Metallic ions released from stainless steel, nickel-free, and titanium orthodontic alloys: toxicity and DNA damage

Chemical analysis of marine microdebris pollution in macroalgae from the coastal areas of Argentina

Marine microdebris (MDs, <5 mm) and mesodebris (MesDs, 5-25 mm), consist of various components, including microplastics (MPs), antifouling or anticorrosive paint particles (APPs), and metallic particles (Mmps), among others. The accumulation of these anthropogenic particles in macroalgae could have significant implications within coastal ecosystems because of the role of macroalgae as primary producers and their subsequent transfer within the trophic chain. Therefore, the objectives of this study were to determine the abundance of MDs and MesDs pollution in different species of macroalgae (P. morrowii, C. rubrum, Ulva spp., and B. minima) and in surface waters from the Southwest Atlantic coast of Argentina to evaluate the ecological damage. MDs and MesDs were chemically characterized using μ-FTIR and SEM/EDX to identify, and assess their environmental impact based on their composition and degree of pollution by MPs, calculating the Polymer Hazard Index (PHI). The prevalence of MDs was higher in foliose species, followed by filamentous and tubular ones, ranging from 0 to 1.22 items/g w.w. for MPs and 0 to 0.85 items/g w.w. for APPs. It was found that macroalgae accumulate a higher proportion of high-density polymers like PAN and PES, as well as APPs based on alkyd, PMMA, and PE resins, whereas a predominance of CE was observed in surrounding waters. Potentially toxic elements, such as Cr, Cu, and Ti, were detected in APPs and MPs, along with the presence of epiplastic communities on the surface of APPs. According to PHI, the presence of high hazard score polymers, such as PAN and PA, increased the overall risk of MP pollution in macroalgae compared to surrounding waters. This study provided a baseline for MDs and MesDs abundance in macroalgae as well as understanding the environmental impact of this debris and their bioaccumulation in the primary link of the coastal trophic chain.

Tribocorrosion and Surface Protection Technology of Titanium Alloys: A Review

Titanium alloy has the advantages of high specific strength, good corrosion resistance, and biocompatibility and is widely used in marine equipment, biomedicine, aerospace, and other fields. However, the application of titanium alloy in special working conditions shows some shortcomings, such as low hardness and poor wear resistance, which seriously affect the long life and safe and reliable service of the structural parts. Tribocorrosion has been one of the research hotspots in the field of tribology in recent years, and it is one of the essential factors affecting the application of passivated metal in corrosive environments. In this work, the characteristics of the marine and human environments and their critical tribological problems are analyzed, and the research connotation of tribocorrosion of titanium alloy is expounded. The research status of surface protection technology for titanium alloy in marine and biological environments is reviewed, and the development direction and trends in surface engineering of titanium alloy are prospected.

The risk of dental restoration-related lead exposure on renal function

OBJECTIVE

To explore the relationship between oral restoration count, blood lead (PbB) level, and renal function as potential heavy metal releases, and the related toxicity of dental restorative materials.

METHODS

A total of 3682 participants from the National Health and Nutrition Examination Survey (January 2017 to March 2020) were included in this cross-sectional analysis. We utilized multivariable linear regression models to investigate the associations between the number of oral restorations and PbB levels or renal function. The mediating effect of PbB on renal function indicators was analyzed using the R mediation package.

RESULTS

Based on the indicators of 3682 participants, we found that the elderly, females, and whites were fit with more oral restoration, which was accompanied by increased PbB levels and decreased renal function. Meanwhile, oral restoration count was positively associated with PbB level (β = 0.023, 95% CI: -0.020 to 0.027), renal function-related urine albumin creatinine ratio (β = 1.541, 95% CI: 0.615-2.468), serum uric acid level (β = 0.012, 95% CI: 0.007 to 0.017), and serum creatinine level, and negatively associated with estimated glomerular filtration rate (eGFR) (β = -0.804, 95% CI: -0.880 to -0.728). Furthermore, the mediation effect test confirmed that PbB played a mediating role in the relationship between restoration count and serum uric acid or eGFR, with mediation effects accounting for 98.0% and 71.0%, respectively.

CONCLUSIONS

Oral restoration negatively affects renal function. Oral restoration-related PbB level is a potential mediating factor.

Examining the role of nickel and NiTi nanoparticles promoting inflammation and angiogenesis

Nickel titanium (NiTi, or Nitinol) alloy is used in several biomedical applications, including cardiac, peripheral vascular, and fallopian tube stents. There are significant biocompatibility issues of metallic implants to nickel ions and nano-/micro-sized alloy particles. Our laboratories have recently shown that microscale CoCr wear particles from metal-on-metal hips crosslink with the innate immune signaling Toll-like receptor 4 (TLR4), prompting downstream signaling that results in interleukin (IL)-1β and IL-8 gene expression. In vivo, NiTi alloy can also generate wear particles on the nanoscale (NP) that have thus far not been studied for their potential to induce inflammation and angiogenesis that can, in turn, contribute to implant (e.g. stent) failure. Earlier studies by others demonstrated that nickel could induce contact hypersensitivity by crosslinking the human, but not the mouse, TLR4. In the present work, it is demonstrated that NiCl₂ ions and NiTi nanoparticles induce pro-inflammatory and pro-angiogenic cytokine/chemokine expression in human endothelial and monocyte cell lines in vitro. These observations prompt concerns about potential mechanisms for stent failure. The data here showed a direct correlation between intracellular uptake of Ni²⁺ and generation of reactive oxygen species. To determine a role for nickel and NiTi nanoparticles in inducing angiogenesis in vivo, 1-cm silicone angioreactors were implanted subcutaneously into athymic (T-cell-deficient) nude mice. The angioreactors contained Matrigel (a gelatinous protein mixture that resembles extracellular matrix) in addition to one of the following: PBS (negative control), VEGF/FGF-2 (positive control), NiCl_2, or NiTi NP. The implantation of angioreactors represents a potential tool for quantification of angiogenic potentials of medical device-derived particles and ions in vivo. By this approach, NiTi NP were found to be markedly angiogenic, while Ni²⁺ was less-so. The angioreactors may provide a powerful tool to examine if debris shed from medical devices may promote untoward biological effects.

Minimization of Adverse Effects Associated with Dental Alloys

Metal alloys are one of the most popular materials used in current dental practice. In the oral cavity, metal structures are exposed to various mechanical and chemical factors. Consequently, metal ions are released into the oral fluid, which may negatively affect the surrounding tissues and even internal organs. Adverse effects associated with metallic oral appliances may have various local and systemic manifestations, such as mouth burning, potentially malignant oral lesions, and local or systemic hypersensitivity. However, clear diagnostic criteria and treatment guidelines for adverse effects associated with dental alloys have not been developed yet. The present comprehensive literature review aims (1) to summarize the current information related to possible side effects of metallic oral appliances; (2) to analyze the risk factors aggravating the negative effects of dental alloys; and (3) to develop recommendations for diagnosis, management, and prevention of pathological conditions associated with metallic oral appliances.

Bioaccumulation, release and genotoxicity of stainless steel particles in marine bivalve molluscs

During the decommissioning and removal of radioactive material in nuclear facilities, fine, tritiated dusts of stainless steel, cement or tungsten are generated that could be accidently released to the environment. However, the potential radio- and ecotoxicological effects these tritiated particles may have are unknown. In this study, stainless steel particles (SSPs) representative of those likely to be tritiated are manufactured by hydrogenation and their tissue-specific bioaccumulation, release (depuration) and subsequent genotoxic response have been studied in the marine mussel, Mytilus galloprovincialis, as a baseline for future assessments of the potential effects of tritiated SSPs. Exposure to 1000 μg L^-1 of SSPs and adopting Cr as a proxy for stainless steel revealed relatively rapid accumulation (∼5 h) in the various mussel tissues but mostly in the digestive gland. Over longer periods up to 18 days, SSPs were readily rejected and egested as faecal material. DNA strand breaks, as a measure of genotoxicity, were determined at each time point in mussel haemocytes using single cell gel electrophoresis, or the comet assay. Lack of chemical genotoxicity was attributed to the rapid processing of SSP particles and limited dissolution of elemental components of steel. Further work employing tritiated SSPs will enable radio-toxicology to be studied without the confounding effects of chemical toxicity.

Toxicity of Orthodontic Brackets Examined by Single Cell Tracking

Subtle toxic effects may be masked in traditional assays that average or summate the response of thousands of cells. We overcome this by using the recent method of single cell tracking in time-lapse recordings. This follows the fate and behavior of individual cells and their progeny and provides unambiguous results for multiple simultaneous biological responses. Further, single cell tracking permits correlation between progeny relationships and cell behavior that is not otherwise possible, including disruption by toxins and toxicants of similarity between paired sister cells. Notably, single cell tracking seems not to have been previously used to study biomaterials toxicity. The culture medium was pre-conditioned by 79 days incubation with orthodontic brackets from seven separate commercial sources. Metal levels were determined by Inductively Coupled Plasma Mass Spectrometry. Metal levels varied amongst conditioned media, with elevated Cr, Mn, Ni, and Cu and often Mo, Pb, Zn, Pd, and Ag were occasionally found. The effect on human dermal fibroblasts was determined by single cell tracking. All bracket-conditioned media reduced cell division (p < 0.05), while some reduced cell migration (p < 0.05). Most bracket-conditioned media increased the rate of asynchronous sister cell division (p < 0.05), a seemingly novel measure for toxicity. No clear effect on cell morphology was seen. We conclude that orthodontic brackets have cytotoxic effects, and that single cell tracking is effective for the study of subtle biomaterials cytotoxicity.

Toxicity assessment and health hazard classification of stainless steels

Stainless steels are widely used iron-based alloys that contain chromium and, typically, other alloying elements. The chromium(III)-rich surface oxide of stainless steels efficiently limits the release (bioaccessibility) of their metal constituents in most physiological environments, influencing the toxicity of the alloy. Of the constituents and impurities of stainless steels, nickel and cobalt are of particular interest, primarily due to skin sensitization and repeated-dose inhalation toxicity of nickel, and (inhalation) carcinogenicity of cobalt. A review of the available toxicological data on stainless steels, and the toxicological, mechanistic, and bioaccessibility data on their constituent metals supports the low toxicity and non-carcinogenicity of stainless steels. The comparative metal release, rather than the bulk composition of stainless steels, needs to be considered when assessing their health hazard classification according to the UN Globally Harmonized System, and the corresponding EU CLP regulation. As an illustrative example, a 28-day inhalation toxicity study on stainless steel powder showed no signs of lung toxicity at exposure levels at which significant toxicity would have been expected on the basis of its bulk nickel content. This finding is associated with the low bioaccessibility of nickel from the alloy in the lungs.

Biocompatible Materials in Otorhinolaryngology and Their Antibacterial Properties

For decades, biomaterials have been commonly used in medicine for the replacement of human body tissue, precise drug-delivery systems, or as parts of medical devices that are essential for some treatment methods. Due to rapid progress in the field of new materials, updates on the state of knowledge about biomaterials are frequently needed. This article describes the clinical application of different types of biomaterials in the field of otorhinolaryngology, i.e., head and neck surgery, focusing on their antimicrobial properties. The variety of their applications includes cochlear implants, middle ear prostheses, voice prostheses, materials for osteosynthesis, and nasal packing after nasal/paranasal sinuses surgery. Ceramics, such as as hydroxyapatite, zirconia, or metals and metal alloys, still have applications in the head and neck region. Tissue engineering scaffolds and drug-eluting materials, such as polymers and polymer-based composites, are becoming more common. The restoration of life tissue and the ability to prevent microbial colonization should be taken into consideration when designing the materials to be used for implant production. The authors of this paper have reviewed publications available in PubMed from the last five years about the recent progress in this topic but also establish the state of knowledge of the most common application of biomaterials over the last few decades.

Differences in Metal Ions Released from Orthodontic Appliances in an In Vitro and In Vivo Setting

The aim was to assess the composition of released metal ions from fixed orthodontic appliances both in an in vitro and in vivo setting and to compare their quantities to evaluate any possible health risks associated with them. For the in vitro setting, a set of 24 as-received sterile SS brackets, 2 SS sterile archwires, and 2 NiTi sterile archwires were aged for 90 days in artificial saliva, and released metal ion concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), using matrix-matched standards for calibration. For the in vivo setting, 15 brackets, 15 SS, and 15 NiTi archwires were retrieved after 90 days of intraoral exposure in 15 subjects. Debris composition on each part of the orthodontic appliance was assessed using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). The present study evidenced a difference in the composition of released metal ions from fixed orthodontic appliances detected in an in vitro and in vivo setting. Generally, the relative content of metal ions was higher in the retrieved debris than that released in artificial saliva. The concentration of released metal ions from all tested alloys was below the upper recommended limit of daily intake; however, possible local effects in terms of hypersensitivity due to their accumulation in the debris cannot be excluded even with such concentrations.

Immunomodulatory Properties and Osteogenic Activity of Polyetheretherketone Coated with Titanate Nanonetwork Structures

Polyetheretherketone (PEEK) is a potential substitute for conventional metallic biomedical implants owing to its superior mechanical and chemical properties, as well as biocompatibility. However, its inherent bio-inertness and poor osseointegration limit its use in clinical applications. Herein, thin titanium films were deposited on the PEEK substrate by plasma sputtering, and porous nanonetwork structures were incorporated on the PEEK surface by alkali treatment (PEEK-TNS). Changes in the physical and chemical characteristics of the PEEK surface were analyzed to establish the interactions with cell behaviors. The osteoimmunomodulatory properties were evaluated using macrophage cells and osteoblast lineage cells. The functionalized nanostructured surface of PEEK-TNS effectively promoted initial cell adhesion and proliferation, suppressed inflammatory responses, and induced macrophages to anti-inflammatory M2 polarization. Compared with PEEK, PEEK-TNS provided a more beneficial osteoimmune environment, including increased levels of osteogenic, angiogenic, and fibrogenic gene expression, and balanced osteoclast activities. Furthermore, the crosstalk between macrophages and osteoblast cells showed that PEEK-TNS could provide favorable osteoimmunodulatory environment for bone regeneration. PEEK-TNS exhibited high osteogenic activity, as indicated by alkaline phosphatase activity, osteogenic factor production, and the osteogenesis/osteoclastogenesis-related gene expression of osteoblasts. The study establishes that the fabrication of titanate nanonetwork structures on PEEK surfaces could extract an adequate immune response and favorable osteogenesis for functional bone regeneration. Furthermore, it indicates the potential of PEEK-TNS in implant applications.

Causation of Oxidative Stress and Defense Response of a Yeast Cell Model after Treatment with Orthodontic Alloys Consisting of Metal Ions

Misaligned teeth have a tremendous impact on oral and dental health, and the most efficient method of correcting the problem is orthodontic treatment with orthodontic appliances. The study was conducted to investigate the metal composition of selected orthodontic alloys, the release of metal ions, and the oxidative consequences that the metal ions may cause in the cell. Different sets of archwires, stainless steel brackets, and molar bands were incubated in artificial saliva for 90 days. The composition of each orthodontic material and quantification of the concentration of metal ions released were evaluated. Metal ion mixtures were prepared to determine the occurrence of oxidative stress, antioxidant enzyme defense system, and oxidative damage to proteins. The beta titanium alloy released the fewest metal ions and did not cause oxidative stress or protein damage. The metal ions from stainless steel and the cobalt-chromium alloy can cause oxidative stress and protein damage only at high concentrations. All metal ions from orthodontic alloys alter the activity of antioxidant enzymes in some way. The determined amounts of metal ions released from orthodontic appliances in a simulated oral environment are still below the maximum tolerated dose, and the concentrations of released metal ions are not capable of inducing oxidative stress, although some changes in antioxidant enzyme activity were observed at these concentrations.

Characterization of Porous Scaffolds Fabricated by Joining Stacking Based Laser Micro-Spot Welding (JS-LMSW) for Tissue Engineering Applications

A novel manufacturing approach was used to fabricate metallic scaffolds. A calibration of the laser cutting process was performed using the kerf width compensation in the calculations of the tool trajectory. Welding defects were studied through X-ray microtomography. Penetration depth and width resulted in relative errors of 9.4%, 1.0%, respectively. Microhardness was also measured, and the microstructure was studied in the base material. The microhardness values obtained were 400 HV, 237 HV, and 215 HV for the base material, HAZ, and fusion zone, respectively. No significant difference was found between the microhardness measurement along with different height positions of the scaffold. The scaffolds' dimensions and porosity were measured, their internal architecture was observed with micro-computed tomography. The results indicated that geometries with dimensions under 500 µm with different shapes resulted in relative errors of ~2.7%. The fabricated scaffolds presented an average compressive modulus ~13.15 GPa, which is close to cortical bone properties. The proposed methodology showed a promising future in bone tissue engineering applications.

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.

Osteoblast Cell Response on Polycrystalline Diamond-Coated Additively Manufactured Scaffolds

Additive manufacturing of metals using selective laser melting can create customized parts with various degrees of complexity and geometry for medical implants. However, challenges remain in accepting orthopedic implants due to the bio-inert surface of metal scaffolds, resulting in a lack of osseointegration. Here, we show that polycrystalline diamond (PCD) coatings on selective laser melted titanium (SLM-Ti) scaffolds can improve the cell-to-material interaction of osteoblasts. The results show that by controlling the uniformity of the diamond coatings, we can mediate the biological response of osteoblasts, such as cell adhesion, proliferation, and spreading. The osteoblasts show favorable cell adhesion and spreading on non-planar PCD-coated scaffolds compared to the un-coated SLM-Ti scaffold. This study plays an important role in understanding the key physicochemical behavior of bone cell growth on customized orthopedic implant materials.

Corrosion behavior of high nitrogen nickel-free austenitic stainless steel in the presence of artificial saliva and Streptococcus mutans

High nitrogen nickel-free austenitic stainless steels (HNSs) have great potentials to be used in dentistry owing to its exceptional mechanical properties, high corrosion resistance, and biocompatibility. In this study, HNSs with nitrogen of 0.88 wt% and 1.08 wt% displayed much lower maximum pit depths than 316L stainless steel (SS) after 21 d of immersion in abiotic artificial saliva (2.2 μm and 1.7 μm vs. 4.5 μm). Microbiologically influenced corrosion (MIC) evaluations revealed that Streptococcus mutans biofilms led to much severer corrosion of 316L SS than HNSs. Corrosion current densities of HNSs were two orders of magnitude lower than that of 316L SS after incubation of 7 d (37.5 nA/cm² and 29.9 nA/cm² vs. 5.63 μA/cm²). The pitting potentials of HNSs were at least 550 mV higher than that of 316L SS in the presence of S. mutans, confirming the better MIC resistance of HNSs. Cytotoxicity assay confirmed that HNSs were not toxic to MC3T3-E1 cells and allowed better sessile cell growth on them than on 316L SS. It can be concluded that HNSs are more suitable dental materials than the conventional 316L SS.

Risk Assessment of Oxidative Stress Induced by Metal Ions Released from Fixed Orthodontic Appliances during Treatment and Indications for Supportive Antioxidant Therapy: A Narrative Review

The treatment with fixed orthodontic appliances could have an important role in the induction of oxidative stress and associated negative consequences. Because of the simultaneous effects of corrosion, deformation, friction, and mechanical stress on fixed orthodontic appliances during treatment, degradation of orthodontic brackets and archwires occurs, causing higher concentrations of metal ions in the oral cavity. Corroded appliances cause the release of metal ions, which may lead to the increased values of reactive oxygen species (ROS) due to metal-catalyzed free radical reactions. Chromium, iron, nickel, cobalt, titanium, and molybdenum all belong to the group of transition metals that can be subjected to redox reactions to form ROS. The estimation of health risk due to the amount of heavy metals released and the level of selected parameters of oxidative stress generated for the time of treatment with fixed orthodontic appliances is presented. Approaches to avoid oxidative stress and recommendations for the preventive use of topical or systemic antioxidants during orthodontic treatment are discussed.

Bioactive Plasma Coatings on Orthodontic Brackets: In Vitro Metal Ion Release and Cytotoxicity

The metal ion release characteristics and biocompatibility of meta-based materials are key factors that influence their use in orthodontics. Although stainless steel-based alloys have gained much interest and use due to their mechanical properties and cost, they are prone to localised attack after prolonged exposure to the hostile oral environment. Metal ions may induce cellular toxicity at high dosages. To circumvent these issues, orthodontic brackets were coated with a functional nano-thin layer of plasma polymer and further immobilised with enantiomers of tryptophan. Analysis of the physicochemical properties confirmed the presence of functional coatings on the surface of the brackets. The quantification of metal ion release using mass spectrometry proved that plasma functionalisation could minimise metal ion release from orthodontic brackets. Furthermore, the biocompatibility of the brackets has been improved after functionalisation. These findings demonstrate that plasma polymer facilitated surface functionalisation of orthodontic brackets is a promising approach to reducing metal toxicity without impacting their bulk properties.

In Vitro Ion Release of Wires in Removable Orthodontic Appliances

Various orthodontic wire compositions and configurations are present on the market for removable appliances; however, there have still been only few studies focusing on the effect of resin color and additives such as glitter on corrosion of metallic wires under different conditions. Thus, the aim of the study was to compare concentrations of released ions (aluminium, chromium, nickel) in a corrosive medium under three different conditions: non-loaded wires, loaded wires, and non-loaded wires treated with Kukis^® cleaning tablets. Six different wires made of three types of steel alloy were embedded in PMMA resin leaving one centimetre of each wire emerging from the resin to come into contact with the corrosive medium. Glitter particles were added to half of the produced test specimens. For the unloaded test series, five specimens of each group were covered in a petri dish with 50 mL of corrosive medium (pH 2.3) following EN-ISO 10271 for seven days at 37 °C. The wires for the mechanically loaded test specimens overlapped the resin by 5 cm and were clamped into a time-switched electric drive for a defined period of time before the samples were taken after a testing time of 7 days. In the third group, unloaded test specimens were transferred from their petri dishes into the prepared Kukis^® solution every 24 h before being stored in the corrosive medium. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the specific ions in the corrosive solution. Statistical analysis showed that the mechanical loading of all wires could significantly raise the diffusion of ions into the corrosive medium. The colour of the resin did not affect the concentration of the released ions. The Kukis^® cleaning tabs could not lower the corrosion of the tested metals, as some of the wires were corroded even more using the brace cleanser. Glitter-containing test specimens showed significantly higher amounts of aluminium. Mechanical loading as well as the presence of glitter particles in the resin significantly affected ion concentrations.

Recent Progress on Wear-Resistant Materials: Designs, Properties, and Applications

There has been tremendous interest in the development of different innovative wear-resistant materials, which can help to reduce energy losses resulted from friction and wear by ≈40% over the next 10-15 years. This paper provides a comprehensive review of the recent progress on designs, properties, and applications of wear-resistant materials, starting with an introduction of various advanced technologies for the fabrication of wear-resistant materials and anti-wear structures with their wear mechanisms. Typical strategies of surface engineering and matrix strengthening for the development of wear-resistant materials are then analyzed, focusing on the development of coatings, surface texturing, surface hardening, architecture, and the exploration of matrix compositions, microstructures, and reinforcements. Afterward, the relationship between the wear resistance of a material and its intrinsic properties including hardness, stiffness, strength, and cyclic plasticity is discussed with underlying mechanisms, such as the lattice distortion effect, bonding strength effect, grain size effect, precipitation effect, grain boundary effect, dislocation or twinning effect. A wide range of fundamental applications, specifically in aerospace components, automobile parts, wind turbines, micro-/nano-electromechanical systems, atomic force microscopes, and biomedical devices are highlighted. This review is concluded with prospects on challenges and future directions in this critical field.

Exposure to the oral environment enhances the corrosion of metal orthodontic appliances caused by fluoride-containing products: Cytotoxicity, metal ion release, and surface roughness

INTRODUCTION

This study aimed to evaluate the metal ion release, cytotoxicity, and surface roughness of clinically used metal orthodontic appliances after immersion in different fluoride product solutions compared with those of new appliances.

METHODS

Used fixed appliances were debonded from 36 patients after their treatment was done. New appliances were as-received. Each used and new group comprised 36 sets of 20 brackets and 4 tubes that were divided into 3 groups by archwire type; stainless steel, nickel-titanium, and beta-titanium. The samples in each group were divided into 3 subgroups and immersed in solutions of fluoride toothpaste, 1.23% acidulated phosphate fluoride, or artificial saliva without fluoride as a control group. The immersion times were estimated from the recommended time for using each fluoride product for 3 months. The samples were then immersed in Dulbecco's Modified Eagle's Medium for 7 days. The cytotoxicity test was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay using primary gingival fibroblasts. Chromium, nickel, and iron ion release were detected using inductively coupled plasma mass spectroscopy. The surface roughness of the brackets and wires was measured by a scanning electron microscope and a noncontact optical 3-dimensional surface characterization and roughness measuring device. The data were analyzed using the paired t test and 2-way analysis of variance.

RESULTS

Used brackets demonstrated a significantly higher ion release, surface roughness, and cytotoxicity than the new brackets. Acidulated phosphate fluoride significantly increased the ion release and surface roughness; however, it significantly decreased cell viability, especially in the titanium molybdenum subgroup.

CONCLUSIONS

Used brackets were significantly prone to further corrosion. Acidulated phosphate fluoride gel should not be used in orthodontic patients with fixed metal appliances.

The Effects of Chemical Etching and Ultra-Fine Grain Structure of Titanium on MG-63 Cells Response

In this work, we study the influence of the surface properties of ultrafine grained (UFG) and coarse grained (CG) titanium on the morphology, viability, proliferation and differentiation of osteoblast-like MG-63 cells. Wet chemical etching in H2SO4/H2O2 and NH4OH/H2O2 solutions was used for producing surfaces with varying morphology, topography, composition and wettability. The topography and morphology have been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition was determined by time of flight mass-spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). The results showed that it is possible to obtain samples with different compositions, hydrophilicity, topography and nanoscale or/and microscale structures by changing the etching time and the type of etching solution. It was found that developed topography and morphology can improve spreading and proliferation rate of MG-63 cells. A significant advantage of the samples of the UFG series in comparison with CG in adhesion, proliferation at later stages of cultivation (7 days), higher alkaline phosphatase (ALP) activity and faster achievement of its maximum values was found. However, there is no clear benefit of the UFG series on osteopontin (OPN) expression. All studied samples showed no cytotoxicity towards MG-63 cells and promoted their osteogenic differentiation.

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.

Oral squamous cell carcinoma around dental implants: a systematic review

OBJECTIVE

This systematic review aimed to evaluate the epidemiologic profile, screen for possible risk factors, and evaluate the spectrum of clinical characteristics of oral squamous cell carcinoma (OSCC) around dental implants (DIs).

METHODS

The systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta- Analyses statement.

RESULTS

Thirty-three articles met the eligibility criteria. In total, the sample consisted of 63 patients, and women comprised the majority (55.5%). The mean age of patients was 66.7 years. Oral potentially malignant disorders were reported in 46% of patients, of which 65.5% occurred in women. The most common lesion found in women was oral lichen planus (52.6%). In 88.8% of patients OSCC around DIs occurred in the mandible, and the most common clinical appearance of the lesions was an exophytic mass (46%). Most of these lesions were initially treated as peri-implantitis.

CONCLUSIONS

Most patients with OSCC around DIs were women without known risk factors. It is important to emphasize that these lesions may present clinical and radiographic features that could resemble peri-implantitis, which can lead to delay in the diagnosis and subsequent treatment.

B-Comet Assay (Comet Assay on Buccal Cells) for the Evaluation of Primary DNA Damage in Human Biomonitoring Studies

Many subjects perceive venous blood collection as too invasive, and thus moving to better-accepted procedures for leukocytes collection might be crucial in human biomonitoring studies (e.g., biomonitoring of occupational or residential exposure to genotoxins) management. In this context, primary DNA damage was assessed in buccal lymphocytes (BLs), fresh whole venous, and capillary blood leukocytes, and compared with that in peripheral blood lymphocytes (PBLs)—the most frequently used cells—in 15 young subjects. Mouthwashes were collected after the volunteers rinsed their mouths with normal saline, and BLs were isolated by density gradient centrifugation. Blood samples were collected by venipuncture or by lancet. Anthropometric and lifestyle information was obtained by the administration of a structured questionnaire. As shown in the Bland-Altman plots, the level of agreement between BLs and PBLs lied within the accepted range, we thus enrolled a wider population (n = 54) to assess baseline DNA damage in BLs. In these cells, mean values of tail length (µm), tail intensity (%), and tail moment were 25.7 ± 0.9, 6.7 ± 0.4 and 1.0 ± 0.1, respectively. No significant association was observed between sex and smoking habit with any of the DNA damage parameters. Conversely, underweight subjects displayed significantly higher genomic instability compared with normal weight group (p < 0.05). In conclusion, we successfully managed to set up and update a non-invasive and well-accepted procedure for the isolation of BLs from saliva that could be useful in upcoming biomonitoring studies.

Epidemiological profile and clinical implications of oral squamous cell carcinoma adjacent to dental implants

OBJECTIVES

Describe the epidemiological profile of patients with oral squamous cell carcinoma (OSCC) around dental implants (DI), investigate the spectrum of clinical and pathological characteristics, and discuss the implications of diagnosis delay of these lesions.

METHODS

Retrospective analysis of patients treated of OSCC adjacent to DI at A.C. Camargo Cancer Center between 2009 and 2020.

RESULTS

Thirty one patients were identified, being women the majority (58.1%). The mean age of the patients was 68.8 years. Never smoker corresponds to 46.9% and never alcohol consumer to 54.9% of the sample. OPMD was reported in 45.2% of patients, affecting mainly women (78.5%). Leukoplakia (63.7%) followed by oral lichen planus (36.3%) was the most common OPMD found in women. OSCC adjacent to DI occurred in the inferior gingiva/alveolar mucosa in 48.3% of cases, and ulceration was the most common clinical appearance (87%). Peri-implantitis (PI) was initial clinical diagnosis in 16.1% of cases.

CONCLUSIONS

Oral squamous cell carcinoma adjacent to DI was more common in women over 70 years old, non-smokers and non-drinker, and the majority had oral leukoplakia before the diagnosis of OSCC. OSCC may present clinical and radiographic features that resemble PI which can delay the diagnosis and impair the prognosis.

Are Metal Ions That Make up Orthodontic Alloys Cytotoxic, and Do They Induce Oxidative Stress in a Yeast Cell Model?

Compositions of stainless steel, nickel-titanium, cobalt-chromium and β-titanium orthodontic alloys were simulated with mixtures of Fe, Ni, Cr, Co, Ti and Mo metal ions as potential oxidative stress-triggering agents. Wild-type yeast Saccharomyces cerevisiae and two mutants ΔSod1 and ΔCtt1 were used as model organisms to assess the cytotoxicity and oxidative stress occurrence. Metal mixtures at concentrations of 1, 10, 100 and 1000 µM were prepared out of metal chlorides and used to treat yeast cells for 24 h. Every simulated orthodontic alloy at 1000 µM was cytotoxic, and, in the case of cobalt-chromium alloy, even 100 µM was cytotoxic. Reactive oxygen species and oxidative damage were detected for stainless steel and both cobalt-chromium alloys at 1000 µM in wild-type yeast and 100 µM in the ΔSod1 and ΔCtt1 mutants. Simulated nickel-titanium and β-titanium alloy did not induce oxidative stress in any of the tested strains.

Metal-based nanoparticles for bone tissue engineering

Tissue is vital to the organization of multicellular organisms, because it creates the different organs and provides the main scaffold for body shape. The quest for effective methods to allow tissue regeneration and create scaffolds for new tissue growth has intensified in recent years. Tissue engineering has recently used some promising alternatives to existing conventional scaffold materials, many of which have been derived from nanotechnology. One important example of these is metal nanoparticles. The purpose of this review is to cover novel tissue engineering methods, paying special attention to those based on the use of metal-based nanoparticles. The unique physiochemical properties of metal nanoparticles, such as antibacterial effects, shape memory phenomenon, low cytotoxicity, stimulation of the proliferation process, good mechanical and tensile strength, acceptable biocompatibility, significant osteogenic potential, and ability to regulate cell growth pathways, suggest that they can perform as novel types of scaffolds for bone tissue engineering. The basic principles of various nanoparticle-based composites and scaffolds are discussed in this review. The merits and demerits of these particles are critically discussed, and their importance in bone tissue engineering is highlighted.

In Vitro Determination of Genotoxicity Induced by Brackets Alloys in Cultures of Human Gingival Fibroblasts

Orthodontic brackets release ions that can be reabsorbed in the oral mucosa, potentially causing complications, including cytotoxic effects and mutagenic alterations. The aim was to evaluate the genotoxicity induced by orthodontic appliance alloys in cultures of human gingival fibroblasts by comet assay. Eluates were obtained from the following brackets alloys: EconoLine (SS: stainless steel), MiniMirage (Ni-Ti: nickel-titanium), Nu-Edge (Co-Cr: cobalt-chromium), In-Vu (PC-polycrystals (PC) aluminum oxide), and Monocrystal IZE (monocrystalline (MC) aluminum oxide). Each bracket was sterilized and exposed to a corrosive process for 35 days. The obtained eluates were tested for genotoxicity of human gingival fibroblasts (HGFA) by the alkaline comet assay. All study groups showed genotoxic effects; there was a significant difference (p < 0.0001) among groups. The eluates obtained from Ni-Ti showed a 16-times greater genotoxic effect. There were differences in genotoxicity after comparing the Ni-Ti with SS (p < 0.01) and Co-Cr brackets (p < 0.001). The ceramic was more genotoxic than metallic brackets (SS and Co-Cr), but less than the Ni-Ti. This in vitro model will be useful for further study of early DNA damage caused by brackets and other biomaterials used in the oral cavity before their introduction into the clinical setting.

Effect of fluoride agents on surface characteristics of NiTi wires. An ex vivo investigation

Aim

To analyze the degree of corrosion of nickel titanium arch wires in patients with and without exposure to fluorides.

Material and methods

This was an ex vivo study comprising of 60 subjects undergoing fixed orthodontic treatment. Group 1(controls) comprised of 30 sets of new unused NiTi wires and unused 11, 15 brackets, Group 2(patients) comprised of 30 sets of non fluoridated NiTi wires and 11, 15 brackets and Group 3(patients) had 30 sets of fluoridated NiTi wires and 11, 15 brackets. NiTi wires were used over 6 months of treatment(0.014″,0.016″, 16 × 22", each wire was used for 2 months and replaced with the next size). All wires were retrieved, stored and analyzed. At 6 months, brackets from 11 to 15 were debonded in both treatment groups. Archwires and brackets in 3 groups were subjected to SEM analysis at 500 and 1000X to observe differences. Additionally, EDX Spectroscopy was undertaken to evaluate surface elemental compositional differences in groups.

Results

Significant differences among groups were evident in brackets and archwires tested. Maximum degradation, cracks and dark spots were seen in wires and brackets exposed to fluoride agents. EDX spectroscopy revealed least Ni% in fluoridated wires and brackets.

Conclusions

Increased leaching of metal ions was evident when wires and brackets are exposed to fluoride agents during treatment. Use of non fluoridated mouthwash and toothpastes may be considered in orthodontic patients without risk of caries to mitigate such effects.

Metals and Metalloids Release from Orthodontic Elastomeric and Stainless Steel Ligatures: In Vitro Risk Assessment of Human Exposure

Elastomeric ligatures are increasingly used as a part of esthetic orthodontic treatment, particularly in children. The aim of the present study was to experimentally test whether these appliances may contribute to exposure to toxic elements. In the present study, elastomeric ligatures (ELs) were incubated in artificial human saliva for 1 month (a typical period of their use) and the release of 21 metals (Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mg, Mo, Ni, Pb, Rb, Tl, Ti, Sb, Sr, Sn, Zn, U, V) and 2 metalloids (As and Ge) was studied using inductively coupled plasma-mass spectrometry. For comparison, stainless steel ligatures (SLs) were incubated for 1, 3, and 6 months (since sometimes their use is prolonged) under similar conditions. The determined metal levels were compared to the corresponding safety limits for human exposure. During 1 month, the ELs released Cd, Co, Cr, Mn, Ni, and Sn at total mean ± SD level of 0.31 ± 0.09, 0.98 ± 0.30, 3.96 ± 1.31, 14.7 ± 8.5, 13.8 ± 4.8, and 49.5 ± 27.7 μg, respectively. Other elements were always below the detection limits. In case of SL, the release of Co, Cr, Fe, Ni, Mn, and Sn was observed, and the determined values increased over the studied period. After 6 months, their total mean ± SD levels amounted to 28.6 ± 0.2, 21.7 ± 0.2, 623.5 ± 3.0, 1152.7 ± 1.8, 5.5 ± 0.3, and 22.6 ± 0.2 μg, respectively. The released metal levels from both ligature types were always below safety limits. The release of Ni from SL during 6 months would constitute 5.0 and 11.5% of tolerable intake in adults and children, respectively. The results of this in vitro study highlight that the use of ligatures in orthodontic treatment can be considered safe in terms of metal exposure although elastic ligatures replaced on a monthly basis appear to be advantageous in comparison to the prolonged use of stainless steel appliances.

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.

Impact of Heavy Metals on Host Cells: Special Focus on Nickel-Mediated Pathologies and Novel Interventional Approaches

BACKGROUND

Heavy metals [arsenic, aluminium, cadmium, chromium, cobalt, lead, nickel (Ni), palladium and titanium] are environmental contaminants able to impact with host human cells, thus, leading to severe damage.

OBJECTIVE

In this review, the detrimental effects of several heavy metals on human organs will be discussed and special emphasis will be placed on Ni. In particular, Ni is able to interact with Toll-like receptor-4 on immune and non-immune cells, thus, triggering the cascade of pro-inflammatory cytokines. Then, inflammatory and allergic reactions mediated by Ni will be illustrated within different organs, even including the central nervous system, airways and the gastrointestinal system.

DISCUSSION

Different therapeutic strategies have been adopted to mitigate Ni-induced inflammatoryallergic reactions. In this context, the ability of polyphenols to counteract the inflammatory pathway induced by Ni on peripheral blood leukocytes from Ni-sensitized patients will be outlined. In particular, polyphenols are able to decrease serum levels of interleukin (IL)-17, while increasing levels of IL- 10. These data suggest that the equilibrium between T regulatory cells and T helper 17 cells is recovered with IL-10 acting as an anti-inflammatory cytokine. In the same context, polyphenols reduced elevated serum levels of nitric oxide, thus, expressing their anti-oxidant potential. Finally, the carcinogenic potential of heavy metals, even including Ni, will be highlighted.

CONCLUSION

Heavy metals, particularly Ni, are spread in the environment. Nutritional approaches seem to represent a novel option in the treatment of Ni-induced damage and, among them, polyphenols should be taken into consideration for their anti-oxidant and anti-inflammatory activities.

Biomonitorization of metal ions in the serum of Iranian patients treated with fixed orthodontic appliances in comparison with controls in eastern Iran

The present study aimed to assess the level of metal ions [chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn)] in the serum of patients with fixed orthodontic appliances. One hundred samples (32 males, 68 females) were collected from patients undergoing fixed orthodontic treatment for different periods. A reference (control) group (24 males, 16 females) who had no appliances was used to properly evaluate the changes in the level of these elements in orthodontic appliance users. The element concentrations were measured using inductively coupled plasma mass spectrometry (ICP-MS). Higher concentrations of metal ions (except for Cr) were found in the serum of the orthodontic group. Bivariate scatter plot showed a highly significant (p < 0.001) correlation between Ni and other elements. The duration of orthodontic treatment increased significantly the Ni levels whereas the bracket type was found to have no significant impact on altering the concentration level of metal ions. The results of the SEM-EDS showed a high variation in the level of metal ions in the brackets and wires. In conclusion, fixed orthodontic appliances increased serum levels of Ni, Zn, Mn, Fe, and Cu but did not change Cr levels.

A Comparison of the Compositional, Microstructural, and Mechanical Characteristics of Ni-Free and Conventional Stainless Steel Orthodontic Wires

Ni-free orthodontic wires were introduced to mitigate concerns associated with the use of Ni-containing alloys in orthodontics. However, limited information is available on their properties and therefore, the aim of this study was to characterize the elemental composition, the microstructure, and the mechanical properties of Ni-free orthodontic wires and compare them with their stainless steel (SS) counterparts. Four Ni-free and four conventional SS wires were included in this study. All the wires were initially imaged with a Scanning Electron Microscopy (SEM) and their elemental compositions were determined by X-ray Energy Dispersive Spectroscopy (EDX). Then, their microstructure was assessed by X-ray Diffraction (XRD) and the indentation modulus, elastic index, Martens Hardness and Vickers Hardness by Instrumented Indentation Testing (IIT). All the wires demonstrated surface cracks and pores oriented parallel to their long axis. The elemental composition of Ni-free alloys showed an increased Mn and Cr content while both SS and Ni-free wires shared the same dominant austenite structure. In conclusion, despite the differences in elemental composition, Ni-free wires demonstrated a similar microstructure and comparable mechanical properties with their conventional SS counterparts and thus may be considered as a promising alternative for patients with Ni supersensitivity.

Facile Surface Modification Method for Synergistically Enhancing the Biocompatibility and Bioactivity of Poly(ether ether ketone) That Induced Osteodifferentiation

Poly(ether ether ketone) (PEEK) is a promising material in biomedical engineering due to its suitable mechanical properties and excellent chemical resistance and biocompatibility. However, the biological inertness of PEEK limits its applications. In this study, we developed a facile approach of immersion to generate a biocompatible and bioactive PEEK that induced osteodifferentiation. First, micropores on the surface of PEEK were introduced by concentrated sulfuric acid and subsequent water immersion, followed by the hydrothermal treatment to reduce residual sulfuric acid. Subsequently, the sulfonated PEEK surface was activated by the oxygen plasma treatment and then coated with a poly(dopamine) (PDA) layer by immersion into the dopamine solution. Finally, the tripeptide Arg-Gly-Asp (RGD) was integrated onto the PDA-coated surface of PEEK by immersion into the RGD peptide solution. The surface characteristics (physical chemistry and biological properties) and the ability to form bonelike apatite were systematically investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, water contact angle analysis, the Archimedes' fluid saturation method, ellipsometry, a quartz crystal microbalance with dissipation monitoring, cell proliferation, real-time reverse transcription polymerase chain reaction analysis, alizarin red staining, immunocytochemistry staining, and simulated body fluid immersion. Collectively, the modified PEEK showed a significantly improved ability to promote cell proliferation, osteogenic differentiation, and bonelike apatite formation in vitro as compared to the PEEK control. These results demonstrate that combined facile surface modifications for PEEK enhance its bioactivity and biocompatibility, and induce osteodifferentiation. This study presents a strategy for broadening the use of PEEK in the application of orthopedic implants and could be industrially scalable in future.

The Photodynamic Properties and the Genotoxicity of Heat-Treated Silicalite-1 Films

We investigated the use of a supported silicalite-1 film (SF) as a promising coating for metallic materials used in the fabrication of prostheses. The role of carbonaceous residua present on high-temperature calcined-SF in generating singlet oxygen for future use as a sterilization method has also been addressed, and the potential genotoxicity of these residua in osteoblast-like cells has been investigated. Calcination of as-synthesized SF induced the appearance of a rather complicated mixture of aliphatic and aromatic species on its outer surface. A series of variously volatile polycyclic aromatic hydrocarbons (PAH), including naphthalene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene, were identified in micromole concentrations. Irradiation of these PAHs on calcined-SF immersed in air-saturated chloroform led to the formation of very low concentrations of singlet oxygen. However, an increased level of DNA damage was observed on calcined-SF by immunofluorescence staining of phosphorylated histone H2AX analyzed by flow cytometry.

An ingestible self-orienting system for oral delivery of macromolecules

Biomacromolecules have transformed our capacity to effectively treat diseases; however, their rapid degradation and poor absorption in the gastrointestinal (GI) tract generally limit their administration to parenteral routes. An oral biologic delivery system must aid in both localization and permeation to achieve systemic drug uptake. Inspired by the leopard tortoise's ability to passively reorient, we developed an ingestible self-orienting millimeter-scale applicator (SOMA) that autonomously positions itself to engage with GI tissue. It then deploys milliposts fabricated from active pharmaceutical ingredients directly through the gastric mucosa while avoiding perforation. We conducted in vivo studies in rats and swine that support the applicator's safety and, using insulin as a model drug, demonstrated that the SOMA delivers active pharmaceutical ingredient plasma levels comparable to those achieved with subcutaneous millipost administration.

Proliferation of Osteoblasts on Laser-Modified Nanostructured Titanium Surfaces

Nanostructured titanium has become a useful material for biomedical applications such as dental implants. Certain surface properties (grain size, roughness, wettability) are highly expected to promote cell adhesion and osseointegration. The aim of this study was to compare the biocompatibilities of several titanium materials using human osteoblast cell line hFOB 1.19. Eight different types of specimens were examined: machined commercially pure grade 2 (cpTi2) and 4 (cpTi4) titanium, nanostructured titanium of the same grades (nTi2, nTi4), and corresponding specimens with laser-treated surfaces (cpTi2L, cpTi4L, nTi2L, nTi4L). Their surface topography was evaluated by means of scanning electron microscopy. Surface roughness was measured using a mechanical contact profilometer. Specimens with laser-treated surfaces had significantly higher surface roughness. Wettability was measured by the drop contact angle method. Nanostructured samples had significantly higher wettability. Cell proliferation after 48 hours from plating was assessed by viability and proliferation assay. The highest proliferation of osteoblasts was found in nTi4 specimens. The analysis of cell proliferation revealed a difference between machined and laser-treated specimens. The mean proliferation was lower on the laser-treated titanium materials. Although plain laser treatment increases surface roughness and wettability, it does not seem to lead to improved biocompatibility.

Effect of radiofrequency electromagnetic fields (RF-EMFS) from mobile phones on nickel release from orthodontic brackets: An in vitro study

BACKGROUND

The worldwide dramatic increase in the use of cell phones has generated great concerns about their potential adverse health effects.

OBJECTIVE

The aim of the present study was to evaluate the effects of radiofrequency electromagnetic fields (RF-EMFs) emitted from mobile phones on the level of nickel release from orthodontic brackets.

METHODS

Twenty stainless steel brackets were divided randomly into experimental and control groups (n=10). Brackets were immersed in artificial saliva at 37°C for 6 months. Experimental group were exposed to GSM 900MHz RF-EMFs emitted from a mobile phone stimulator for 4hours. The specific absorption rate (SAR) was 2.287W/kg. The concentration of nickel in the artificial saliva in both groups was evaluated by using the cold-vapour atomic absorption spectrometry. The Mann-Whitney test was used to assess significant differences in nickel release between the exposed and non-exposed groups.

RESULTS

The mean nickel levels in the exposed and non-exposed groups were 11.95 and 2.89μg/l, respectively. This difference between the concentrations of nickel in the artificial saliva of these groups was statistically significant (P=0.001).

CONCLUSION

Exposure to RF-EMFs emitted from mobile phones can lead to human exposure to higher levels of nickel in saliva in patients with orthodontic appliances. As nickel exposure can lead to allergic reaction in humans and considering this point that about 10-20% of the population can be hypersensitive to nickel, further studies are needed to evaluate the effects of radiofrequency electromagnetic fields (RF-EMFs) emitted from common devices such as mobile phones or Wi-Fi routers on the level of nickel release from orthodontic brackets.

Molybdenum Disulfide Surface Modification of Ultrafine-Grained Titanium for Enhanced Cellular Growth and Antibacterial Effect

The commercially pure Ti (CP Ti) and equal-channel angular pressing (ECAP) processed Ti can contribute to the downsizing of medical devices with their superior mechanical properties and negligible toxicity. However, the ECAP-processed pure Ti has the risk of bacterial infection. Here, the coarse- and ultrafine-grained Ti substrates were surface-modified with molybdenum disulfide (MoS2) to improve the cell proliferation and growth with antibacterial effect for further dental applications. According to in vitro tests using the pre-osteoblast of MC3T3-E1 cell and a bacterial model of Escherichia coli (E. coli), MoS2 nanoflakes coated and ECAP-processed Ti substrates showed a significant increase in surface energy and singlet oxygen generation resulting in improved cell attachment and antibacterial effect. In addition, we confirmed the stability of the surface modified Ti substrates in a physiological solution and an artificial bone. Taken together, MoS2 modified and ECAP-processed Ti substrates might be successfully harnessed for various dental applications.

Role of dental hardware in oral cavity squamous cell carcinoma in the low-risk nonsmoker nondrinker population

BACKGROUND

Oral cavity squamous cell carcinoma (SCC) arising in nonsmokers and nondrinkers remains poorly characterized. We hypothesized that these patients had prior exposure to metallic dental hardware.

METHODS

We utilized a questionnaire querying the lifetime oral health status of 54 patients. Demographics and extensive oral health history were collected.

RESULTS

The majority of patients (74%) had prior exposure to metallic dental hardware. The younger population with almost exclusively oral tongue cancer had a high prevalence of metallic orthodontic braces (40%) within 15 years before diagnosis. In the 51+ year age group, 82% had crowns, dental implants, and/or dentures with metallic elements.

CONCLUSION

Exposure to metallic dental hardware has increased in the past few decades given the rise of orthodontic braces and older adults retaining more teeth. Although this study does not prove a causal relationship between oral cavity SCC and dental hardware, this is a step toward identifying and investigating their role.

The metal content of generic orthodontic brackets compared with proprietary brackets

Background

With minimal manufacturer information, a variety of ‘generic’ orthodontic brackets are available online from overseas distributors. The present study investigated the metal composition of generic orthodontic brackets compared with two well-known ‘proprietary’ brands.

Materials and methods

Ranging in price from AU$2.99 to $65, five sets of different generic brackets were obtained directly from China via eBay (G1, G2…G5). Proprietary brackets were obtained from American Orthodontics (P1) and Rocky Mountain Orthodontics (P2). The 11, 12, 13 and 14 brackets from each set were liquefied in an acid solution and subjected to trace element analysis using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) with respect to nickel, chromium, iron, copper, molybdenum, manganese, cadmium, mercury, arsenic and lead. Statistical analysis investigated the compositional consistency within and between each brand.

Results

The composition of P1 and P2 agreed with the manufacturer’s data. The generic groups typically had low molybdenum and higher copper content and approximated either 17-4 or AISI304 stainless steels or a combination of both. No relationship between brand and consistency of manufacture could be identified. The cheapest bracket contained lead.

Conclusions

Generic and proprietary brackets showed differences in their metal composition that may have biocompatibility implications.

Evaluation of scalp hair nickel and chromium level changes in patients with fixed orthodontic appliance: a one-year follow-up study

BACKGROUND AND OBJECTIVES

The release of metal ions from orthodontic appliances is part of the dissolution and biomechanical processes of alloys. Nickel (Ni) and chromium (Cr) are the elements commonly used in the manufacture of various components of fixed orthodontic appliances, including bands, brackets and wires. This study was aimed to measure the Ni and Cr ions levels in the scalp hair of patients treated with fixed orthodontic appliances in comparison of the control group.

MATERIALS AND METHODS

The patient group consisted of 24 patients treated with fixed orthodontic appliances for one year, while the control group included 28 healthy individuals without orthodontic appliances. Analysis of the Cr and Ni was performed using atomic absorption spectrophotometer by graphite furnace method. The data were analyzed via student and paired samples t-test and ANOVA repeated measurement test.

RESULTS

After one year, the levels of Ni and Cr in two groups showed significant differences (0.086 ± 0.007 and 0.258 ± 0.009 µg/g for control group and 0.149 ± 0.010 and 0.339 ± 0.013 µg/g for patient group, respectively for Ni and Cr, p < .001). ANCOVA test by removing the effects of age, gender and the baseline levels of Ni and Cr showed that changes in these ions in the scalp hair of both groups after one year were statistically significant.

CONCLUSION

Due to the slightly elevated levels of Ni and Cr ions in the scalp hair of patients treated with fixed orthodontic appliances and considering the cytotoxic and allergic effects of these ions, changing the ingredients in fixed orthodontic appliances is suggested for the future.

Do Dietary Habits Influence Trace Elements Release from Fixed Orthodontic Appliances?

The objective was to investigate the effect of dietary habits on the release of Cr and Ni ions from orthodontic appliances by hair mineral analysis. Patients (N = 47) underwent electronic questionnaire survey to investigate the effect of dietary habits on Cr and Ni levels in hair. The research was carried out on hair sampled at the beginning and in the 4th, 8th, and 12th months of the treatment. The content of Cr and Ni in the collected samples was determined by ICP-OES. The study showed that consumption of acidic dietary products may have the effect on increasing the release of Cr and Ni ions from orthodontic appliances. The release of Cr from orthodontic appliances in patients who consumed fruit juice, coffee, yoghurt, and vinegar was higher. The coefficients enabling comparison of metal ions release pattern at a given sampling points were defined. The comparison of the coefficients yielded the information on the possible magnification of metal ions released as the result of the additional factor consumption of acidic food or drink that intensifies metal ions release. The following magnification pattern was found for chromium: coffee (7.57 times) > yoghurt (2.53) > juice (1.86) > vinegar (1.08), and for nickel: vinegar (2.2) > coffee (1.22) > juice (1.05). Yoghurt did not intensify the release of nickel. Concluding, orthodontic patients should avoid drinking/eating coffee, yoghurt, fruit juices, and vinegar.

Effect of incubation duration, growth temperature, and abiotic surface type on cell surface properties, adhesion and pathogenicity of biofilm-detached Staphylococcus aureus cells

The goal of this study was to investigate the effect of growth conditions such as the temperature (20, 30 and 37 °C), incubation duration (24 and 48 h) and surface type (stainless steel and polycarbonate) on the cell surface physicochemical properties and adhesion to abiotic surfaces of biofilm-detached and planktonic Staphylococcus aureus cells. This study tested also the hypothesis that S. aureus planktonic cells exhibit distinct pathogenic properties compared with their sessile counterparts. The results showed that the changes of the growth conditions promoted changes in the zeta potential, hydrophobicity, electron donor/acceptor character of the studied cell populations. Biofilm-detached cells showed a greater adhesion to stainless steel and polycarbonate compared with planktonic cells. Compared with planktonic cells, sessile ones showed higher cytotoxic effect against HeLa cells, DNase activity, and siderophore levels. The higher cytotoxic effect and production of DNase and siderophore increased with the increase of temperature and duration of incubations. Based on the obtained data, the S. aureus biofilm-detached cells were found to be distinct in many physiological properties compared with their planktonic counterparts.

Metal release profiles of orthodontic bands, brackets, and wires: an in vitro study

AIM

The present study evaluated the temporal release of Co Cr, Mn, and Ni from the components of a typical orthodontic appliance during simulated orthodontic treatment.

MATERIALS AND METHODS

Several commercially available types of bands, brackets, and wires were exposed to an artificial saliva solution for at least 44 days and the metals released were quantified in regular intervals using inductively coupled plasma quadrupole mass spectrometry (ICP-MS, Elan DRC+, Perkin Elmer, USA). Corrosion products encountered on some products were investigated by a scanning electron microscope equipped with an energy dispersive X-ray microanalyzer (EDX).

RESULTS

Bands released the largest quantities of Co, Cr, Mn, and Ni, followed by brackets and wires. Three different temporal metal release profiles were observed: (1) constant, though not necessarily linear release, (2) saturation (metal release stopped after a certain time), and (3) an intermediate release profile that showed signs of saturation without reaching saturation. These temporal metal liberation profiles were found to be strongly dependent on the individual test pieces. The corrosion products which developed on some of the bands after a 6-month immersion in artificial saliva and the different metal release profiles of the investigated bands were traced back to different attachments welded onto the bands.

CONCLUSION

The use of constant release rates will clearly underestimate metal intake by the patient during the first couple of days and overestimate exposure during the remainder of the treatment which is usually several months long. While our data are consistent with heavy metal release by orthodontic materials at levels well below typical dietary intake, we nevertheless recommend the use of titanium brackets and replacement of the band with a tube in cases of severe Ni or Cr allergy.