INTRODUCTION

In the initial phase of orthodontic treatment, focusing on tasks such as crowding correction, minor tooth adjustments, alignment, and leveling, clinicians seek wires that apply light and continuous forces efficiently, minimizing treatment duration and potential damage to supporting structures.[1] Nickel titanium (NiTi) wires, particularly those with a low modulus of elasticity, have revolutionized orthodontics since their introduction. Initially described by Andreasen and Hilleman and further developed by Burstone and Miura.[2] NiTi archwires offer various advantages owing to their unique crystalline forms: Martensitic (M) and austenitic (A). These wires can be engineered to exhibit superelasticity, a property reliant on the coexistence of these phases, enabling them to absorb deflection stresses and exert consistent forces over a wide range of deflections, particularly beneficial in aligning archwires.[3] NiTi wires can be classified based on their crystal structure, phase transformation, and stiffness into stabilized martensitic, superelastic active austenitic, thermodynamic-active martensitic, and graded thermodynamic categories, each offering distinct force characteristics. Notably, thermodynamically active martensitic NiTi alloys, such as those incorporating copper, exhibit preset transition temperature ranges, allowing for controlled force application.[4] Copper NiTi (CuNiTi) archwires, for instance, improved shape memory, reduced hysteresis, and enhanced thermal stability, promoting faster tooth movement with lower activation loads and diminished discomfort for patients. Despite manufacturers’ claims and theoretical advantages, studies reveal discrepancies in aligning efficiency and root resorption among NiTi alloys, prompting the need for comprehensive investigations.[5,6] External apical root resorption (EARR), a concern in orthodontics, necessitates accurate diagnostic tools like cone-beam computed tomography (CBCT) to assess three-dimensional changes in root surfaces. While continuous forces applied during initial alignment facilitate tooth movement, they may also exacerbate EARR, highlighting the importance of understanding how different NiTi alloys impact this phenomenon. Therefore, this study aims to evaluate and compare EARR levels associated with stabilized nitinol (high force), superelastic active austenitic NiTi (medium force), and thermodynamic-active martensitic NiTi (low force) using CBCT, filling a crucial gap in understanding the interplay between different NiTi alloy characteristics and EARR outcomes in orthodontic therapy.

MATERIAL AND METHODS Study design

The study is a prospective, single-centered randomized clinical trial designed as a double-blinded and parallel groups with non-stratified permuted block randomization with an allocation ratio (1:1). No changes were made in methodology after trial commencement.

Participants, eligibility criteria

This study was approved by the institutional ethical committee and was conducted between 2021 and 2023 to evaluate root resorption in orthodontic treatment using different types of NiTi alloy arch wires. This trial was registered at ClinicalTrials.gov with the identifier number CTRI/2021/05/033728. Informed consent was obtained from all participants before the initiation of treatment.

Participants were selected based on specific inclusion and exclusion criteria. Inclusion criteria included patients seeking fixed appliance orthodontic treatment with moderate crowding in the mandibular arch, requiring extraction of mandibular first premolars, and having complete lower permanent dentition, excluding third molars. Exclusion criteria included previous orthodontic treatment, <6 mm of lower incisor crowding or spaced incisors, blocked-out teeth, periodontal issues, systemic conditions, continuous medication, traumatic injuries, and dental restorations.

Sample size

Sample size was determined using G*POWER3.1.9.2 software, with 66 subjects needed for 80% power at a 5% alpha level. All the participants were equally divided into three groups: Group I received CuNiTi 35°C (ORMCO, South Lone Hill, Glendora), Group II received Superelastic (3M UNITEK, Monrovia, USA), and Group III received Nitinol Classic (3M UNITEK, Monrovia, USA) with MBT Prescription-0.022 slot Mini 2000 (ORMCO, Southlone Hill, Glendora) brackets.

Randomization

Sequence generation: A computer random number generator (http://www.graphpad.com/quickcalcs/randomn2.cfm) was used to develop a simple non-stratified randomization with an equal allocation ratio (1:1). Each number in the resultant random table was given a study number by an independent person to develop the Allocation Table, which included the study number and allocation group for the participants. The Allocation Table was the only document that could unmask the groups, so it was kept sealed away from the investigators until the completion of data measurement and analysis.

After recruiting patients who met the inclusion criteria, the participants were randomly allocated using the permuted random block technique with a 1:1:1 allocation ratio by a third person who is not associated with the research. The allocation sequence was concealed from the researcher by sequentially numbered, opaque, sealed, and stapled envelopes before the intervention. All the trial documents were labelled with the study ID number, which was used for participant identification and data collection without unmasking the allocation group. This allowed the investigator to complete data collection and measurements blindly. The outcome assessor, participants, and the statistician were blinded; however, the operator could not be blinded to the allocation groups because the clinicians could know the type of archwires from their flexibility.

Intervention

The study utilized the straight wire technique with MBT Prescription-0.022 slot brackets, and subjects were reviewed at 4-week intervals and the average sequence of wires will be as follows: 0.012-inch, 0.014- inch, 0.018-inch, 0.016 inch × 0.022-inch, 0.017 inch × 0.025-inch, and 0.019-inch × 0.025-inch NiTi wires on a 0.022-inch slot in each group. CBCT images of 6 mandibular anterior teeth were taken before and after orthodontic alignment to analyze the root length and root volume. The images were examined using Xoran 3.1.62 software. To assess alignment efficiency, mandibular impressions were taken and study models were prepared at the beginning of fixed orthodontic treatment and thereafter every month till the completion of alignment.

Primary outcome methodology Evaluation of root length

To analyze EARR using CBCT in mandibular anterior teeth, the linear length between the root apex and cementoenamel junction (CEJ) was measured by a single examiner. The maximum linear length between CEJ and root apex was measured using axial multiplanar reconstruction at a 0.25-mm isometric voxel, which is based on an axial-guided navigation technique.[7] The axial movement of the cursor on sagittal or coronal multiplanar reconstruction defined the reference points [Figures 1-3].

Figure 1: Reference points Cemento enamel junction(CEJ) to Root apex (yellow colour arrows) to measure linear length (red line) (a) Reference points to measure linear length (CEJ to Root apex) on central incisor; (b) Reference points to measure linear length (CEJ to Root apex) on lateral incisor; (c) Reference points to measure linear length (CEJ to Root apex) on canine.

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Figure 2: Axial multiplanar reconstruction with identification of cementoenamel junction (CEJ) as a reference point. (a) Coronal (b) sagittal (c) multiplanar reconstruction identifies CEJ at the intersection of the axial cursor with coronal and sagittal cursors.

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Figure 3: Axial multiplanar reconstruction with identification of root apex as reference points. (a) Coronal (b) sagittal (c) multiplanar reconstruction identifies the root apex at the intersection of axial cursor with coronal and sagittal cursors.

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The distance between the reference points was marked in the sagittal or coronal multiplanar reconstruction, providing measurements in millimeters [Figure 4]. EARR was measured before and after levelling and alignment, and data were recorded using Microsoft Office ExcelTM 2007.

Figure 4: Tracing with CBCT software measuring tool on (a and b) sagittal and (c and d) coronal.

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Evaluation of root volume

Digital Imaging and Communications in Medicine datasets were imported into ITK-Snap software (version 3.2, http://www.itksnap.org) to generate stereolithographic (STL) data [Figure 5]. The radiographer assigned a number to each STL image; the primary investigator (P.P.) was blinded to the codes. The corresponding STL images for T0 and T1 were imported into Geomagic (Geomagic, Cary, N.C.).

Figure 5: Three-dimensional segmentation of the lower anterior teeth.

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The reference plane was constructed between the highest point of the labial and palatal CEJ. T0 to T1 STL images were segmented immediately below the reference plane, and the root portion was analyzed.[8] Root volumes were computed using Geomagic software [Figure 6].

Figure 6: Three-dimensional segmentation of individual root at the reference plane and root volume was measured.

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Secondary outcome methodology Alignment efficiency

The alignment efficiency is measured by the time taken for the completion of the preliminary clinical levelling phase of treatment, which is usually a passive engagement of a rectangular 19 × 25 NiTi wire in the slots of the attachments from the molar to the contralateral molar. The incisal edges of the anterior teeth and the buccal cusps of posterior teeth are at the same horizontal level, and the teeth are lined up in an arch form by the completion of the Alignment phase of mechanotherapy.

RESULTS Statistical analysis

Data were analyzed using IBM Statistical Package for the Social Sciences (SPSS) version 20 software (IBM SPSS, IBM Corp., Armonk, NY, USA). Descriptive statistics, Kolmogorov–Smirnov tests for assessing the normality of study data, one-way analysis of variance, Chi-square test, Wilcoxon signed-rank tests, Kruskal–Wallis analysis of variance, and Friedman’s tests were performed. Bar charts were used for data visualization. Non-parametric tests were primarily used, except for the variables age, time span for alignment, and Little’s irregularity index, which followed a normal distribution based on the Kolmogorov–Smirnov test (P ≤ 0.05). P ≤ 0.05 was considered statistically significant [Table 1].

Table 1: Basic characteristics of the three groups.

CuNiTi Superelastic NiTi Nitinol P-value Gender: Male/Female in no. 10/12 10/12 10/12 1.00 Age in Years: Mean (SD) 16.0364 (1.02982) 16.1227 (1.06589) 16.1227 (1.06589) 0.952 Little’s irregularity index Mean (SD) 6.977 (0.6055) 6.891 (0.5264) 7.000 (0.5944) 0.804 Participant flow

A total of 66 patients were invited to participate in the study, with 22 participants each in the CuNiTi group, superelastic NiTi group, and nitinol group. The participant flow is depicted in the consolidated standards of reporting trials (CONSORT) flowchart [Figure 7].

Figure 7: Consort flowchart of participants through each stage of the trial. CuNiTi: Copper nickel-titanium, NiTi: Nickel-titanium.

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Baseline data

Kolmogorov–Smirnov tests confirmed that the data were normally distributed (P > 0.05). It presents the baseline descriptive statistics of the root lengths and volumes at the start of the study (T0) for the three groups.

Primary outcome measures Changes in root length

Descriptive statistics for changes in root length between time points T0 and T1 are summarized in [Table 2]. All three groups showed a reduction in root length over time, with the nitinol group demonstrating the highest mean reduction in root length across all teeth. For example, the mean reduction in root length for tooth 43 was highest in the nitinol group (0.709 mm), compared to 0.504 mm in the superelastic NiTi group and 0.372 mm in the CuNiTi group.

Table 2: Comparison of tooth-wise and average root lengths between the 2 time points in CuNiTi, superelastic NiTi, and nitinol group.

Tooth/Average Time CuNiTi Superelastic NiTi Nitinol Mean Standard deviation P-value Mean Standard deviation P-value Mean Standard deviation P-value 43 T0 13.632 0.4612 0.038* 13.536 0.5287 0.005* 13.505 0.4981 0.002* T1 13.259 0.5188 13.032 0.5550 12.668 0.6312 42 T0 12.591 0.4196 0.083 12.591 0.4185 0.02* 12.945 0.2988 <0.001* T1 12.423 0.3250 12.118 0.5261 12.241 0.4228 41 T0 11.932 0.7761 0.085 11.882 0.6645 0.034* 12.227 0.8119 0.012* T1 11.677 0.7400 11.345 0.7321 11.727 0.7778 31 T0 11.714 0.4279 0.008* 11.795 0.3199 <0.001* 11.773 0.2931 <0.001* T1 11.500 0.3854 11.264 0.2441 11.323 0.2092 32 T0 12.377 0.4566 0.034* 12.350 0.5405 0.003* 12.300 0.4821 0.003* T1 12.159 0.4827 11.786 0.5609 11.745 0.6108 33 T0 13.764 1.2211 0.239 13.309 0.9133 0.034* 13.714 0.4074 <0.001* T1 13.445 1.2015 12.727 0.9468 13.005 0.3124 Average T0 12.6673 0.33884 0.013* 12.5782 0.28455 <0.001* 12.7436 0.18009 <0.001* T1 12.4114 0.32193 12.0445 0.35219 12.1186 0.13145 Changes in root volume

Root volume changes from T0 to T1 are detailed in [Table 3]. Similar to root length, the nitinol group showed the greatest reductions in root volume across most teeth, with tooth 41 exhibiting a mean reduction of 59.05 mm3, compared to 40.91 mm3 in the superelastic NiTi group and 39.09 mm3 in the CuNiTi group.

Table 3: Comparison of toothwise and average root volume between the 2 time points in CuNiTi, Superelastic NiTi, and nitinol group.

Tooth Time CuNiTi Superelastic NiTi Nitinol Mean Standard deviation P-value Mean Standard deviation P-value Mean Standard deviation P-value 43 T0 481.86 10.311 <0.001* 477.68 13.674 <0.001* 467.41 17.306 <0.001* T1 446.05 5.085 431.45 15.420 414.27 15.545 42 T0 435.73 26.350 <0.001* 408.05 47.409 0.054 451.32 18.339 <0.001* T1 409.36 22.214 376.45 55.252 407.50 15.826 41 T0 371.45 50.759 0.013* 355.41 42.432 0.002* 374.05 15.610 <0.001* T1 332.36 60.450 314.50 50.488 315.00 50.386 31 T0 375.36 15.598 <0.001* 361.64 11.358 <0.001* 374.77 12.444 <0.001* T1 350.86 14.717 331.14 15.914 342.00 11.002 32 T0 408.05 43.702 0.009* 368.64 25.231 <0.001* 373.45 5.894 <0.001* T1 380.00 40.780 334.95 21.140 329.77 6.294 33 T0 453.18 36.542 0.016* 420.86 41.881 0.034* 470.23 20.894 <0.001* T1 419.59 36.388 387.23 45.350 407.73 41.880 Average T0 420.9395 8.76745 <0.001* 398.7114 17.25982 <0.001* 418.5395 6.42481 <0.001* T1 389.7041 9.04710 362.6205 19.24404 369.3800 7.45151 Tooth-wise comparisons

Tooth-wise mean differences in root length and root volume across the three groups are presented in [Tables 4 and 5]. The Kruskal–Wallis test showed significant differences between groups for both root length and volume (P < 0.05). Post hoc analysis revealed that the nitinol group experienced significantly greater reductions in both parameters compared to the CuNiTi and superelastic NiTi groups.

Table 4: Inter-group comparison of toothwise mean differences in root lengths from T0 to T1.

Tooth Group n Mean Standard deviation Standard error Mean rank P-value 43 CuNiTi 22 0.372727 0.1162174 0.0247776 15.91 <0.001* SE NiTi 22 0.504545 0.1214095 0.0258846 30.00 Nitinol 22 0.836364 0.1940679 0.0413754 54.59 42 CuNiTi 22 0.168182 0.1286796 0.0274346 12.95 <0.001* SE NiTi 22 0.472727 0.1386390 0.0295579 35.00 Nitinol 22 0.704545 0.1495303 0.0318800 52.55 41 CuNiTi 22 0.254545 0.1654065 0.0352648 16.45 <0.001* SE NiTi 22 0.536364 0.1648822 0.0351530 42.95 Nitinol 22 0.500000 0.0925820 0.0197386 41.09 31 CuNiTi 22 0.213636 0.2053927 0.0437899 20.57 <0.001* SE NiTi 22 0.531818 0.2476295 0.0527948 41.57 Nitinol 22 0.450000 0.2087377 0.0445030 38.36 32 CuNiTi 22 0.218182 0.2084783 0.0444477 17.36 <0.001* SE NiTi 22 0.563636 0.0492366 0.0104973 39.59 Nitinol 22 0.554545 0.2132007 0.0454545 43.55 33 CuNiTi 22 0.318182 0.0852803 0.0181818 12.77 <0.001* SE NiTi 22 0.581818 0.0732664 0.0156204 38.14 Nitinol 22 0.709091 0.1715728 0.0365794 49.59

Table 5: Intergroup comparison of toothwise mean differences in root volumes from T0 to T1.

Tooth Group n Mean Standard deviation Standard error Mean rank P-value 43 CuNiTi 22 35.82 11.379 2.426 21.20 <0.001* SE NiTi 22 46.23 9.375 1.999 33.39 Nitinol 22 53.14 3.091 0.659 45.91 42 CuNiTi 22 26.36 8.732 1.862 14.64 <0.001* SE NiTi 22 31.59 24.071 5.132 35.18 Nitinol 22 43.82 8.633 1.841 50.68 41 CuNiTi 22 39.09 14.145 3.016 29.50 0.047* SE NiTi 22 40.91 13.925 2.969 29.27 Nitinol 22 59.05 38.424 8.192 41.73 31 CuNiTi 22 24.50 5.738 1.223 24.77 0.024* SE NiTi 22 30.50 9.733 2.075 35.73 Nitinol 22 32.77 10.000 2.132 40.00 32 CuNiTi 22 28.05 12.423 2.649 20.86 <0.001* SE NiTi 22 33.68 11.378 2.426 31.77 Nitinol 22 43.68 2.169 0.462 47.86 33 CuNiTi 22 33.59 16.279 3.471 26.86 <0.001* SE NiTi 22 33.64 8.307 1.771 24.23 Nitinol 22 62.50 37.261 7.944 49.41 Secondary outcome

The time span for alignment was significantly different between the groups, with the highest time in the nitinol group, followed by the superelastic NiTi group and the CuNiTi group [Table 6].

Table 6: Comparison of time span (in days) between the study groups.

Group n Mean Standard deviation Standard error 95% CI lower bound 95% CI upper bound F-value P-value CuNiTi 22 105.50 7.190 1.533 102.31 108.69 15.42 <0.001* Superelastic NiTi 22 112.14 7.803 1.664 108.68 115.60 Nitinol 22 118.23 7.801 1.663 114.77 121.69 DISCUSSION

This study was designed to determine whether there are any clinical differences between nitinol, superelastic NiTi, and CuNiTi archwires in terms of root resorption and alignment efficiency. The results showed a statistically significant difference between the three types of NiTi arch wires.

Superelastic NiTi archwires need to be bent by 50–70° to effectively harness their super-elastic properties. This level of deformation is achievable in clinical settings due to the degree of crowding and reduced interbracket distances found in lower anterior crowding cases. The main difference between superelastic and thermal wires is in the force levels. Thermally active wires produce significantly lower working forces than superelastic wires of the same size.[9,10]In vitro studies[11] prefer thermal wires to superelastic wires during the alignment phase because of their lower working forces and ability to express the particular characteristic of superelasticity at lower deflection levels. Moreover, these wires permit so-called “full-bracket engagement” at the start of treatment and in subjects with severe dental crowding, decreasing the risk of generating excessive forces.

In the present study, the end of the leveling phase was chosen as the time point for the evaluation of the effect of the three different arch wire materials, owing to the possibility of using only one type of arch wire material before the continuation of treatment that would require both types of arch wires. In addition, the amount of root shortening 6–12 months after bracket placement is of high predictive value for the severity of root resorption after the completion of treatment.[12] Mandibular incisors were selected for the study because they are more prone to tooth resorption, while a small reduction in their length is easy to detect using radiographic techniques.

The results of the present study reflected an overall reduction in root length and root volume in the three groups after levelling and alignment. CuNiTi showed the least root resorption, followed by superelastic NiTi and Nitinol.

The results of the current study were consistent with those of Nabbat and Yassir[13] and Alzahawi et al.[14] who found that lower incisors appeared to be significantly affected by root resorption in the group treated with super-elastic NiTi wires. Jain et al.[5] observed higher root resorption in super-elastic NiTi wires (0.59 mm) than in heat-activated NiTi (0.50 mm); however, the difference was not statistically significant. This may be related to the continuous force exerted by the super-elastic NiTi wires. Whereas, intermittent forces could produce less root resorption because the period of inactive tooth movement provides the chance for the resorbed cementum to heal. Weiland[15] stated that the perimeter, area, and volume of resorption lacunae were significantly larger (140%) when the teeth were moved with superelasticity than when they were moved with steel wires. The continuous force of 0.8-1 N used for tipping tooth movement is more detrimental than an initially higher but rapidly dissipating force. This finding underscores the importance of continuous radiographic follow-up during orthodontic treatment to monitor root resorption evaluating root resorption, especially when using superelastic NiTi and nitinol wires. The results also highlight the efficiency of thermally active CuNiTi wires in producing significantly lower working forces, which could be optimal in preserving the integrity of periodontal structures, thus minimizing root resorption during the levelling phase of mechanotherapy.

An orthodontic force can be defined as heavy or light according to the ratio between the magnitude of the force applied and the affected root–bone surface. Because of the surface area of the periodontal structure involved, an ideal archwire should be able to deliver differential forces to the arch segments.

The results of this study reflected a statistically significant reduction in the average root length of the six mandibular anterior teeth at the post-alignment time point with nitinol, superelastic, and CuNiTi. A similar observation was reflected in the average root volume between the 2 time points in the three groups. The amount of resorption observed in our study with superelastic NiTi wires (0.53 mm) is close to the values reported by Jain et al. (0.59 mm).[5] However, the root resorption observed in our study with CuNiTi (0.25 mm) was significantly lower than that reported by Jain et al. (0.50 mm).[5] This difference could be due to variations in the manufacturer and batch differences. It has been established that wires of similar types from different manufacturers do not necessarily possess similar properties because these manufacturing conditions are not consistent. Furthermore, it is established that notable differences exist from production lot to production lot of wires from the same manufacturer.[16]

Alzahawi et al.[14] reported significantly higher values than the root resorption values in the current study, which could be due to overestimation usually observed with periapical radiographs. The greater reduction in root length and volume observed in canines compared to central and lateral incisors may be attributed to the increased load at the apical area during distal tipping and uprighting movements. These findings highlight the importance of considering differential forces across the dental arch to optimize outcomes and minimize adverse effects during orthodontic treatment.

While the current study provided valuable insights, prior studies evaluating the efficacy of initial aligning archwires often faced limitations such as variations in bracket schemes, ligation techniques, extraction methods, and observation periods. To address these gaps, this study standardized these variables, ensuring a robust evaluation of the three types of NiTi wires.

In terms of alignment efficiency, CuNiTi wires outperformed superelastic NiTi and nitinol wires, requiring the shortest time to achieve alignment. This finding is consistent with the study by de Castro Serafim et al.[17] who also reported superior alignment with CuNiTi wires. The ability of CuNiTi wires to express their superelastic properties fully, even with smaller deflections, likely contributed to their efficiency in achieving alignment. This contrasts with findings by Abdelrahman et al.[2] and Pandis et al.,[18] where no significant differences in alignment efficiency were noted among different NiTi wires. These differences may stem from variations in study designs, including wire dimensions, irregularity indices, and observation periods. The authors in their study were not conclusive about the amount of irregularity, and the observation period was expanded to 6 weeks until the initial alignment was completed with a 0.014-inch arch wire. The authors reasoned that large deflections in the wire were required to express the super-elastic property, which was not fully expressed in their study.

Pandis et al.[18] reached a similar conclusion by comparing the efficiencies of CuNiTi and NiTi archwires. He reported that severe crowding (>5 mm on the irregularity index) showed a significantly higher probability of duration of crowding alleviation relative to dental arches with a score of <5 (138.5 vs. 113.1 days). The values reported in the current study were CuNiTi versus superelastic NiTi versus nitinol (105, 112, and 118 days). Pandis et al.[18] confined a 0.16 dimension wire during the entire period of 6 months observation, while the current study employed full dimensions rectangular wires in the three groups, achieving complete slot engagement, greater deflection, and higher superelasticity, resulting in increased alignment efficiency. The results of the present study are consistent with a clinical trial by phermsang-ngarm[19] who reported that heat-activated NiTi wires required less alignment time than super-elastic NiTi wires. However, studies by Nabbat and Yassir[13] Azizi et al.[20] Atik et al.[21] Aydin et al.[12] found that both superelastic NiTi and CuNiTi were equally effective in the aligning stage of orthodontic treatment. The abovementioned studies had limitations that could hinder the complete expression of the properties of the respective NiTi wires, such as an irregularity index that requires non-extraction orthodontic treatment, smaller-dimension round wires, and a limited span of observation spanning around 6–12 weeks.

CONCLUSION

The following are the salient conclusions from the present study.

Root resorption of mandibular incisors after levelling was statistically different between the three groups of NiTi wires

Root resorption was minimal with CuNiTi and maximum with conventional nitinol wires

CuNiTi exhibited superior alignment efficiency over superelastic NiTi and conventional nitinol wires.

Clinical implications

This study supports the hypothesis that adding copper to NiTi wires reduces loading stress while maintaining high unloading stress, minimizing orthodontically induced inflammatory root resorption, and improving tooth movement efficiency. The lower deactivation forces and rapid tooth movement provided by CuNiTi allow for early engagement of thicker and rectangular wires, offering better torque and rotational control from the beginning of treatment.

In low-friction mechanics, thermal wires are preferable during the alignment phase due to their lower working forces and ability to express superelastic properties at lower deflections. They enable full-bracket engagement at treatment onset, reducing excessive force risks in cases of severe crowding. Their ability to produce consistent low forces over extended activation ranges minimizes the need for frequent reactivation.

In conventional straight-wire mechanics, superelastic NiTi wires are more suitable, as thermal wires may struggle to overcome ligature friction. Superelastic NiTi is ideal for moderate crowding or when arch form and torque control are required early in treatment. However, in cases of severe crowding or periodontal concerns, rectangular CuNiTi (35°C and 40°C) is recommended due to its controlled force delivery and superior torque control.

While statistically significant differences in alignment efficiency were observed among the three wire types, their clinical significance may be less pronounced, particularly given the higher cost of CuNiTi, which is twice that of superelastic NiTi.