Thermal and mechanical characteristics of stainless steel, titanium-molybdenum, and nickel-titanium archwires

Multi-Force Bio-Active™ Archwires and Various Contemporary NiTi Multi-Force Archwires: Properties and Characteristics-A Review

The manufacturing of orthodontic archwires made from NiTi alloy has undergone numerous changes from the second half of the last century to modern times. Initially, superelastic-active austenitic NiTi alloys were predominant, followed by thermodynamic-active martensitic NiTi alloys, and, finally, the most recent development was graded thermodynamic alloys. These advancements have been the subject of extensive investigation in numerous studies, as they necessitated a deeper understanding of their properties. Furthermore, it is imperative that we validate the information provided by manufacturers regarding these archwires through independent studies. This review evaluates existing studies on the subject with a specific focus on the Bio-active multi-force NiTi archwire, by examining its mechanical, thermal, and physicochemical properties before and after clinical use. This archwire consists primarily of Ni and Ti, with traces of Fe and Cr, which release graduated, biologically tolerable forces which increase in a front-to-back direction and are affected by the temperature of the environment they are in. The review provides information to practicing orthodontists, facilitating informed decisions regarding the selection and use of Bio-active™ archwires for individual patient treatments.

Thermal Behavior Changes of As-Received and Retrieved Bio-Active® (BA) and TriTanium® (TR) Multiforce Nickel-Titanium Orthodontic Archwires

Multiforce nickel-titanium (NiTi) orthodontic archwires release progressively increasing forces in a front-to-back direction along their length. The properties of NiTi orthodontic archwires depend on the correlation and characteristics of their microstructural phases (austenite, martensite and the intermediate R-phase). From a clinical and manufacturing point of view, the determination of the austenite finish (Af) temperature is of the greatest importance, as in the austenitic phase, the alloy is most stable and exhibits the final workable form. The main purpose of using multiforce orthodontic archwires is to decrease the intensity of the applied forces to the teeth with a small root surface area, such as the lower central incisors, and also provide forces high enough to move the molars. With the optimally dosed forces of multiforce orthodontic archwires in the frontal, premolar and molar segments, the feeling of pain can be reduced. This will contribute to the greater cooperation of the patient, which is of utmost importance to achieve optimal results. The aim of this research was to determine the Af temperature at each segment of as-received and retrieved Bio-Active^® and TriTanium^® archwires with dimensions of 0.016 × 0.022 inches, investigated by the differential scanning calorimetry (DSC) method. A classical Kruskal-Wallis one-way ANOVA test and multi-variance comparison based on the ANOVA test statistic using the Bonferroni corrected Mann-Whitney test for multiple comparisons were used. The incisor, premolar and molar segments have different Af temperatures, and they decrease from the anterior to posterior so that the posterior segment has the lowest Af. Bio-Active^® and TriTanium^® with dimensions of 0.016 × 0.022 inches can be used as first leveling archwires by additional cooling and are not recommended for use on patients with mouth breathing.

Application of Copper Nanoparticles in Dentistry

Nanoparticles based on metal and metallic oxides have become a novel trend for dental applications. Metal nanoparticles are commonly used in dentistry for their exclusive shape-dependent properties, including their variable nano-sizes and forms, unique distribution, and large surface-area-to-volume ratio. These properties enhance the bio-physio-chemical functionalization, antimicrobial activity, and biocompatibility of the nanoparticles. Copper is an earth-abundant inexpensive metal, and its nanoparticle synthesis is cost effective. Copper nanoparticles readily intermix and bind with other metals, ceramics, and polymers, and they exhibit physiochemical stability in the compounds. Hence, copper nanoparticles are among the commonly used metal nanoparticles in dentistry. Copper nanoparticles have been used to enhance the physical and chemical properties of various dental materials, such as dental amalgam, restorative cements, adhesives, resins, endodontic-irrigation solutions, obturation materials, dental implants, and orthodontic archwires and brackets. The objective of this review is to provide an overview of copper nanoparticles and their applications in dentistry.

Thermal and mechanical characterization of thermoplastic orthodontic aligners discs after molding process

Polymeric aesthetic aligners were introduced in orthodontics as an innovative alternative to fixed appliances, however, their compositions and the thermal molding process may influence the biomechanical characteristics of these aligners. In this study four different clear aligner brands were used, ACE 035 Essix, C + Essix, Crystal 0.75 and Crystal 1.0, whose aim was to identify the thermal-processing influence on the mechanical and physicochemical properties of these materials, and to suggest a orthodontic sequence of wear for these appliances to achieve more effective treatment results. For the tensile tests the sample size calculation was based on probability distributions from the F test. The effect size used was 0.3, type 1 error of 0.05. Statistical Yield strength and Young's Modulus results were evaluated using the Shapiro-Wilk test. The groups were compared using the parametric test of analysis of variance, with Tukey post-test. Differences were statistically considered at the p < 0.05. The Infrared spectroscopy analysis showed no changes in the samples' chemical structure after thermal-processing. However, in the polypropylene aligner, differences were verified in the region attributed to the crystalline phase. Differential Scanning Calorimetry analysis for the same sample showed a crystallinity fraction decrease due to relaxation between polymer chains after molding. In the tensile tests evaluated, the tensile strength and 'Young's modulus presented higher values for aligners containing 100% polyethylene terephthalate glycol. Performing an analogy exercise of the properties of orthodontic wires used in conventional fixed appliances and, relating them to orthodontic plastics, aligners composed of different materials and/or thicknesses could be used in increasing sequence in terms of the modulus of elasticity, starting with C+, which has a lower elastic modulus value, using the ACE 035 as an intermediate and finishing with the Crystal 0.75 and 1.0, providing the desired stiffness to the aligners for the final phase.

The Antimicrobial Properties of Nanotitania Extract and Its Role in Inhibiting the Growth of Klebsiella pneumonia and Haemophilus influenza

Titanium dioxide (TiO2) is an antimicrobial agent which is considered of potential value in inhibiting the growth of multiple bacteria. Klebsiella pneumonia and Haemophilus influenza are two of the most common respiratory infection pathogens, and are the most. Klebsiella pneumonia causes fatal meningitis, while Haemophilus influenza causes mortality even in younger patients. Both are associated with bacteremia and mortality. The purpose of this study was to test a new antibacterial material, namely nanotitania extract combined with 0.03% silver that was developed at Universiti Malaysia Sabah (UMS) and tested against K. pneumonia and H. influenza. The nanoparticles were synthesized through a modified hydrothermal process, combined with molten salt and proven to have excellent crystallinity, with the band-gap energy falling in the visible light spectrum. The nanoparticle extract was tested using a macro-dilutional method, which involved combining it with 0.03% silver solution during the process of nanoparticle synthesis and then introducing it to the bacteria. A positive control containing the bacteria minus the nanoparticles extract was also prepared. 25 mg/mL, 12.5 mg/mL, and 6.25 mg/mL concentrations of the samples were produced using the macro dilution method. After adding the bacteria to multiple concentrations of nanoparticle extract, the suspensions were incubated for 24 h at a temperature of 37 °C. The suspensions were then spread on Mueller-Hinton agar (K. pneumonia) and chocolate blood agar (H. influenza), where the growth of bacteria was observed after 24 h. Nanoparticle extract in combination with silver at 0.03% was proven to have potential as an antimicrobial agent as it was able to inhibit H. influenza at all concentrations. Furthermore, it was also shown to be capable of inhibiting K. pneumonia at concentrations of 25 mg/mL and 50 mg/mL. In conclusion, the nanoparticle extract, when tested using a macro-dilutional method, displayed antimicrobial properties which were proven effective against the growth of both K. pneumonia and H. influenza.

Physicochemical Research of Clinically Retrieved CU-NI-TI Orthodontic Archwires

In modern orthodontics, thermally activated archwires are used more widely in clinical practice, because they have unique properties like superelasticity and bio-compatibility. The aim of the present study was to characterize commercial 35° C Cu-NiTi archwires in terms of their phase transition behavior, chemical composition, surface topography properties after clinical usage, as well as the influence of the autoclaving process. Materials and methods. 35° C Thermo-Active Copper NiTi (CuNiTi) of ORMCO, Glendora, CA, USA (as-received, as-received autoclaved and clinically retrieved) with rectangular cross-section and dimension 0.016x0.022 inch, were investigated. The physicochemical research was conducted via Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDX) and X-ray Diffraction Analysis (XRD). The autoclaving was done in Runyes model B autoclave. Results. The DSC results revealed the austenite start (9.8° C; 26.47° C) and austenite finish (28° C; 31.74° C) temperatures for the as-received and autoclaved archwires respectively. For clinically retrieved samples the austenite finish temperature (Af) is around 27° C. The XRD patterns of the as-received and clinically retrieved samples show almost identical diffraction patterns. Rough surface of the CuNiTi alloy was revealed by the SEM analysis. Autoclaving process seems to have no effects on archwires’ structure and chemical composition. Chemical content of the investigated as-received CuNiTi are Ni, Ti and Cu: 47.07 wt% and 46.81 wt% and 6.11 wt%, respectively. The autoclaving process seems to have little influence on the transition temperature. The results from our study showed little difference (~7 °C) in the finish transition temperatures (Af), compared to the manufacturer’s claim. No intermediate R phase was detected by DSC. Conclusion. A good knowledge of the structural changes that occur in CuNiTi alloys in the oral cavity is useful for the orthodontists in order to optimize orthodontic treatment.

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.

Influence of different storage temperatures on the mechanical properties of NiTi, Cu-NiTi and SS orthodontic archwires: An in vitro study

OBJECTIVE

Due to their exceptional temperature sensitivity, the mechanical properties of Nickel-titanium and Copper Nickel-titanium wires may be influenced by their storage temperature. This in turn may have clinical implications and may also affect the outcomes. This study analyzed the influence of storage temperatures on the mechanical properties of orthodontic wires in a laboratory setting.

MATERIALS AND METHODS

Stainless steel (SS), Nickel-Titanium (NiTi), and three variants of Copper-NiTi (Cu-NiTi 27°C, 35°C and 40°C), 0.017×0.025 inches in size were analysed using a three-point bending test in a pre-heated chamber at 36°C. The orthodontic wires were stored for twenty-four hours before the mechanical testing at four different temperatures (5°, 22°, 36° and 60°C).

RESULTS

The obtained results showed that the mechanical forces exerted by 27°C Copper-NiTi exhibit the most stable behaviour after having been stored at different temperatures, whereas 35°C Copper-NiTi showed the highest variability. As to be expected, Stainless steel shows no changes in its bending mechanical properties.

CONCLUSION

Furthermore, the results of this investigation reflect the importance of controlling the storage temperature of orthodontic NiTi and Copper-NiTi wires tested in a research environment in order to avoid unexpected bias.

An archwire for non-invasive improvement of occlusal cant and soft tissue chin deviation

Nonsurgical improvement of an occlusal cant, lip cant, and soft tissue chin deviation has been considered not possible merely through orthodontic treatment without surgical intervention. The purpose of this report was to illustrate a possible new field in orthodontics for a non-invasive improvement of the occlusal cant and soft tissue chin deviation through orthodontic approach by an innovative orthodontic archwire (Yin-Yang wire) and the others.

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.

Controlled Molar Inclination during Maxillary Dental Expansion Using a Straight Rectangular Archwire

Purpose

The purpose of this study was to examine whether the amount of transversal dental expansion, controlled using a straight rectangular beta-titanium alloy (TMA®) wire, has an influence on changes in maxillary first molar inclination.

Materials and Methods

Twenty patients requiring bilateral maxillary dental arch expansion were treated using a 0.018”-slot preadjusted edge-wise fixed appliance. Once leveled and aligned, the maxillary dental arches were expanded using a 0.016” × 0.022” straight TMA® wire. Changes in arch width and maxillary first molar inclination were assessed before (T0) and after (T1) expansion using three-dimensional scanned models. Mann–Whitney U-test, Wilcoxon signed-rank test, and Kruskal–Wallis test were used, where appropriate, to compare changes between and within groups.

Results

Intermolar width expanded at a rate of 0.8 ± 0.3 mm/month, and first molar buccal crown tipping occurred at 2.1° ± 1.2° (P < 0.05). Changes in inclination between minor expansion (1.0–2.5 mm) and moderate expansion (2.6–4.0 mm) groups were not statistically significant (1.8 ± 0.5 vs. 2.2 ± 1.2; P > 0.05).

Conclusions

Use of a straight rectangular TMA® wire in conjunction with a fixed orthodontic appliance successfully expanded the maxillary dental arch. The amount of expansion had no effect on molar inclination.

Initial arch wires used in orthodontic treatment with fixed appliances

BACKGROUND

Initial arch wires are the first arch wires to be inserted into the fixed appliance at the beginning of orthodontic treatment and are used mainly for the alignment of teeth by correcting crowding and rotations. With a number of different types of orthodontic arch wires available for initial tooth alignment, it is important to understand which wire is most efficient, as well as which wires cause least amount of root resorption and pain during the initial aligning stage of treatment. This is an update of the review entitledInitial arch wires for alignment of crooked teeth with fixed orthodontic braces, which was first published in 2010.

OBJECTIVES

To assess the effects of initial arch wires for the alignment of teeth with fixed orthodontic braces, in terms of the rate of tooth alignment, amount of root resorption accompanying tooth movement, and intensity of pain experienced by patients during the initial alignment stage of treatment.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 5 October 2017), the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library, 2017, Issue 9), MEDLINE Ovid (1946 to 5 October 2017), and Embase Ovid (1980 to 5 October 2017. The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of initial arch wires to align teeth with fixed orthodontic braces. We included only studies involving participants with upper or lower, or both, full arch fixed orthodontic appliances.

DATA COLLECTION AND ANALYSIS

Two review authors were responsible for study selection, 'Risk of bias' assessment and data extraction. We resolved disagreements by discussion between the review authors. We contacted corresponding authors of included studies to obtain missing information. We assessed the quality of the evidence for each comparison and outcome as high, moderate, low or very low, according to GRADE criteria.

MAIN RESULTS

For this update, we found three new RCTs (228 participants), bringing the total to 12 RCTs with 799 participants. We judged three studies to be at high risk of bias, and three to be at low risk of bias; six were unclear. None of the studies reported the adverse outcome of root resorption. The review assessed six comparisons.1. Multistrand stainless steel versus superelastic nickel-titanium (NiTi) arch wires. There were five studies in this group and it was appropriate to undertake a meta-analysis of two of them. There is insufficient evidence from these studies to determine whether there is a difference in rate of alignment between multistrand stainless steel and superelastic NiTi arch wires (mean difference (MD) -7.5 mm per month, 95% confidence interval (CI) -26.27 to 11.27; 1 study, 48 participants; low-quality evidence). The findings for pain at day 1 as measured on a 100 mm visual analogue scale suggested that there was no meaningful difference between the interventions (MD -2.68 mm, 95% CI -6.75 to 1.38; 2 studies, 127 participants; moderate-quality evidence).2. Multistrand stainless steel versus thermoelastic NiTi arch wires. There were two studies in this group, but it was not appropriate to undertake a meta-analysis of the data. There is insufficient evidence from the studies to determine whether there is a difference in rate of alignment between multistrand stainless steel and thermoelastic NiTi arch wires (low-quality evidence). Pain was not measured.3. Conventional NiTi versus superelastic NiTi arch wires. There were three studies in this group, but it was not appropriate to undertake a meta-analysis of the data. There is insufficient evidence from these studies to determine whether there is any difference between conventional and superelastic NiTi arch wires with regard to either alignment or pain (low- to very low-quality evidence).4. Conventional NiTi versus thermoelastic NiTi arch wires. There were two studies in this group, but it was not appropriate to undertake a meta-analysis of the data. There is insufficient evidence from these studies to determine whether there is a difference in alignment between conventional and thermoelastic NiTi arch wires (low-quality evidence). Pain was not measured.5. Single-strand superelastic NiTi versus coaxial superelastic NiTi arch wires. There was only one study (24 participants) in this group. There is moderate-quality evidence that coaxial superelastic NiTi can produce greater tooth movement over 12 weeks (MD -6.76 mm, 95% CI -7.98 to -5.55). Pain was not measured.6. Superelastic NiTi versus thermoelastic NiTi arch wires. There were three studies in this group, but it was not appropriate to undertake a meta-analysis of the data. There is insufficient evidence from these studies to determine whether there is a difference in alignment or pain between superelastic and thermoelastic NiTi arch wires (low-quality evidence).

AUTHORS' CONCLUSIONS

Moderate-quality evidence shows that arch wires of coaxial superelastic nickel-titanium (NiTi) can produce greater tooth movement over 12 weeks than arch wires made of single-strand superelastic NiTi. Moderate-quality evidence also suggests there may be no difference in pain at day 1 between multistrand stainless steel arch wires and superelastic NiTi arch wires. Other than these findings, there is insufficient evidence to determine whether any particular arch wire material is superior to any other in terms of alignment rate, time to alignment, pain and root resorption.

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.

Differences in cytocompatibility, dynamics of the oxide layers' formation, and nickel release between superelastic and thermo-activated nickel-titanium archwires

Superelastic (SE) and thermo-activated (TA) nickel-titanium (NiTi) archwires are used in everyday orthodontic practice, based on their acceptable biocompatibility and well-defined shape memory properties. However, the differences in their surface microstructure and cytotoxicity have not been clearly defined, and the standard cytotoxicity tests are too robust to detect small differences in the cytotoxicity of these alloys, all of which can lead to unexpected adverse reactions in some patients. Therefore, we tested the hypothesis that the differences in manufacture and microstructure of commercially available SE and TA archwires may influence their biocompatibility. The archwires were studied as-received and after conditioning for 24 h or 35 days in a cell culture medium under static conditions. All of the tested archwires, including their conditioned medium (CM), were non-cytotoxic for L929 cells, but Rematitan SE (both as received and conditioned) induced the apoptosis of rat thymocytes in a direct contact. In contrast, TruFlex SE and Equire TA increased the proliferation of thymocytes. The cytotoxic effect of Rematitan SE correlated with the higher release of Ni ions in CM, higher concentration of surface Ni and an increased oxygen layer thickness after the conditioning. In conclusion, the apoptosis assay on rat thymocytes, in contrast to the less sensitive standard assay on L929 cells, revealed that Rematitan SE was less cytocompatible compared to other archwires and the effect was most probably associated with a higher exposition of the cells to Ni on the surface of the archwire, due to the formation of unstable oxide layer.

Mechanical properties of cobalt-chromium wires compared to stainless steel and β-titanium wires

Background:

Previous studies have reported on mechanical properties of different orthodontic wires. However, there is a paucity of information that comparing the mechanical properties of Blue Elgiloy (BE) when compared to stainless steel and TMA, as finishing wires as received by different companies.

Aims:

The aim of this study was to evaluate the mechanical properties of BE wires compared to stainless steel (SS) and titanium Molybdenum alloy (TMA) also known as β titanium as provided by two companies.

Materials and Methods:

Six 0.016 x 0.022-14mm-samples of each wire were fixed individually to Instron machine and were tested in loading and unloading for three times. The initial load was set for 500 Kg at a speed of 1mm/min and displacement was adjusted for (0.5, 1mm in loading and 0.5 mm unloading at 25°C).

Statistics Analysis:

Variables were compared between groups by ANOVA test using SPSS statistical software.

Results:

BE shows comparable forces to SS when loaded 0.5 and showed decreased forces in 1mm loading compared to SS, and higher than TMA. BE also showed no forces at unloading and high deformation.

Conclusion:

BE from the two companies showed comparable mechanical properties while SS and TMA were different. The deformation of BE and its decreased forces in unloading may limit its clinical use.

Torque expression capacity of 0.018 and 0.022 bracket slots by changing archwire material and cross section

Background

The aim of this study is to calculate and compare the play and torque expression of 0.018 and 0.022 bracket slots when engaged with archwires of different size, cross section and material.

Methods

Eight orthodontic brackets, two of slot height 0.018 and six of slot height 0.022, from different manufacturers, were measured and fixed to a vertical support. Twenty-four archwires of differing size, cross section and material were selected, measured and tested in each bracket of compatible slot width. Compression testing by Instron dynamometer and geometric calculations enabled us to determine the play angle of each bracket/archwire combination, and the angle at which a clinically efficacious force couple, sufficient for dental movement, is exerted.

Results

All bracket/archwire combinations considered were found to have play angles far above the ideal. This is ascribable to the slots being oversized with respect to the manufacturers' claims. Likewise, some archwires were found to be oversized, while others undersized.

When the same archwire was tested with brackets from different manufacturers, the play and torque expression differed, despite the same nominal dimensions of the slots. When the same bracket was tested with the same size archwires, their construction material was found to influence the torque expression, due to the difference in elastic modulus, but not the wire/slot play.

Conclusions

The dimensional precision of orthodontic brackets and archwires and the rigidity of the latter have a profound influence on the torque expression of pre-angled appliances.

[Is the shape memory effect a reality for 35° Copper Ni-Ti(®)? Study by means of differential scanning calorimetry]

INTRODUCTION

Copper-nickel-titanium alloys are supposed to deliver a shape memory effect: when they are brought to a low temperature phase and subjected to a plastic deformation, they should recover their initial shape by simple heating. Nickel-titanium alloys can display different crystallographic phases: martensite, austenite and an inconstant intermediate R-phase. The shape memory effect is generally associated with the transition from martensite to austenite but it could also accompany the transition from R-phase to austenite. Since oral temperatures are not compatible with a fully martensitic alloy, this study aims, for 35° Copper Ni-Ti(®), to assess the R-phase presence at oral temperatures and to verify the possibility of using the R-phase shape memory effect under clinical conditions.

MATERIALS AND METHODS

Thirty consecutive 35° Copper Ni-Ti(®) archwires from two different batches were examined by differential scanning calorimetry with partial cycles limited to temperatures encountered within the oral cavity (from 0 °C to 50 °C). The presence of an intermediate crystallographic phase was assessed on the thermograms. The transformation temperatures were determined and the two batches were compared using the Mann-Whitney U Test.

RESULTS

Upon heating, all wires transformed directly from martensite to austenite. Af (mean  = 33.5 °C, SD  = 0.8 °C) was generally below the temperature stated by the manufacturer and a statistically significant difference (p ≤ 0.01) was found between the two batches.

CONCLUSIONS

No R-phase was detected and transformation temperatures were not constant. This study questions the supposed shape memory effect displayed by 35° Copper Ni-Ti(®) wires under clinical conditions.

Initial arch wires for tooth alignment during orthodontic treatment with fixed appliances

BACKGROUND

Initial arch wires are the first arch wires to be inserted into the fixed appliance at the beginning of orthodontic treatment and are used mainly for the alignment of teeth by correcting crowding and rotations. With a number of different types of orthodontic arch wires available for initial tooth alignment, it is important to understand which wire is most efficient, as well as which wires cause the least amount of root resorption and pain during the initial aligning stage of treatment. This is an update of the review 'Initial arch wires for alignment of crooked teeth with fixed orthodontic braces' first published in the Cochrane Database of Systematic Reviews 2010, Issue 4.

OBJECTIVES

To assess the effects of initial arch wires for alignment of teeth with fixed orthodontic braces in relation to alignment speed, root resorption and pain intensity.

SEARCH METHODS

We searched the following electronic databases: the Cochrane Oral Health Group's Trials Register (to 2 August 2012), CENTRAL (The Cochrane Library 2012, Issue 7), MEDLINE via OVID (1950 to 2 August 2012) and EMBASE via OVID (1980 to 2 August 2012). We also searched the reference lists of relevant articles. There was no restriction with regard to publication status or language of publication. We contacted all authors of included studies to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of initial arch wires to align teeth with fixed orthodontic braces. Only studies involving participants with upper and/or lower full arch fixed orthodontic appliances were included.

DATA COLLECTION AND ANALYSIS

Two review authors were responsible for study selection, validity assessment and data extraction. All disagreements were resolved by discussion amongst the review team. Corresponding authors of included studies were contacted to obtain missing information.

MAIN RESULTS

Nine RCTs with 571 participants were included in this review. All trials were at high risk of bias and a number of methodological limitations were identified. All trials had at least one potentially confounding factor (such as bracket type, slot size, ligation method, extraction of teeth) which is likely to have influenced the outcome and was not controlled in the trial. None of the trials reported the important adverse outcome of root resorption.Three groups of comparisons were made.(1) Multistrand stainless steel initial arch wires compared to superelastic nickel titanium (NiTi) initial arch wires. There were four trials in this group, with different comparisons and outcomes reported at different times. No meta-analysis was possible. There is insufficient evidence from these trials to determine whether or not there is a difference in either rate of alignment or pain between stainless steel and NiTi initial arch wires.(2) Conventional (stabilised) NiTi initial arch wires compared to superelastic NiTi initial arch wires. There were two trials in this group, one reporting the outcome of alignment over 6 months and the other reporting pain over 1 week. There is insufficient evidence from these trials to determine whether or not there is any difference between conventional (stabilised) and superelastic NiTi initial arch wires with regard to either alignment or pain.(3) Single-strand superelastic NiTi initial arch wires compared to other NiTi (coaxial, copper NiTi (CuNiTi) or thermoelastic) initial arch wires. The three trials in this comparison each compared a different product against single-strand superelastic NiTi. There is very weak unreliable evidence, based on one very small study (n = 24) at high risk of bias, that coaxial superelastic NiTi may produce greater tooth movement over 12 weeks, but no information on associated pain or root resorption. This result should be interpreted with caution until further research evidence is available. There is insufficient evidence to determine whether or not there is a difference between either thermoelastic or CuNiTi and superelastic NiTi initial arch wires.

AUTHORS' CONCLUSIONS

There is no reliable evidence from the trials included in this review that any specific initial arch wire material is better or worse than another with regard to speed of alignment or pain. There is no evidence at all about the effect of initial arch wire materials on the important adverse effect of root resorption. Further well-designed and conducted, adequately-powered, RCTs are required to determine whether the performance of initial arch wire materials as demonstrated in the laboratory, makes a clinically important difference to the alignment of teeth in the initial stage of orthodontic treatment in patients.

Calorimetric and thermomechanical properties of titanium-based orthodontic wires: DSC-DMA relationship to predict the elastic modulus

Orthodontic treatment is strongly dependent on the loads developed by metal wires, and the choice of an orthodontic archwire should be based on its mechanical performance. The desire of both orthodontists and engineers would be to predict the mechanical behavior of archwires. To this aim, Gum Metal (Toyota Central R&L Labs., Inc.), TMA (ORMCO), 35°C Copper NiTi (SDS ORMCO), Thermalloy Plus (Rocky Mountain), Nitinol SE (3M Unitek), and NiTi (SDS ORMCO) were tested according to dynamic mechanical analysis and differential scanning calorimetry. A model was also developed to predict the elastic modulus of superelastic wires. Results from experimental tests have highlighted that superelastic wires are very sensitive to temperature variations occurring in the oral environment, while the proposed model seems to be reliable to predict the Young's modulus allowing to correlate calorimetric and mechanical data. Furthermore, Gum Metal wire behaves as an elastic material with a very low Young's modulus, and it can be particularly useful for the initial stage of orthodontic treatments.

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 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.