Elemental release from dental casting alloys into biological media with and without protein

Toxic or not toxic? The specifications of the standard ISO 10993-5 are not explicit enough to yield comparable results in the cytotoxicity assessment of an identical medical device

Background

Medical device manufacturers are obliged to prove the biocompatibility of their products when they come into contact with the human body. The requirements for the biological evaluation of medical devices are specified by the international standard series ISO 10993. Part five of this series describes the performance of in vitro cytotoxicity tests. This test evaluates the effects of medical device use on cell health. The existence of the specific standard suggests that the tests will produce reliable and comparable results. However, the ISO 10993-5 offers wide latitude in the test specifications. In the past, we noticed inconsistencies of the results from different laboratories.

Objective

To determine if the specifications of the standard ISO 10993-5 are explicit to ensure the comparability of test results and, if not, identify potential influencing factors.

Methods

An interlaboratory comparison was conducted for the in vitro cytotoxicity test according to ISO 10993-5. Fifty-two international laboratories evaluated the cytotoxicity for two unknown samples. One was polyethylene (PE) tubing, which is expected to be non-cytotoxic and the other was polyvinyl chloride (PVC) tubing, for which a cytotoxic potential was presumed. All laboratories were asked to perform an elution test with predefined extraction specifications. The other test parameters were freely chosen by the laboratories according to the guidelines set by the standard.

Results

To our surprise only 58 percent of the participating laboratories identified the cytotoxic potential of both materials as expected. Particularly for PVC a considerable variation of the results between the laboratories was observed [mean = 43 ± 30 (SD), min = 0, max = 100]. We showed that ten percent serum supplementation to the extraction medium, as well as longer incubation of the cells with the extract, greatly increased the test sensitivity for PVC.

Conclusion

The results clearly show that the specifications set by the ISO 10993-5 are not explicit enough to obtain comparable results for an identical medical device. To set requirements that ensure reliable cytotoxicity assessments, further research will be necessary to identify the best test conditions for specific materials and/or devices and the standard needs to be revised accordingly.

Interactive Effects of Copper-Doped Urological Implants with Tissue in the Urinary Tract for the Inhibition of Cell Adhesion and Encrustation in the Animal Model Rat

The insertion of a ureteral stent provides acute care by restoring urine flow and alleviating urinary retention or dysfunction. The problems of encrustation, bacterial colonization and biofilm formation become increasingly important when ureteral stents are left in place for a longer period of time. One way to reduce encrustation and bacterial adherence is to modify the stent surface with a diamond-like carbon coating, in combination with copper doping. The biocompatibilities of the Elastollan^® base material and the a-C:H/Cu-mulitilayer coating were tested in synthetic urine. The copper content in bladder tissue was determined by atomic absorption spectroscopy and in blood and in urine by inductively coupled plasma mass spectrometry. Encrustations on the materials were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. A therapeutic window for copper ions of 0.5–1.0 mM was determined to kill bacteria without affecting human urothelial cells. In the rat animal model, it was found that copper release did not reach toxic concentrations in the affecting tissue of the urinary tract or in the blood. The encrustation behavior of the surfaces showed that the roughness of the amorphous carbon layer with the copper doping is probably the causal factor for the higher encrustation.

The Association Between Some Macro and Trace Elements in Saliva and Periodontal Status

Changes in the macro and trace element composition of saliva might be indicative for pathological changes in periodontal tissues. However, there is a lack of evidence in the literature showing associations between mineral elements and periodontal status. The aim of this study was to determine whether such associations occur. Totally, 190 systemically healthy non-smoker participants (mean age 32.2 ± 6.02; 50 periodontally healthy, 50 gingivitis, 50 chronic periodontitis, and 40 aggressive periodontitis individuals) were included in this cross-sectional study. Salivary levels of some macro and trace elements were measured by using inductively coupled plasma mass spectrometry (ICP-MS). Kruskal-Wallis's test was used for statistical analysis. Statistically significant differences were found in sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), vanadium (V), chromium Cr), manganese (Mn), iron (Fe), rubidium (Rb), strontium (Sr), and selenium (Se) concentrations among the groups. Significant increases in the essential minerals Na, Mg, K, Ca, Fe, and Se occurred in both periodontitis groups when compared to the gingivitis and periodontally healthy groups. Lower Se, Sr, Fe, Mn, and V concentrations were found in the aggressive periodontitis group than in the chronic periodontitis group. The results of this study demonstrated that assessment of mineral element concentrations in saliva might be useful in assessing periodontal health and disease. However, further studies are required to determine whether the change in a specific mineral element is the result of periodontal disease or is involved in its pathogenesis.

Toxic effects of four kinds of dental restorative materials on fibroblast HGF-1 and impacts on expression of Bcl-2 and Bax genes

The aim of this study was to investigate and discuss the toxic effect of four kinds of dental restorative materials on fibroblast HGF-1 and their impacts on the expression of B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein (Bax) genes. One hundred and ninety-two patients (240 diseased teeth), who received dental restoration in the Department of Stomatology of Xuzhou Stomatology Hospital from March 2014 to March 2015, were selected and randomly divided into four groups; namely, silver amalgam group, glass-ionomer cement group, nichrome group and novel nano-composite resin group, with 60 teeth in each group. The diseased teeth were restored. The fibroblast HGF-1 was incubated in the water extracts from the four kinds of materials and ordinary cell culture fluid (negative control). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to measure the levels of Bcl-2 and Bax. A flow cytometer was applied to detect cell apoptosis. RT-qPCR results showed that compared with those in the negative control group, the mRNA expression levels of Bcl-2 in the cells of silver amalgam group, glass-ionomer cement group and nichrome group were decreased, while those of Bax were upregulated (P<0.05). The mRNA expression of Bcl-2 in glass-ionomer cement group was the highest among these three groups; the mRNA expression of Bax in nichrome group was the highest of all groups. The western blotting results revealed the same tendency as those of RT-qPCR. The results via the flow cytometer showed that cell apoptosis in nichrome group, silver amalgam group and glass-ionomer cement group was increased significantly (P<0.05) compared with that in the negative control group. The novel nano-composite resin has no obvious toxic effect on cells, and its clinical application effect is better than that of traditional dental restorative materials, which is worthy of application and generalization in clinical practice.

Predicting patient exposure to nickel released from cardiovascular devices using multi-scale modeling

Many cardiovascular device alloys contain nickel, which if released in sufficient quantities, can lead to adverse health effects. However, in-vivo nickel release from implanted devices and subsequent biodistribution of nickel ions to local tissues and systemic circulation are not well understood. To address this uncertainty, we have developed a multi-scale (material, tissue, and system) biokinetic model. The model links nickel release from an implanted cardiovascular device to concentrations in peri-implant tissue, as well as in serum and urine, which can be readily monitored. The model was parameterized for a specific cardiovascular implant, nitinol septal occluders, using in-vitro nickel release test results, studies of ex-vivo uptake into heart tissue, and in-vivo and clinical measurements from the literature. Our results show that the model accurately predicts nickel concentrations in peri-implant tissue in an animal model and in serum and urine of septal occluder patients. The congruity of the model with these data suggests it may provide useful insight to establish nickel exposure limits and interpret biomonitoring data. Finally, we use the model to predict local and systemic nickel exposure due to passive release from nitinol devices produced using a wide range of manufacturing processes, as well as general relationships between release rate and exposure. These relationships suggest that peri-implant tissue and serum levels of nickel will remain below 5 μg/g and 10 μg/l, respectively, in patients who have received implanted nitinol cardiovascular devices provided the rate of nickel release per device surface area does not exceed 0.074 μg/(cm² d) and is less than 32 μg/d in total.

STATEMENT OF SIGNIFICANCE

The uncertainty in whether in-vitro tests used to evaluate metal ion release from medical products are representative of clinical environments is one of the largest roadblocks to establishing the associated patient risk. We have developed and validated a multi-scale biokinetic model linking nickel release from cardiovascular devices in-vivo to both peri-implant and systemic levels. By providing clinically relevant exposure estimates, the model vastly improves the evaluation of risk posed to patients by the nickel contained within these devices. Our model is the first to address the potential for local and systemic metal ion exposure due to a medical device and can serve as a basis for future efforts aimed at other metal ions and biomedical products.

The anti-bacterial activity of titanium-copper sintered alloy against Porphyromonas gingivalis in vitro

This study investigates the anti-bacterial property of Ti-Cu sintered alloys against Porphyromonas gingivalis. The anti-anaerobic property of Ti-Cu sintered alloys against P. gingivalis was investigated by antibacterial activity test, DNA measurement, DAPI staining and morphology observation. The antibacterial rates of the Ti-5Cu against P. gingivalis after 18 and 24 h incubation were 36.04 and 54.39%, and those of Ti-10Cu were 68.69 and 75.39%, which were lower than their anti-aerobic abilities. The concentration of P. gingivalis DNA gradually decreased with the increasing Cu content, which was nearly 50% after 24 h incubation on Ti-10Cu. SEM results showed that the shape of P. gingivalis changed and the bacteria broke apart with the addition of Cu and the extension of the culture time. Ti-Cu sintered alloys could not only kill anaerobic bacteria but also reduce the activity of the survived bacteria. The anti-anaerobic mechanism was thought to be in associated with the Cu ion released from Ti-Cu alloy.

Cell death affected by dental alloys: Modes and mechanisms

Previous reports have demonstrated that ions released from dental alloys might cause cytotoxicity. However, how dental alloys influence the organism has not been extensively studied. In order to make it clear, the cytotoxic effect of four dental alloys on L929 cells was evaluated by flow cytometry (FCM) and Real-time quantitative PCR assay (Real-time qPCR) to identify the cell death mode and its biological mechanism. The cells were treated with the leach liquors of cobalt-chromium (Co-Cr), commercially pure titanium (CP-Ti), palladium-based (Pd-based) and gold-platinum (Au-Pt) alloys for 48 and 72 h. FCM results indicated, apart from Au-Pt alloy, the major cell death of dental alloys was time-dependent early apoptosis rather than necrosis/late apoptosis. Caspase 3 and Caspase 9 mRNA expression were determined by Real-time qPCR, and shared the same trend in each group over time. Hence, except for Au-Pt alloy, dental alloys might cause time-dependent early apoptosis via the intrinsic pathway.

Biocompatibility and Biostability of Metallic Endovascular Implants: State of the Art and Perspectives

This work was partly supported by the Natural Science and Engineering Research Council (NSERC) of Canada.

More than a million metallic endovascular devices are implanted each year, but the quest for the perfect material continues. The importance of interfacial properties in the overall biocompatibility of metals and alloys has been recognized for a long time. In particular, these properties modulate the hemocompatibility of devices in contact with blood and, in turn, strongly influence implantation outcomes. In this article, the relative properties of metallic materials commonly used in endovascular applications are reviewed. Particular emphasis is given to the corrosion behavior of metallic endovascular materials and the specific surface treatments used in the production processes. Issues relative to corrosion assays will also be reviewed in terms of their relevance to in vivo applications. The potential adverse effects of degradation products with respect to endovascular applications will be described. Finally, this review addresses future perspectives of metallic devices in endovascular procedures in view of the recent promises of antiproliferative strategies that are likely to profoundly modify current procedures.

Corrosion behavior of dental alloys used for retention elements in prosthodontics

The purpose of this study was to investigate the corrosion behavior of 10 different high noble gold-based dental alloys, used for prosthodontic retention elements, according to ISO 10271. Samples of 10 high-noble and noble gold-based dental alloys were subjected to: (i) static immersion tests with subsequent analysis of ion release for eight different elements using mass spectrometry; (ii) electrochemical tests, including open-circuit potential and potentiodynamic scans; and (iii) scanning electron microscopy, followed by energy-dispersive X-ray microscopy. The results were analyzed using one-way ANOVA and Sidak multiple-comparisons post-hoc test at a level of significance of α = 0.05. Significant differences were found among the 10 alloys studied for all ions (P < 0.001). The potentiodynamic analysis showed values from -82.5 to 102.8 mV for the open-circuit potential and from 566.7 to 1367.5 mV for the breakdown potential. Both the open-circuit and the breakdown potential varied considerably among these alloys. Scanning electron microscopy analysis confirmed the existence of typically small-diameter corrosion defects, whilst the energy-dispersive X-ray analysis found no significant alteration in the elemental composition of the alloys. The results of this study reveal the variability in the corrosive resistance among the materials used for retention elements in prosthodontics.

Biocorrosion properties of antibacterial Ti-10Cu sintered alloy in several simulated biological solutions

Ti-10Cu sintered alloy has shown strong antibacterial properties against S. aureus and E. coli and good cell biocompatibility, which displays potential application in dental application. The corrosion behaviors of the alloy in five different simulated biological solutions have been investigated by electrochemical technology, surface observation, roughness measurement and immersion test. Five different simulated solutions were chosen to simulate oral condition, oral condition with F(-) ion, human body fluids with different pH values and blood system. It has been shown that Ti-10Cu alloy exhibits high corrosion rate in Saliva pH 3.5 solution and Saliva pH 6.8 + 0.2F solution but low corrosion rate in Hank's, Tyrode's and Saliva pH 6.8 solutions. The corrosion rate of Ti-10Cu alloy was in a order of Hank's, Tyrode's, Saliva pH 6.8, Saliva-pH 3.5 and Saliva pH 6.8 + 0.2F from slow to fast. All results indicated acid and F(-) containing conditions prompt the corrosion reaction of Ti-Cu alloy. It was suggested that the Cu ion release in the biological environments, especially in the acid and F(-) containing condition would lead to high antibacterial properties without any cell toxicity, displaying wide potential application of this alloy.

Influence of shape and finishing on the corrosion of palladium-based dental alloys

PURPOSE

The purpose of this study was to evaluate the effects of the surface treatment and shape of the dental alloy on the composition of the prosthetic work and its metallic ion release in a corrosive medium after casting.

MATERIALS AND METHODS

Orion Argos (Pd-Ag) and Orion Vesta (Pd-Cu) were used to cast two crowns and two disks. One of each was polished while the other was not. Two as-received alloys were also studied making a total of 5 specimens per alloy type. The specimens were submersed for 7 days in a lactic acid/sodium chloride solution (ISO standard 10271) and evaluated for surface structure characterization using SEM/EDAX. The solutions were quantitatively analysed for the presence of metal ions using ICP-MS and the results were statistically analysed with one-way ANOVA and a Tukey post-hoc test.

RESULTS

Palladium is released from all specimens studied (range 0.06-7.08 µg·cm^-2·week^-1), with the Pd-Cu alloy releasing the highest amounts. For both types of alloys, ion release of both disk and crown pairs were statistically different from the as-received alloy except for the Pd-Ag polished crown (P>.05). For both alloy type, disk-shaped pairs and unpolished specimens released the highest amounts of Pd ions (range 0.34-7.08 µg·cm^-2·week^-1). Interestingly, in solutions submerged with cast alloys trace amounts of unexpected elements were measured.

CONCLUSION

Shape and surface treatment influence ion release from dental alloys; polishing is a determinant factor. The release rate of cast and polished Pd alloys is between 0.06-0.69 µg·cm^-2·week^-1, which is close to or exceeding the EU Nickel Directive 94/27/EC compensated for the molecular mass of Pd (0.4 µg·cm^-2·week^-1). The composition of the alloy does not represent the element release, therefore we recommend manufacturers to report element release after ISO standard corrosion tests beside the original composition.

Annealing of Co-Cr dental alloy: effects on nanostructure and Rockwell hardness

PURPOSE

The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique.

MATERIALS AND METHODS

Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring 4 × 2 × 2 mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant.

RESULTS

The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness (48.16 ± 3.02 HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness (27.40 ± 3.98 HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 Å).

CONCLUSION

After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

Human epithelial tissue culture study on restorative materials

OBJECTIVES

Health condition of the gingival tissues contacting the surfaces of fixed prostheses is a result of multiple etiologic factors. The aim of the investigation discussed here was to evaluate the attachment and proliferation rate of cultured human epithelial cells on three commonly used restorative materials under in vitro conditions.

METHODS

Morphological and chemical structure of polished lithium-disilicate (IPS e.max Press, Ivoclar Vivadent AG, Germany), yttrium modified zirconium dioxide (5-TEC ICE Zirkon Translucent, Zirkonzahn GmbH Srl, Germany) and cobalt chromium alloy (Remanium star, Dentaurum GmbH & Co. KG, Germany) discs were examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). Human epithelial cells harvested and cultured from one donor, were applied to investigate cell attachment (24h observation) and proliferation (72h observation) via dimethylthiazol-diphenyl tetrazolium bromide (MTT) and AlamarBlue(®) (AB) assays on control surface (cell-culture plate) and on the restorative materials (n=3×20 specimens/material).

RESULTS

SEM and AFM revealed typical morphology and roughness features for the materials. Zirconia presented significantly higher Ra value. EDS confirmed typical elements on the investigated restorative materials: lithium-disilicate (Si, O); Zirconia (Zi, Y, O); CoCr (Co, Cr, W). All surfaces except CoCr exhibited significant cell proliferation according to MTT and AB assays after 72h compared to 24h. Among the restorative materials, CoCr samples showed the highest cell attachment as indicated by MTT assay. AB results showed that attachment and proliferation of human epithelial cells is supported more on lithium-disilicate. Both assays indicated the lowest value for zirconia.

CONCLUSIONS

The results indicate that the restorative materials examined are equally suitable for subgingival restorations. Lithium-disilicate exhibited the best biocompatibility.

CLINICAL SIGNIFICANCE

The examined materials are indicated for use in restorative procedures, directly contacting the sulcular epithelial tissues. Thus it is essential to monitor the biological acceptibility of these materials in order to better understand their clinical properties. The results indicate that Lithium-disilicate is a suitable material for such purposes.

Urinary levels of nickel and chromium associated with dental restoration by nickel-chromium based alloys

This paper aims to investigate if the dental restoration of nickel–chromium based alloy (Ni–Cr) leads to the enhanced excretions of Ni and Cr in urine. Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni–Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination. Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry. Compared to the control group, the urinary level of Ni was significantly higher in the patient group of <1 month of the restoration duration, among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain. Urinary levels of Cr were significantly higher in the three patient groups of <1, 1 to <3 and 3 to <6 months, especially in those with a higher metal crown exposure index. Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups. Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration. Potential short- and long-term effects of Ni–Cr alloy restoration need to be investigated.

Evaluation of the shear bond strength of the union between two CoCr-alloys and a dental ceramic

INTRODUCTION

Based on the importance of the integrity of the metal/ceramic interface, the purpose of this work was to evaluate the shear bond strength of the metal-ceramic union of two Co-Cr alloys (Wirobond C, Bego; Remanium 2000, Dentaurum) combined with Omega 900 ceramic (Vita Zahnfabrik).

MATERIAL AND METHOD

Eleven cylindrical matrixes were made for each alloy, and the metallic portion was obtained with the lost wax casting technique with standardized waxing of 4mm of height and of 4mm of diameter. The ceramic was applied according to the manufacturer's recommendations with the aid of a teflon matrix that allowed its dimension to be standardized in the same size as the metallic portion. The specimens were submitted to the shear bond test in an universal testing machine (EMIC), with the aid of a device developed for such intention, and constant speed of 0.5mm/min.

RESULTS AND CONCLUSIONS

The mean resistance was 48.387MPa for Wirobond C alloy, with standard deviation of 17.718, and 55.956MPa for Remanium 2000, with standard deviation of 17.198. No statistically significant difference was observed between the shear strength of the two metal-ceramic alloys.

Oral Keratinocyte Responses to Nickel-based Dental Casting Alloys In Vitro

Adverse reactions of oral mucosa to nickel-based dental casting alloys are probably due to corrosion metal ion release. We exposed H400 oral keratinocytes to two Ni-based dental alloys (Matchmate and Dsign10) as well as NiCl 2 (1—40 μg/mL Ni2+). Alloy derived Ni2+ media concentrations were determined. Direct culture on both alloys resulted in inhibited growth with a greater effect observed for Dsign10 (higher ion release). Indirect exposure of cells to conditioned media from Dsign10 negatively affected cell numbers (~64% of control by 6 days) and morphology while Matchmate-derived media did not. Exposure to increasing NiCl2 negatively affected cell growth and morphology, and the Granulocyte-macrophage colony-stimulating factor (GM-CSF) transcript was significantly up-regulated in cells following direct and indirect exposure to Dsign10. NiCl2 exposure up-regulated all cytokine transcripts at 1 day. At day 6, IL-1β and IL-8 transcripts were suppressed while GM-CSF and IL-11 increased with Ni2+ dose. Accumulation of Ni2+ ions from alloys in oral tissues may affect keratinocyte viability and chronic inflammation.

Elemental ion release from four different fixed prosthodontic materials

OBJECTIVE

Elemental release is important because it plays a significant role in material biocompatibility. The aim of this study was to investigate the release of metal ions from four fixed prosthodontic materials.

METHODS

Specimens were prepared using the conventional lost wax technique for gold and nickel-chromium (Ni-Cr) alloys, and by cutting blocks and bar for CAD-CAM ceramic and stainless-steel (St-St) alloy, respectively. All specimens were polished (600grit SiC paper), and ultrasonically cleaned with ethanol for 5min. After they were immersed in 0.9% sodium chloride (NaCl) and 1% lactic acid, and were kept at 37 degrees C for 7 days, the elemental release (mug/cm(2)) from each material was analyzed by using inductively coupled plasma mass spectroscopy. The rate (n=5) was statistically analyzed by ANOVA/Tukey test (p<0.05). Two immersion blank solutions were used as a negative control group.

RESULTS

Higher elemental release (mean+/-S.D.) of all elements from all materials was evident into the lactic acid solution except for Ag. In the gold alloy, there was significant difference (p<0.05) between Zn and other released elements in the NaCl solution, and it also revealed significant difference between Pd or Ag and Cu which detection value was more than Zn (but no statistical difference) into lactic acid solution. The Ni was significantly more released from Ni-Cr alloy than the other elements into both NaCl and lactic acid solutions. The same was observed for Fe released from St-St alloy. There was more significant release of K than Al from CAD-CAM ceramic in only NaCl solution.

SIGNIFICANCE

Transient exposure of tested materials to an acidic environment is likely to significantly increase the elemental release from them. The significant higher release of Ni from Ni-Cr alloy, and Zn, Cu from gold alloy was evident.

Potentiometric stripping analysis of zinc and copper in human teeth and dental materials

Potentiometric stripping analysis (PSA) with oxygen as the oxidant has been used to determine soluble zinc and copper levels in exfoliated human teeth (all of which required extraction for orthodontic reasons) and commercial dental materials. The soluble zinc and copper contents of teeth were slightly below the zinc and copper contents in whole teeth reported by other researchers, except in the case of tooth with removed amalgam filling. Soluble zinc and copper concentrations of the dental materials and metal ceramic crowns were 0.50-6.30, and of 2.00-4.30 microg/g, respectively. The results of this work suggest that PSA may be a good method for zinc and copper leaching studies during the investigation of dental prosthetic materials' biocompatibility. Corrosive action of acidic media as evidenced by SEM micrographs caused the leaching of metal ions from teeth.

Relationship between radial diffusion of copper ions released from a metal disk and cytotoxic effects. Comparison with results obtained using extracts

The extended use of metallic biomaterials yields to increasing sources of metal ions within the human body and may result in inflammation of the surrounding tissues, cell damage, and cancer. The aim of this study was to investigate the relationship between the radial diffusion of metal ions released from a metal disk by the corrosion process and the toxic effect on a cell line that grew around it. Results obtained with the metal disks (direct contact) were compared with assays made with extracts obtained from the dissolution of a metallic sample ex situ and then added to the cell culture to elucidate the cause of apparent inconsistencies in previous reports. The change of copper concentration due to corrosion and transient diffusion of copper ions from the copper disks into the cell line was evaluated according to Fick's 2nd law. Surviving cells distribution was interpreted considering the radial and time-dependence of copper concentration. We concluded that the toxic effect on those cells close to metallic biomaterials may be underestimated when only the extract methodology is employed for cytotoxic tests or when during the experiments with disks the presence of concentration gradients and the non-homogeneous distribution of dead cells are disregarded.

Corrosion of nickel-based dental casting alloys

OBJECTIVES

To study the microstructure, corrosion behaviour and cell culture response of two nickel-based dental casting alloys before and after a heat treatment to simulate porcelain firing.

METHODS

The microstructure was studied using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Corrosion behaviour was evaluated by electrochemical measurements in artificial saliva at different values of pH in the presence of a crevice. 3T3 mouse fibroblasts were exposed indirectly to alloy specimens and the number of viable cells counted after 3 and 6 days compared to a control culture.

RESULTS

Small changes in microstructure were observed after heat treatment but had a negligible effect on the corrosion properties in the conditions tested. The alloy with a lower bulk level of Cr (12.6 wt.%) showed lower corrosion resistance, indicated by an increased passive current density and this stability was greatly reduced at pH 2.5, where crevice corrosion was observed. Selective dissolution occurred at regions within the microstructure containing lower levels of Cr and Mo. Furthermore, the proliferation of 3T3 mouse fibroblasts was reduced (p<0.05) when exposed indirectly to this alloy. The alloy containing a higher level of Cr (25 wt.%) showed superior corrosion resistance, which was associated with a more uniform distribution of Cr in the alloy microstructure.

SIGNIFICANCE

The presence of crevices combined with an inhomogeneous distribution of Cr in the microstructure can lead to accelerated corrosion of Ni-based alloys with lower Cr contents. This effect can be avoided by increasing the Cr content of the alloy.

Zn2+ release from zinc and zinc oxide particles in simulated uterine solution

Zn(2+) release from Zn and ZnO particles with different sizes in simulated uterine solution were investigated by absorbance measurements. The effects of pH and human serum albumin (HSA) on Zn(2+) release were also studied. The morphology of Zn and ZnO particles was observed by scanning electron microscopy, and the corrosion products of zinc nanoparticles were analyzed by XRD. The results indicate that the maximum release ratios of Zn(2+) from Zn and ZnO nanoparticles are higher than those from Zn and ZnO microparticles. Zn(2+) release ratio depends not only on the pH of the simulated uterine solution but also the presence of human serum albumin. It decreases as the pH of the uterine solution increases. The trends of Zn(2+) release ratios are almost the opposite for solutions with and without HSA. XRD analysis results indicate that zinc oxide is the main corrosion product of zinc particles.

Corrosion behavior and surface characterization of titanium in solution containing fluoride and albumin

The objective of this study was to demonstrate the role of albumin on the corrosion behavior of titanium in a solution containing 2.0 g/l fluoride and either 0.1 or 1.0 g/l albumin. The corrosion behavior and surface characterization of passive films on titanium immersed in such a solution were examined. In addition, the change in pH and the concentration of dissolved titanium in the solution were examined. The results showed that the corrosion of titanium in a solution containing fluoride was distinct, and that adding albumin to the solution containing fluoride suppressed corrosion. Fluorine was detected on the titanium surface immersed in the solution containing fluoride, and dissolution of the titanium was confirmed. The titanium immersed in a solution containing both fluoride and albumin had an albumin film regardless of the albumin concentration. In addition, the amount of dissolved titanium from the titanium immersed in the solution was less than when the solution contained no albumin. It was suggested that the formation of adsorbed albumin films on or in the passive film acted to not only protect the titanium from attack by the fluoride but also suppressed dissolution of the titanium-fluoride compounds.

Use of the fertilized hen's egg in the evaluation of embryotoxicity of dental alloys

In this study, embryotoxic effects of five commercially available dental alloys were investigated by using fertilized hens' eggs. One sample of each alloy was conditioned in one of the conditioning media, physiological saline (PS), 0.1 M phosphate-buffered saline (PBS, pH 7.4), and 0.1 M protein (3% bovine serum albumin, BSA) containing PBS (pH 6.8), respectively. The test solutions were injected into the fertilized hen's eggs via air sac at the beginning of the incubation. Various concentrations of a highly embryotoxic substance, AFB1, was also used as positive control test material. Mortality of the AFB1 treatment groups increased with increasing concentrations of AFB1 and the mortality values were significantly (p < 0.05) higher than those of the controls and eluent injected groups. The eluents of five commercially available dental alloys tested in the study did not have significant embryotoxic effects. Cu- and Pd-containing alloys displayed relatively high but statistically insignificant embryotoxic effects. Chick embryo might be used in determination of the embryotoxic effects of the dental alloys with its several advantages. Nevertheless, the test should be further standardized and new methods such as micronucleus test showing possible genotoxic effects of the materials should be used.

Potentiometric stripping analysis of lead and cadmium leaching from dental prosthetic materials and teeth

Potentiometric stipping analysis (PSA) was applied for the determination of lead and cadmium leaching from dental prosthetic materials and teeth. The soluble lead content in finished dental implants was found to be much lower than that of the individual components used for their preparation. Cadmiumwas not detected in dental implants and materials under the defined conditions. The soluble lead and cadmium content of teeth was slightly lower than the lead and cadmium content in whole teeth (w/w) reported by other researchers except in the case of a tooth with removed amalgam filling. The results of this work suggest that PSA may be a good method for lead and cadmium leaching studies for investigation of the biocompatibility of dental prosthetic materials.

In vitro biocorrosion of Ti-6Al-4V implant alloy by a mouse macrophage cell line

Corrosion of implant alloys releasing metal ions has the potential to cause adverse tissue reactions and implant failure. We hypothesized that macrophage cells and their released reactive chemical species (RCS) affect the alloy's corrosion properties. A custom cell culture corrosion box was used to evaluate how cell culture medium, macrophage cells and RCS altered the Ti-6Al-4V corrosion behaviors in 72 h and how corrosion products affected the cells. There was no difference in the charge transfer in the presence (75.2 +/- 17.7 mC) and absence (62.3 +/- 18.8 mC) of cells. The alloy had the lowest charge transfer (28.2 +/- 4.1 mC) and metal ion release (Ti < 10 ppb, V < 2 ppb) with activated cells (releasing RCS) compared with the other two conditions. This was attributed to an enhancement of the surface oxides by RCS. Metal ion release was very low (Ti < 20 ppb, V < 10 ppb) with nonactivated cells and did not change cell morphology, viability, and NO and ATP release compared with controls. However, IL-1beta released from the activated cells and the proliferation of nonactivated cells were greater on the alloy than the controls. In summary, macrophage cells and RCS reduced the corrosion of Ti-6Al-4V alloys as hypothesized. These data are important in understanding host tissue-material interactions.