Influence of fluoride-containing acidic artificial saliva on the mechanical properties of Nickel-Titanium orthodontics wires

Corrosion-induced changes in surface properties and roughness of orthodontic wires

INTRODUCTION

This study aimed to investigate the surface free energy and surface roughness (SR) of metallic alloys under the influence of acid solutions.

METHODS

The experiment involved the use of 270 rectangular wire samples measuring 0.019 × 0.025-in. These samples were sourced from 3 different commercial brands: Dentsply GAC, American Orthodontics, and Orthoclassic. This in vitro study categorized the samples into 3 groups based on the solutions employed: deionized water, citric acid, and phosphoric acid. Each group consisted of 90 samples, with 30 samples representing each type of alloy-stainless steel, nickel-titanium, and titanium molybdenum alloy (TMA). The wire segments were immersed in their respective solutions for 72 hours at a controlled temperature of 37°C, with continuous orbital agitation at 130 rpm. After the immersion period, the study analyzed both surface free energy and SR. The mean values obtained were subjected to an analysis of variance at a significance level of 5%.

RESULTS

All alloys displayed hydrophobic behavior, as indicated by interaction free energy values <0. In acidic environments (phosphoric acid and citric acid), significant differences were observed among different brands and alloys, affecting surface energy and interaction free energy. Variations in SR among metallic alloys included steel with the lowest SR variations, followed by nickel-titanium and TMA. Notably, the TMA alloy stood out with significantly higher surface energy compared with that of the other alloys (P <0.001).

CONCLUSIONS

In this study, all examined alloys demonstrated a hydrophobic nature, suggesting a limited attraction to water. Notably, TMA exhibited the least hydrophobic behavior among the alloys studied. However, when exposed to citric acid, TMA displayed the most substantial alterations in its surface properties. These results underscored the significance of accounting for the distinctive properties of each alloy and their responses to diverse challenges, such as exposure to acidic solutions, during the selection of orthodontic wires for orthodontics treatment.

Nanomaterials Application in Orthodontics

Nanotechnology has gained importance in recent years due to its ability to enhance material properties, including antimicrobial characteristics. Nanotechnology is applicable in various aspects of orthodontics. This scientific work focuses on the concept of nanotechnology and its applications in the field of orthodontics, including, among others, enhancement of antimicrobial characteristics of orthodontic resins, leading to reduction of enamel demineralization or control of friction force during orthodontic movement. The latter one enables effective orthodontic treatment while using less force. Emphasis is put on antimicrobial and mechanical characteristics of nanomaterials during orthodontic treatment. The manuscript sums up the current knowledge about nanomaterials' influence on orthodontic appliances.

Impact of Peracetic Acid on the Dynamic Cyclic Fatigue of Heat-Treated Nickel-Titanium Rotary Endodontic Instrument

Peracetic acid (PAA) is widely used as a sterilizing/disinfecting agent, and, in endodontics, it has been introduced as a promising irrigant in root canal treatment. It has been used at different concentrations to achieve various functions. However, endodontic instruments in contact with PAA of a certain concentration may affect their fatigue resistance. Therefore, the aim of this study was to investigate the impact of PAA on the cyclic fatigue resistance of three commercial heat-treated nickel-titanium (NiTi) rotary files. Three types of heat-treated NiTi rotary files were selected: One Curve (OC), ProTaper Gold (PTG), and Wave One Gold (WOG). Each type was divided into three subgroups (n = 6 for each file type): (1) untreated instruments; (2) files immersed in 0.002% PAA; and (3) files immersed in 0.35% PAA. The performance of each file type was tested in a simulated canal. The number of cycles to fracture (NCF) was determined to assess cyclic fatigue resistance of the files. Independent sample t-test was applied to compare each treated file within a subgroup with its respective control group, and one-way ANOVA was used for comparison among the main groups. All types of tested files revealed a significant decline in the cyclic fatigue resistance after exposure to 0.002% PAA except the PTG (P=0.209). After exposure of the files to a higher concentration (0.35% PAA), a dramatic reduction was demonstrated by all the groups. Before and after exposure of the files to PAA, PTG displayed the highest cyclic fatigue resistance, followed by the WOG, while the OC showed the lowest resistance. Exposure of heated-treated NiTi files to PAA in a relatively high or low concentration adversely affects the cyclic fatigue resistance. The PTG files demonstrated the best performance among the tested types and can be disinfected with 0.002% PAA for clinical purpose.

Evaluation of biofilm accumulation on and deactivation force of orthodontic Ni-Ti archwires before and after exposure to an oral medium: A prospective clinical study

Background. This in vitro study aimed to evaluate biofilm accumulation on and deactivation force of orthodontic nickeltitanium (NiTi) archwires before and after exposure to an oral medium.

Methods. Four commercial brands of orthodontic NiTi 0.016" archwires were examined before and after exposure to the oral medium for 4 weeks. Six archwire segments, 30 mm in length, from each manufacturer were tested in a device with four selfligating brackets, channel 0.022", adapted to a universal test machine to evaluate the deactivation force between 0.5 and 3 mm of deflection. The presence of biofilm on the archwire surfaces was evaluated by scanning electron microscopy, before and after exposure to the oral medium. The Wilcoxon and kappa tests were applied to the biofilm scores, three-way ANOVA for repeated measures (Bonferroni post-test), and linear regression between biofilm and deactivation force.

Results. The exposure to the oral medium promoted moderate to severe presence of debris on the archwire surfaces and caused a reduction in deactivation force for the Ormco and GAC brands, while maintaining them with adequate force levels. The MORELLI and ORTHOMETRIC archwires underwent no significant reduction in deactivation force; moreover, these maintained elevated levels of force after exposure to the oral medium. The Spearman test indicated a low correlation between biofilm accumulation and deflection force for the Morelli (R2=0.132 and P=0.683) and Orthometric (R2=0.308 and P=0.330) brands. On the other hand, the GAC (R=0.767 and P=0.004) and ORMCO (R=0.725 and P=0.008) brands exhibited statistically significant correlation between these variables.

Conclusion. Exposure to the oral medium for one month might give rise to significant changes in the dissipation of forces of orthodontic NiTi archwires, resulting from biofilm accumulation.

Antibacterial and Remineralization Efficacy of Casein Phosphopeptide, Glycomacropeptide Nanocomplex, and Probiotics in Experimental Toothpastes: An In Vitro Comparative Study

Objective  This article evaluates the antibacterial and remineralization potential of experimentally prepared toothpastes containing different mixtures of nano casein phosphopeptides (nCPP), nano amorphous calcium phosphate (nACP), probiotic ­ Lactobacillus rhamnosus B-445 ( L. rhamnosus ), and nano glycomacropeptide (nGMP).

Materials and Methods  Five experimental toothpaste samples were prepared and grouped, such that group (A0) was the experimental toothpaste base formula. Groups (A1), (A2), (A3), and (A4) were the experimental toothpastes containing: nCPP; nCPP and nACP; nCPP, nACP, and L. rhamnosus , and nCPP, nACP, and nGMP, ­respectively. Group (A5) was the commercial group (GC MI Paste Plus). The five groups were screened against Streptococcus mutans (ATCC 25175) growth, and investigated for their remineralizing potentials on demineralized bovine enamel using Vickers ­microhardness test (Vickers hardness number [VHN]). Scanning electron microscope (SEM) images were obtained for the demineralized and remineralized enamel of the two most effective toothpastes against in vitro bacterial induced enamel demineralization. Statistical analysis was performed using one-way analysis of variance (ANOVA) as well as repeated measures ANOVA followed by Tukey’s post hoc test.

Results  Both (A3) and (A4) were significantly higher in mean inhibition zone ­diameters than group (A1) and (A2). Group (A4) showed the highest statistical ­significance in the mean difference between VHN values of demineralization and 15 days remineralization period. SEM images showed the deposition of nano-sized particles fill the ­microrough surface pattern of the etched enamel.

Conclusion  All these findings suggest the use of probiotic, nCPP–nACP, and nGMP as a dental anticariogenic and remineralizing active agents.

Oral antiseptics and nickel-titanium alloys: mechanical and chemical effects of interaction

The effect of oral antiseptics on the corrosion of nickel-titanium (NiTi) alloys with various coating was investigated. Uncoated, titanium nitride-coated and rhodium-coated NiTi archwires (0.020 × 0.020″) were tested in interaction with artificial saliva pH 4.8 and oral antiseptics based on hyaluronic acid (Gengigel), chlorhexidine (Curasept) and essential oils in alcohol base (Listerine). The dynamics of nickel and titanium ions release were recorded during 28 days. Springback ratio and modulus of resilience were assessed by three-point bending test. The results showed that corrosion of NiTi is related to type of antiseptic mouth rinse and coating formulations. Exposure to an artificial saliva and antiseptics tend to reduce flexibility and resilience of NiTi archwires. The influence of the media is more significant than the influence of the type of the alloys coating. The largest release of nickel ions is in the first 3 days. Antiseptics do not cause further deterioration of the elastic properties in uncoated NiTi compared to saliva. As a result of exposure of nitrified NiTi wires in Listerine, there is bigger release of nickel ions, decrease in elastic properties and lower force delivery in unload. Listerine tends to reduce elastic properties of rhodium-coated wires also. In conclusion, except for Listerine, changes of mechanical characteristics induced by antiseptics are small and would not have a clinically important impact. Generally, Curasept would be the most suitable option.

Assessment of the hardness of different orthodontic wires and brackets produced by metal injection molding and conventional methods

Background:

This study was conducted to assess the hardness of orthodontic brackets produced by metal injection molding (MIM) and conventional methods and different orthodontic wires (stainless steel, nickel-titanium [Ni-Ti], and beta-titanium alloys) for better clinical results.

Materials and Methods:

A total of 15 specimens from each brand of orthodontic brackets and wires were examined. The brackets (Elite Opti-Mim which is produced by MIM process and Ultratrimm which is produced by conventional brazing method) and the wires (stainless steel, Ni-Ti, and beta-titanium) were embedded in epoxy resin, followed by grinding, polishing, and coating. Then, X-ray energy dispersive spectroscopy (EDS) microanalysis was applied to assess their elemental composition. The same specimen surfaces were repolished and used for Vickers microhardness assessment. Hardness was statistically analyzed with Kruskal–Wallis test, followed by Mann–Whitney test at the 0.05 level of significance.

Results:

The X-ray EDS analysis revealed different ferrous or co-based alloys in each bracket. The maximum mean hardness values of the wires were achieved for stainless steel (SS) (529.85 Vickers hardness [VHN]) versus the minimum values for beta-titanium (334.65 VHN). Among the brackets, Elite Opti-Mim exhibited significantly higher VHN values (262.66 VHN) compared to Ultratrimm (206.59 VHN). VHN values of wire alloys were significantly higher than those of the brackets.

Conclusion:

MIM orthodontic brackets exhibited hardness values much lower than those of SS orthodontic archwires and were more compatible with NiTi and beta-titanium archwires. A wide range of microhardness values has been reported for conventional orthodontic brackets and it should be considered that the manufacturing method might be only one of the factors affecting the mechanical properties of orthodontic brackets including hardness.