.016") orthodontic thermo-activated NiTi wires: An in vitro study

Background . This study evaluated the phase transformation of NiTi orthodontic wires and forces they release on deactivation. Methods. The structural phase transformations of the following five thermo-activated nickel-titanium (NiTi) wires were evaluated using differential scanning calorimetry (DSC): Flexy Thermal Sentalloy® (GAC International), NiTi (35ºC) (Eurodonto), Thermo-Plus® (Morelli), FlexyNiTi® Flexy Thermal (35ºC) (Orthometric) and Damon® CuNiTi (35ºC) (ORMCO Corp.). The wires had a cross-section of 0.40 mm (0.016"). In addition, the forces they released were investigated using the three-point bending test. Five arches of each wire were tested using DSC (-20/80ºC at 10ºC/min), and six arches from each wire were sectioned for bending tests. The data were analyzed with ANOVA and post hoc Tukey tests. Pearson’s correlation test was performed between the results yielded by the DSC tests and those by three-point analyses (P=0.05). Results. The DSC analysis showed differences between the NiTi alloys from all the manufacturers, with no differences between the lots of the same brand. ORMCO and Orthometric wires exhibited similar TTR values in cooling (P=0.49), and statistically similar TTR values in heating (P=0.056). The three-point bending test showed different patterns in releasing forces. A correlation was found between the DSC analysis and the three-point bending test results. Conclusion. The higher the temperature transformation was, the larger was the variation of force. All the wires presented higher forces at 3-mm deflection from 155 (±12.3) to 168.1 (±8) cN. The DSC analysis and the three-point bending test showed differences between the NiTi alloys from all the manufacturers.

Coated nickel titanium archwires and their uncoated counterparts: In-vitro contemporary comparison of unloading forces

OBJECTIVE

To compare the unloading forces between aesthetic nickel titanium (NiTi) wires coated with rhodium and epoxy resin, as well as their uncoated equivalents. Additionally, intragroup comparisons between the different deactivation forces were evaluated, and the inner alloy cores were determined.

MATERIAL AND METHODS

Forty-four 0.018" NiTi wire segments were equally divided into 4 groups: E- NiTi coated with epoxy resin, C- NiTi uncoated, R- heat-activated NiTi coated with rhodium, and T- heat-activated NiTi uncoated. The unloading values were recorded at 0.5, 1, 2, and 3mm using a 3-point bending test, according to the method in ISO Standard 15.841. Cross-sectional scanning electron microscopy was used to assess the inner alloy core thickness of the wires.

RESULTS

The intergroup comparison was successively: at 0.5mm: E (1.21)>C (0.60)=R (0.63)=T (0.58); at 1mm: E (1.30)=C (1.23)>R (0.91)=T (0.80); at 2mm:C (1.93)>E (1.36)=R (1.20) and R (1.20)=T (1.00) and E (1.36)>T (1.00); at 3mm:C (2.44)>R (2.02)>E (1.62)=T (1.68). The intragroup comparisons showed for all groups that the forces were statistically higher at 3mm than the other deactivations (p<0.01). Group E presented a reduced inner alloy core (.0155).

CONCLUSION

The unloading forces demonstrated variability between the wires tested and between the different deactivations. Therefore, depending on the type of movement required and the periodontal conditions, orthodontists should pay attention during archwire selection.

Effect of Clinical Use and Sterilization Process on the Transition Temperature Range of Thermally NiTi Alloys

Background:

Thermally activated nickel-titanium wires have been widely used by orthodontists due to more constant forces, generation over longer activation spans, greater resistance to permanent deformation, superelasticity characteristics when cyclically loaded, better spring-back and less hysteresis.

Objective:

The purpose of this study was to evaluate the influence of clinical use and sterilization process on the Transition Temperature Range (TTR) of thermoset nickel-titanium wires using Differential Scanning Calorimetry (DSC).

Methods:

Sections from four nickel-titanium wires (0.019 × 0.025-inch) belonging to four different brands were assessed in four different states. Two of the wires were assessed in the “as received” state, one after 60 days of clinical use, and one after 60 days of clinical use and subjected to a sterilization process (autoclaving). The segments of each archwire were tested using DSC at temperatures ranging from −80°C to 150°C at a rate of 10°C/min.

Results:

All the nickel-titanium memory thermoset wires presented with desirable property for clinical use. The shape memory property was not influenced by clinical use and sterilization process.

Conclusion:

There was no change in TTR of the nickel-titanium wires after clinical use and sterilization.

Evaluation of the force generated by gradual deflection of 0.016-inch NiTi and stainless steel orthodontic wires in self-ligating metallic and esthetic brackets

Background

The purpose of this study was to evaluate the deflection forces of 0.016-inch Nitinol and stainless steel orthodontic wires, in association to different self-ligating brackets.

Material and Methods

Specimens were mounted in a clinical simulation model and evaluated in a Universal Testing Machine (INSTRON 3342), using a 10N load cell and ISO 15,841, as a protocol. Eight of these models were prepared, each one for the bonding of each set of self-ligating accessories to be tested: Damon Q, Damon Clear (Ormco), In-Ovation R, In-Ovation C (GAC), BioQuick, QuickClear (Forestadent), SmartClip and Clarity SL (3M). Data were subjected to One-way ANOVA, followed by Tukey tests (P<0.05).

Results

Elastic deflection results showed that the deactivation forces increased with increase in wire deflection in the different brackets evaluated. For the different combinations, Clarity SL generated the greatest force and Damon Clear presented the lowest force when compared to the other brackets in all alloys and deflections. BioQuick and QuicKlear were those with the most similar behavior with each other.

Conclusions

Strength values increased with gradual increase in wire deflection in all evaluated brackets. Clarity SL generated the greatest and Damon Clear the lowest force when compared to the other brackets in all alloys and deflections tested.

Key words:Brackets, orthodontic wires, deflection.

Flexural properties of rectangular nickel-titanium orthodontic wires when used as ribbon archwires

OBJECTIVE

To compare the flexural properties of rectangular nickel-titanium (Ni-Ti) orthodontic wires in occlusoapical and faciolingual orientations using a standardized test method.

MATERIALS AND METHODS

Twenty-two rectangular Ni-Ti wire groups were tested in occlusoapical (ribbon) orientation: eight conventional Ni-Ti products, five superelastic Ni-Ti products, and nine thermal Ni-Ti products (n = 10 per group). Six products of thermal Ni-Ti wire were tested in faciolingual (edgewise) orientation. A three-point bending test was performed to measure deactivation force at 3.0-, 2.0-, 1.0-, and 0.5-mm deflections of each rectangular wire at 37.0 ± 0.5°C. Analysis of variance and post hoc Student-Newman-Keuls tests were used to compare the mean values of the different groups (α = .05).

RESULTS

The ranges of deactivation forces varied greatly with different kinds, sizes, products, and deflections of Ni-Ti wires. One product of conventional and superelastic Ni-Ti wires had steeper force-deflection curves. Four products had similarly shaped flat force-deflection curves, whereas the sixth product had a moderately steep force-deflection curve. Thermal Ni-Ti wires had smaller deactivation forces ranging from 0.773 N (78.8 g) to 2.475 N (252.4 g) between deflections of 1.0 and 0.5 mm, whereas wider ranges of force from 3.371 N (343.7 g) to 9.343 N (952.7 g) were predominantly found among conventional Ni-Ti wires between deflections of 3.0 and 2.0 mm.

CONCLUSIONS

Clinicians should critically select archwires for use in the occlusoapical orientation not only based on Ni-Ti wire type, size (0.022 × 0.016-in or 0.025 × 0.017-in), and product but also with deactivation deflections from 0.5 and 1.0 mm to obtain light forces in the occlusoapical orientation.

Force System with Vertical V-Bends: A 3D In Vitro Assessment of Elastic and Rigid Rectangular Archwires

A proper understanding of the force system created by various orthodontic appliances can make treatment of patients efficient and predictable. Reducing the complicated multi-bracket appliances to a simple two-bracket system for the purpose of force system evaluation will be the first step in this direction. However, much of the orthodontic biomechanics in this regard is confined to 2D experimental studies, computer modeling/analysis or theoretical extrapolation of existing models. The objective of this protocol is to design, construct and validate an in vitro 3D model capable of measuring the forces and moments generated by an archwire with a V-bend placed between two brackets. Additional objectives are to compare the force system generated by different types of archwires among themselves and to previous models. For this purpose, a 2 x 4 appliance representing a molar and an incisor has been simulated. An orthodontic wire tester (OWT) is constructed consisting of two multi-axis force transducers or load cells (nanosensors) to which the orthodontic brackets are attached. The load cells are capable of measuring the force system in all the three planes of space. Two types of archwires, stainless-steel and beta-titanium of three different sizes (0.016 x 0.022 inch, 0.017 x 0.025 inch and 0.019 x 0.025 inch), are tested. Each wire receives a single vertical V-bend systematically placed at a specific position with a predefined angle. Similar V-bends are replicated on different archwires at 11 different locations between the molar and incisor attachments. This is the first time an attempt has been made in vitro to simulate an orthodontic appliance utilizing V-bends on different archwires.

Effects of autoclaving versus cold chemical (glutaraldehyde) sterilization on load-deflection characteristics of aesthetic coated archwires

INTRODUCTION

The effect of any sterilization methods (cold [chemical] or hot) on load-deflection characteristics of aesthetic coated archwires has not yet been investigated. Thus, we assessed it.

METHODS

In this experimental in vitro study, 90-coated archwires from 3 brands were purchased. Ten wires from each brand (n=30) underwent cold and 10 underwent hot sterilization, while 10 left unsterilized as negative controls. Load-deflection curves were established for each wire (as five 0.2mm intervals between 1.0 and 1.8mm displacements), using a three-bracket test. After determining the plateau phase that was present in all wires, the averages of plateau phase pertaining to loading and unloading curves and their discrepancies (hysteresis) were calculated for each subgroup (n=10). Average plateau values were compared using two-way ANOVA, Tukey, and independent-samples t-test (α=0.05).

RESULTS

Average loading and unloading values were 906.6±129.7 and 295.9±84.5g respectively (t-test P<0.0001). Comparing loading plateaus, ANOVA indicated significant difference among wire brands (P<0.0001) but not among sterilization types (P=0.4793). Comparing unloading plateaus, ANOVA showed significant differences among wire brands (P<0.0001) and sterilization types (P=0.0008). Tukey showed that only cold sterilization and negative control differed significantly (P<0.001); cold and hot sterilization methods, or control and autoclaving were not significantly different (P>0.05). Comparing hysteresis plateaus, ANOVA indicated difference among wire brands (P<0.0053) but not among sterilization types (P=0.9166).

CONCLUSIONS

Cold sterilization might reduce unloading plateau of orthodontic wires, but sterilization in general might not affect loading or hysteresis plateaus. Different brands had different plateaus of loading, unloading and hysteresis.

Nonsurgical treatment for a severe anterior and lateral open bite and multiple congenitally missing teeth: a case report with 4-year follow-up

This case report describes the treatment of a severe anterior and lateral open bite combined with multiple congenitally missing teeth. A 10-year-old girl presented with an open gonial angle, absence of lip sealing, and soft tissue pogonion retrusion. She had an open bite of 8.5 mm, agenesis of the upper right and left lateral incisors and the upper left first premolar, and transverse maxillary deficiency. Nonsurgical treatment was planned aiming at controlling the vertical pattern, establishing the correct overbite, and closing the spaces on the upper arch, to provide satisfactory occlusion and facial and dental esthetics.

Force level of small diameter nickel-titanium orthodontic wires ligated with different methods

Background

The aim of this study was to compare the deflection force in conventional and thermally activated nickel-titanium (NiTi) wires in passive (Damon Q) and active (Bioquick) self-ligating brackets (SLB) and in conventional brackets (CB) tied by two different methods: elastomeric ligature (EL) and metal ligature (ML).

Methods

Two wire diameters (0.014 and 0.016 in.) and 10 specimens per group were used. The specimens were assembled in a clinical simulation device and tested in an Instron Universal Testing Machine, with a load cell of 10 N. For the testing procedures, the acrylic block representative of the right maxillary central incisor was palatally moved, with readings of the force at 0.5, 1, 2, and 3 mm, at a constant speed of 2 mm/min and temperature of 36.5 °C.

Results

The conventional NiTi released higher forces than the thermally activated NiTi archwires in large deflections. In general, the SLB showed lower forces, while the ML had higher forces, with both showing a similar force release behavior, constantly decreasing as the deflection decreased. The EL showed an irregular behavior. The active SLB showed smaller forces than passive, in large deflections.

Conclusions

The SLB and the ML exhibit standard force patterns during unloading, while the elastomeric ligatures exhibit a randomly distributed force release behavior.

Evaluation of deflection forces of orthodontic wires with different ligation types

The aim of this study was to evaluate deflection forces of orthodontic wires of different alloys engaged into conventional brackets using several ligation types. Stainless steel, conventional superelastic nickel-titanium and thermally activated nickel-titanium archwires tied into conventional brackets by a ring-shaped elastomeric ligature (RSEL), a 8-shaped elastomeric ligature (8SEL) and a metal ligature (ML) were tested. A clinical simulation device was created especially for this study and forces were measured with an Instron Universal Testing Machine. For the testing procedure, the block representing the maxillary right central incisor was moved 0.5 and 1 mm bucco-lingually at a constant speed of 2 mm/min, and the forces released by the wires were recorded, in accordance with the ISO 15841 guidelines. In general, the RSEL showed lighter forces, while 8SEL and ML showed higher values. At the 0.5 mm deflection, the 8SEL presented the greatest force, but at the 1.0 mm deflection the ML had a statistically similar force. Based on our evaluations, to obtain lighter forces, the thermally activated nickel-titanium wire with the RSEL are recommended, while the steel wire with the 8SEL or the ML are recommended when larger forces are desired. The ML exhibited the highest force increase with increased deflections, compared with the elastomeric ligatures.

Evaluation of the force generated by gradual deflection of orthodontic wires in conventional metallic, esthetic, and self-ligating brackets

Objective:

The purpose of this study was to evaluate the deflection forces of Nitinol orthodontic wires placed in different types of brackets: metallic, reinforced polycarbonate with metallic slots, sapphire, passive and active self-ligating, by assessing strength values variation according to gradual increase in wire diameter and deflection and comparing different combinations in the different deflections.

Material and Methods:

Specimens were set in a clinical simulation model and evaluated in a Universal Testing Machine (INSTRON 3342), using the ISO 15841 protocol. Data were subjected to One-way ANOVA, followed by Tukey tests (p<0.05).

Results:

Self-ligating brackets presented the most similar behavior to each other. For conventional brackets there was no consistent behavior for any of the deflections studied.

Conclusions:

Self-ligating brackets presented the most consistent and predictable results while conventional brackets, as esthetic brackets, showed very different patterns of forces. Self-ligating brackets showed higher strength in all deflections when compared with the others, in 0.020-inch wires.

Evaluation of force released by deflection of orthodontic wires in conventional and self-ligating brackets

Introduction:

The aim of the study was to evaluate deflection forces of rectangular orthodontic wires in conventional (Morelli^TM), active (In-Ovation R^TM) and passive (Damon 3MX^TM) self-ligating brackets.

Material and Methods:

Two brands of stainless steel and nickel-titanium (NiTi) wires (Morelli^TM and GAC^TM), in addition to Ormco^TM copper-nickel-titanium wires were used. Specimens were assembled in a clinical simulation device especially designed for this study and tested in an Instron universal testing machine. For the testing procedures, an acrylic structure representative of the maxillary right central incisor was lingually moved in activations of 0 to 1 mm, with readings of the force released by deflection in unloading of 0.5, 0.8 and 1 mm at a constant speed of 2 mm/min. Inter-bracket forces with stainless steel, NiTi and CuNiTi were individually compared by two-way ANOVA, followed by Tukey’s tests.

Results:

Results showed that there were lower forces in conventional brackets, followed by active and passive self-ligating brackets. Within the brands, only for NiTi wires, the Morelli^TM brand presented higher forces than GAC^TM wires.

Conclusions:

Bracket systems provide different degrees of deflection force, with self-ligating brackets showing the highest forces.

Comparison of the superelasticity of different nickel-titanium orthodontic archwires and the loss of their properties by heat treatment

The aim of this work is to describe and compare mechanical properties of eight widely used nickel-titanium orthodontic wires under uniform testing conditions and to determine the influence of the heat treatments on the loss of the superelasticity. Ten archwires from two batches from eight different manufacturers were evaluated. A three-point bending test was performed, in accordance with ISO 15841:2006, on 80 round nickel-titanium archwire segments of 0.016 inch. To obtain a load-deflection curve, the centre of each segment was deflected to 3.1 mm and then unloaded until force became zero. On the unloading curve, deflection at the end of the plateau and forces delivered at that point, and at 3, 2, 1 and 0.5 mm of deflection, were recorded. Plateau slopes were calculated from 3 and from 2 mm of deflection. Data obtained were statistically analysed to determine inter-brand, intra-brand and inter-batch differences (P < 0.05). The results show that at 2 mm of deflection, maximum differential force exerted among brands [Nitinol SuperElastic (1.999N)-Sentalloy M (1.001 N)] was 0.998 N (102 gf). The Nitinol SuperElastic plateau slope (0.353 N/mm) was the only one that was statistically different from 2 mm of deflection, as compared with the other brand values (0.129-0.155 N/mm). Damon Optimal Force described the gentlest slope from 3 mm of deflection (0.230 N/mm) and one of the longest plateaus. Titanol and Orthonol showed the most notable intra-brand differences, whereas inter-batch variability was significant for Nitinol (Henry Schein), Euro Ni-Ti and Orthonol. Superelasticity degree and exerted forces differed significantly among brands. Superelasticity of Nitinol SuperElastic was not observed, while Damon Optimal Force and Proclinic Ni-Ti Superelástico (G&H) showed the most superelastic curves. Intra-brand and inter-batch differences were observed in some brands. In all cases, the heat treatment at 600 °C produces precipitation in the matrix. The precipitates are rich in titanium and this fact produce changes in the chemical composition of the matrix and the loss of the superelasticity. At 400 °C these precipitates are not produced and the forces delivered by the wires are very similar with wires untreated.

The influence of distal-end heat treatment on deflection of nickel-titanium archwire

OBJECTIVE

The aim of this in vitro study was to evaluate the deflection-force behavior of nickel-titanium (NiTi) orthodontic wires adjacent to the portion submitted to heat treatment.

MATERIAL AND METHODS

A total of 106 segments of NiTi wires (0.019 x 0.025-in) and heat-activated NiTi wires (0.016 x 0.022-in) from four commercial brands were tested. The segments were obtained from 80 archwires. For the experimental group, the distal portion of each segmented archwire was subjected to heat treatment (n = 40), while the other distal portion of the same archwire was used as a heating-free control group (n = 40). Deflection tests were performed in a temperature-controlled universal testing machine. Unpaired Student's t-tests were applied to determine if there were differences between the experimental and control groups for each commercial brand and size of wire. Statistical significance was set at p < 0.05.

RESULTS

There were no statistically significant differences between the tested groups with the same size and brand of wire.

CONCLUSIONS

Heat treatment applied to the distal ends of rectangular NiTi archwires does not permanently change the elastic properties of the adjacent portions.

En-masse retraction with a preformed nickel-titanium and stainless steel archwire assembly and temporary skeletal anchorage devices without posterior bonding

Objective

To evaluate the therapeutic effects of a preformed assembly of nickel-titanium (NiTi) and stainless steel (SS) archwires (preformed C-wire) combined with temporary skeletal anchorage devices (TSADs) as the sole source of anchorage and to compare these effects with those of a SS version of C-wire (conventional C-wire) for en-masse retraction.

Methods

Thirty-one adult female patients with skeletal Class I or II dentoalveolar protrusion, mild-to-moderate anterior crowding (3.0-6.0 mm), and stable Class I posterior occlusion were divided into conventional (n = 15) and preformed (n = 16) C-wire groups. All subjects underwent first premolar extractions and en-masse retraction with pre-adjusted edgewise anterior brackets, the assigned C-wire, and maxillary C-tubes or C-implants; bonded mesh-tube appliances were used in the mandibular dentition. Differences in pretreatment and post-retraction measurements of skeletal, dental, and soft-tissue cephalometric variables were statistically analyzed.

Results

Both groups showed full retraction of the maxillary anterior teeth by controlled tipping and space closure without altered posterior occlusion. However, the preformed C-wire group had a shorter retraction period (by 3.2 months). Furthermore, the maxillary molars in this group showed no significant mesialization, mesial tipping, or extrusion; some mesialization and mesial tipping occurred in the conventional C-wire group.

Conclusions

Preformed C-wires combined with maxillary TSADs enable simultaneous leveling and space closure from the beginning of the treatment without maxillary posterior bonding. This allows for faster treatment of dentoalveolar protrusion without unwanted side effects, when compared with conventional C-wire, evidencing its clinical expediency.

Mechanical properties of NiTi and CuNiTi shape-memory wires used in orthodontic treatment. Part 1: stress-strain tests

OBJECTIVE

This research aimed to compare, through traction tests, eight types of superelastic and heat-activated NiTi archwires, by six trade companies (GAC, TP, Ormco, Masel, Morelli and Unitek) to those with addition of copper (CuNiTi 27°C and 35°C, Ormco).

METHODS

The tests were performed in an EMIC mechanical testing machine, model DL10000, capacity of 10 tons, at the Military Institute of Engineering (IME).

RESULTS

The results showed that, generally, heat-activated NiTi archwires presented slighter deactivation loadings in relation to the superelastic ones. Among the archwires that presented deactivation loadings biologically more adequate are the heat-activated by GAC and by Unitek. Among the superelastic NiTi, the CuNiTi 27°C by Ormco were the ones that presented slighter deactivation loadings, being statistically (ANOVA) similar to the ones presented by the heat-activated NiTi archwires from Unitek. When compared the CuNiTi 27°C and 35°C archwires, it was observed that the 27°C presented deactivation forces of, nearly, ⅓ of the presented by the 35°C.

CONCLUSIONS

It was concluded that the CuNiTi 35°C archwires presented deactivation loadings biologically less favorable in relation to the other heat-activated NiTi archwires, associated to lower percentage of deformation, on the constant baselines of deactivation, showing less adequate mechanical behavior under traction, in relation to the other archwires.

Degradation of orthodontic wires under simulated cariogenic and erosive conditions

This study examined the effect of cariogenic and erosive challenges (CCs and ECs, respectively) on the degradation of copper-nickel-titanium (CuNiTi) orthodontic wires. Sixty wire segments were divided into four treatment groups and exposed to CCs, ECs, artificial saliva, or dry storage (no-treatment control). CC and EC were simulated using a demineralizing solution (pH 4.3) and a citric acid solution (pH 2.3), respectively. Following treatment, the average surface roughness (Ra) of the wires was assessed, and friction between the wires and a passive self-ligating bracket was measured. CuNiTi wires subjected to ECs exhibited significantly higher Ra values than did those that were stored in artificial saliva. In contrast, surface roughness was not affected by CCs. Finally, friction between the treated wires and brackets was not affected by ECs or CCs. Our results indicate that CuNiTi orthodontic wires may suffer degradation within the oral cavity, as ECs increased the surface roughness of these wires. However, rougher surfaces did not increase friction between the wire and the passive self-ligating bracket.

Comparison of mechanical properties of beta-titanium wires between leveled and unleveled brackets: an in vitro study

Background

The objective of this study is to evaluate the force-deflection behavior of beta-titanium alloy wires between two leveled and unleveled bracket alignment scenarios using a three-point bending test.

Methods

Six groups of ten beta-titanium alloy wire segments (0.017 × 0.025-in. diameter) of different manufacturers (Orthometric, Ortho Organizers, GAC, Morelli, and Ormco) were used. Both brackets were bonded to an acrylic jig with a 10-mm interbracket distance. A 1-mm deflection test in two hypothetical conditions (with aligned brackets and by simulating a 2-mm horizontal displacement of the brackets) was explored. Forces of activation and deactivation of the wires during both tests were compared by an analysis of variance (ANOVA) tests followed by a Tukey test.

Results

A statistically significant difference was found in the force-deflection behavior between some of the wires in both simulated in vitro conditions. For the leveled-type alignment scenario, the differences between wires were up to 70 g (range 110 to 179 g). For the unleveled-type alignment scenario, these differences were up to 65 g (range 111 to 175 g).

Conclusions

The study showed some significant differences in forces generated during activation and deactivation among the five types of beta-titanium wires tested. In comparing leveled and unleveled brackets during activation, only Orthometric Beta Flexy and Ormco Beta-titanium were different between them.

Influence of bracket-slot design on the forces released by superelastic nickel-titanium alignment wires in different deflection configurations

Objective:

To evaluate how different bracket-slot design characteristics affect the forces released by superelastic nickel-titanium (NiTi) alignment wires at different amounts of wire deflection.

Materials and Methods:

A three-bracket bending and a classic-three point bending testing apparatus were used to investigate the load-deflection properties of one superelastic 0.014-inch NiTi alignment wire in different experimental conditions. The selected NiTi archwire was tested in association with three bracket systems: (1) conventional twin brackets with a 0.018-inch slot, (2) a self-ligating bracket with a 0.018-inch slot, and (3) a self-ligating bracket with a 0.022-inch slot. Wire specimens were deflected at 2 mm and 4 mm.

Results:

Use of a 0.018-inch slot bracket system, in comparison with use of a 0.022-inch system, increases the force exerted by the superelastic NiTi wires at a 2-mm deflection. Use of a self-ligating bracket system increases the force released by NiTi wires in comparison with the conventional ligated bracket system. NiTi wires deflected to a different maximum deflection (2 mm and 4 mm) release different forces at the same unloading data point (1.5 mm).

Conclusion:

Bracket design, type of experimental test, and amount of wire deflection significantly affected the amount of forces released by superelastic NiTi wires (P &lt; .05). This phenomenon offers clinicians the possibility to manipulate the wire's load during alignment.

Effect of dry heat and steam sterilization on load-deflection characteristics of β-titanium wires: An in vitro study

BACKGROUND

Sterilization techniques could affect the characteristics of orthodontic wires. The aim of the present study was to evaluate the effect of steam and dry heat sterilization techniques on load-deflection behavior of five types of β-titanium alloy wires.

MATERIALS AND METHODS

The samples consisted of 30 straight lengths of five types of β-titanium alloy wires: Titanium Molybdenum Alloy (TMA) Low Friction (TMAL), TMA Low Friction Colored (HONE), Resolve (RES), BetaForce (BETA), and BETA CNA (CNA). Thirty wire segments were divided into three groups of 10. Group 1 was the control group and the group 2 samples were sterilized by dry heat in an oven (60 minutes at 160°C) and group 3 by steam in an autoclave (15 minutes at 121°C). Then all the wire samples underwent a three-point bending test in a testing machine to evaluate load-deflection properties. Data was analyzed by repeated measures ANOVA and Scheffé's test (α = 0.05).

RESULTS

The results showed that dry heat sterilization significantly increased force levels during both loading and unloading of CNA, BETA and RES and during loading of HONE (P < 0.05). Steam sterilization significantly increased force levels during both loading and unloading of BETA and during unloading of HONE (P < 0.05), with no effects on the load-deflection characteristics of TMAL, CNA and RES (P > 0.05).

CONCLUSION

It appears dry heat sterilization increases stiffness of RES, BETA, CNA and HONE but autoclave sterilization did not have any effect on load-deflection characteristics of most of the β-titanium wires tested, indicating that clinicians who want to provide maximum safety for their patients can autoclave TMAL, RES and CNA before applying them.

Comparison of deactivation forces between thermally activated nickel-titanium archwires

OBJECTIVE

The aim of the present study was to investigate and compare load-deflection characteristics of commercially available thermally activated nickel-titanium archwires using a three-point bending test.

MATERIALS AND METHODS

Sixty thermally activated 0.019×0.025-inch nickel-titanium archwires from six different manufacturers were investigated. The superelastic properties of these archwires were evaluated by conducting a three-point bending test under identical testing conditions. Forces generated at deactivation for a deflection of 0.5, 1, 2 and 3 mm at a temperature of 37° C were selected for statistical comparison of the data. The results of forces of deactivation at all deflections applied were compared by two-way analysis of variance and the Tukey test.

RESULTS

Statistical differences (P<0.05) were found at all force levels during deactivations. The results showed that the range of forces displayed great variation in quantitative behaviour. None of the archwires showed permanent deformation after the three-point bending test.

CONCLUSIONS

This study revealed significant differences in deactivation forces among the six types of thermally activated nickel-titanium archwires tested. NiTinol Termoativado (Aditek) and NeoSentalloy F200 (GAC) produced the least amount of force in all four deactivation categories.

Efeitos dos fios de nivelamento de níquel-titânio e de aço inoxidável na posição dos incisivos inferiores

OBJETIVO: estudar os efeitos do nivelamento realizado com fios de NiTi termoativado e de aço inoxidável, avaliando-se as possíveis alterações na posição dos incisivos inferiores, em casos com extrações, correlacionando com o tempo de tratamento. MÉTODOS: a amostra foi composta de 36 indivíduos, de ambos os sexos, leucodermas brasileiros, com idade média inicial de 15 anos e 5 meses, portadores de más oclusões de Classes I e II, distribuídos em dois grupos. No Grupo 1 (n=17), o nivelamento foi realizado com a sequência 1, utilizando-se três fios - 0,016" e 0,019"x0,025" de NiTi termoativado, e 0,019"x0,025" de aço inoxidável. No Grupo 2 (n=19), foi testada a sequência 2, na qual foram utilizados apenas fios de aço inoxidável (0,014"; 0,016"; 0,018"; 0,020" e 0,019"x0,025" com torque passivo nos incisivos inferiores). Os dados foram coletados utilizando-se o método cefalométrico computadorizado e comparados pelo teste t de Student com o nível de significância de 5%. RESULTADOS: no Grupo 1, os incisivos inferiores inclinaram-se para lingual, com movimento significativo apenas da coroa (1,6mm). No Grupo 2, os incisivos inferiores permaneceram estáveis. Não houve alteração vertical em nenhum dos grupos. CONCLUSÕES: a sequência 2 proporcionou um melhor controle dos incisivos inferiores, não alterando suas posições iniciais, enquanto a sequência 1 permitiu a expressão do torque da prescrição utilizada, levando a uma inclinação lingual desses dentes. O tempo de tratamento foi menor utilizando-se a sequência 1. As variações biomecânicas estudadas apresentaram vantagens e desvantagens que devem ser conhecidas e ponderadas pelo ortodontista no planejamento do caso.

Mechanical properties of beta-titanium wires

OBJECTIVE

To evaluate the force-deflection behavior of six beta-titanium wires using a three-point bending test.

MATERIALS AND METHODS

The wires timolium (TIM), titanium molybdenum (ORG), beta titanium (BETA), resolve (RES), titanium molybdenum alloy (TMA), and TMA low friction (TMAL) were adapted into two stainless steel brackets, with no angulation or torque. Both brackets were bonded to an acrylic jig with a 10-mm interbracket distance. A testing machine (Instron) applied deflections of 0.2 to 2.0 mm. Force-deflection diagrams were determined from a passive position to an activation of 2 mm and then during deactivation. Forces of activation and deactivation at a deflection of 1 mm were compared by analysis of variance.

RESULTS

Results demonstrated that significant differences (P < .05) in force were observed among wires. During activation, forces for the wires were ranked from lowest to highest as TMAL = TMA = RES<ORG = BETA<TIM. During deactivation, forces for the wires were ranked from lowest to highest as TIM<ORG = BETA<RES =  TMA<TMAL. The wires exhibited similar activation-deactivation diagrams.

CONCLUSION

This study revealed significant differences in force during activation and deactivation among the six types of beta-titanium wires tested.

Influence of Friction Resistance on Expression of Superelastic Properties of Initial NiTi Wires in "Reduced Friction" and Conventional Bracket Systems

Objectives. The aim of this study was to assess the influence of resistance to sliding on expression of superelastic properties of NiTi wires. Methods and Materials. A three-point bending test was performed for 0.014 NiTi wire engaged in self-ligating (Damon, SmartClip, In-Ovation) and conventional brackets (Victory) ligated with regular and reduced friction modules (Slide). The wire was deflected in the buccal direction and allowed to straighten. The maximum load, unloading plateau and unloading capacity were registered. Results. The lowest activation load was required in the active self-ligating group (In-Ovation 2.2 ± 0.4 N) and reduced friction module group (Victory/Slide 2.9 ± 0.4 N), followed by the passive self-ligating systems (Damon 3.6 ± 0.7 N, SmartClip 3.7 ± 0.4 N). Higher activation load was obtained in the conventionally ligated group (Victory/module 4.5 ± 0.4 N). Unloading plateau phase with the load magnitude ranging from 1.27 ± 0.4 N (In-Ovation) to 1.627 ± 0.4 N (Slide) was distinct in all groups but one (Victory). Conclusions. Higher friction at flanking points reduces the net force delivered by the wire. Unloading plateau phase of NiTi load-deflection curve disappears in the conventionally ligated group thus indicating to an incomplete expression of NiTi superelastic properties. A rigid passive bracket clip amplifies resistance to sliding in an active configuration and produces a permanent deflection of the wire.

Influence of stress and phase on corrosion of a superelastic nickel-titanium orthodontic wire

INTRODUCTION

The purpose of this investigation was to study the effect of stress and phase transformation on the corrosion properties of a superelastic nickel-titanium orthodontic wire.

METHODS

The phase transformation profiles of superelastic nickel-titanium (Sentalloy, GAC International, Bohemia, NY) and beta-titanium (TMA, Ormco, Orange, Calif) archwires were analyzed by using differential scanning calorimetry. The force/deflection behavior of the wires at 37 degrees C was measured in a 3-point bending test per modified American Dental Association specification no. 32. Electrochemical testing consisted of monitoring the open circuit potential (OCP) for 2 hours followed by polarization resistance and cyclic polarization tests on archwire segments engaged in a 5-bracket simulation apparatus with bend deflections of 0.75, 1.5, or 3 mm in artificial saliva at 37 degrees C. Nondeflected segments were also tested. Sentalloy was additionally examined for bending and corrosion at 5 degrees C, where it exists as martensite and is devoid of stress-induced phase transformation. OCP at 2 hours and corrosion current density (i(corr)) were analyzed by using ANOVA and Tukey tests (alpha = .05) (n = 10 per deflection).

RESULTS

Significant differences (P < 0.05) in OCP with deflection were found for the TMA and the Sentalloy wires at 5 degrees C, but not for Sentalloy at 37 degrees C. Significant differences (P < 0.05) in i(corr) with deflection were also observed. All 3 wire groups had their lowest mean i(corr) values when not deflected. The i(corr) for superelastic Sentalloy (37 degrees C) peaked at 0.75 mm deflection before the wire's stress-induced phase transformation point and then decreased with further deflection and transformation. The i(corr) values for TMA and Sentalloy at 5 degrees C, both of which do not undergo phase transformation with deformation, continuously increased from 0 to 1.5 mm deflection before decreasing at the 3.0-mm deflection.

CONCLUSIONS

Stress increased the corrosion rate in nickel-titanium and beta-titanium orthodontic wires. Alterations in stress/strain associated with phase transformation in superelastic nickel-titanium might alter the corrosion rate in ways different from wires not undergoing phase transformation.

Force-deflection comparison of superelastic nickel-titanium archwires

This in vitro study compared the force-deflection behavior of 6 superelastic nickel-titanium orthodontic archwires (0.016 x 0.022 in) under controlled moment and temperature. To simulate leveling, maxillary canine brackets and first molar tubes were bonded in such a manner as to remove the tip and angulation from the system. The wires (n = 10) were passively self-ligated into stainless steel brackets attached to an acrylic jig to simulate the maxillary arch. A testing machine recorded deactivations of 3 distances (5, 4, and 3 mm) at 37 degrees C in the canine position. Force-deflection measurements were recorded from the deactivations only. Forces produced during deactivation, at deflections of 2.5, 2.0, and 1.5 mm, were compared by analysis of variance. Significant differences (P < 0.0001) in forces were observed among the wires at the various deflections. All wires exhibited superelastic behavior, and rankings were derived according to statistically significant differences for each deflection distance.