Viability and Proliferation Assessment of Gingival Fibroblasts Cultured on Silver Nanoparticle-Doped Ti-6Al-4V Surfaces

PURPOSE

To investigate the biocompatibility of silver nanoparticle (AgNP)-doped Ti-6Al-4V surfaces by evaluating the viability and proliferation rate of human gingival fibroblasts (HGFs)-as the dominant cells of peri-implant soft tissues-seeded on the modified surfaces.

MATERIALS AND METHODS

AgNPs (sizes 8 nm and 30 nm) were incorporated onto Ti-6Al-4V specimen surfaces via electrochemical deposition, using colloid silver dispersions with increasing AgNP concentrations of 100 ppm, 200 ppm, and 300 ppm. One control and six experimental groups were included in the study: (1) control (Ti-6Al-4V), (2) 8 nm/100 ppm, (3) 8 nm/200 ppm, (4) 8 nm/300 ppm, (5) 30 nm/100 ppm, (6) 30 nm/200 ppm, and (7) 30 nm/300 ppm. HGF cell primary cultures were isolated from periodontally healthy donor patients and cultured in direct contact with the group specimens for 24 and 72 hours. The cytotoxicity of AgNP-doped Ti-6Al-4V specimens toward HGF was assessed by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) and BrdU (5-bromo-2'-deoxyuridine) assay tests. Calcein AM and ethidium homodimer (EthD-1) fluorescent stains were used to determine the live and dead cells. The morphology and attachment properties of the HGFs were determined via scanning electron microscopy (SEM).

RESULTS

Energy dispersive x-ray (EDX) analysis confirmed the presence of AgNPs on the specimens. The MTT test revealed that AgNPs of both sizes and all concentrations presented a decreased cellular metabolic activity compared to the control discs. All concentrations of both sizes of AgNPs affected the cell proliferation rate compared to the control group, as revealed by the BrdU assay. Overall, cytotoxicity of the modified Ti-6Al-4V surfaces depended on cell exposure time. Observation via confocal microscopy confirmed the results of the MTT and BrdU assay tests. Specifically, most cells remained alive throughout the 72-hour culture period. SEM images revealed that adjacent cells form bonds with each other, creating confluent layers of conjugated cells.

CONCLUSIONS

The findings of the present study indicate that Ti-6Al-4V surfaces modified with 8 nm and 30 nm AgNPs at concentrations of 100 ppm, 200 ppm, and 300 ppm do not produce any serious cytotoxicity toward HGFs. The initial arrest of the HGF proliferation rate recovered at 72 hours. These results on the antibacterial activity against common periodontal pathogens, in combination with the results found in a previous study by the same research group, suggest that AgNP-doped Ti-6Al-4V surfaces are potential candidates for use in implant abutments for preventing peri-implant diseases.

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.

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.

Trace metal ions release from fixed orthodontic appliances and DNA damage in oral mucosa cells by in vivo studies: A literature review

An overview of professional literature referring to the release of metal ions from fixed orthodontic appliances and their influence on oral mucosa in conditions of in vivo are presented, along with a detailed analysis of the exposure of the cells of cheek mucosa epithelium to metal ions. Electronic databases (PubMed, Elsevier, Ebsco) were searched with no language restrictions. The relevant orthodontic journals and reference lists were checked for all eligible studies. A total of 38 scientific articles were retrieved in the initial search. However, only 7 articles met the inclusion criteria. Statistically significant differences in the levels of the amount of nickel ions, cobalt ions and chromium ions were observed in cells of cheek mucosa. The most biocompatible material used in the production of fixed orthodontic appliances is titanium, and the least biocompatible material is steel, which releases the largest amount of nickel and chromium. Metal ions are released from fixed orthodontic appliances only in the first phase of treatment. It is recommended to conduct further, long-term research on a larger number of patients to define the influence of using fixed orthodontic appliances and biological effect they might have on tissues.

The effect of recasting on biological properties of Ni-Cr dental alloy

INTRODUCTION

Increases in market prices of gold over the last 20 years have led to expansion of basic dental alloys, which, primarily due to their good mechanical properties and acceptable prices, have found their place in everyday dental practice. However, within the procedure of making dental prosthetic restorations, the alloys are melted and cast, which leads to changes in their physical, mechanical and biological properties.

OBJECTIVE

The objective of the study was to test biocompatibility of a Ni-Cr dental alloy (WIRON 99) depending on the number of melting and casting processes.

METHODS

The working method included the testing of cytotoxicity of the alloy obtained by casting after one, after four, and after eight successive processes of melting. Cytotoxicity of samples was tested by means of a 24-hour and a three-day cytotoxicity test, done on L929 fibroblasts.

RESULTS

A repeatedly melted and cast alloy shows a reduced biocompatibility and causes specific responses of the tissues in the surrounding area. Since the cytotoxic effect is more significant in the extended contact with the culture cells, a three-day cytotoxicity test showed discrete changes which were the indicator of cell growth inhibition in the cell culture.

CONCLUSION

The obtained results confirm the working hypothesis that repeated alloy melting and casting will decrease biocompatibility of dental alloys and will lead to specific responses of the tissue in the surrounding area.

The cytotoxicity of dental alloys studied on cell culture

The metal alloys used in dental practice are the subject of numerous discussions referring to the effect they have on oral cavity tissues. Numerous scientists established that the organic molecules did not exert a significant influence on the degradation of metallic implants. The aim of this study was to test the cytotoxic potential of the most used dental alloys, the Ni-Cr alloy and the Co-Cr alloy. The tests were made on cell culture of pure cell line dermal fibroblasts and of those obtained from skin biopsies, for both, dental alloys and their eluates. The results were compared with control samples. At seven days after inoculation, we observed the relative similarity between the Ni-Cr alloy and the Co-Cr alloy, where the cells did not detach from the plate and they grow to the edge of the material. In case of the eluates, there were no fragments detached, the cells having a relatively high confluence. Therefore, the cytotoxic effects of the two alloys are similar, even if there are speculations in the literature according to which Ni-Cr alloys would have a more pronounced effect. In conclusion, our study revealed non-cytotoxicity of these two dental alloys, and we believe so they can be used successfully in dental practice.

Cytocompatibility of pure metals and experimental binary titanium alloys for implant materials

OBJECTIVE

This study was performed to evaluate the biocompatibility of nine types of pure metal ingots (Ag, Al, Cr, Cu, Mn, Mo, Nb, V, Zr) and 36 experimental titanium (Ti) alloys containing 5, 10, 15, and 20 wt% of each alloying element.

METHODS

The cell viabilities for each test group were compared with that of CP-Ti using the WST-1 test and agar overlay test.

RESULTS

The ranking of pure metal cytotoxicity from most potent to least potent was as follows: Cu>Al>Ag>V>Mn>Cr>Zr>Nb>Mo>CP-Ti. The mean cell viabilities for pure Cu, Al, Ag, V, and Mn were 21.6%, 25.3%, 31.7%, 31.7%, and 32.7%, respectively, which were significantly lower than that for the control group (p<0.05). The mean cell viabilities for pure Zr and Cr were 74.1% and 60.6%, respectively (p<0.05). Pure Mo and Nb demonstrated good biocompatibility with mean cell viabilities of 93.3% and 93.0%, respectively. The mean cell viabilities for all the Ti-based alloy groups were higher than 80% except for Ti-20 Nb (79.6%) and Ti-10 V (66.9%). The Ti-10 Nb alloy exhibited the highest cell viability (124.8%), which was higher than that of CP-Ti. Based on agar overlay test, pure Ag, Cr, Cu, Mn, and V were ranked as 'moderately cytotoxic', whereas the rest of the tested pure metals and all Ti alloys, except Ti-10 V (mild cytotoxicity), were ranked as 'noncytotoxic'.

SIGNIFICANCE

The results obtained in this study can serve as a guide for the development of new Ti-based alloy implant systems.

[Systemic reactions to orally applied metal alloys]

Orally applied metal alloys can cause undesirable physical effects. A distinction needs to be made in this respect between local and systemic reactions and toxic and immunological reactions. A case is presented which illustrates this problem. In this case, the application of orthodontic appliances was probably the trigger for an exacerbation of nickel allergy. The oral exposure to nickel resulted in hand eczema. The patient was also exposed to nickel by single-unit fixed dental prostheses, a removable dental prosthesis, and food, as a result of which removal of the orthodontic appliances did not result in complete healing. Therefore, the single-unit fixed dental prostheses also had to be removed and food had to be prepared henceforward in nickel free pans.

Influence of recasting different types of dental alloys on gingival fibroblast cytotoxicity

STATEMENT OF PROBLEM

Surplus alloy from the initial casting is commonly reused with the addition of new alloy. This recasting procedure could affect the cytotoxicity of dental alloys.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of repeated casting of high-noble and base metal alloys on gingival fibroblast cytotoxicity.

MATERIAL AND METHODS

Disk-shaped specimens (5 × 2 mm, n=60) of a high-noble (Au-Pt) and 2 base metal (Ni-Cr and Cr-Co, n=20) alloys were prepared with 100% new alloy and 50%, 65%, and 100% once recast alloy. The elemental composition of specimens was analyzed with X-ray energy-dispersive spectroscopy. Five specimens from each group were conditioned in saline with 3% fetal bovine serum albumin. The conditioning media were analyzed for elemental release with atomic absorption spectroscopy. Cytotoxic effects were assessed on human gingival fibroblast with a 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyl tetrazolium bromide (MTT) colorimetric assay. The data were analyzed with 1-way and 2-way ANOVA and Tukey's HSD multiple comparison test (α-=.05).

RESULTS

Elemental compositions of Co-Cr and Au-Pt alloys were significantly different among casting protocols. Elemental release of Co-Cr and Ni-Cr alloys was significantly different between new and recast specimens (P<.001). Nickel release increased with recast alloy addition. The 2-way ANOVA showed a significant effect of the casting procedure (P<.001) alloy group (P<.001) and their interaction for cytotoxicity (P<.001). The Ni-Cr alloy groups with 65% and 100% recast alloy had lower cellular activity than all other specimens (P<.001).

CONCLUSIONS

The results of this study indicated that alloys containing nickel have increased cytotoxic effects and that composition of the alloys affected the cytotoxicity. Furthermore, recasting nickel-containing alloys with 65% surplus metal addition significantly increased the cytotoxic activity.

[Surface aspect of fixed restaurations and parodontal influences]

Any new class of materials requires a new cutting technology which, unless complied with properly, may negatively impact on the advantages and performance of the material. The modifications appeared as a result of the technological processes in the structure or surface aspect of the materials not only affects the mechanical resistance of the restorations but also casts doubts on their biological qualities.

AIM

This study evaluates the impact of biomaterials involved in fixed restorations on the periodontal architecture, bearing extremely important connotations in the long run.

MATERIAL AND METHODS

The "in vitro" testing was conducted on culture cells for the cytotoxic effect of certain restorative materials--metallic alloys used in prosthetic restorations, composite materials, in collaboration with the Virology Laboratory of the Public Health Institute.The tested materials were metallic alloys, composite materials and acrylic resins used for the construction of standard sized plates (out of each material) in order to avoid the differences that might arise from the technological process. Artificial saliva processed to reach a pH = 7 was prepared in the Biophysics Laboratory of UMF Iasi. Material samples and the saliva inoculated with these were tested. -p.

RESULTS AND DISCUSSIONS

The cytotoxic effect of the tested materials on the celular cultures takes on extremely diverse forms, from discrete morphological modifications of the cells with regard to the size, shape, internal structure (for the noble and semi-noble alloys) up to the partial stripping-off of the celular film, the modification of density and coloration. In the case of the witness of non-inoculated culture, the testing results showed the presence of a continuous film, with cells having the same size, transparency and colouring, with an unaltered polyhedral contour, with visible nuclei, an image also kept in the case of the saliva witness.

CONCLUSIONS

The involvement of restaurative materials in triggering, maintaining and aggravating a periodontal pathology indicates the capital role played by the dentist in the identications of lesions during measures by avoiding or excluding etiological agents before an obvious lesions occurs in the process of active dispensarization.

[The center of pathological (toxic) action of metals in an people organisms and a role of galvanic currents in its induction]

Chronic influence of metals on an organism differs from their sharp toxic action. In some exposed to long chronic metals influence people appear chronic inflammatory diseases, including oncological, on a background of neurologic symptoms develop. Today the overwhelming majority of the population is more 40-50 years old have metal alloys in the form of dental artificial limbs and various implantates in a body. Because of metal corrosion in organisms of these people concentration of metal ions is created. Galvanic currents induced at presence of any metals in an organism, promote corrosion, and carry of metal ions inside organism. If these currents are strong (the potential difference more 150 MB), local inflammatory pathologies development in organism due to concentration in the center of metal ions.

[Study on the cytotoxicity induced by ceramic alloys]

AIM

To investigate the cytotoxicity of 3 kinds of dental ceramic alloys.

METHODS

Methods of 4-methyl-thiazolyl tetrazolium assay (MTT) and single cell gel electrophoresis (comet assay) were used to detect the influence on mouse fibroblast L929 relative growth rate (relative growth rate, RGR) and damage of DNA induced by three kinds of ceramic alloys.

RESULTS

RGR of the golden alloy group was 87.7 ± 11.3 which showed no significant difference when compared with the cobalt-chromium alloy group and the control group, while among other groups, there were statistically significant differences in RGR (P<0.05); the rank of DNA damage of nickel-chromium alloy was severe, while the ranks of cobalt-chromium alloy and golden alloy group were moderate and mild respectively.

CONCLUSION

The influence of golden alloy and cobalt-chromium alloy on RGR is significantly lower than nickel-chromium alloy, meanwhile the damage of DNA caused by golden alloy is lightest, so it is a kind of dental ceramic alloy with good biocompatibility.

Dental devices: classification of dental amalgam, reclassification of dental mercury, designation of special controls for dental amalgam, mercury, and amalgam alloy. Final rule

The Food and Drug Administration (FDA) is issuing a final rule classifying dental amalgam into class II, reclassifying dental mercury from class I to class II, and designating a special control to support the class II classifications of these two devices, as well as the current class II classification of amalgam alloy. The three devices are now classified in a single regulation. The special control for the devices is a guidance document entitled, "Class II Special Controls Guidance Document: Dental Amalgam, Mercury, and Amalgam Alloy." This action is being taken to establish sufficient regulatory controls to provide reasonable assurance of the safety and effectiveness of these devices. Elsewhere in this issue of the Federal Register, FDA is announcing the availability of the guidance document that will serve as the special control for the devices.

The issue of corrosion in dental implants: a review

Pure titanium or titanium alloys, and to a lesser extent, zirconium, are metals that are often used in direct contact with host tissues. These metallic biomaterials are highly reactive, and on exposure to fluid media or air, quickly develop a layer of titanium dioxide (TiO2) or zirconium dioxide (ZrO2). This layer of dioxide forms a boundary at the interface between the biological medium and the metal structure, determining the degree of biocompatibility and the biological response of the implant. Corrosion is the deterioration a metal undergoes as a result of the surrounding medium (electrochemical attack), which causes the release of ions into the microenvironment. No metal or alloy is entirely inert in vivo. Corrosion phenomena at the interlace are particularly important in the evolution of both dental and orthopedic implants and one of the possible causes of implant failure after initial success. This paper comprises a review of literature and presents results of our laboratory experiments related to the study of corrosion, with special emphasis on dental implants. In situ degradation of a metallic implant is undesirable because it alters the structural integrity of the implant. The issue of corrosion is not limited to a local problem because the particles pmduced as a result could migrate to distant sites, whose evolution would require further studies.

[Cytotoxicity of several materials of full crowns on human gingival fibroblast cells in vitro]

PURPOSE

To evaluate the cytotoxicity of Ni-Cr base metal alloy, gold casting alloy and castable dental ceramic on human gingival fibroblast cells (HGFC)ain vitro.

METHODS

HGFC were cultured with extractions of Ni-Cr base metal alloy, gold casting alloy and castable dental ceramic. Relative growth rate (RGR) was analyzed with a methyl thiazolyl tetrazolium (MTT) assay. The shape of HGFCs was observed when HGFCs were directly contacted with three prosthodontic materials. Factor analysis was performed using Stata 9.1 software.

RESULTS

The relative growth rates of HGFCs cultured with gold casting alloy were 1.016,1.014,0.824 and 0.796,respectively. The relative growth rates of HGFCs cultured with Ni-Cr base metal alloy were 1.028,1.079,0.903 and 0.809,respectively. The relative growth rates of HGFCs cultured with castable dental ceramic were 1.018,1.030,0.924 and 0.818, respectively. There was significant difference of RGR between the gold casting alloy and the Ni-Cr base metal alloy groups(P=0.021). No significant difference of RGR was observed between the gold casting alloy and castable dental ceramic groups (P>0.05).No significant difference of RGR was observed between the Ni-Cr base metal alloy and castable dental ceramic groups (P>0.05). Cytotoxical grades of Ni-Cr base metal alloy, gold casting alloy and castable dental ceramic were 0 to 1. HGFC could grow around the three prosthodontic materials.

CONCLUSIONS

Ni-Cr base metal alloy has more cytotoxic effect in direct contact test than in extraction test on HGFC. Gold casting alloy and castable dental ceramic have good biocompatibility. Supported by Medical PI Project for Provincial Advancement through Science and Education of Jiangsu Province (RC2007099).

Effect of nitride film coatings on cell compatibility

OBJECTIVE

To evaluate the cytotoxicity of nickel-based alloy surfaces after nitride film coatings.

METHODS

A total of 120 disc-shaped specimens (1.5 x 12.0mm) were prepared from nickel (Ni) alloy ingots and metallurgically ground with silicon carbide (SiC) sandpaper to 1200 grit and used as the ground group. Ninety specimens from the ground group were selected and further polished with 1.0 microm aluminum powder slurry and assigned as the polished group. Titanium nitride (TiN) and titanium-aluminum nitride (TiAlN) film coatings were deposited onto 30 polished specimens each by a reactive radio frequency magnetron sputter deposition system and used as coated groups, respectively. The morphological changes and cytoskeleton of tested human gingival fibroblasts were observed using fluorescence microscopy at 3h and 24h time periods, respectively. An MTT assay was used to assess cell viability at 24h. The results were statistically analyzed (n=5, ANOVA, Scheffe', p<0.05).

RESULTS

After 3h of incubation, cells began to spread on the test surfaces. Spindle-shaped fibroblasts with well-developed cytoskeleton and distinct actin fibers were observed at the 24h incubation point on the polished and coated specimens. Results of the MTT assay revealed that the TiN and TiAlN film coated groups were significantly higher in cell proliferation and viability than the polished and control groups (p<0.05).

SIGNIFICANCE

The biocompatibility of Ni-based alloy was increased significantly after nitride film coating.

Biocompatibility of dental casting alloys

Most cast dental restorations are made from alloys or commercially pure titanium (cpTi). Many orthodontic appliances are also fabricated from metallic materials. It has been documented in vitro and in vivo that metallic dental devices release metal ions, mainly due to corrosion. Those metallic components may be locally and systemically distributed and could play a role in the etiology of oral and systemic pathological conditions. The quality and quantity of the released cations depend upon the type of alloy and various corrosion parameters. No general correlation has been observed between alloy nobility and corrosion. However, it has been documented that some Ni-based alloys, such as beryllium-containing Ni alloys, exhibit increased corrosion, specifically at low pH. Further, microparticles are abraded from metallic restorations due to wear. In sufficient quantities, released metal ions-particularly Cu, Ni, Be, and abraded microparticles-can also induce inflammation of the adjacent periodontal tissues and the oral mucosa. While there is also some in vitro evidence that the immune response can be altered by various metal ions, the role of these ions in oral inflammatory diseases such as gingivitis and periodontitis is unknown. Allergic reactions due to metallic dental restorations have been documented. Ni has especially been identified as being highly allergenic. Interestingly, from 34% to 65.5% of the patients who are allergic to Ni are also allergic to Pd. Further, Pd allergy always occurrs with Ni sensitivity. In contrast, no study has been published which supports the hypothesis that dental metallic materials are mutagenic/genotoxic or might be a carcinogenic hazard to man. Taken together, very contradictory data have been documented regarding the local and systemic effects of dental casting alloys and metallic ions released from them. Therefore, it is of critical importance to elucidate the release of cations from metallic dental restorations in the oral environment and to determine the biological interactions of released metal components with oral and systemic tissues.

The cytotoxicity of orthodontic metal bracket immersion media

The purpose of the present study was to evaluate the cytotoxic effects of four different orthodontic metal bracket immersion media on primary human oral gingival fibroblasts (HGFs) and one permanent human osteogenic sarcoma cell line (U2OS). Four different metal brackets (Unitek, Tomy, Ormco, and Dentaurum) were immersed in buffer solutions of NaHNO(3) (1 mM) with a pH of 4 or 7, as well as artificial saliva. The concentrations for the experiments were 0.01, 0.1, and 1.0 mul/ml. At the end of the period of bracket immersion, morphological observations were conducted using light microscopy. The tetrazolium reduction assay was used to detect the survival rate of the target cells. Statistical analysis was conducted using one-way analysis of variance. The results showed microscopically no morphological changes of the HGF or U2OS cells exposed to the metal bracket immersion media. At pH 4, the survival rates of the U2OS cells and the HGFs differed statistically for the Unitek (P = 0.003) and Ormco (P = 0.000) groups. At pH 7, the survival rate for the HGFs and the U2OS cells differed statistically for the Dentaurum (P = 0.021) and Unitek (P = 0.03) groups. The results demonstrate that differing cells exhibit various cellular reactions on exposure to metal bracket immersion media, although the four types of brackets appear to be biocompatible with HGF and U2OS cells.

Decrease of trace elements in erythrocytes and plasma after removal of dental amalgam and other metal alloys

The objective of this study was to determine the concentration changes of 13 elements in erythrocytes and plasma after the removal of dental amalgam and other metal alloys. Blood samples from 250 patients were collected, separated into erythrocytes and plasma, and analyzed by inductively coupled plasma-mass spectrometry. The 250 patients were divided into 3 groups (Negative, Zero, and Positive) depending on their estimation of quality of life in an earlier study. Magnesium in plasma, selenium and mercury in plasma, and erythrocytes showed decreased concentrations after amalgam removal in all groups (p < 0.05). Titanium in plasma, copper in plasma, and erythrocytes and zinc in plasma exhibited decreased concentrations after amalgam removal in the Negative and Positive groups (p < 0.05). Silver in plasma and gold in erythrocytes decreased in the Zero and Positive groups after amalgam removal (p < 0.05). Copper in erythrocytes and silver and gold in plasma showed higher concentrations after amalgam removal in the Negative compared to the Positive group (p < 0.05), suggesting that patients in the Negative group excrete metals slowly. Moreover, the cobalt levels in plasma were lowest in the Negative group and only this group showed a significant increase in vitamin B12 levels in blood after amalgam removal.

The safety of nickel containing dental alloys

Nickel is a constituent of many dental alloys. This paper reviews mainly papers published after 1985 with regards to biological reactions to nickel in dentistry. Nickel is an allergen, but there is no evidence that individual patients are at a significant risk of developing sensitivity solely due to contact with nickel-containing dental appliances and restorations. Hypersensitivity reactions to nickel are only likely to occur with prior sensitization from non-dental contacts and even these are rare. Clinical evidence has been presented to show that small doses of nickel, e.g. from dental appliances, may induce tolerance to this allergen. The papers reviewed report low rates of release of nickel from dental alloys. Some nickel compounds, which are mildly cytotoxic, have been implicated as carcinogens by inhalation in industrial settings, but these compounds are not present in dentistry-related operations, including dental technology procedures. Nickel-containing alloys and compounds have not been associated with increased cancer risk by oral or dermal routes of exposure. It is concluded that, subject to use according to established techniques, nickel-containing dental alloys do not pose a risk to patients or members of the dental team.

Ion release from dental casting alloys as assessed by a continuous flow system: Nutritional and toxicological implications

OBJECTIVES

The aims of this study were to quantify the metallic ions released by various dental alloys subjected to a continuous flow of saliva and to estimate the nutritional and toxicological implications of such a release.

METHODS

Four pieces of three nickel-based, one noble, one high-noble and two copper-aluminum alloys were cast and then immersed in a continuous flow of artificial saliva for 15 days. To simulate three meals a day, casts were subjected to thrice-daily episodes, lasting 30 min each and consisting of pH decreases and salinity increases. After 15 days, the metallic ions in the artificial saliva were analyzed. Data were expressed as averaged release rate: microg/cm2/day of ion released for each alloy. The highest value of 95% Cl of each ion was adapted to a hypothetical worst scenario of a subject with 100 cm2 of exposed metal surface. The results were compared with the tolerable upper daily intake level of each ion.

RESULTS

The copper-aluminum alloys released copper, aluminum, nickel, manganese and iron. The nickel-based alloys essentially released nickel and chromium, while the beryllium-containing alloy released beryllium and significantly more nickel. The noble and high-noble alloys were very resistant to corrosion. The amount of ions released remained far below the upper tolerable intake level, with the exception of nickel, released by beryllium-containing nickel-based alloy, whose levels approach 50% of this threshold.

SIGNIFICANCE

The daily amount of ions released seems to be far below the tolerable upper intake levels for each ion.

Ion release and cytotoxicity of stainless steel wires

Heat treatment is generally applied to orthodontic stainless steel (SS) wires to relieve the stresses that result from their manipulation by orthodontists. The quality and thickness of the oxide films formed on the surface of heat-treated wires can vary, and it is believed that these oxide films can influence the properties of heat-treated wires. The aim of this study was to investigate the influence of heat treatment and cooling methods on the amount of metal ions released and to examine the cytotoxicity of heat-treated wires. In this study, four types of SS wires (Remanium, Permachrome, Colboloy and Orthos) with a cross-sectional area of 0.41 x 0.56 mm were investigated. These wires were heat-treated in a vacuum, air, or argon environment, and were cooled in either a furnace or a water bath. Four control groups and 24 experimental groups were classified according to the type of wires, heat treatment conditions and cooling methods. In each group, the amount of nickel released as well as its cytotoxicity was investigated. The concentration of dissolved nickel ions in artificial saliva was measured for a period of up to 12 weeks. In all groups, the concentration of dissolved nickel ions in artificial saliva was lowest for the vacuum heat treatment-furnace cooling group and a significant difference was shown compared with the other experimental groups. The concentration of dissolved nickel ions in artificial saliva was highest in the groups heat-treated in air (P < 0.05), while the amount of nickel released was highest in the Remanium and Colboloy (P < 0.05). The cytotoxicity was mild in all the experimental groups but the response index of the air groups was slightly higher than in the other groups. According to these results, SS wires retain their high corrosion resistance and low ion release rate when heat-treated in a vacuum and cooled in a furnace.

The effects of recasting on the cytotoxicity of base metal alloys

STATEMENT OF PROBLEM

Cytotoxicity of cast alloys depends on their composition and element release, which may be affected by recasting of the alloy.

PURPOSE

This study investigated the effect of recasting on the element release and cytotoxicity of 5 base metal alloys.

MATERIAL AND METHODS

The alloys tested consisted of: 2 Ni-Cr (Remanium CS and Wiron 99); a Ni-Cr with Cu (CB Soft); a Co-Cr (Wirobond C); and a Cu-base (Thermobond). Alloy specimens (disks 3 x 5 mm) were cast as follows: 100% new alloy; 50% new with 50% recast; and 100% recast (n = 6). Cytotoxicity was tested using Balb/C 3T3 fibroblasts and the MTT assay. Six replicates were tested for each alloy, and the controls consisted of 6 wells containing cells with no alloy specimens. The release of elements from the alloys into culture medium was also investigated. The data were analyzed by 2-way analysis of variance (ANOVA) followed by the Tukey Honestly Significant Difference test (family error rate =.05).

RESULTS

At all 3 variations of casting, Remanium CS and Wiron 99 were the least cytotoxic, followed by Wirobond C, CB Soft, and Thermobond. ANOVA revealed significant differences between the groups (P <.001). Post hoc analysis showed that overall, Thermobond was significantly more cytotoxic than all of the other alloys tested (P <.05). For the 100% new alloy groups the cytotoxicity of Co-Cr alloy Wirobond C was similar to that of the Ni-Cr alloys Remanium CS and Wiron 99; however, when the alloys were recast, Wirobond C became significantly more cytotoxic and as toxic as the Ni-Cr alloy containing Cu (CB Soft). Moreover, recasting significantly increased the cytotoxicity of all the alloys (P <.05) and the amounts of elements released from them.

CONCLUSION

The Cu content in an alloy increased its cytotoxicity level remarkably. Recasting of alloys significantly increased their cytotoxicity level. The Co-Cr alloy was more adversely affected by the recasting than the Ni-Cr alloys.

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.

In vitro cytotoxicity of orthodontic archwires in cortical cell cultures

There have been a number of studies regarding the toxicity of orthodontic archwires, but little is known concerning the mechanism of their toxicity. This investigation used murine cortical cell cultures to examine the in vitro neurotoxicity of commonly used orthodontic metallic archwire alloys. The materials examined included 0.016 inch nickel-titanium (NiTi), copper-nickel-titanium, titanium-molybdenum, Elgiloy, and stainless steel archwire alloys. Standard sized samples of each material were placed on tissue culture inserts suspended above the cell cultures. Neuronal death was determined using the lactate dehydrogenase release assay 24 hours after exposure to the archwires. The results indicated that NiTi, copper-nickel-titanium and titanium-molybdenum alloys were not neurotoxic, while stainless steel and Elgiloy were significantly toxic. Washing the archwires for 7 days in a saline solution did not alter the toxicity. However, the free radical scavenger, trolox, blocked the toxicity of both stainless steel and Elgiloy, indicating that the death was free radical mediated. The caspase inhibitor, Z-VAl-Ala-Asp-fluoromethylketone (zVAD-FMK), blocked the toxicity of stainless steel, but not Elgiloy, suggesting that stainless steel induced apoptosis. Further evidence that stainless steel induced apoptosis was provided by propidium staining which showed nuclear chromatin condensation and fragmentation into discrete spherical or irregular shapes, characteristic of apoptosis. The specific metal responsible for the toxicity was not determined; the metals common to each of the toxic archwires were nickel, iron, and chromium.

Effects of Ce on the short-term biocompatibility of Ti-Fe-Mo-Mn-Nb-Zr alloy for dental materials

Effects of Ce on the short-term biocompatibility of Ti-Fe-Mo-Mn-Nb-Zr alloy designed for implant materials were studied by acute toxicity test, hemolytic test, and MTT assay. The elements and their concentration in surface films and extraction media of Ti alloys were investigated with XPS and ICP, respectively. The primary compositions of the surface films of Ti alloys with 0.3% Ce and without Ce were TiO2 and Nb2O5. There were 0.2 mg/l Fe and 0.16 mg/l Mn in the extraction medium of Ti alloy without Ce, while 0.27 mg/l Fe and 0.87 mg/l Mn in the extraction medium of Ti alloy with 0.3% Ce. The concentrations of Fe and Mn in the medium were too low to have any significant effects on human health. There was no sign of cytotoxicity in these tests. The cytotoxicity levels of Ti alloys without Ce and with 0.3% Ce were graded 0 and 1, respectively. The hemolytic degrees of Ti alloys without Ce and with 0.3% Ce were 0.558% and 0.67%, respectively. The cells being incubated in the extraction medium were normal. These phenomena indicated that Ce was innocuous within the concentration range of this study. In addition, the hemolytic ratio and toxicity level of Ti alloy with 0.3% Ce were a little higher than that of Ti alloy without Ce. This meant that Ce would slightly increase the toxicity of Ti alloy.

Evaluation of biocompatibility of metallic dental materials in cell culture model

Biocompatibility of metals for dental use was tested using a three-dimensional model consisting of oral keratinocytes cultured on de-epidermised sub-mucosa. The toxicity of orthodontic metallic wire and soldering material was assessed through parameters such as the morphology and growth rate of the keratinocytes, as well as by classical histology, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The sharp composition of metallic wires and soldering materials was assessed by Auger Electron Spectroscopy (AES). The results of our experiment showed that the new model revealed inhibition of keratinocyte growth and stratification near soldering material, whereas mucosal cells were able to grow and layer out on dental wire. It is concluded that this experimental model, which simulates the oral environment, is useful for studying the effects of materials for dental use for its sensibility and reproducibility. Moreover it can provide morpho-functional information which cannot be achieved by traditional methods.

[Evaluation on biocompatibility of Ti-Fe-Mo-Mn-Nb-Zr alloy]

In this study, the general toxicity tests including acute toxicity test, haemolysis test, MTT assay of Ti-Fe-Mo-Mn-Nb-Zr alloys were carried out. The morphology of these cells was also observed under phase-contrast microscope. By using X-ray photoelectron spectroscopy(XPS), the kind and mol% of element in surface film were studied. The kind and concentration of element in dipping fluid were investigated by ICP atomic emission spectrometry. The results showed the primary component is TiO2 in surface film. The dipping fluid of Ti-Fe-Mo-Mn-Nb-Zr alloys contains Fe 0.2-1.07 mg/l and Mn 0.16-0.5 mg/l; such dental materials are beneficial to health. No cytotoxic effect was disclosed by in vitro and in vivo tests. The level of cytotoxicity was grade 0 and 1; the haemolysis degree was 0.558%-0.642%, i.e. less than 5%. The cells growing in the extract showed normal morphology. These data indicate that Ti-Fe-Mo-Mn-Nb-Zr alloy, as a dental material, has good biocompatibility.

Effects of base-metal casting alloys on cytoskeletal filaments in cultured human fibroblasts

PURPOSE

The present study was designed to determine the cytotoxic effects of some widely used dental base-metal casting alloys (Ni-Cr and Co-Cr) on the cytoskeleton in cultured human fibroblasts, and to evaluate whether any structural alteration is associated with the application of these alloys.

MATERIALS AND METHODS

Ten specimens from six different alloys were prepared as 5-mm disks. Five of ten samples from each group were polished; the remaining five samples were left sandblasted with 50-microm Al2O3. All samples were directly exposed to human fibroblasts in a 24-well cell culture dish for 120 hours. Then, cells were fixed and stained with antibodies against major cytoskeletal elements--actin, vimentin, and microtubules--by immunofluorescent staining methods. Cells were analyzed in 3-D to document the cytoskeletal alterations using a laser confocal microscope.

RESULTS

Disintegration of actin filaments was observed in lamellipodia of fibroblasts by the effect of both polished and sandblasted Ni-Cr and Co-Cr samples, with the exception of the polished Co-Cr alloy (Wirocast). Moreover, intracytoplasmic actin-decorated stress fibers were found bent and occasionally tangled in the sandblasted Ni-Cr (Wiron 99) and Co-Cr alloys (Wirocast and Co-Cr Degussa). Vimentin, a mesenchymal cell intermediate filament protein normally showing an intracellular meshwork pattern, was not affected by any of the polished or sandblasted alloys. Microtubules mainly remained intact in all dental alloy-treated groups.

CONCLUSION

Taken together, it is possible to postulate that Ni-Cr and Co-Cr dental alloys, especially sandblasted forms, may have detrimental effects on the actin-based cytoskeleton, at least tested in vitro.

In vivo study on metal release from fixed orthodontic appliances and DNA damage in oral mucosa cells

Interest in the amount of metal ion intake from dental alloys has grown. Fixed orthodontic appliances usually include brackets, bands, and archwires made of stainless steel, nickel-titanium, or nickel-cobalt alloys, and these can release metal ions. The purpose of this study was to investigate the biocompatibility in vivo of fixed orthodontic appliances, evaluating the presence of metal ions in oral mucosa cells, their cytotoxicity, and their possible genotoxic effects. Mucosa samples were collected by gentle brushing of the internal part of the right and left cheeks of 55 orthodontic patients and 30 control subjects who were not receiving orthodontic treatment. The cells were immediately prepared for cell viability and the comet assay. Nickel and cobalt cellular content was quantified by inductively coupled plasma mass spectrometry (ICP-MS). The results indicate that nickel and cobalt concentrations were 3.4-fold and 2.8-fold higher, respectively, in the patients than in the controls; cellular viability was significantly lower in the patients than in the controls, and there was a significant negative correlation with metal levels. The biologic effects, evaluated by alkaline comet assay, indicated that both metals induced DNA damage (more cells with comets and apoptotic cells). There were significant positive correlations between (1) cobalt levels and the number of comets and apoptotic cells, (2) nickel levels and number of comet cells, and (3) cobalt levels and comet tails. This study corroborates that nickel and cobalt released from fixed orthodontic appliances can induce DNA damage in oral mucosa cells.

Cytotoxicity of dental casting alloys after conditioning in distilled water

PURPOSE

This study investigated the cytotoxicity of various types of dental casting alloys after they had been conditioned in distilled water.

MATERIALS AND METHODS

The casting alloys investigated included one high-noble alloy (Bioherador N) and six base-metal alloys, including four Ni-Cr alloys (Remanium CS, Heranium NA, Wiron 99, CB Soft), one Co-Cr alloy (Wirobond C), and one Cu-based alloy (Thermobond). Ten disks from each alloy were conditioned in distilled water at 37 degrees C for either 72 or 168 hours. The cytotoxicity of the alloys was then tested on Balb/C 3T3 fibroblasts, which were exposed to the alloys for 3 days at 37 degrees C. Cell viability was determined by the MTT method. The data were analyzed by ANOVA, and follow-up comparison between the groups was carried out using Tukey and t tests.

RESULTS

ANOVA revealed a significant effect of alloy type and conditioning time (P < .001). Bioherador N was significantly less toxic than all the other alloys in the 72-hour conditioned group. After 168 hours of conditioning, its cytotoxicity was not different (P > .05) from that of Remanium CS, Wiron 99, and Wirobond C. Thermobond and CB Soft were significantly more toxic than the other alloys at both conditioning times.

CONCLUSION

Conditioning of base-metal alloys, other than those containing Cu, for 168 hours in distilled water makes their cytotoxicity levels comparable to that of the high-noble alloy.

Direct and indirect induction of apoptosis in human mesenchymal stem cells in response to titanium particles

The most frequent complication of total joint arthroplasty is periprosthetic osteolysis initiated by an inflammatory response to orthopaedic wear debris, which if left untreated, can result in implant instability and failure, eventually requiring revision surgery. We have previously reported that osteogenic differentiation of human marrow stroma-derived mesenchymal stem cells (hMSCs) is suppressed upon exposure to titanium particles, accompanied by reduced bone sialoprotein (BSP) gene expression, diminished production of collagen type I and BSP, decreased cellular viability and proliferation, and inhibition of extracellular matrix mineralization. In this study, we have further investigated hMSC cytotoxicity upon exposure to submicron particles of commercially pure titanium (cpTi) and zirconium oxide (ZrO(2)). Our results showed that direct exposure to cpTi and ZrO(2) particles compromises cell viability through the induction of apoptosis, eliciting increased levels of the tumor suppressor proteins p53 and p73, in a manner dependent on material composition, particle dosage, and time. Additionally, conditioned medium collected from hMSCs exposed to cpTi particles, but not to ZrO(2) particles, is cytotoxic to hMSCs, inducing apoptosis in the absence of particles. These findings demonstrate that exposure to orthopaedically derived wear particles can compromise hMSC viability through the direct and indirect induction of apoptosis. Thus, prolonged in vivo exposure of marrow-derived hMSCs to implant-derived wear debris is likely to reduce the population of viable osteoprogenitor cells, and may contribute to poor periprosthetic bone quality and implant loosening.

Toxicity of metal ions used in dental alloys: a study in the yeast Saccharomyces cerevisiae

Metal ions are released from dental alloys into the oral environment, which can cause biological responses over short and extended periods. Since most toxic metal ions are capable of inducing oxidative stress on cells through the mitochondrial respiratory chain, mitochondria may contribute to and be a target of metal toxicity. In this study, we investigated the effect of metal ions on growth of the budding yeast, Saccharomyces cerevisiae, and on the morphology and function of yeast mitochondria. Moreover, we tested whether mitochondrial respiratory activity contributes to metal toxicity. Metal ions affected yeast cell growth. The toxicity of metal ions to yeast cells, ranked in decreasing order are as follows: Hg > Ag > Au > Cu, Ni, Co, Zn. This result mostly correlates with the degree of toxicity of those metal ions to growth of human cells. The MIC90 of Hg, Ag and Au ions in synthetic complete media are 0.325, 5 and 320 microM, respectively. None of the toxic metal ions resulted in loss of mitochondrial respiratory activity. However, respiration-deficient rho0 cells appeared to be resistant to Ag ion, but not to Hg and Au ions. Furthermore, at high concentrations, Ag ion caused morphological changes in mitochondria. These studies indicate that yeast may be used as a model system to screen for toxic effect of metals ions from dental alloys, and that oxidation activity in mitochondria may play a role in acute toxicity of silver ion.

Biological reactivity of zirconia-hydroxyapatite composites

Materials and devices intended for end-use applications as implants and medical devices must be evaluated to determine their biocompatibility potential in contact with physiological systems. The use of standard practices of biological testing provides a reasonable level of confidence concerning the response of a living organism to a given material or device, as well as guidance in selecting the proper procedures to be carried out for the screening of new or modified materials. This article presents results from cytotoxicity assays of cell culture, skin irritation, and acute toxicity by systemic and intracutaneous injections for powders, ceramic bodies, and extract liquids of hydroxyapatite (HA), calcia partially stabilized zirconia (ZO), and two types of zirconia-hydroxyapatite composites (Z4H6 and Z6H4) with potential for future use as orthopedic and dental implants. They indicate that these materials present potential for this type of application because they meet the requirements of the standard practices recommended for evaluating the biological reactivity of ATCC cell cultures (CCL1 NCTC clone 929 of mouse connective tissue and CCL 81 of monkey connective tissue) and animals (rabbit and mouse) with direct or indirect patient contact, or by the injection of specific extracts prepared from the material under test. In addition, studies involving short-term intramuscular and long-term implantation assays to estimate the reaction of living tissue to the composites studied, and investigations on long-term effects that these materials can cause on the cellular metabolism, are already in progress.

[Biocompatibility and resistance to corrosion of orthodontic wires]

Various materials are currently used to make orthodontic wires. This article suggests a synthesis on their resistance to corrosion and biocompatibility. In the first part, after a review of some basic notions on the corrosion processes, the authors develop the electrochemical characteristics of the three main groups of alloys used in orthodontics. They study more precisely corrosion resistance of nickel-titanium alloys and, through their own experimental results, they show that this type of alloy is subject to corrosion in acid and fluoridated environment. In the second part, the authors study those alloys biocompatibility. They first mention nickel toxicity and allergy induced by this element. Then, biocompatibility of alloys used in orthodontics is assessed following studies on the release of metallic elements from orthodontic wires, and studies on cell-compatibility when in contact with those wires. It is proved that the state of materials surface has a very high influence on their biocompatibility. As a conclusion, in spite of numerous studies carried out so far, showing a satisfactory biological behaviour of those orthodontic wires, many questions are yet to be answered: long term in vivo performances of those materials have not yet been exactly assessed. Further studies must definitely be carried out.

On the in vitro biocompatibility of Elgiloy, a co-based alloy, compared to two titanium alloys

AIM

The aim of the present investigation was to contribute to an understanding of the effects of surface topography and chemical composition on the corrosion behavior and thus the biocompatibility of Elgiloy (RMO, Denver, CO, USA), a common Co-based alloy.

MATERIAL AND METHODS

The results are compared with those obtained for a binary NiTi alloy, Neo Sentalloy (GAC, Central Islip, NY, USA) and a beta-III-Ti alloy, TMA (Ormco, Glendora, CA, USA). In the present study, the surface topography and the chemical composition of two different grades of Elgiloy, Blue Elgiloy (soft) and Yellow Elgiloy (ductile), were examined by means of scanning electron microscopy (SEM) and energy-dispersive spectroscopy analysis (EDS). Their corrosion behavior in half-strength Ringer solution and in an artificial saliva solution according to Barrett [1] was investigated using potentiodynamic corrosion testing (PDC). The photometry-based PAN method was used to quantify the released Ni and Co ions. The in vitro biocompatibility of the two grades of Elgiloy was tested in three different cell cultures: in L929, a commercially available mouse fibroblast cell line, and in primary human epithelial cells and fibroblasts.

RESULTS

The results of the corrosion testing showed satisfactorily high pitting corrosion potentials but lower repassivation potentials and a strong increase in current density once pitting had occurred. The photometric results revealed the release of Ni and Co ions in both tested electrolytes. The tested native surfaces exhibited numerous grinding and polishing grooves, inclusions and inhomogeneities of the microstructure. After corrosion testing the same surfaces displayed numerous signs of corrosion, especially in areas with microstructural inhomogeneities. In vitro biocompatibility testing showed a substantially reduced dehydrogenase activity in the presence of Elgiloy. The reduced quality of surface finish resulting from the manufacturing process led in the case of the tested Elgiloy types to decreased corrosion resistance with consequently reduced in vitro biocompatibility.

CONCLUSIONS

In this context it is also conceivable that patients with a proven allergy to nickel, cobalt or chromium may react sensitively to the deployment of this alloy, at least in the surface quality tested by us. From this aspect, the introduction of a binding standard for the surface quality of materials used in orthodontic appliances is urgently recommended.

An investigation of the cytotoxic effects of dental casting alloys

PURPOSE

This study investigated the cytotoxicity of a high-noble alloy (Bioherador N) and six commercially available base-metal alloys, including four Ni-Cr alloys (Remanium CS, Heranium NA, Wiron 99, CB Soft), one Co-Cr alloy (Wirobond C), and one Cu-based alloy (Thermobond).

MATERIALS AND METHODS

Ten specimens from each alloy were prepared in the form of disks, which were placed in 24-well tissue culture plates together with a suspension containing Balb/C 3T3 fibroblasts (5 x 10(5) cells/mL). After 3 days of incubation at 37 degrees C, cell viability was determined by the MTT method.

RESULTS

Variations in cytotoxicity of the alloys were observed and related to their composition. One-way ANOVA showed statistically significant differences in cytotoxicity of the alloys (P < .001). Tukey's multiple comparisons (alpha = .05) revealed that Bioherador N was significantly less cytotoxic than all the other alloys. Thermobond was the most cytotoxic, followed by CB Soft, and both of these alloys were significantly more cytotoxic than all the others.

CONCLUSION

The cytotoxicity of casting alloys tested in this study was markedly affected by their composition. Differences were found in the cytotoxicity of alloys classified within the same category. The presence of Cu in the composition of the alloy adversely affected cell viability.

In vitro biological response to core and flowable dental restorative materials

OBJECTIVES

In vitro cytotoxicities of commercially available core and flowable dental restorative materials were assessed and compared to traditional resin composites. Our hypothesis was that the increased resin diluents added to achieve higher flow in flowables would increase cytotoxicities, whereas the higher filler content of core materials would decrease cytotoxicities relative to traditional resin composites.

METHODS

Specimens were made under aseptic conditions, then extracted into an artificial saliva solution for 0-4 weeks, to assess the effect of aging on cytotoxicity. After extraction, specimens were tested for cytotoxicity in vitro using Balb/c fibroblasts in direct contact format. Cells were exposed to the materials for 48h, after which the mitochondrial activity of the cells was measured (MTT method). Cellular activity was normalized to Teflon negative controls.

RESULTS

Core materials were uniformly and severely (<50% of Teflon cellular activity) cytotoxic initially, but several materials (Corepaste, Definite core) improved somewhat with aging in artificial saliva. Flowable materials were uniformly and severely cytotoxic with no trend toward improvement with aging. The Definite-flow was the least cytotoxic of the flowable materials, but it too was severely cytotoxic.

SIGNIFICANCE

Commercially available core and flowable restorative materials showed severe in vitro cytotoxicities that are worse than some traditional composites and most dental casting alloys and amalgams used today. Of particular note was the persistent cytotoxicity of these materials after 4 weeks of extraction with artificial saliva. These cytotoxicities indicate a continuing release of mass from these materials at levels that have biological relevance in vitro. In vivo relevance of these cytotoxicities is less clear, but these results indicate a higher biological risk for these materials compared to traditional materials that exhibit less initial toxicity and improve with aging time.

Assessment of dental material degradation product toxicity using a bioluminescent bacterial assay

OBJECTIVES

This study examined dental material degradation product toxicity using the Microtox bacterial bioluminescence assay as well as the effects on toxicity of selective leaching, chelation with protein, the physical form of the products, and synergistic/antagonistic interactions among released ions.

METHODS

Polarization was used to produce ionically dissolved (ID) and precipitated corrosion products from Litecast B alloy specimens, which were then chemically analyzed to determine their composition and to identify metal valence states. Corrosion product toxicity, as well as that of the individual alloying elements, alone and in the presence of mucin, was analyzed using Microtox. A mathematical approach identified synergistic/antagonistic interactions and determined element contribution to product toxicity. The mechanism by which the Microtox test bacterium interacts with solid products was explored. The toxicity of methyl methacrylate (MMA) monomer was also examined.

RESULTS

Precipitated corrosion products were found to be more toxic than ID products. The metals in the precipitate have been shown to be available to the test bacterium. Be and Ni were the most toxic elements in the products and contributed significantly to their toxicity. Synergistic and slightly antagonistic interactions were observed in the ID and precipitated products, respectively. Mucin decreased toxicity of all elements except Be. MMA monomer toxicity was found to be low compared to metal toxicity.

SIGNIFICANCE

Microtox is useful for evaluating dental degradation product biocompatibility and has significant promise for use in other types of studies, such as determining the effectiveness of antimicrobial treatments.

Elements released from dental casting alloys and their cytotoxic effects

PURPOSE

This in vitro study investigated the element release from seven commercially available dental casting alloys and tested their cytotoxic effects.

MATERIALS AND METHODS

The casting alloys tested were one high-noble alloy (Bioherador N) and six base-metal alloys, including four Ni-Cr alloys (Remanium CS, Heranium NA, Wiron 99, CB Soft), one Co-Cr alloy (Wirobond C), and one Cu-based alloy (Thermobond). Ten specimens from each alloy were prepared in the form of disks, and each of the seven dental casting alloys (10 disks per group) were conditioned in distilled water at 37 degrees C for either 72 or 168 hours. The conditioning media were analyzed for element release, and the cytotoxic effects were assessed on Balb C fibroblasts using MTT assay.

RESULTS

Element release was greater at 168 hours of conditioning than at 72 hours. The extract from the high-noble alloy showed the least amount of element release (only Zn), with no cytotoxic effects. The greatest amount of element release was detected in the Cu-based alloy Thermobond and the Ni-Cr alloy CB Soft; their extracts were significantly more toxic than all the other alloy extracts. The cytotoxic effects of the other Ni-Cr alloy extracts were not statistically significantly different from the high-noble alloy extract. However, the Co-Cr alloy (Wirobond C) extract was significantly more cytotoxic than the high-noble alloy extract.

CONCLUSION

Element release from casting alloys is proportional to the conditioning time. The content of Cr and Mo in the alloy protects the alloy from dissolution, while the Cu content makes it more susceptible to corrosion and dissolution, rendering it more cytotoxic.

Multiple parameter cytotoxicity index on dental alloys and pure metals

Palladium (Pd) is a metal frequently used for dental alloys. In order to elucidate controversial options about Pd concerning its biological performances, our study consists in the evaluation of commercial and experimental PFM and C&B precious and semi-precious dental alloys. This investigation was also designated to the establishment of a cytotoxicity index (CI) such as it was described for hemocompatibility testing. The following materials were tested: 36 commercial alloys (Au-, Pd- and Ag-base), 14 experimental alloys (Pd-base established by an experience plan) and pure metals (Ag, Au, Cu, Ni, Cr, In, Sn, Pt, Ti, Zn). The cells culture experiments were carried out with epithelial L132 cells and NIH 3T3 fibroblasts. In vitro cell viability tests show that Pt, Sn, In, Ti, Au and Pd have no cytotoxic effect; Cr, Cu and Ag are toxic, Ni, Zn, and Co are highly toxic. An identical ranking was found with the inflammatory and proliferation tests. Toxic and highly toxic metals induced slight or strong prosthetic dental restoration morphological alterations after 3-days cultures and mostly cell death after 6-days cultures. These effects are dependent on the leakage of the element into the culture medium as revealed by ICP. The addition of Au gives benefit to Pd-Ag alloys, but does not produce any major effect on Pd-Cu alloys. This qualitative ranking can quantitatively be confirmed by cytocompatibility testing after application of a CI.

Biological interactions of dental cast alloys with oral tissues

OBJECTIVE

All dental cast alloys release metal ions into the oral environment which have the potential to interact with the oral tissues. Amount and type of metal elements released are varying and not directly related to the composition of the alloy. The aim of the present literature survey was to describe the interactions of dental cast alloys with living tissues and to relate them to clinically adverse local reactions of the oral tissues.

RESULTS

Interactions of dental cast alloys with the oral tissues take place by different mechanisms; e.g. bacterial adherence promotion, toxic and subtoxic effects and allergy. Whereas bacterial adhesion promotion may be counteracted by adequate oral hygiene measures, the other mechanisms may lead to clinically adverse local reactions due to the metal present. However, the number of cases, where such a relation can be safely diagnosed, is small. Safe ground is felt with proven allergies. The comparatively high allergy rate towards nickel should be the impetus to replace those alloys whenever there is a suitable alternative. Medical and dental impairments as well as general medication may lead to symptoms allegedly attributed to metal restorations.

CONCLUSIONS AND SIGNIFICANCE

Patients relating oral symptoms to metal restorations should be subjected to a thorough dental and general medical examination in order to exclude non-material related diseases being the cause for their complaints/symptoms. These cases are a challenge for the collaboration between the medical and dental professions.

Cytotoxicity of orthodontic bands, brackets and archwires in vitro

OBJECTIVES

In orthodontic therapy, different materials are used and subjected to a damp oral environment, which can modify their properties. In order to evaluate the biocompatibility of metallic and non-metallic orthodontic appliances their in vitro cytotoxicity has been measured.

METHODS

Twenty-eight new and nine clinically used materials, including brackets, molar bands and archwires were used. The metallic materials were made of stainless steel, gold-plated steel, pure titanium, nickel-titanium, titanium-molybdenum and silver-based soldering alloy. The non-metallic materials were in polycarbonates and ceramics. After a release period of the material in the culture medium (0.1 mg/ml) for 3 and 14 days, the viability of fibroblasts L929 cultivated with this medium was compared to negative control with MTT assay.

RESULTS

The results showed the non-cytotoxicity of the materials. The metallic and non-metallic materials were similar in terms of cytotoxicity. The cytotoxicity of clinically used samples was equivalent to that of the same non-used samples, except a cytotoxic sample, at 14 days, corresponding to a soldered and clinically used molar band. The 3 day results were different from the 14 day results in six cases out of 37.

SIGNIFICANCE

In spite of the presence of one cytotoxic sample, the orthodontic materials can be considered as non cytotoxic. However, the practitioner should pay attention to the composition and the polish of soldering silver-based alloys containing copper and zinc in order to limit cytotoxic ion release. The cytotoxicity of the used sample related to ion release might be related to some clinical sub-acute effects related with orthodontic materials, thus a long term release period may be suitable to evaluate in vitro the sub-acute clinical effects of alloys.

Human peripheral blood monocytes versus THP-1 monocytes for in vitro biocompatibility testing of dental material components

Monocytes play a central role in the response of tissues to biomaterials. Monocytic cell lines such as the THP-1 cell line have been used extensively as models for primary monocytes (directly from blood) in biocompatibility research. However, little information exists about the appropriateness of these cell lines as models. Thus, the current study compared the biological response of both primary peripheral blood monocytes (PBMs) and the THP-1 cell line to four common components of dental materials known to be released into the oral environment: nickel ions, 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), and 2,2-bis[4(2-hydroxy-3-methacryloloxy)-phenyl]propane (Bis-GMA). Comparisons were made by constructing dose-response curves for each type of monocyte and the four components. The 50% cytotoxicity values (TC50 values) were then statistically compared. In addition, the response of the monocytes to the materials with and without lipopolysaccharide (LPS) stimulation were assessed by measuring TNF-alpha secretion from the monocytes. The results showed that the PBMs were 5-10 times less sensitive than the THP-1 monocytes to these dental components, but that both cell lines ranked the components identically. TNF-alpha secretion from both types of monocytes often showed similar trends, although some inconsistent results were noted. The current study supports the use of THP-1s as a model for ranking the cytotoxicity of components of dental biomaterials. Furthermore, the secretory activity of PBMs appears to be generally well represented by the THP-1s. However, sufficient differences between these cell types exist to recommend confirmation of any critical results obtained with THP-1s using PBMs.

Ag, Cu, Hg and Ni ions alter the metabolism of human monocytes during extended low-dose exposures

The monocyte and macrophage play an important role in the biological response to dental biomaterials. However, the effects of low-level, extended exposures of monocytes to metal ions which are known to be released from dental alloys is not known. Thus, in the current study we characterized the metabolic activity of monocytes in the presence of low doses of Ag, Cu, Hg and Ni ions for up to 4 weeks. THP-1 human monocytes were exposed in vitro to concentrations of metal ions at 1-10% of those known to be lethal during 24 h exposures. Mitochondrial function [succinic dehydrogenase (SDH) activity] and total cellular protein [bicinchoninic acid (BCA) assay] were assessed at weekly intervals during metal exposure. Each metal ion caused a unique pattern of effects from the monocytes. These effects were sometimes delayed until several weeks into the exposure (Cu, Ni). Large increases in total protein or SDH activity per cell were observed (Cu 150%, Hg 40-60%, Ni 50%), but these increases were always transient. The differences between concentrations with minimal effects and those which were lethal (8 versus 12 micromol L(-1) for Ag, 1.0 versus 1.5 micromol L(-1) for Hg) were small. Finally, concentrations which caused total suppression of cellular activity were sometimes preceded by an increased activity (Hg, Ni). We concluded that metal ions alter monocyte metabolic activity during extended exposures in vitro, but that the concentrations required are often near long-term lethal levels. Clinically, these results imply that the levels of metals released from dental alloys may be significant to monocytic function.

Effect of toothbrushing on the toxicity of casting alloys

STATEMENT OF PROBLEM

The biological properties of casting alloys have been assessed largely under passive conditions. The effect of common intraoral stresses such as brushing, toothpastes, and low pH on alloy toxicity are not known.

PURPOSE

This study assessed the toxicity of 5 types of casting alloys commonly used in prosthodontics after toothbrushing, brushing in an acidic environment, or brushing with toothpaste. These toxicities were compared with those observed without any brushing.

MATERIAL AND METHODS

Au-Pt, Au-Pd, Pd-Cu-Ga, Ni-Cr-Be, and Ni-Cr (no Be) alloys were brushed for 48 hours in a toothbrushing machine at 90 strokes/minute and 200g force. Alloys were brushed with either saline at pH 7, saline at pH 4 (acidified with sodium lactate), or saline with 1:7 (wt/wt) toothpaste. After the brushing regimen, the cytotoxicity of the alloys was assessed in a standard in vitro test. Cytotoxicities of the alloys after different brushing treatments were compared with unbrushed (control) specimens. Analysis of variance (ANOVA) and Tukey multiple comparison intervals (alpha=.05) were used to identify significant differences among brushing conditions.

RESULTS

Brushing at pH 7 significantly increased the toxicity of the Pd-Cu-Ga alloy (15% to 20% over unbrushed specimens). Brushing at pH 4 increased the toxicity of the Au-Pt and Au-Pd alloys by 30% and the Pd-Cu-Ga alloy by >40%. The Ni-based alloys were not affected by acid. After being brushed with toothpaste, both Ni-based alloys were significantly more toxic, but Ni-Cr-Be was the worst, increasing more than 60% in toxicity over the controls. The toxicity of the Au-Pd alloy also increased significantly (15%).

CONCLUSION

Brushing dental casting alloys may increase their cytotoxicity in vitro, but the increase depends heavily on the alloy type and brushing condition.