Comparison of the transformation temperatures of heat-activated Nickel-Titanium orthodontic archwires by two different techniques

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.

Additively manufactured metallic biomaterials

Metal additive manufacturing (AM) has led to an evolution in the design and fabrication of hard tissue substitutes, enabling personalized implants to address each patient's specific needs. In addition, internal pore architectures integrated within additively manufactured scaffolds, have provided an opportunity to further develop and engineer functional implants for better tissue integration, and long-term durability. In this review, the latest advances in different aspects of the design and manufacturing of additively manufactured metallic biomaterials are highlighted. After introducing metal AM processes, biocompatible metals adapted for integration with AM machines are presented. Then, we elaborate on the tools and approaches undertaken for the design of porous scaffold with engineered internal architecture including, topology optimization techniques, as well as unit cell patterns based on lattice networks, and triply periodic minimal surface. Here, the new possibilities brought by the functionally gradient porous structures to meet the conflicting scaffold design requirements are thoroughly discussed. Subsequently, the design constraints and physical characteristics of the additively manufactured constructs are reviewed in terms of input parameters such as design features and AM processing parameters. We assess the proposed applications of additively manufactured implants for regeneration of different tissue types and the efforts made towards their clinical translation. Finally, we conclude the review with the emerging directions and perspectives for further development of AM in the medical industry.

Application of an arched, Ni-Ti shape-memory connector in repairing distal tibiofibular syndesmosis ligament injury

Objective

To investigate the clinical effect of internal fixation of a Ni–Ti arched shape-memory connector in the treatment of distal tibiofibular syndesmosis ligament injury.

Methods

From January 2013 to January 2016, 108 cases of ankle fracture with distal tibiofibular syndesmosis ligament injury in our hospital were selected, and all of them were fixed with ASCs or screw fixation. The functional evaluation and efficacy evaluation were performed according to the Olerud Molander Ankle Score (Omas) and SF-36. At the same time, follow-ups recorded the incidence of postoperative complications: osteoarthritis, superficial infection, symptomatic hard and soft tissue irritation, early removal and poor reduction of internal fixation, and later loss of reduction.

Results

In the ASC(Ni–Ti Arched shape-memory Connector) group, the incidence of symptomatic hardware, soft tissue or superficial infection decreased to 2.77%(from 13.8% or 11.1% in SCREW group). The early removal rate(2.77%) of internal fixation was also lower than that of the screw group. While the incidence of osteoarthritis is 13.8% in SCREW group, the incidence of osteoarthritis in the later follow-up was also as low as 1.38% in ASC group. Loss of fracture reduction due to removal of the fixation device for the distal tibiofibular syndesmosis ligament was not observed in the ASC group. With two postoperative scoring systems (OMAS and SF-36), patients in the ASC group significantly get higher score than that in SCREW group.

Conclusion

The design of the Ni–Ti arched shape-memory connector can be adapted to the irregular anatomical structure of the malleolus and the ability to continue to contract by body temperature. The use of ASCs in fixation of articular ligaments can preserve a slight range of motion, and the results suggest that ASCs can effectively reduce the incidence of fixation looseness, fracture, infection and other complications.

Application of a Ni-Ti arched shape-memory connector in unstable lateral malleolus fractures: A retrospective study

PURPOSE

To compare the outcomes of the arched shape-memory connector (ASC) only fixation and the lateral one-third tubular plate fixation in managing unstable Type A or B lateral malleolus fractures according to the Weber (AO) classification, and to evaluate the feasibility and reliability of ASC only fixation in treating these fractures.

METHODS

From January 2010 to January 2015, 148 patients with Type A or B (Weber (AO) classification) lateral malleolus fractures treated with the arched shape-memory connector (ASC) only fixation or lateral plate fixation were included. There were 66 patients in the ASC only fixation group and 82 patients in the lateral plate group. Intergroup differences were absent regarding patient and fracture characteristics. The incision length, complete-union time, major complications and complaints, incidence of hardware removal, and final radiographic and functional evaluations were compared.

RESULTS

The follow-up time averaged 18.2 months in the ASC fixation group and 17.2 months in the lateral plate group. The ASC only fixation group had significantly decreased wound infection (4.55% versus 14.63%) and skin necrosis (none versus 7.32%). Of patients who underwent ASC only fixation 3.03% reported lateral ankle pain, 7.58% received palpable hardware, and 3.03% reported hardware irritation, while the corresponding observations in the lateral plate group were 19.51%, 54.88%, and 14.63%, respectively, representing a statistical difference. Furthermore, compared with the lateral plate group, the incidence of hardware removal was markedly lower in the ASC fixation group (12.12% versus 30.49%). In terms of reduction accuracy, complete-union time, and AOFAS scores, no appreciable differences were observed.

CONCLUSIONS

ASC only fixation is a reliable alternative for managing Type A or B lateral malleolus fractures, leading to fewer soft tissue complications, fewer hardware complaints, and a reduced need for hardware removal, and a reduced need for hardware removal. In addition, ASC can be used for augmented plate fixation in certain comminuted fracture patterns.

Thermo-Mechanical Properties of Glass Fiber Reinforced Shape Memory Polyurethane for Orthodontic Application

OBJECTIVES

Glass fiber reinforced shape memory polyurethane (GFRSMPU) has great potential to be an alternative kind of material for orthodontic archwires for overcoming the disadvantages of metal wires in terms of esthetic and allergy and deficiency of pure shape memory polyurethane (SMPU) wires in mechanical properties. The objective of this study was to investigate the thermo-mechanical properties and shape recovery functions of GFRSMPU and evaluate the feasibility of using this composite for orthodontic archwires.

MATERIAL AND METHODS

GFRSMPU were made from short cut glass fibers and SMPU by mixing extrusion. Scanning electron microscope (SEM) and differential scanning calorimetry (DSC) were performed to investigate the distribution of glass fibers in the mixture and glass transition temperature (T_g). Then the thermo-mechanical properties, including tensile modulus, flexural modulus and stress relaxation effects, were measured. Furthermore, shape recovery functions of GFRSMPU characterized by the shape recovery ratio and force were investigated through shape recovery tests, typodont models and finite element analysis (FEA).

RESULTS

SEM images indicated that an excellent dispersity of glass fibers was obtained after double-extrusion. DSC experiments showed T_g was not enormously affected with the existence of glass fibers, but the mechanical properties of GFRSMPU were greatly improved. Shape recovery tests showed reduction of shape recovery ratio of the GFRSMPU material with the addition of glass fibers, but dentition aligning time was reduced by 50% in the simulation performed on identical typodont models with GFRSMPU archwires filled with 30 wt.% glass fibers. The FEA results illustrated that the reacting forces of GFRSMPU archwires with 30 wt.% glass fiber was increased by 96.36% compared with pure SMPU archwires.

CONCLUSIONS

The mechanical properties of GFRSMPU can be considerably improved by adding glass fibers, and the shape memory function would be well preserved too. Enhanced SMPU owns a good application prospect in orthodontics for dentation aligning on the preliminary stage, as well as other medical fields.

Resistance to sliding in orthodontics: misconception or method error? A systematic review and a proposal of a test protocol

Resistance to sliding (RS) between the bracket, wire, and ligature has been largely debated in orthodontics. Despite the extensive number of published studies, the lack of discussion of the methods used has led to little understanding of this phenomenon. The aim of this study was to discuss variables affecting RS in orthodontics and to suggest an operative protocol. The search included PubMed©, Medline©, and the Cochrane Library©. References of full-text articles were manually analyzed. English-language articles published between January 2007 and January 2017 that performed an in vitro analysis of RS between the bracket, wire, and ligature were included. Study methods were analyzed based on the study design, description of materials, and experimental setup, and a protocol to standardize the testing methods was proposed. From 404 articles identified from the database search and 242 records selected from published references, 101 were eligible for the qualitative analysis, and six for the quantitative synthesis. One or more experimental parameters were incompatible and a meta-analysis was not performed. Major factors regarding the study design, materials, and experimental setup were not clearly described by most studies. The normal force, that is the force perpendicular to the sliding of the wire and one of the most relevant variable in RS, was not considered by most studies. Different variables were introduced, often acting as confounding factors. A protocol was suggested to standardize testing procedures and enhance the understanding of in vitro findings.

Evaluation of the mechanical properties and surface topography of as-received, immersed and as-retrieved orthodontic archwires

Background and aims

This experimental study mainly aims at comparing the most important mechanical properties of the new orthodontic archwires, those immersed in fluorinated solution, the as-retrieved ones and the intra-oral used ones.

Methods

A total of 270 arch wires were tested, using tensile testing and three-point bending tests. The tested archwires were made of Stainless Steel, Nickel Titanium, Beta-Titanium and physiognomic covered Nickel Titanium. The tested archwires were subjected to three types of treatments: immersion into fluorinated solution, immersion into carbonated drinks and intra-oral use.

Results

The immersion caused variations of the activation and deactivation forces of all arch wires. The most affected arch wires, in terms of bending characteristics, were the intra-oral used ones.

Conclusions

The alteration of mechanical properties of the orthodontic arch wires by their immersion into fluorinated solutions and soft drinks could not be statistically demonstrated.