Mechanical properties of orthodontic wires in tension, bending, and torsion

Comparisons of Two Different Treatment Methods for Impacted Maxillary Canines: A Retrospective Study

Background: The impaction of the maxillary canine is a common occurrence, and orthodontists must be prepared to manage it. The purpose of this article is to present a study of the efficacy of a double-wire orthodontic appliance compared to a control group in the alignment of impacted maxillary canines in the dental arch. Methods: To diagnose an impacted maxillary canine, a panoramic radiograph was taken and a detailed analysis was performed by the same orthodontist. This article presents the results of 28 impacted maxillary canines with inclusion criteria of A2 (tooth angulation to the midline 16°-45°), V1 (vertical height of the tooth crown above the cementoenamel junction but less than half the length of the root of the maxillary lateral incisor), and O3 (medial position of the canine crown of more than half but less than the entire root width of the lateral incisor) positions in 21 patients (7 males and 14 females) with a mean age of 14.02 years (SD = 1.61) who were treated by the same orthodontist for impacted maxillary canines using a fixed double-wire orthodontic appliance. The analyzed data were compared with the control group (treated with a fixed orthodontic appliance and active ligature), which was matched for pretreatment age and the A2, V1, and O3 positions of the impacted maxillary canine. Results: With both methods, the impacted maxillary canines were aligned and guided into a correct position in the dental arch, but the mean active orthodontic traction of 31 ± 4.2 weeks in the SG was statistically significantly shorter (p < 0.05) in comparison to 37 ± 6.3 weeks in the CG, and the number of visits was statistically significantly (p < 0.05) fewer in the SG (5 ± 2) than in the CG (11 ± 5). Conclusions: The findings of this study are important to the field of orthodontics and show that the alignment of impacted maxillary canines with A2, V1, and O3 positions can be achieved with both methods, but with the double-wire appliance, the treatment time was shorter and the number of visits was statistically significantly fewer. The results of this study suggest that this approach may be more efficient and cost-effective compared to conventional methods.

Evaluation of Surface Changes of Stainless Steel Miniplates and Screws Following Retrieval from Maxillofacial Trauma and Orthognathic Surgery Patients: A Comparative Study

Background

This study examines the surface changes of stainless steel miniplates and screws after their retrieval from patients who underwent maxillofacial trauma and orthognathic surgery. The assessment focuses on comparing the alterations in these materials, aiming to contribute to our understanding of their durability and performance in clinical settings.

Materials and Methods

A total of 60 stainless steel miniplates and screws were collected from 30 patients who had previously undergone either maxillofacial trauma or orthognathic surgery. The retrieved miniplates and screws were carefully removed from the patients and cleaned to remove any organic debris. Each specimen was then examined for surface changes. Surface changes were evaluated using visual inspection, scanning electron microscopy (SEM), and roughness measurements. Visual inspection provided a qualitative assessment, while SEM allowed for a more detailed examination of the surfaces. Roughness measurements were conducted using a profilometer.

Results

Visual inspection revealed varying degrees of surface changes in the retrieved miniplates and screws. These changes included scratches, corrosion, and discoloration. SEM analysis confirmed the presence of surface alterations, with some specimens showing more significant damage, such as pitting and cracks. Roughness measurements indicated an increase in surface roughness for both miniplates and screws, suggesting that the surfaces had become less smooth.

Conclusion

This comparative study of stainless steel miniplates and screws retrieved from maxillofacial trauma and orthognathic surgery patients demonstrated that these materials undergo surface changes over time.

Recent Advances in Orthodontic Archwires: A Review

Orthodontic archwires are the primary aid to achieve desirable tooth movement. These wires are also considered to be the backbone of orthodontic treatment. Orthodontic archwires are available in various materials. The journey of advancement of these wires has shown immense growth in aesthetics as well as the mechanical properties of the materials used to ultimately provide patient satisfaction. This review highlights the properties of orthodontic archwires and the disadvantages associated with these wires which limit their use in today's era. The major role of the clinician is to choose the most appropriate alloy as per the needs of the patient. This can be done by accurately analyzing the properties of every material. The introduction of robotic systems in bending archwires and the properties of newer materials like organic polymer wires and bactericide archwires have also been described in this review. Thus, this review article focuses on the recent advances in orthodontic archwires and their properties for selection as per need.

Development of a tooth movement model of root resorption during intrusive orthodontic treatment

There is a high risk of external apical root resorption (EARR) following the application of intrusive orthodontic forces to the apical root. However, there is a lack of suitable animal models to study this phenomenon in depth. This study compared the usability of three different types of loops, namely, vertical helical loop, box loop, and L loop, for preparing a rat model of orthodontic tooth movement with invasive forces. Results showed a significant downward movement in the first molar of the rat after L loop placement for 14 days. Three-dimensional reconstructed images showed root resorption and length shortening on the apical root and decreased bone volume and trabecular thickness in the alveolar bone under compression. Histological staining revealed odontoclasts on the root resorption fossa. This study showed that orthodontic tooth movement using the L loop provides an effective experimental animal model of EARR.

Effect of Real-Time Environment on Mechanical Properties of Preformed Stainless Steel Archwires: An In Vivo Study

Introduction

Clinicians should be aware of any effect the oral environment may have on archwires. Laboratory models fail to closely imitate intraoral conditions. The aim was to evaluate the change in mechanical properties of preformed stainless steel archwires after 15 weeks of exposure to the oral environment.

Methods

Three commercially manufactured 0.019 × 0.025″ stainless steel archwires were evaluated. Young's modulus, yield strength, spring factor, and hardness were studied. The unexposed distal end cuts (control samples) and archwires were tested after 15 weeks of intraoral exposure (test samples). Tension tests, Vickers microhardness tests, and nanoindentation tests were carried out.

Results

Normality was tested using the Shapiro-Wilk test. Statistical analyses included the paired t-test for intragroup comparisons and Kruskal-Wallis ANOVA with the post hoc Dunn test for comparison of mean percentage reduction in values. At T15, Young's modulus showed a statistically significant decrease. Changes in yield strength and spring factor were not significant for groups other than American Orthodontics wires. The reduction in hardness was significant in 3M Unitek. Vickers, tension, and nanoindentation tests demonstrated an expansive range between hardness and Young's modulus so determined.

Conclusion

3M Unitek archwires showed the highest difference in Young's modulus. Yield strength values increased in Ortho Organizers archwires. Spring factor decreased only in 3M Unitek archwires. Hardness values obtained from various tests did not produce identical results.

Investigation of the effects of orthodontic brackets coated by silver hydroxyapatite, copper oxide, and titanium oxide nanoparticles on wire-bracket friction

Objectives:

Coating orthodontic brackets with metal nanoparticles seem to affect surface roughness and friction. We aim to compare the effects of coating brackets with copper oxide (CuO), titanium dioxide (TiO2), and silver hydroxyapatite (S-HAP) on friction between brackets and various sizes and materials of orthodontic wires.

Material and Methods:

In this experimental study, we selected four groups of stainless steel (SS) brackets with eight orthodontic wires (SS and nickel-titanium [Niti]) in different sizes. Three groups were coated with CuO, TiO2, and S-HAP nanoparticles using dip coating. Then, we attached a 100 g weight to the wires and hung it from the universal testing machine. The wire passed through the brackets at a speed of 0.5 mm/min for 25 s. Finally, the friction between wires and brackets was compared using a two-way analysis of variance.

Results:

The results showed that friction of brackets coated with TiO2 was significantly lower than S-HAP (P = 0.021) and did not differ significantly between CuO and the control (P = 1). Furthermore, friction between CuO brackets was not significantly different from other groups (P > 0.05). Niti round wires had significantly lower friction with all brackets compared to 0.16 × 0.22 square inch Niti wire (p< 0.05), which, in turn, showed significantly lower friction compared to 0.16 × 0.22 square inch stainless steel (SS) wire (P = 0.008).

Conclusion:

Coating brackets with TiO2 and CuO nanoparticles can reduce the friction Moreover, Niti round wires show the least friction compared to rectangular or SS wires with all types of brackets.

Nitinol Type Alloys General Characteristics and Applications in Endodontics

A very extensive literature review presents the possibilities and needs of using, in endodontics, the alloys commonly known as nitinol. Nitinol, as the most modern group of engineering materials used to develop root canals, is equilibrium nickel and titanium alloys in terms of the elements’ atomic concentration, or very similar. The main audience of this paper is engineers, tool designers and manufacturers, PhD students, and students of materials and manufacturing engineering but this article can also certainly be used by dentists. The paper aims to present a full material science characterization of the structure and properties of nitinol alloys and to discuss all structural phenomena that determine the performance properties of these alloys, including those applied to manufacture the endodontic tools. The paper presents the selection of these alloys’ chemical composition and processing conditions and their importance in the endodontic treatment of teeth. The results of laboratory studies on the analysis of changes during the sterilization of endodontic instruments made of nitinol alloys are also included. The summary of all the literature analyses is an SWOT analysis of strengths, weaknesses, opportunities, and threats, and is a forecast of the development strategy of this material in a specific application such as endodontics.

What Are the Chances of Resilon to Dominate the Market Filling Materials for Endodontics?

This paper is a literature review with additional virtual analyses of the authors’ own experimental research results. Knowledge from various areas was synergistically combined, appropriately for concurrent engineering, presenting several possible methodological approaches used in research, optimizing the selection of engineering materials and the conditions of their application with particular application in endodontics. Particular attention was paid to the theoretical aspects of filling material strengths, weaknesses, opportunities, and threats SWOT analysis. Attention was paid to the original concepts of Sustainable Dentistry Development in conjunction with Dentistry 4.0, which includes endodontics as an important element. The dentists’ actions, among others, in conservative dentistry, along with endodontics, requires close cooperation with engineers and the enginering sciences. Methods of root canal preparation were described, together with selected tools, including those made of nitinol. Principles concerning the process of cleaning and shaping the pulp complex are presented. The importance of obturation methods, including the Thermo-Hydraulic-Condensation THC technique, and the selection of filling materials with the necessary sealants for the success of endodontic treatment are discussed. The experimental studies were carried out in vitro on human teeth removed for medical reasons, except for caries, for which two groups of 16 teeth were separated. After the root canal was prepared, it was filled with studs and pellets of a filling material based on polyester materials, which has gained the common trade name of resilon or, less frequently, RealSeal (SybronEndo) with an epiphany sealant. The teeth for the first group were obturated by cold lateral condensation. In the second case the obturation was performed using the Thermo-Hydraulic-Condensation technique using System B and Obtura III. The experimental leakage testing was done using a scanning electron microscope SEM and a light stereoscopic microscope LSM, as typical research tools used in materialography. The research results, in a confrontation with the data taken from the literature studies, do not indicate the domination of resilon in endodontics.

Changes in the mechanical properties of two nickel-titanium archwires after 3 months of clinical usage

BACKGROUND

Nickel-titanium archwires have unique mechanical properties that make them the archwire of choice during the first phase of orthodontic treatment. However, during its clinical use when subjected to oral conditions, these properties can undergo great changes.

MATERIALS AND METHODS

A sample of 24 randomly chosen superelastic NiTi orthodontic archwires (12 TE and 12 PSE) with a 0.014-inch round section from the same manufacturer were distributed into four groups of six archwires each. The first two groups were new wires (as-received), which were used as controls (T0), and the other two were collected after 3 months of clinical usage (as-retrieved) in orthodontic patients (T1). Mechanical properties were measured by mechanical tensile testing and three-point bending tests under the same experimental and temperature conditions (36°C) in a universal testing machine. Comparisons between the groups at T0 and T1 were performed with t-tests and Mann-Whitney U tests. A paired t-test and Wilcoxon signed rank sum test were used for intragroup comparisons (T1-T0).

RESULTS

At baseline, PSE wires presented significantly (P < 0.05) higher load at fracture, range, ultimate tensile strength (UTS), yield strength, springback, maximum tension and flexural ultimate strength (FUS) than those of TE wires. At T1, a significant decrease in load at fracture and UTS in PSE wires and in FUS in TE wires was found. After 3 months of clinical usage, the changes (T1-T0) in the mechanical properties of both alloys were similar.

CONCLUSIONS

After 3 months of clinical usage, wires lost some of their mechanical properties and had less resistance to breakage. However, the as-received differences between both wires were maintained after clinical usage.

Comparative Evaluation of Dimensional Accuracy, Surface Characteristics, and Load Deflection Attributes of 0.019" × 0.025" Stainless Steel Wires Sourced from Six Different Commercial Houses: An In Vitro Study

Aims & Objectives:

The aim of the study was to evaluate and compare dimensional accuracy, surface characteristics and load deflection attributes of SS wires sourced from six different commercial houses.

Materials & Methods:

0.019” x 0.025” SS wire samples were divided into 6 groups and evaluated and compared for the aforementioned properties. Dimensional accuracy, surface roughness, frictional resistance, load deflection rate and ultimate tensile strength were evaluated and compared.

Results:

Dimensional accuracy did not vary significantly. Surface Profilometry proved 3M Unitek (Group 1) to be the wire with least irregularities. According to SEM, Modern Orthodontics (Group 6) and 3M Unitek (Group 1) in terms of ‘Sa’ and ‘Sq’ respectively had the smoothest surface finish. SS wires sourced from G&H Orthodontics (Group 2) exhibited least frictional resistance. Load deflection rates varied for all the groups for all three parameters under the study. UTS was best for SS wires sourced from Rabbit Force Orthodontics (Group 5).

Conclusion:

No wire from a single commercial house excels in all the parameters that were evaluated, each one having its aces and minuses.

Comparative Evaluation of the Force and Load Deflection Rate for Different Loop Springs with Varying Designs, Wire Dimensions, and Materials: A Finite Element Method Study

Objective: To evaluate and compare the force and load deflection rate generated by differing unit displacement through 1 to 4 mm of springs that vary in design (Double Delta Closing Loop, Double Vertical T Crossed Closing Loop, Double Vertical Helical Closing Loop and Ricketts Maxillary Retractor), constituting wire materials (stainless steel and beta titanium), and wire dimensions (0.017" × 0.025" and 0.019" × 0.025").

Materials and methods: Computer-assisted design (CAD) model of the said loop springs was created and converted to the finite element method (FEM). The boundary conditions assigned were restraining anterior segment of the loops in all the 3 axes and displacement of the posterior segment progressively only along the x-axis in increments of 1, 2, 3, and 4 mm. Force and load deflection rate were calculated for each incremental displacement.

Results: For all loop designs, force and load deflection rate increased with incremental displacement. Loop springs of beta titanium and 0.017" × 0.025" dimension showed lesser force and load deflection rate than those of stainless steel and 0.019" × 0.025", respectively. Ricketts Maxillary Retractor showed the least force and load deflection rate. Comparable force and load deflection values were found for 0.017" × 0.025" Double Vertical T Crossed Loop and 0.019" × 0.025" Double Vertical Helical Closing Loop.

Conclusions: Variations in wire dimensions, materials, and designs have a profound effect on force and load deflection rate of the different loop springs studied.

Comparison of spring characteristics of titanium-molybdenum alloy and stainless steel

Background

Titanium-molybdenum alloy (TMA) and stainless steel (SS) wires are commonly used in orthodontics as arch-wires for tooth movement. However, plastic deformation phenomenon in these arch-wires seems to be a major concern among orthodontists. This study aimed to compare the mechanical properties of TMA and SS wires with different dimensions.

Material and Methods

Seventy-two wire samples (36 TMA and 36 SS) of three different sizes (19×25, 17×25 and 16×22) were analyzed in vitro, with 12 samples in each group. Various mechanical properties of the wires, including spring-back, bending moment and stiffness were determined using a universal testing machine. Student’s t-test showed statistically significant differences in the mean values of all the groups. In addition, metallographic comparison of SS and TMA wires was conducted under an optical microscope.

Results

The degree of stiffness of 16×22-sized SS and TMA springs was found to be 12±2 and 5±0.4, respectively, while the bending moment was estimated to be 1927±352 (gm-mm) and 932±16 (gm-mm), respectively; the spring-back index was determined to be 0.61±0.2 and 0.4±.09, respectively (p<0.001). There were no statistically significant differences in spring-back index in larger dimensions of the wires.

Conclusions

Systematic analysis indicated that springs made of TMA were superior compared to those made of SS. Although both from economic and functionality viewpoints the use of TMA is suggested, further clinical investigations are recommended.

Key words:Bending moment, optical microscope, spring-back, stainless steel, stiffness, titanium‒molybdenum alloy.

Comparative Evaluation of Frictional Properties, Load Deflection Rate and Surface Characteristics of Different Coloured TMA Archwires - An Invitro Study

INTRODUCTION

During tooth movement the success of sliding mechanics is dependent upon various factors which include frictional resistance at bracket-archwire interface, surface roughness of archwire materials and elastic properties of archwires. Ion implantation techniques reduce the frictional force and allow better tooth movement clinically.

AIM

The main objective of this study was to evaluate and compare the frictional properties, load deflection rate and surface characteristics of Honey dew and Purple coloured (Ion implanted) TMA wires with uncoated TMA wires.

MATERIALS AND METHODS

Fifteen archwire samples were divided into three groups comprising of five samples in each group namely, Group I - Uncoated TMA wires (Control), Group II - Purple coloured TMA wires and Group III- Honey dew TMA wires. Friction and load deflection rate testing were performed with the Instron Universal testing machine and the surface characteristics of the wires were evaluated before and after sliding using Scanning Electron Microscope.

RESULTS

The mean frictional characteristics and surface roughness for Honey dew TMA wires was lesser than Purple coloured TMA wires which was statistically significant. Both the coloured TMA wires showed low frictional characteristics and less surface roughness than uncoated TMA wires (the control). The mean load deflection rate was low for both coloured ion implanted TMA wires when compared to uncoated TMA wires which was statistically significant.

CONCLUSION

Coloured ion implanted TMA wires, especially Honey dew TMA wires have low friction, low load deflection rate and improved surface finish. Hence they can be used in frictionless as well as sliding mechanics, where uncoated TMA wires are inefficient.

Effect of electrical spot welding on load deflection rate of orthodontic wires

Background:

One of the methods used for joining metals together is welding, which can be carried out using different techniques such as electric spot welding. This study evaluated the effect of electric spot welding on the load deflection rate of stainless steel and chromium-cobalt orthodontic wires.

Materials and Methods:

In this experimental-laboratory study, load deflection rate of 0.016 × 0.022 inch stainless steel and chromium cobalt wires were evaluated in five groups (n =18): group one: Stainless steel wires, group two: chromium-cobalt wires, group three: stainless steel wires welded to stainless steel wires, group four: Stainless steel wires welded to chromium-cobalt wires, group five: chromium-cobalt wire welded to chromium-cobalt wires. Afterward, the forces induced by the samples in 0.5 mm, 1 mm, 1.5 mm deflection were measured using a universal testing machine. Then mean force measured for each group was compared with other groups. The data were analyzed using repeated measure analysis of variance (ANOVA), one-way ANOVA, and paired t-test by the SPSS software. The significance level was set as 0.05.

Results:

The Tukey test showed that there were significant differences between the load deflection rates of welded groups compared to control ones (P < 0.001).

Conclusion:

Considering the limitation of this study, the electric spot welding process performed on stainless steel and chromium-cobalt wires increased their load deflection rates.

Mechanical properties of orthodontic wires made of super engineering plastic

Most orthodontic equipment is fabricated from alloys such as stainless steel, Co-Cr and Ni-Ti because of their excellent elastic properties. In recent years, increasing esthetic demands, metal allergy and interference of metals with magnetic resonance imaging have driven the development of non-metallic orthodontic materials. In this study, we assessed the feasibility of using three super engineering plastics (PEEK, PES and PVDF) as orthodontic wires. PES and PVDF demonstrated excellent esthetics, although PEEK showed the highest bending strength and creep resistance. PEEK and PVDF showed quite low water absorption. Because of recent developments in coloration of PEEK, we conclude that PEEK has many advantageous properties that make it a suitable candidate for use as an esthetic metal-free orthodontic wire.

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.

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 the orthodontic load systems created with elastomeric power chain to close extraction spaces on different rectangular archwires

INTRODUCTION

The 3-dimensional load system (forces and moments) was quantified at the canine bracket during space closure with sliding mechanics with elastomeric chain on dry and wet stainless steel and beta-titanium 0.019 × 0.025-in archwires.

METHODS

A custom-made maxillary dentoform simulating first premolar extractions was attached to an orthodontic force tester. The canine was attached to a load cell through an adaptor with silicone simulating the periodontal ligament. The orthodontic force tester simultaneously measured the entire load system produced at the canine bracket by an elastomeric chain. The effects of archwire material, time (activation and 1 hour), and lubrication were analyzed by using 3-way repeated measures analysis of variance (ANOVA, α = 0.05).

RESULTS

Stainless steel provided a greater (P = 0.001) load system than did beta-titanium. The force was greatest on the canine in the lingual axis. The greatest moment was about the y-axis. The moment-to-force ratio, the most critical ratio, was greater for beta-titanium than stainless steel; however, both were close to the ideal 10:1.

CONCLUSIONS

With a stainless steel archwire for retraction sliding mechanics, a canine will experience a greater load system in all 3 dimensions than with a beta-titanium wire. Both archwires produced a moment-to-force ratio adequate for translation.

Efficiency, behavior, and clinical properties of superelastic NiTi versus multistranded stainless steel wires: a prospective clinical trial

OBJECTIVE

To investigate efficiency, behavior, and properties of superelastic NiTi vs multistranded stainless steel wires in Begg and preadjusted edgewise appliance (PEA) under moderate to severe crowding conditions.

MATERIAL AND METHODS

Ninety-six participants (48 male, 48 female), aged 12-18 years old (mean age  =  15.2 ± 1.95), with moderate (≤ 6 mm; mean  =  5.3 ± 0.48) to severe (> 6 mm; mean  =  7.9 ± 0.66) initial crowding were distributed into four groups: superelastic NiTi PEA (n  =  24), superelastic NiTi Begg (n  =  24), multistranded (coaxial) stainless steel PEA (n  =  25), and multistranded (coaxial) stainless steel Begg (n = 23). In this study, 0.16-inch superelastic (austenitic active) NiTi and 0.175-inch multistranded (six stranded, coaxial) stainless steel wires were used in a 0.022-inch slot (Roth prescription) PEA and Begg appliance with a follow-up of six weeks.

RESULTS

Analysis of variance revealed no significant difference in reduction of crowding between superelastic NiTi PEA and multistranded (coaxial) stainless steel PEA groups, but reduction in crowding was significantly greater in the superelastic NiTi Begg group compared with the multistranded (coaxial) stainless steel Begg group with F (3, 44)  =  8.896, P < .001, and effect size (ω) 0.57 in moderate crowding and F (3, 44)  =  122.341, P < .001, and effect size (ω) 0.93 in severe crowding. Linear regression demonstrated significant (P < .05) positive correlation between amount of initial crowding and reduction in crowding in all groups except the multistranded (coaxial) stainless steel Begg group, wherein a negative correlation did exist.

CONCLUSION

Superelastic NiTi performed significantly better than multistranded (coaxial) stainless steel wire in the Begg appliance. However, in PEA, there was no significant difference.

Um novo fio de aço inoxidável para aplicações ortodônticas

OBJETIVO: desenvolver uma metodologia para fabricação de fios ortodônticos de aço inoxidável austeno-ferrítico SEW 410 Nr. 14517 por meio dos processos convencionais de laminação e trefilação. MÉTODOS: o aço austeno-ferrítico foi elaborado em um forno elétrico de indução. A qualidade dos fios foi avaliada por ensaios de tração e medidas de microdureza. A ductilidade e a manuseabilidade foram analisadas por meio da confecção de componentes ortodônticos. RESULTADOS E CONCLUSÕES: os valores encontrados mostraram que os fios de aço inoxidável austeno-ferrítico atenderam às normas BS 3507:1976 e ISO 5832-1, e apresentaram ótima ductilidade para confecção de componentes ortodônticos com dobras complexas.

Wire load-deflection characteristics relative to different types of brackets

OBJECTIVE

To test the hypothesis that the dimension of the bracket, both in labial and in lingual orthodontics, is a relevant parameter to determine the forces acting on the teeth, and that some wires commonly used in labial orthodontics (0.016"-diameter SS, TMA and Nitinol) are not suitable for the first phase of lingual treatment.

MATERIALS AND METHODS

An ideal dental cast was bonded with eight different brackets (Damon 3MX, Ovation, Time 2, Innovation and Smart Clip Clarity on the vestibular face; STB, Adenta Time and Innovation-L on the lingual). After photographic documentation, the interbracket distance was calculated for each type of bracket, using ImageJ software. The mean elasticity modulus of the tested wires was obtained from the review of the available literature. The theoretical wire load on every tooth was calculated mathematically at three different levels of deflection (0.5mm; 1.0mm and 1.5mm), on both the labial and lingual sides, for all types of bracket.

RESULTS

The lingual arch in the anterior segment is always shorter than the vestibular arch. The different brackets, having different dimensions, have an influence on the interbracket distance, and, consequently, on the wire load. At large deflections, superelastic NiTi expresses light and continuous forces, which are significantly lower than the other examined alloys.

CONCLUSION

The initial hypothesis was supported. Because of the reduced interbracket distance, the adoption of superelastic wires is required in lingual mechanics and with smaller diameter compared to labial mechanotherapy, in particular during the first phases of treatment. The use of a bracket with reduced mesiodistal dimensions can contribute to reduce the load on the teeth.

Clinical variability in arch wires: a preliminary study evaluating mechanical and surface characteristics of two different sized rectangular stainless steel wires

Experimental characterization of arch wires has been performed in many previous studies; however with the advent of new arch wire materials being introduced, some new experimental methods and characterization are required. Since literature is available for comparison, this paper examines mechanical and physical characteristics of steel arch wires to quantify their variability in engineering terms. Furthermore, the effect of wire size on properties was evaluated using two of the most common wire sizes. Finally, manufacturing consistency was verified by testing samples from different lots.

Root Resorption on Torqued Human Premolars Shown by Tartrate-Resistant Acid Phosphatase Histochemistry and Transmission Electron Microscopy

Objective: To identify clastic cells on the root surfaces of torqued human premolars.

Materials and Methods: A continuous force of 600 cNmm was applied to upper first premolars in patients 13–16 years of age by using a precise biomechanical model with superelastic wires (NiTi-SE). The 28 teeth in 14 patients were divided into five groups (control [nonmoved], and moved for either 1, 2, 3, or 4 weeks) and processed for tartrate-resistant acid phosphatase (TRAP) histochemistry and transmission electron microscopy.

Results: Mononuclear TRAP-positive cells appeared at 2 weeks, wheras large multinucleated TRAP-positive cells were numerous at 3 and 4 weeks. Ultrastructural examination revealed many clastic cells in contact with resorption lacunae. In addition, some cementoblast-like cells appeared secreting new cementum over previously resorbed lacunae.

Conclusions: In general, resorption lacunae and the number of clastic cells, which increased with the duration of the applied force, were found on the cementum surface at the pressure areas. Some signs of cementum repair were also noticed, even with the maintenance of the level of the force.

In-vitro evaluation of the material characteristics of stainless steel and beta-titanium orthodontic wires

INTRODUCTION

The exact composition and material properties of the metal alloys used in orthodontics are usually not identified by or even available from manufacturers. This makes meaningful comparisons between wires impossible and is unacceptable with regard to biocompatibility issues. The aim of this study was to investigate the material characteristics of contemporary stainless steel (SS) and beta-titanium (beta-Ti) wires, also known as titanium-molybdenum alloy (TMA), for comparison.

METHODS

Twenty-two different SS and beta-Ti wires, preferably straight wires sized 0.43 x 0.64 mm, (0.017 x 0.025 in) were tested blindly for wire dimensions, chemical compositions, bending and tensile properties, and surface characteristics.

RESULTS

Four chemical compositions were found for the beta-Ti wires: titanium-11.5, molybdenum-6, zirconium-4.5 tin; titanium-3, aluminum-8, vanadium-6, chromium-4, molybdenum-4, zirconium; titanium-6, aluminum-4, vanadium, and titanium-45 niobium. The SS wires were of AISI type 304 or the nickel-free variant BioDur 108. All beta-Ti wires showed high surface roughness values. TMA 02 significantly had the highest E-modulus, TMA 02 and TMA 11 had the highest 0.2% yield strength, TMA 02 had the highest hardness, and TMA 12 was the most ductile wire of the beta-Ti wires. All SS wires showed high 0.2% yield strength, SS 10 significantly had the lowest E-modulus and was the most ductile wire, and SS 08 significantly showed the lowest hardness values of all SS wires.

CONCLUSIONS

Significant differences were found between SS and beta-Ti wires, but there was little or no difference between the mechanical and physical characteristics tested in each subgroup. However, the morphological analysis clearly demonstrated that the finishing phase (annealing, polishing) of the wires' production process lacks the quality one would expect with regard to good mechanical properties and biocompatibility issues. Accurate specifications are urgently needed concerning the quality of orthodontic wires on the market.

Morphological characterization and in vitro biocompatibility of a porous nickel–titanium alloy

Disks consisting of macroporous nickel-titanium alloy (NiTi, Nitinol, Actipore) are used as implants in clinical surgery, e.g. for fixation of spinal dysfunctions. The morphological properties were studied by scanning electron microscopy (SEM) and by synchrotron radiation-based microtomography (SRmuCT). The composition was studied by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and energy-dispersive X-ray spectroscopy (EDX). The mechanical properties were studied with temperature-dependent dynamical mechanical analysis (DMA). Studies on the biocompatibility were performed by co-incubation of porous NiTi samples with isolated peripheral blood leukocyte fractions (polymorphonuclear neutrophil granulocytes, PMN; peripheral blood mononuclear leukocytes, PBMC) in comparison with control cultures without NiTi samples. The cell adherence to the NiTi surface was analyzed by fluorescence microscopy and scanning electron microscopy. The activation of adherent leukocytes was analyzed by measurement of the released cytokines using enzyme-linked immunosorbent assay (ELISA). The cytokine response of PMN (analyzed by the release of IL-1ra and IL-8) was not significantly different between cell cultures with or without NiTi. There was a significant increase in the release of IL-1ra (p<0.001), IL-6 (p<0.05), and IL-8 (p<0.05) from PBMC in the presence of NiTi samples. In contrast, the release of TNF-alpha by PBMC was not significantly elevated in the presence of NiTi. IL-2 was released from PBMC only in the range of the lower detection limit in all cell cultures. The material, clearly macroporous with an interconnecting porosity, consists of NiTi (martensite; monoclinic, and austenite; cubic) with small impurities of NiTi2 and possibly NiC(x). The material is not superelastic upon manual compression and shows a good biocompatibility.

Pseudoelasticity and thermoelasticity of nickel-titanium alloys: a clinically oriented review. Part II: Deactivation forces

The purpose of this review was to organize a systematic reference to help orthodontists evaluate commonly used orthodontic nickel-titanium alloys. Part I of the article reviewed the data available in the literature regarding the temperature transitional ranges of the alloys. The thermomechanical behavior of these compounds is, in fact, strictly dependent upon the correlation between the temperature transitional range and the oral temperature range. Part II focuses on the mechanical characteristics of the alloys, such as the magnitude of the forces delivered and correlations with the temperature transitional range and oral temperature.

Pseudoelasticity and thermoelasticity of nickel-titanium alloys: a clinically oriented review. Part I: Temperature transitional ranges

The purpose of this review was to organize a systematic reference to help orthodontists evaluate commonly used orthodontic nickel-titanium alloys. Part I of the article reviews the data available in the literature regarding the temperature transitional ranges of the alloys. The thermomechanical behavior of these compounds is, in fact, strictly dependent on the correlation between the temperature transitional range and the oral temperature range. Part II of the article will focus on the mechanical characteristics of the alloys, such as the magnitude of the forces delivered and its correlations with temperature transitional range and oral temperature.

Resistance to sliding of orthodontic appliances in the dry and wet states: influence of archwire alloy, interbracket distance, and bracket engagement

Having established dimensional and mechanical characteristics, the resistances to sliding (RS) were measured in vitro for various archwires against stainless steel brackets. Using stainless steel ligatures, a constant normal force (300g) was maintained while second-order angulation (straight theta) was varied from -12 degrees to +12 degrees. Using miniature bearings to simulate contiguous teeth, five experiments each were run in the dry or wet states with human saliva at 34 degrees C as a function of four archwire alloys, five interbracket distances, and two bracket engagements. Outcomes were objectively analyzed to establish when theta=0, and the relative contact angles ( theta(r)) were replotted. Critical contact angles (theta(c)) that were determined via experimentation were in good agreement with theory. Slopes and y-intercepts were tabulated from linear regression equations of RS against theta plots in both the passive (theta < or = theta (c)) and active ( theta > or = theta(c)) configurations, for which theta = theta(c) identified the boundary between classical friction and binding phenomena. Stiffer archwires and shorter interbracket distances exacerbated binding, whereas, once corrected for differing bracket engagement, RS was independent of slot dimension. Unlike earlier results in the passive configuration, in the active configuration couples comprised of titanium alloys (NiTi and (beta-Ti) had higher RS values in the wet versus the dry state. For those archwire alloys evaluated, two empirical expressions were adduced that comprise the binding component, the yield strength or elastic limit, and the beam length, which implicitly represent the stiffness, flexibility, and interbracket distance.

An overview of nickel-titanium alloys used in dentistry

The nickel-titanium alloy Nitinol has been used in the manufacture of endodontic instruments in recent years. Nitinol alloys have greater strength and a lower modulus of elasticity compared with stainless steel alloys. The super-elastic behaviour of Nitinol wires means that on unloading they return to their original shape following deformation. These properties are of interest in endodontology as they allow construction of root canal instruments that utilize these favourable characteristics to provide an advantage when preparing curved canals. This review aims to provide an overview of Nitinol alloys used in dentistry in order for its unique characteristics to be appreciated.

On mechanical properties of square and rectangular stainless steel wires tested in torsion

Forty different sizes and types of square and rectangular stainless steel wires, supplied by five different manufacturers, were tested in torsion. The study simulated the situation occurring when torque is applied to an individual tooth. We used standard brackets with 0.018-inch slot heights, with an interbracket distance of 4 mm. The results show that variation in cross-sectional dimension and edge bevel leads to variable torsional play (third-order clearance). As an example 0.016 x 0.022-inch wires have a mean torsional play of as much as 18.5 degrees, with a range of 16.6 degrees to 20.4 degrees. We have shown that when 0.016 x 0.022-inch wires are used, one must apply from 24.6 degrees to 29.2 degrees of twist to get 20 Nmm of torsional moment. This variation is mostly due to a rather wide range in torsional play. As a result, the prediction by which a predetermined torsional moment can be delivered becomes uncertain. The results show that because the working range in torsion of stainless steel wires is somewhat limited, precise delivery of torsional moment, based on the condition present in the oral cavity, is difficult. Torsional stiffness varies considerable within the various dimensional groups, this being the result of variation in cross-sectional geometry and material properties.

Elastic responses to longitudinal torsion of single-strand, rectangular, orthodontic archwire segments

OBJECTIVES

This study was undertaken to characterize elastic responses of orthodontic archwire segments in longitudinal torsion, to compare experimental results with predictions from structural engineering theory, and to examine the potential interaction between flexural and torsional responses of archwires.

METHODS

Passively straight and deflected rectangular wire segments were activated in torsion to states beyond their elastic limits. The wire parameters that were controlled included: the alloy, the cross-sectional size, and the gauge length. The research design included 48 cells and 240 separate tests. From torque-twist plots, values of elastic stiffness, elastic range, and unit elastic range were obtained. Raw experimental data were subjected to analyses of variance and means to a Tukey's post-hoc test. Mean stiffness and elastic range outcomes were compared with theoretical values.

RESULTS

Most plots were generally characteristic of Hookean materials. All three wire parameters significantly influenced the three dependent variables; few statistical interactions emerged. Theoretical stiffness values were reasonably comparable to those obtained experimentally; however, the elastic range predictions were conservative. Torsion theory predicts unit elastic ranges independent of gauge length; the experimental data displayed a nonlinear relationship. The minor influences of flexural deformations on the responses of wire segments activated in torsion are suggested as clinically inconsequential.

SIGNIFICANCE

Few clinically relevant, controlled studies of archwire torsion have been published. A modified or new formula is needed to predict elastic range magnitudes of archwires in torsion. When flexure and torsion exist in an archwire, it may be possible to separate them to determine overall structural response.

Effects of clinical recycling on mechanical properties of nickel-titanium alloy wires

The purpose of this investigation was to determine the effects of clinical recycling on the load-deflection characteristics and the surface topography of nickel-titanium alloy wires. Thirty wires each of Nitinol and NiTi were subjected to a three-point bending test in an as-received condition (T0) and after clinical exposure of one cycle (T1) and two cycles (T2). Ten wires made up the sample at each of these time points. One cycle was defined as 8 weeks, plus or minus 1 week, of clinical use. Wires undergoing two recycles were cold sterilized after their first clinical exposure. Statistical analyses were done by one-factor repeated measures ANOVA and Scheffe F test. Recycling produced significant changes in both the loading and unloading characteristics of NiTi wires, but only with the loading forces associated with nitinol wires. Representative scanning electron micrographs demonstrated increased pitting of both nitinol and NiTi wires. Several areas were also observed to be smoothened on nitinol wires and scored on NiTi wires.

Bending properties of superelastic and nonsuperelastic nickel-titanium orthodontic wires

Cantilever bending properties were evaluated for several clinically popular sizes of three superelastic and three nonsuperelastic brands of nickel-titanium orthodontic wires in the as-received condition, and for 0.016-inch diameter wires after heat treatment at 500 degrees and at 600 degrees C, for 10 minutes and for 2 hours. A torque meter apparatus was used for the bending experiments, and the specimen test-span length was 1/4 inch (6 mm). In general, the bending properties were similar for the three brands of superelastic wires and for the three brands of nonsuperelastic wires. For the three brands of superelastic wires, heat treatment at 500 degrees C for 10 minutes had minimal effect on the bending plots, whereas heat treatment at 500 degrees C for 2 hours caused decreases in the average superelastic bending moment during deactivation; heat treatment at 600 degrees C resulted in loss of superelasticity. The bending properties for the three brands of nonsuperelastic wires were only slightly affected by these heat treatments. The differences in the bending properties and heat treatment responses are attributed to the relative proportions of the austenitic and martensitic forms of nickel-titanium alloy (NiTi) in the microstructures of the wire alloys.

Torsional properties of implant grade titanium

The purpose of this research was to evaluate the torsional strength and ductility of CP titanium in the as received condition, heat treated below the alpha----beta transition temperature, and glass bead blasted. Results were compared to as-received samples of implant quality 316L stainless steel. Little or no effect of any of the treatments was noted. The torsional strength of all titanium samples was comparable to 316L stainless and the torsional ductility of the titanium was significantly greater than 316L stainless (p less than .01). These results are significantly different than those obtained when torsion testing bone screws of the same material. A hypothesis is proposed for the differences in these results.

[Materials science studies on the soldering of different orthodontic wires]

In orthodontic technique both soldering and welding are standard methods for the application of auxiliaries and for the modification of force systems by joining wires of different cross-sections. Two cobalt-chromium alloys (Blue Elgiloy, Crozat) and an austenitic stainless steel alloy (Remanium) were soldered by an electrochemically generated hydrogen-oxygen flame forming an overlapped joint design. For characterization of the soldered joint testing procedures included microhardness tests, metallographic examination, tension-shear tests and surface analysis of the fractured joints by scanning electron microscopy. For any given soldering technique with an overlapped joint design the correct joint length is determined by the ratio t/s = 3 (t = overlapped length; s = diameter of the smaller wire).

Mechanical properties and clinical applications of orthodontic wires

This review article describes the mechanical properties and clinical applications of stainless steel, cobalt-chromium, nickel-titanium, beta-titanium, and multistranded wires. The consolidation of this literature will provide the clinician with the basic working knowledge on orthodontic wire characteristics and usage. Mechanical properties of these wires are generally assessed by tensile, bending, and torsional tests. Although wire characteristics determined by these tests do not necessarily reflect the behavior of the wires under clinical conditions, they provide a basis for comparison of these wires. The characteristics desirable in an orthodontic wire are a large springback, low stiffness, good formability, high stored energy, biocompatibility and environmental stability, low surface friction, and the capability to be welded or soldered to auxiliaries. Stainless steel wires have remained popular since their introduction to orthodontics because of their formability, biocompatibility and environmental stability, stiffness, resilience, and low cost. Cobalt-chromium (Co-Cr) wires can be manipulated in a softened state and then subjected to heat treatment. Heat treatment of Co-Cr wires results in a wire with properties similar to those of stainless steel. Nitinol wires have a good springback and low stiffness. This alloy, however, has poor formability and joinability. Beta-titanium wires provide a combination of adequate springback, average stiffness, good formability, and can be welded to auxiliaries. Multistranded wires have a high springback and low stiffness when compared with solid stainless steel wires. Optimal use of these orthodontic wires can be made by carefully selecting the appropriate wire type and size to meet the demands of a particular clinical situation.

Relative wire stiffness due to lingual versus labial interbracket distance

Orthodontic treatment of patients with lingual appliances necessitates modifications of the conventional mechanotherapy used with labial appliances. When the brackets are placed on the lingual instead of the labial surface, the interbracket distances in the anterior region of the arches are decreased significantly. The purpose of this study was to determine by how much these interbracket distances are decreased, and to quantitate what effect this has on relative wire stiffness. Lingual and labial brackets were placed on models of 30 orthodontically treated patients and a ratio comparing the lingual to labial interbracket distances was calculated to be 1:1.47. Twenty-five orthodontic wires at lengths of 1 inch and 1.47 inches were then evaluated for their stiffness in first-, second-, and third-order bending. The results showed that the decreased interbracket distance associated with lingual appliances makes a wire seem approximately 3 times as stiff as when used with labial appliances for first- and second-order bends, and approximately 1 1/2 times as stiff for third-order bends. Wire equivalence charts were developed to help orthodontists make direct comparisons between labial and lingual arch wires in regard to stiffness. These charts should prove useful to the clinician during initial alignment and final detailing when adequate arch wire flexibility is essential.

Comparative range of orthodontic wires

ADA specification No. 32 for determining the range (elastic limit) of orthodontic wires uses the bending of a wire section treated as a cantilever beam. An alternative method for defining the range of orthodontic wires proposed by Waters (1981) is to wrap wire sections around mandrels of varying diameters and measure the deformation imparted after unwrapping. Four brass mandrels with a total of 46 test diameters ranging from 3.5 to 60.0 mm were used in this study. Wire sections 9 cm in length were rolled on the mandrel with a hand lathe. The mandrel cross section required to produce a predetermined amount of deformation (2 mm arc height for a 5 cm chord) was defined as the yield diameter for that particular wire. No individual wire was tested twice so as to avoid introduction of strain history. Test samples of 488 different orthodontic wires supplied by nine commercial distributors were evaluated (a total of 4,747 samples). Stainless steel wires of identical dimensions had a large variation in range, depending on the state of strain hardening and heat treatment. For example, 0.020 inch round wire had yield diameters ranging from 22.8 mm for Australian special plus orange (TP Laboratories) to 42.9 mm for Nubryte gold (G.A.C. International). Chromium cobalt wires had less range than stainless steel before heat treatment, but increased greatly in range after heat treatment. Nitinol (Unitek) had the greatest range of all wires tested (yield diameter of 8.7 mm for 0.016 inch Nitinol). Multistranded stainless steel wires had yield diameters between 9.0 and 14.0 mm.

Comparison of bending and tension tests for orthodontic wires

Stainless steel, cobalt-chromium-nickel (Elgiloy), nitinol, and beta titanium wires with diameters from 0.010 to 0.040 inch and in rectangular sizes from 0.017 X 0.025 to 0.019 X 0.025 inch were evaluated with the American Dental Association specification no. 32 bending test and the conventional tension test. The modulus of elasticity (E) and yield strength (YS) obtained with the two mechanical testing procedures are reported for as-received wires and after heat treatment at 900 degrees F for the stainless steel and selected Elgiloy wires. Measured values of E and YS in bending were almost invariably higher than the corresponding values obtained in tension. The only general agreement between the modulus of elasticity in bending and tension was for the 0.040-inch diameter stainless steel wires. Anomalously high values of E in bending were also found for most of the heat-treated stainless steel and Elgiloy groups. Difficulties with the bending test are attributed to loading effects at both ends of the test span and deviation of the bent specimen from a circular arc. Improved procedures are described for performing the tension test on the relatively small cross-section orthodontic wires.