Cell death affected by dental alloys: Modes and mechanisms

Oral Galvanism Side Effects: Comparing Alloy Ions and Galvanic Current Effects on the Mucosa-like Model

The interaction of different dental alloys with the oral environment may cause severe side effects (e.g., burning sensation, inflammatory reactions, carcinogenesis) as a result of oral galvanism. However, the pathogenesis of side effects associated with oral galvanism is still unclear, and the effects of direct current and alloy corrosion ions are considered potentially contributing factors. Therefore, the aim of this study was to systemically compare the damaging effects of (1) galvanism as a synergistic process (direct current + corrosion ions), (2) direct current separately, and (3) corrosion ions separately on an in vitro mucosa-like model based on a cell line of immortalized human keratinocytes (HaCaTs) to reveal the factors playing a pivotal role in dental alloys side effects. For this, we chose and compared the dental alloys with the highest risk of oral galvanism: Ti64-AgPd and NiCr-AgPd. We showed that galvanic current may be the leading damaging factor in the cytotoxic processes associated with galvanic coupling of metallic intraoral appliances in the oral cavity, especially in the short-term period (28 days). However, the contribution of corrosion ions (Ni2+) to the synergistic toxicity was also shown, and quite possibly, in the long term, it could be no less dangerous.

Bio-inspired nanocomposite coatings on orthodontic archwires with corrosion resistant and antibacterial properties

The corrosion resistance and antibacterial properties of fixed orthodontic devices are insufficient in the complex oral cavity, which delays tooth movement and causes enamel demineralization. To overcome the challenges, this research constructs a series of polydopamine-graphene oxide (PDA-GO) nanocoatings on representative NiTi archwires via self-assembly. The morphology, chemical structure, and multifunctional properties of coatings showed tunability dependent on the PDA/GO ratio. Optimized PDA-GO coatings with uniform and dense characteristics prolonged the diffusion path for the corrosive medium and reduced Ni dissolution in NiTi alloys. Meanwhile, the applied coatings endowed NiTi alloys with antibacterial activity against Streptococcus mutans due to the surface structures and inherent properties of PDA-GO. In vitro cytotoxicity tests further verified their good biocompatibility. This bio-inspired nanocomposite coating provides a practical reference for modification of dental metal surfaces to better behave in the intraoral environment.

The Impact of Commercially Available Dry Mouth Products on the Corrosion Resistance of Common Dental Alloys

Dental implants are thought to be implanted for life, but throughout their lifespan, they function in aggressive oral environment, resulting in corrosion of the material itself as well as possible inflammation of adjacent tissues. Therefore, materials and oral products for people with metallic intraoral appliances must be chosen carefully. The purpose of this study was to investigate the corrosion behavior of common titanium and cobalt-chromium alloys in interaction with various dry mouth products using electrochemical impedance spectroscopy (EIS). The study showed that different dry mouth products lead to different open circuit potentials, corrosion voltages, and currents. The corrosion potentials of Ti64 and CoCr ranged from -0.3 to 0 V and -0.67 to 0.7 V, respectively. In contrast to titanium, pitting corrosion was observed for the cobalt-chromium alloy, leading to the release of Co and Cr ions. Based on the results, it can be argued that the commercially available dry mouth remedies are more favorable for dental alloys in terms of corrosion compared to Fusayama Meyer's artificial saliva. Thus, to prevent undesirable interactions, the individual characteristics of not only the composition of each patient's tooth and jaw structure, but also the materials already used in their oral cavity and oral hygiene products, must be taken into account.

Cytotoxicity of Commercially Pure Titanium (cpTi), Silver-Palladium (Ag-Pd), and Nickel-Chromium (Ni-Cr) Alloys Commonly Used in the Fabrication of Dental Prosthetic Restorations

INTRODUCTION

The longevity of dental implants is affected by the ability to avoid any hypersensitivity or corrosive reactions in the oral cavity. The aim of the current study was to evaluate the cytotoxic effect of commercially pure titanium (cpTi), silver-palladium (Ag-Pd), and nickel-chromium (Ni-Cr) on human gingival fibroblast (HGF).

METHODS

The sample size used was 10 discs from each alloy used with dimensions of 4x3mm. The HGF was derived from healthy patients subjected to gingivectomy procedures. Of the specimens, 50% were incubated in artificial saliva and the other half in Dulbecco's Modified Eagle medium (DMEM). The extract of each alloy in both media was collected and applied on HGF. After 24 hours the morphology of the HGF cells was examined to detect any apoptosis or cell death. Also, cell viability was evaluated by the use of a 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Statistical analysis was performed using students' t-test and two-way ANOVA with a significance level of p<0.05.

RESULTS

In the case of morphological examination of HGF and MTT assessment, only cpTi alloy specimens didn't display any cytotoxic effect. Ni-Cr was the most cytotoxic alloy of the three. Also, MTT activities of all three alloys were decreased when they were incubated in artificial saliva.

CONCLUSION

cpTi exhibited the highest corrosion resistance in comparison to Ag-Pd and Ni-Cr alloys. Ag-Pd alloys showed acceptable resistance to corrosion that is due to the passivity effect. Also, artificial saliva increased the cytotoxic effect of the tested alloys more than DMEM.

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.

Toxicological Risks of the Cobalt-Chromium Alloys in Dentistry: A Systematic Review

Background: The toxicological risk of Co-Cr dental alloys is actually a sensitive subject with the European regulatory changes, namely regulation (EU) 2017/745 and annex VI to the CLP regulation (EC) 1972/2008. Objectives: The objective of this review is to conduct a rigorous analysis of the cytocompatibility of cobalt-chromium (Co-Cr) dental alloys. Considering various parameters such as cytotoxicity, type IV hypersensitivity reaction, sensitization, and irritation, we investigated evidence of toxicity of Co-Cr in human dental applications. Data sources: Specific search strategies were performed in three electronic databases, namely Medline, Embase, and Web of Science, using a main restriction in the search regarding the publication date (1995-2022). Study selection: Out of a total of 836 articles, only 21 studies were selected and analyzed according to PRISMA methodology. Results: Among them, 10 in vitro studies using human samples and 11 in vivo studies on human patients were distinguished. Most of the in vitro studies confirmed that Co-Cr alloys have a good cytocompatibility compared to Ni alloys. Regarding the in vivo studies, it appeared that Co-Cr could rarely cause sensitization, irritation, and allergic reactions. Reactions were mainly observed for people allergic to Co or Cr. Nevertheless, titanium-based materials showed better results. Conclusions: This study proposes a new state of the art on Co-Cr dental alloys and will thus be very useful for carrying out additional studies. Relevance: This review will help practitioners in their daily clinical choice.

Metal Ion Emission and Corrosion Resistance of 3D-Printed Dental Alloy

Background: Prosthetic rehabilitation requires application of materials with different chemical, mechanical and biological properties which must provide longevity, esthetics, and safe use. Corrosion resistance and metal ion emission are the major factors defining biocompatibility of base dental alloys. Digitalization in Dentistry leads to development of new materials suitable for CAD/CAM technologies. Cobalt-chromium powder alloys are used for additive manufacturing of PFM crowns. The aim of this study is to evaluate corrosion resistance and metal ion emission of Cobalt-chromium dental alloy for 3D printing. Materials and methods: 35 metal copings were designed using digital files of intraoral scans of 35 patients. CoCr dental alloy EOS CobaltChrome SP2 (EOS, Germany) was used to produce the copings by DMLS (direct laser metal sintering). Tests for presence of free Cobalt ions were conducted at several stages of the production process. Open circuit potential measurements were conducted 2 hours, 24 hours, and 7 days after placing the copings in artificial saliva. Metal ion emission was assessed by inductively coupled plasma mass spectrometry (ICP–MS) after 24 hour- and 7 day-period of stay in the solution. Results: Tests for free Cobalt ions were positive at all stages during production of the metal copings. Eocp measurements showed high corrosion resistance which increased in time. ICP-MS showed significantly higher amount of cobalt and chromium ions after 7-day period of stay compared to 24-hour period. Conclusion: Studied alloy showed high corrosion resistance at in vitro conditions. Detected ion emission requires further investigations on the biological properties.

The apoptotic and autophagic effects of cast Au-Pt, and differently manufactured Co-Cr and cp-Ti on three-dimensional oral mucosal model

The application of digitally manufactured dental metals has aroused the attention on their biocompatibilities. Three-dimensional oral mucosal model (3D OMM) would provide excellent assessments to the biocompatibility. In the current study, we set to measure metal ion release levels in the extracts of cast gold-platinum alloy (Au-Pt), differently manufactured cobalt-chromium alloy (Co-Cr) and commercially pure titanium (cp-Ti). We further tested two scaffold materials of 3D OMM to determine the better one for the succedent work. Lastly, we evaluated the apoptotic and autophagic effects of cast Au-Pt, and differently manufactured Co-Cr and cp-Ti on mucosal cells based on 3D OMM. We found that, in the construction of 3D OMM, Matrigel showed better performance than bovine acellular dermal matrix. Thus, Matrigel was chosen to construct the 3D OMM in the succedent studies. The results of ion release and biological assessments showed that, firstly, cast Au-Pt and cp-Ti triggered less early apoptotic cells and ion release than cast Co-Cr, implying better chemical stability and biocompatibility of them; secondly, digitally manufactured (including CAD/CAM milling and SLM) Co-Cr showed significantly lower ion release levels and lesser early apoptotic effects on 3D OMM as compared to the cast one. Although cast cp-Ti released much more ions than CAD/CAM milling one, manufacturing methods had no impact on apoptotic effect of cp-Ti. Therefore, we believe that digital methods possess same or even better chemical stability and biocompatibility than conventional casting one. Thirdly, although increased autophagic levels are observed in all test groups, so far there is no evidence that the test metals trigger different levels of autophagy as compared to each other. In addition, correlation analysis indicates that Co, W, and Mn appear to be the potential inducements for the apoptotic and autophagic effects of Co-Cr.

Removal of dental alloys and titanium attenuates trace metals and biological effects on liver and kidney

To determine whether the potential effects on liver and kidney caused by dental alloys could be reduced or terminated by the removal of nickel-chromium (Ni-Cr) alloy, cobalt-chromium (Co-Cr) alloy, and commercially pure titanium (CP-Ti), they were placed in the cheek pouches of Syrian hamsters according to ISO 10993-10. Then, the peak/plateau and end times of trace metals in the blood were determined with or without the removal of the dental alloys. Based on these time points, the trace metals and their effects on liver and kidney were examined. We found that trace metals released from these dental alloys and titanium were accumulated transiently in the blood, liver, and kidney but had no effect on the histopathology of the liver or kidney. Although the functions of the liver and kidney were compromised, the function of these tissues seemed to be clinically acceptable compared to those in control Syrian hamsters. In addition, the apoptotic effect on renal cells was terminated by removing the Ni-Cr and Co-Cr alloys, and that on hepatocytes was also eliminated by removing the Ni-Cr alloy. In contrast, the effect of the Co-Cr alloy on hepatocytes was temporary and recovered by itself. Taken together, Ni- and Co-based dental alloys and titanium have no effect on the histopathology or function of liver and kidney. Moreover, Ni-Cr and Co-Cr alloys induce transient trace metal accumulation and apoptotic effects in liver and kidney, which can be reduced or terminated by the removal of the alloys, while CP-Ti shows favorable biocompatibility.

Effects on cytotoxicity and antibacterial properties of the incorporations of silver nanoparticles into the surface coating of dental alloys

The aim of this study was to research the changes in cytotoxicity and antibacterial properties after silver nanoparticles (AgNPs) were incorporated into the surface coating of dental alloys. AgNPs were attached to cobalt chromium alloys and pure titanium using a hydrothermal method, according to the reaction: AgNO₃+NaBH₄→ Ag+1/2H₂+1/2B₂H₆+NaNO₃. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was used to evaluate the cytotoxicity of the alloys when in contact with osteogenic precursor cells (MC3T3-E1) from mice and mesenchymal stem cells (BMSC) from rats. The antibacterial properties of dental alloys incorporating three different concentrations (10, 4, and 2 μmol/L) of AgNPs were tested on Staphylococcus aureus (SA) and Streptococcus mutans (MS). High cytotoxicity values were observed for all dental alloys that contained 0% of AgNPs (the control groups). The incorporation of AgNPs reduced cytotoxicity values. No significant difference was observed for antibacterial performance when comparing dental alloys containing AgNPs to the respective control groups. The results demonstrated that the cobalt chromium alloys and pure titanium all had cytotoxicity to MC3T3-E1 and BMSC and that the incorporation of AgNPs could reduce this cytotoxicity. The concentrations of AgNPs adopted in this study were found to have no antibacterial action against SA or MS.

In vitro study of the inflammatory cells response to biodegradable Mg-based alloy extract

Biodegradable Mg-based alloys have shown great potential as bone fixation devices or vascular stents. As implant biomaterials, the foreign body reaction (FBR) is an important issue to be studied, where the inflammatory cells play a key role. Here, we used two inflammatory cell lines i.e. THP-1 cells and THP-1 macrophages, to evaluate the effect of Mg–Nd–Zn–Zr alloy (denoted as JDBM) extracts on cell viability, death modes, cell cycle, phagocytosis, differentiation, migration and inflammatory response. The results showed that high-concentration extract induced necrosis and complete damage of cell function. For middle-concentration extract, cell apoptosis and partially impaired cell function were observed. TNF-α expression of macrophages was up-regulated by co-culture with extract in 20% concentration, but was down-regulated in the same concentration in the presence of LPS stimulation. Interestingly, the production of TNF-α decreased when macrophages were cultured in middle and high concentration extracts independent of LPS. Cell viability was also negatively affected by magnesium ions in JDBM extracts, which was a potential factor affecting cell function. Our results provide new information about the impact of Mg alloy extracts on phenotype of immune cells and the potential mechanism, which should be taken into account prior to clinical applications.