In vitro biocompatibility of nickel-titanium esthetic orthodontic archwires

Effects of various coating methods on the mechanical, physical, and aesthetic properties of GUMMETAL® archwires: In vitro study

PURPOSE

The objective of this study was to evaluate the mechanical, physical, and aesthetic properties of GUMMETAL® (GM) orthodontic archwires after the application of various aesthetic coating materials.

METHODS

This in vitro study included 180 orthodontic wires: five experimental groups used 0.016×0.022-inch GM as the core-based wire followed by the application of epoxy, polytetrafluoroethylene (PTFE), clear ceramic, white ceramic, or silicone; and four control groups: 0.016×0.022-inch GM, 0.019×0.025-inch GM, 0.016×0.022-inch stainless steel (SS), and 0.019×0.025-inch SS. Frictional forces, force deflection rate, yield strength, aesthetic colour value, corrosive and wear resistance were compared between the experimental and control groups.

RESULTS

Among the coated wires, white ceramic exhibited the highest frictional force (2.06±0.20 N) and silicone showed the lowest values (0.88±0.12 N). There were significant differences in static friction between experimental and control groups (P<0.001). PTFE coating had the highest force deflection rate (9.03±0.12 N/mm) and yield strength (10.0±0.14 N/mm) among coated wires and white ceramic exhibited the lowest values (6.86±0.14 N/mm and 7.74±0.17 N/mm for force deflection rate and yield strength, respectively). Differences in force deflection rate and yield strength between experimental and control groups were statistically significant (P<0.001). All coated wire groups had a clinical difference in colour when compared to A1 shade. Coated and uncoated wires showed good corrosion resistance after one week in corrosive saliva with no detectable loss of mass.

CONCLUSIONS

This study has shown that coating wires can improve some aspects of the wire properties but not all when compared to uncoated GM and SS. Future investigation of the materials used in this study is required to further characterize their properties.

In vitro wearing away of orthodontic brackets and wires in different conditions: A review

Introduction

The release of metallic ions from orthodontic brackets and wires typically depends on their quality (chemical composition) and the medium to which they are exposed, e.g., acidic, alkaline, substances with a high fluoride concentration, etc. This review examines corrosion and wear of orthodontic brackets, wires, and arches exposed to different media, including: beverages (juices), mouthwashes and artificial saliva among others, and the possible health effects resulting from the release of metallic ions under various conditions.

Objective

This review aims to determine the exposure conditions that cause the most wear on orthodontic devices, as well as the possible health effects that can be caused by the release of metallic ions under various conditions.

Sources

A search was carried out in the Scopus database, for articles related to oral media that can corrode brackets and wires. The initial research resulted in 8,127 documents, after applying inclusion and exclusion criteria, 76 articles remained.

Conclusion

Stainless steel, which is commonly used in orthodontic devices, is the material that suffers the most wear. It was also found that acidic pH, alcohols, fluorides, and chlorides worsen orthodontic material corrosion. Further, nickel released from brackets and wires can cause allergic reactions and gingival overgrowth into patients.

Nickel and chromium ion release from coated and uncoated orthodontic archwires under different pH levels and exposure times

OBJECTIVES

The purpose of this study was to determine and compare nickel and chromium ion release from traditional stainless steel and nickel titanium wires and newer esthetic archwires under different pH conditions, for different time intervals.

METHODS

Ten pieces of 10-mm segments of five different orthodontic archwires were submerged in buffer solutions of pH 4.0, 5.5, and 7.0, for 4 and 13 weeks. The sample solutions were analyzed using ICP-MS. First, the results were analyzed by three-way ANOVA to determine any significant differences in metal concentration (ppb) between the different groups. Then, a post-hoc multiple pairwise comparison by Tukey's Studentized Range (HSD) Test was conducted to further compare the different materials and pH conditions.

RESULTS

For nickel, uncoated NiTi had the highest nickel ion release (ppb), while AO Iconix had the lowest average nickel ion release, with a significant difference (p < 0.0001). The average nickel release increased with time and decreased with pH. For chromium, materials with uncoated stainless steel had the highest average chromium ion release, whereas AO Iconix had the lowest average chromium ion release, with a statistically significant difference (p < 0.0001). Chromium ion release increased with time and decreased with pH.

CONCLUSIONS

There were significant differences in metal ion release between different pH conditions, materials, and time points. The metal ion release increased with increase in time and decrease in pH. Overall, the coated archwires showed less metal ion release than the uncoated wires.

In vitro Streptococcus mutans adhesion and biofilm formation on different esthetic orthodontic archwires

OBJECTIVES

To evaluate the ability of different esthetic archwires to retain oral biofilms in vitro.

MATERIALS AND METHODS

Seven different brands of coated orthodontic archwires were tested: two epoxy coated, two polytetrafluoroethylene coated, two rhodium coated, and one silver plus polymer coated. Conventional uncoated metallic archwires were used as controls. Streptococus mutans adherence to archwires was quantified by colony count following 24 hours of biolfilm growth, and total wire-associated biofilm was measured using a crystal violet staining assay. For both tests, two conditions were used: 0% sucrose and 3% sucrose. For statistical analysis, P < .05 was considered as statistically significant.

RESULTS

For S. mutans colony forming units per biofilm, there were no statistically significant differences among the various archwires (P = .795 for 0% sucrose; P = .905 for 3% sucrose). Regarding total biofilm formed on archwires in the 3% sucrose condition, there were statistically significant differences in crystal violet staining only for the comparison between Niti Micro Dental White and Copper Ni-Ti wires (P < .05).

CONCLUSIONS

The clinical use of esthetic-coated orthodontic wires may be considered to have similar risks as uncoated archwires for biofilm retention.

Comparison of Cell Viability and Chemical Composition of Six Latest Generation Orthodontic Wires

Orthodontic wires are made of alloys containing different metals, including nickel. It is important to evaluate their biocompatibility prior to use, owing to their long-term use in patients. This in vitro study compared the cytotoxicity and chemical composition of six latest orthodontic wires: Fantasia®, Tanzo®, FLI®, NT3®, DuoForce®, and Gummetal®. The before-use group consisted of wires that were not used in the mouth, and the after-use group consisted of wires that were used in the mouth for two months. The wires were placed in contact with human gingival fibroblasts (HGF) for 72 h, and cytotoxicity was determined using the resazurin test. The chemical composition and surface characterisation were evaluated by spectrometry and scanning electron microscopy. The groups were compared using ANOVA and Kruskal–Wallis test. Only the FLI® wires produced a 36% reduction in HGF viability (p < 0.05) and presented greater irregularities and loss of polymer structure. After-use wires showed a significant reduction in the percentage of nickel and the appearance of new elements (oxygen and carbon). Therefore, it can be concluded that no toxic ion release was noticed in this study. Rhodium-coated wires were more stable than PTFE-coated wires, and only the FLI® wires showed a slight cytotoxic effect.

Evaluation of toxicity and response to oxidative stress generated by orthodontic bands in human gingival fibroblasts

OBJECTIVE

To evaluate the cytotoxicity of stainless-steel orthodontic bands and their influence on the expression of the antioxidant genes in human gingival fibroblasts.

MATERIALS AND METHODS

Ten bands of each brand (Dentsply-Sirona, Dentaurum, TP Orthodontics, and Morelli) were conditioned in 0.2 g/mL culture medium at 37°C for 14 days, and the corresponding conditioned media were applied over the fibroblasts. Cell viability was assessed after 24, 48, and 72 hours of exposure to the conditioned media by trypan blue exclusion assay. Expression of the antioxidant defense genes peroxiredoxin 1 (PRDX1), superoxide dismutase 1 (SOD1), and glutathione peroxidase 1 (GPX1) were evaluated by quantitative polymerase chain reaction after 24 hours of exposure. These parameters were compared to those of the cells not exposed to the conditioned media of the bands (control).

RESULTS

All bands promoted a reduction in the number of viable cells in the periods of 48 and 72 hours (P < .01). Analysis of gene expression showed a significant increase in the levels of PRDX1 transcripts caused by the conditioned media of the Dentsply-Sirona, TP Orthodontics, and Morelli bands (P < .01) as well as induction of SOD1 by the conditioned media of the Dentaurum and Morelli (P < .01). Expression of GPX1 was not influenced by the conditioned media.

CONCLUSIONS

The orthodontic bands showed toxicity to fibroblasts and increased the expression of PRDX1 and SOD1 antioxidant genes, indicating induction of oxidative stress in the cells.

Effect of 0.05% Sodium Fluoride Mouthwash on Surface Roughness and Friction between Ceramic Brackets and Rhodium-Coated and Uncoated Stainless Steel Wires

Objectives:

This study aimed to assess the effect of 0.05% sodium fluoride (NaF) mouthwash on the surface roughness and friction between ceramic brackets and rhodium-coated (RC) and uncoated stainless steel (SS) wires.

Materials and Methods:

This experimental study was performed on 48 maxillary premolar ceramic brackets. Twenty-four pieces of RC-SS wires were used. Samples were divided into four groups. Groups 1 and 2 were immersed in artificial saliva, and groups 3 and 4 were immersed in a solution consisting of artificial saliva (9%) and mouthwash (91%). To assess surface roughness, images were obtained from the surface of wires and brackets with atomic force microscopy (AFM) and scanning electron microscopy (SEM) before and after the intervention. To assess friction, the wires were ligated into brackets, and friction was measured at a crosshead speed of 0.5 mm/minute using a universal testing machine. Data were analyzed using one-way analysis of variance (ANOVA) at the 0.05 significance level.

Results:

Friction during sliding in RC wires was significantly less than that in SS wires (P<0.05). Increase in the friction in SS wires by mouthwash was significantly greater compared to RC wires (P<0.05). Surface roughness coefficients of the wires before the intervention were not significantly different. The surface roughness of the wires significantly increased after the intervention and it was greater in SS wires than in RC wires (P<0.05).

Conclusion:

Considering the lower friction and surface roughness of SS-RC wires compared to SS wires, SS-RC wires may be a better alternative for use with ceramic brackets.

Cytotoxicity and oxidative stress induced by nickel and titanium ions from dental alloys on cells of gastrointestinal tract

The aim was to explore the biological effect of nickel (Ni) and titanium (Ti) ions released from dental alloys. NiTi alloy were exposed to 40 mL of artificial saliva (pH = 4.8, t = 37 °C). The dynamics of Ni and Ti ions release during corrosion were recorded on the 3th, 7th and 14th day. Biological effect of Ni and Ti ions released from alloy was explored on cell lines of human tongue CAL 27, liver Hep G2 and colon Caco-2. Neutral Red uptake assay for the estimation of cell viability/cytotoxicity and 2',7'-dichlorofluorescein diacetate fluorimetric assay for reactive oxygen species were used. Cells were exposed to the following concentration of corrosion products: 5.0×, 1.0×, 0.5 and 0.1× during the period of 24, 48 and 72 h. To check the effect of each metal separately, cells were exposed to nickel-chloride and titanium-dioxide of corresponding concentration. The release of Ni is higher than of Ti (15.1-30.4 μg/L for Ni and 9.0-17.3 μg/L for Ti, respectively) and 5× higher concentrations are needed to induce cytotoxic effect. Ni and Ti ions alone do not induce a major cytotoxic effect, but their combination does indicating their synergistic effect. Increase in concentration of Ni and Ti tends to increase cytotoxicity, Ti more than Ni. Cytotoxicity and induction of free radicals are in strong positive linear correlation. Ions released from NiTi alloy during 14 days do not induce significant cytotoxic effect and would not have a clinically important impact. Cytotoxic effect is largely the result of the induction of free radicals.

Thickness of orthodontic clear aligners after thermoforming and after 10 days of intraoral exposure: a prospective clinical study

Background

Clear aligners (CA) are among the most chosen orthodontic therapies for patients who require an invisible treatment. Previous studies showed that the thermoforming process and the complexity of the intraoral environment might alter the properties of these devices. The aim of the current prospective clinical study was to assess the thickness changes of the CA after 10 days of intraoral use. The secondary aim was to assess the reproducibility of the thermoforming process, in terms of aligner thickness.

Materials and methods

CA from 18 consecutive patients (13 women, 5 men, mean age 28.8 ± 9.6 years) were investigated. Before intraoral exposure (T0), the thickness of the unused CA was measured at different occlusal points on a 3D model with a dedicated software (Geomagic Qualify 2013; 3D Systems, Rock Hill, SC, USA). Two CA configurations were studied: passive maxillary aligner (P—no tooth movement; no shape for attachments) and active maxillary aligner (A—tooth movement; shape for attachments and divot). The used aligners were returned after 10 days (T1) and the thickness measurements were repeated. A Student’s t test for paired data (T1 vs. T0) was applied to compare the thicknesses of used and unused devices (significance level after Bonferroni correction for multiple comparison was set at p < 0.0014). Furthermore, to study the reproducibility of the thermoforming process, P and A aligners were thermoformed twice, and the thicknesses of the two unused thermoformed devices were compared by means of Student’s t test for paired data (significance level after Bonferroni correction for multiple comparison was set at p < 0.0014) and Dahlberg’s error.

Results

The thermoforming process showed good reproducibility for both aligner configurations, with a maximum Dahlberg’s error of 0.13 mm. After intraoral use, the thickness of P showed some statistically significant, but not clinically relevant, thickness changes as compared to the unused aligners, while A did not show any significant changes.

Conclusion

Considering the thickness changes, the thermoforming process is reliable both with active and passive aligner configurations. Also, the CA examined show good thickness stability after physiological intraoral ageing in a population of healthy adults.

Comparative Analysis of the Chemical Composition and Microstructure Conformation Between Different Dental Implant Bone Drills

Background: Hardness is considered an important parameter for evaluating the clinical performance of dental implant bone drills. It is connected to the chemical composition, microstructure conformation and manufacture of the surgical drills. Methods: Microstructure of five dental implant drills using scanning electronic microscopy (SEM) integrated with energy dispersive X-ray spectrometry. Vickers microhardness was measured using a CV 2000 microhardness tester with an indentation force of 500 g. Results: Composition of the implant drills was typical of martensitic stainless steel (MSS). The drills contained 13%–17% of Cr; Mo, Si and Mn were present as minor ligands. The examined bone drills showed different external surface conformation and hardness in relation to the different industrial production processes. A rougher external surface and a higher hardness value are characteristics of the surgical bone drills produced by hot forming; the implant drills produced by machining showed mailing lines on their external surface and a lower hardness. Conclusions: Different compositions and treatments were used by the manufacturers to improve the hardness of the external layer of the dental implant drills making them prone to a diverse heat generation during the implant site preparation.

In vitro cytotoxicity of different thermoplastic materials for clear aligners

OBJECTIVES

To investigate the in vitro cytotoxicity of different thermoplastic materials for clear aligners on human primary gingival fibroblasts (HGFs).

MATERIALS AND METHODS

Four materials for clear aligners were considered in this study: Duran (Scheu-Dental GmbH, Iserlohn, Germany), Biolon (Dreve Dentamid GmbH, Unna, Germany), Zendura (Bay Materials LLC, Fremont, CA, USA), and SmartTrack (Align Technology, San Jose, CA, USA). Three out of four materials (Duran, Biolon, Zendura) were assessed as thermoformed and nonthermoformed, whereas the SmartTrack was assessed only as thermoformed. The samples were placed at 37°C in airtight test tubes containing Dulbecco's Modified Eagle's Medium (DMEM; 0.1 mg/mL) for 14 days. The cell viability of HGFs cultured with this medium was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Data were analyzed by means of one-way and two-way analysis of variance and post hoc tests (α = 0.05).

RESULTS

Each material exhibited a slight cytotoxic effect after 14 days. The highest cytotoxicity level on HGFs was achieved by Biolon (64.6% ± 3.3 of cell viability), followed by Zendura (74.4% ± 2.3 of cell viability), SmartTrack (78.8% ± 6.3 of cell viability), and finally Duran (84.6% ± 4 of cell viability), which was the least cytotoxic. In the comparison between nonthermoformed and thermoformed materials for Duran, Biolon, and Zendura, the thermoformed materials showed the highest level of cytotoxicity (P < .001).

CONCLUSIONS

Under the experimental conditions of this study, all the materials for clear aligners presented a slight cytotoxicity. Biolon was the most cytotoxic and the thermoforming process increased the cytotoxicity of the materials.

Short-term "in vivo" study on cellular DNA damage induced by acrylic Andresen activator in oral mucosa cells

OBJECTIVES

To analyse through comet assay and micronucleus test the viability and DNA damage occurred in buccal mucosa epithelial cells after a short-term exposure to Andresen activator resin monomers.

SETTING AND SAMPLE POPULATION

Test group consisting of 26 subjects was treated with Andresen activator; 16 subjects who had never undergone orthodontic treatment were enrolled in the control group.

MATERIAL & METHODS

Buccal mucosa samples were collected before treatment and after 7, 15, 30, 60 and 90 days. The analyses performed on the cells included the following: cellular viability, comet assay and micronucleus test. Mean ± SD were calculated for cellular viability, tail moment, tail intensity, tail length, micronuclei, binuclear and bud cells. Significance (P < 0.05) was evaluated with Dunnett's test.

RESULTS

Cellular viability did not change during observational time, and its trend was similar to the controls. Tail moment and tail intensity significantly increased after 30 and 60 days, respectively, whereas tail length remained unchanged over time in the test group; the same parameters did not change in the control group. In the test group, micronuclei, binuclear and bud cells significantly increased after 30, 60 and 90 days, respectively.

CONCLUSION

The resin monomers of the Andresen activator cause genotoxic effects detectable through comet assay and micronucleus test, but they do not produce clear cytotoxic effects after a 90 days exposure.

Comparison of deflection forces of esthetic archwires combined with ceramic brackets

Coated archwires and ceramic brackets have been developed to improve facial esthetics during orthodontic treatment. However, their mechanical behavior has been shown to be different from metallic archwires and brackets. Therefore, the aim of this study was to compare the deflection forces in coated nickel-titanium (NiTi) and esthetic archwires combined with ceramic brackets. Material and Methods Non-coated NiTi (NC), rhodium coated NiTi (RC), teflon coated NiTi (TC), epoxy coated NiTi (EC), fiber-reinforced polymer (FRP), and the three different conventional brackets metal-insert polycrystalline ceramic (MI-PC), polycrystalline ceramic (PC) and monocrystalline ceramic (MC) were used. The specimens were set up on a clinical simulation device and evaluated in a Universal Testing Machine (Instron). An acrylic device, representative of the right maxillary central incisor was buccolingually activated and the unloading forces generated were recorded at 3, 2, 1 and 0.5 mm. The speed of the testing machine was 2 mm/min. ANOVA and Tukey tests were used to compare the different archwires and brackets. Results The brackets presented the following decreasing force ranking: monocrystalline, polycrystalline and polycrystalline metal-insert. The decreasing force ranking of the archwires was: rhodium coated NiTi (RC), non-coated NiTi (NC), teflon coated NiTi (TC), epoxy coated NiTi (EC) and fiber-reinforced polymer (FRP). At 3 mm of unloading the FRP archwire had a plastic deformation and produced an extremely low force in 2; 1 and 0.5 mm of unloading. Conclusion Combinations of the evaluated archwires and brackets will produce a force ranking proportional to the combination of their individual force rankings.

Characterization and coating stability evaluation of nickel-titanium orthodontic esthetic wires: an in vivo study

The objective of this study was to compare coating dimensions and surface characteristics of two different esthetic covered nickel-titanium orthodontic rectangular archwires, as-received from the manufacturer and after oral exposure. The study was designed for comparative purposes. Both archwires, as-received from the manufacturer, were observed using a stereomicroscope to measure coating thickness and inner metallic dimensions. The wires were also exposed to oral environment in 11 orthodontic active patients for 21 days. After removing the samples, stereomicroscopy images were captured, coating loss was measured and its percentage was calculated. Three segments of each wire (one as-received and two after oral exposure) were observed using scanning electron microscopy for a qualitative analysis of the labial surface of the wires. The Lilliefors test and independent t-test were applied to verify normality of data and statistical differences between wires, respectively. The significance level adopted was 0.05. The results showed that the differences between the wires while comparing inner height and thickness were statistically significant (p < 0.0001). In average, the most recently launched wire presented a coating thickness twice that of the control wire, which was also a statistically significant difference. The coating loss percentage was also statistically different (p = 0.0346) when the latest launched wire (13.27%) was compared to the control (29.63%). In conclusion, the coating of the most recent wire was thicker and more uniform, whereas the control had a thinner coating on the edges. After oral exposure, both tested wires presented coating loss, but the most recently launched wire exhibited better results.

Biocompatibility and Inflammatory Potential of Titanium Alloys Cultivated with Human Osteoblasts, Fibroblasts and Macrophages

The biomaterials used to maintain or replace functions in the human body consist mainly of metals, ceramics or polymers. In orthopedic surgery, metallic materials, especially titanium and its alloys, are the most common, due to their excellent mechanical properties, corrosion resistance, and biocompatibility. Aside from the established Ti6Al4V alloy, shape memory materials such as nickel-titanium (NiTi) have risen in importance, but are also discussed because of the adverse effects of nickel ions. These might be reduced by specific surface modifications. In the present in vitro study, the osteoblastic cell line MG-63 as well as primary human osteoblasts, fibroblasts, and macrophages were cultured on titanium alloys (forged Ti6Al4V, additive manufactured Ti6Al4V, NiTi, and Diamond-Like-Carbon (DLC)-coated NiTi) to verify their specific biocompatibility and inflammatory potential. Additive manufactured Ti6Al4V and NiTi revealed the highest levels of metabolic cell activity. DLC-coated NiTi appeared as a suitable surface for cell growth, showing the highest collagen production. None of the implant materials caused a strong inflammatory response. In general, no distinct cell-specific response could be observed for the materials and surface coating used. In summary, all tested titanium alloys seem to be biologically appropriate for application in orthopedic surgery.