Comparison of 20 nm silver nanoparticles synthesized with and without a gold core: Structure, dissolution in cell culture media, and biological impact on macrophages.

Widespread use of silver nanoparticles raises questions of environmental and biological impact. Many synthesis approaches are used to produce pure silver and silver-shell gold-core particles optimized for specific applications. Since both nanoparticles and silver dissolved from the particles may impact the biological response, it is important to understand the physicochemical characteristics along with the biological impact of nanoparticles produced by different processes. The authors have examined the structure, dissolution, and impact of particle exposure to macrophage cells of two 20 nm silver particles synthesized in different ways, which have different internal structures. The structures were examined by electron microscopy and dissolution measured in Rosewell Park Memorial Institute media with 10% fetal bovine serum. Cytotoxicity and oxidative stress were used to measure biological impact on RAW 264.7 macrophage cells. The particles were polycrystalline, but 20 nm particles grown on gold seed particles had smaller crystallite size with many high-energy grain boundaries and defects, and an apparent higher solubility than 20 nm pure silver particles. Greater oxidative stress and cytotoxicity were observed for 20 nm particles containing the Au core than for 20 nm pure silver particles. A simple dissolution model described the time variation of particle size and dissolved silver for particle loadings larger than 9 µg/ml for the 24-h period characteristic of many in-vitro studies.

Biocompatibility of gold and stainless steel chains used for forced eruption of impacted teeth - an in vitro investigation.

OBJECTIVE: Surgical approaches for the mobilization of impacted teeth involve the use of gold chains to connect the impacted tooth with the orthodontic appliance. In this study we have compared the local effects gold plated stainless steel with stainless steel specimen using an in vitro model of the gingival mucosa and monolayer cultures of cells of the alveolus. STUDY DESIGN: Local effects on differentiation, proliferation, and apoptosis and inflammatory response were tested using organotypic cultures of gingival cells. Cytotoxicity was measured by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays with monolayer cultures of human periodontal cells. RESULTS: The data obtained in this study could not reveal any differences in favor of using gold plated chains during the mobilization of impacted teeth. CONCLUSION: For patients not suffering from allergies against nickel there might be no rationale to favor gold plated chains, as there are no functional aspects to favor gold plated chains over stainless steel chains.

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.

In vitro evaluation of cytotoxicity of permanent prosthetic materials.

OBJECTIVES: To assess qualitative and quantitative cytotoxicity effect on permanent prosthetic materials to human gingival fibroblasts. METHODS: Human gingival tissues were collected (with informed consent) from patients undergoing periodontal surgical procedures and fibroblasts were cultured in vitro. Cell type was determined by performing proteomic analysis. Selected prosthetic materials including titanium, feldspathic ceramic, gold and chrome-cobalt alloy specimens (5×2 mm) were fabricated. The toxicity of prepared specimens was tested by exposing them to cell culture medium for 48, 72, 96 and 120 hours at 37°C under sterile conditions. Cell viability was estimated using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. The data concerning cell viability were statistically analyzed using two-way ANOVA test and Tukey multiple comparison test. RESULTS: Results obtained after 48 hours showed no toxic effect of titanium compared to control group. Cytotoxic effect was observed in gold alloy and feldspathic ceramic, however, it was not significant compared to control group. Chrome-cobalt alloy significantly reduced cell viability compared to control group (p≤0.001). Cytotoxicity diminished with increasing incubation time of specimens. After 120 hours of incubation all tested materials, except chrome-cobalt alloy, had no cytotoxicity. CONCLUSIONS: Titanium proved to be non-toxic. Gold alloy and feldspathic ceramic had short-term cytotoxic effect. Chrome-cobalt alloy had highest cytotoxic effect on fibroblast cells.

In vitro biocompatibility of novel Au-Pt-based metal-ceramic alloys.

The aim of this research was to evaluate the effect of individual metallic elements within experimental Au-Pt-based metal-ceramic alloys on in vitro biocompatibility. A binary Au-10 at.% Pt alloy (AP10) was designed as a parent alloy. Six ternary AP10-X (X = In/Fe/Sn/Zn) alloys and four quaternary (AP10-In2)-Y (Y = Fe/Sn/Zn) with different compositions were cast into square plates with size 10X10X0.5 mm(3) and subjected to porcelain-firing thermal cycling. A commercial alloy was used as a control. In vitro biocompatibility was investigated using L929 murine aneuploid fibrosarcoma cell line. The test samples and cells were incubated at 37°C in a 5% CO(2) atmosphere for 72 h. Alamar™ Blue Assay was carried out to determine the respiratory viability of cultures maintained in the presence of the different materials. The cell only control showed significantly higher levels of cell viability than all six of the ternary alloys and two of the four quaternary alloys, (AP10-In2)-Zn2.1 and (AP10-In2)-Sn1.0 (P < 0.05). The quaternary alloys showed slightly higher levels of cell viability than the ternary alloys, with the exception of AP10-Sn0.9. No statistical differences were seen between the ternary and quaternary alloy groups. Acceptable cell viability was observed on the surfaces of all the alloys.

Evaluation of cytotoxicity of accessories used for traction of impacted teeth

Aim: To test the hypothesis that gold-coated orthodontic accessories used for canine traction are less cytotoxic than those made of stainless steel. Methods: Six different orthodontic accessories were evaluated, three of them made from stainless steel (1 – bracket, 2 – button, 3 – mesh pad) and three made from a gold-coated alloy (4 – small mesh pad, 5 button, 6 – big mesh pad). Three control groups were also analyzed: Positive control (C+), consisting of Tween 80 cell detergent;Negative control (C-), consisting of PBS; and Cell control (CC), consisting of cells not exposed to any material. Dye-uptake technique, in which neutral red dye is incorporated into viable cells, was used to assess the cytotoxicity of the accessories. Viable cell counting was performed using a spectrophotometer. Data were analyzed statistically by A NOVA and Tukey’s test. Results:Statistically significant differences (P< 0.05) were found between Groups 1-3 and Groups 4-6. However, no differences were found between Groups 1-3 and Groups C- and CC, and neither between Groups 4-6 and Group C+. Conclusions: The tested hypothesis was not confirmed since gold-coated orthodontic accessories were found to be more cytotoxic than those made of stainless steel.

In vitro cytotoxicity evaluation of elemental ions released from different prosthodontic materials.

OBJECTIVES: This study investigated the cytotoxicity of elemental ions contained in four fixed prosthodontic materials (gold, nickel-chromium, stainless-steel alloys and CAD-CAM ceramics). MATERIALS AND METHODS: According to the determination of elements released from prosthodontic materials by using inductively coupled plasma mass spectroscopy, similar amounts of elements Pd, Ag, Zn, Cu, Ni, Cr, Mo, Be, Fe, Al, and K were prepared as salt solutions. Wells with a tenfold higher concentration of the tested elements were used as positive controls, while a well without any tested element was used as a negative control. These salt solutions were tested for cytotoxicity by culturing mouse L-929 fibroblasts in the salt solutions for a 7-day period of incubation. Then, the percentage of viable cells for each element was measured using trypan blue exclusion assay. The data (n=5) were statistically analyzed by ANOVA/Tukey test (p<0.05). RESULTS: The results showed a statistically significant difference for the cytotoxic effect of the tested elements salt solutions. For the released element concentrations the lowest percentage of viable cells (mean+/-SD) was evident with Zn, Cu or Ni indicating that they are the highly toxic elements. Be and Ag were found to be intermediate in cytotoxic effect. Fe, Cr, Mo, Al, Pd or K were found to be the least cytotoxic elements. SIGNIFICANCE: Zn and Cu released from gold alloys, and Ni released from nickel-chromium alloys, which are commonly used as fixed prosthodontic restorations, show evidence of a high cytotoxic effect on fibroblast cell cultures.

Cytocompatibility and electrochemical properties of Ti-Au alloys for biomedical applications.

The purpose of this study was to develop Ti-Au alloys with a higher resistant to corrosion, better biocompatibility, and better mechanical properties than the commercially pure titanium and its alloys. Ti-Au alloys were designed with a gold content that ranged from 0 to 5.0 at % in steps of 1.0 at %. Properties of the alloys including chemical composition, microstructure, phase, hardness, electrochemical properties, and the cytotoxicity were investigated. Only the alpha phase existed in the Ti-Au alloys. The addition of gold to the titanium decreased the alpha to beta transformation temperature. The acicular alpha phase became thinner and the hardness value increased with increasing gold content. In the electrochemical tests, Ti-Au alloys had a higher resistant to corrosion than had pure titanium and did not exhibit pitting corrosion in artificial saliva. The cytotoxicities of the Ti-Au alloys were similar to that of pure titanium. Therefore, Ti-Au alloys could be used as biomaterials in the medical and dental fields.

The mystery of the split earlobe.

The ancient art of body piercing has rejuvenated in the recent years as part of the fashion process. The ear is the most frequent body part to be pierced to wear jewelry. Split earlobes are commonly presented to plastic surgeons and the recurrence rate is high. The etiology of the acquired split earlobe was thought to be attributable to either trauma or heavy earrings. In this study, the authors explored the cause of the split earlobe and recurrence after surgical repair. Twenty-five patients who were using gold earrings presented with split earlobe and were studied, and the etiology of the condition was analyzed. A questionnaire was completed and the tissue obtained during surgical repair of the split earlobes was submitted for histopathological studies. This group of patients was compared with 17 subjects having stretched earlobe who were using heavy gold earrings. The control group consists of 50 subjects using gold earrings with normal earlobes. Clinical presentation and the histological studies suggest that allergy to metals used in the earring could lead to split earlobe. There is a difference between the split earlobe and stretched earlobe; the latter results from constant pull by heavy earrings. The authors present a new theory regarding the etiology of split earlobe and recommend that avoiding the offending metal in the earring is indispensable to prevent recurrence.

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.

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.

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.

Corrosion and biocompatibility testing of palladium alloy castings.

OBJECTIVE: The biocompatibility of palladium-copper alloys has been questioned in the literature. The intention of the present work was to study: (a) the release of ions in an immersion test from a copper-containing alloy, Option((R)) (79% Pd, 10% Cu, 9% Ga, 2% Au), compared with an alloy without Cu, IS85 (82% Pd, 6% Ga, 3.5% Sn, 3.5% In, 2.5% Ag, 2.5% Au); (b) the effect of oxide films produced by preoxidation on corrosion resistance; and (c) the possibility of biologically synergetic effects of ions released. METHODS: Specimens of both alloys were cast, rubbed and ultrasonically cleaned. Metallographic specimens were prepared after (a) casting and (b) preoxidizing treatment at approximately 1000 degrees C and studied by SEM and EDS. Immersion tests were carried out in a solution of 0.1mol/l of NaCl and 0.1mol/l of lactic acid at 37 degrees C for 7 days. The alloy specimens were tested in the following three steps: (1) as preoxidized; (2) after subsequent removal of a 0.1mm thick layer by grinding; and (3) after an additional removal of approximately 0.1mm by grinding. The test solutions were analyzed by means of ICP to record the amounts of ions that had leached out from the alloy specimens. The biocompatibility was studied by cell culture tests and the HET-CAM method. Test solutions were prepared by dissolving PdCl(2) and CuCl(2) to appropriate concentrations. RESULTS: The metallographic investigations revealed moderate segregations in interdendritic regions and grain boundaries. After preoxidation in air a zone of oxidation from 25 up to 200 microm thickness for Option and from 5 to 10 microm for IS85 was found. Oxidation was observed along a rim for both alloys and for Option also along interdendritic positions. The oxides were seen as small, dark spots <1 microm in a metallic matrix. These results indicate that: (1) the oxidation of the copper-containing palladium alloy is far more severe than that of the alloy with no copper; and (2) the elemental release from these oxides is substantially larger than that from the corrosion of the metallic structure. The results of the cell culture testing showed that Cu was most toxic, followed by Cu(2+)+Pd(2+) (1:2), based on the determination of the concentration that caused 50% cytotoxicity. The HET-CAM testing showed Cu(2+)+Pd(2+) (1:2) to have the highest irritation score. SIGNIFICANCE: The copper-containing Pd alloy developed a 0.1mm thick rim with small oxide particles in a metallic matrix during preoxidation. If this rim is not completely removed, significantly more Cu, Ga and Pd ions have been shown to leach into the test solution than from the alloy structure. No synergetic effect of Cu and Pd ions was observed in cultured cells, while the mixture Pd(2+)+Cu(2+) (1:2) was most irritating to mucous membrane as evaluated by the HET-CAM method.

[Cytotoxicity study of high gold content Degutan surfaces of various degrees of roughness with fibroblasts (BALB 3T3) and osteoblasts (hFOB 1.19)]. / Zytotoxizitätsuntersuchung von hochgoldhaltigen Degutan-Oberflächen unterschiedlicher Rauhigkeit mit Fibroblasten (BALB 3T3) und Osteoblasten (hFOB 1.19).

The cytotoxicity of Degutan surfaces with different degrees of roughness, and the effect of surface structures on osteoblast proliferation and differentiation, was investigated with standardised cell culture systems. Fibroblast cell lines (BALB/3T3) and osteoblast cell lines (hFOB 1.19) were used. The number and variability of the cells were determined for assessment of proliferation and alkaline phosphatase activity, collagen I and osteocalcin production were used as parameters for differentiation. In the early phase, the largest numbers of cells and greatest proliferation were measured on polished Degutan surfaces. In the late phase, however, larger numbers of cells and a greater degree of proliferation were to be seen on sandblasted and sandblasted/heat-treated Degutan surfaces. No differences were found for collagen I, osteocalcin production or alkaline phosphatase activity. Neither the osteoblasts nor the fibroblasts revealed a toxic effect of Degutan. The results for osteoblast differentiation correlate with recent studies on identical structured titanium surfaces. In view of the immeasurable amount of ion release, Degutan may be considered an ideal model for an inert material surface.

Evaluation of the biocompatibility of various dental alloys: Part 2--Allergenical potentials.

The metal alloys which were investigated histopathologically in the first part of this study, were examined with respect to their allergic potentials using the patch test. Results from 60 subjects (aged 17-23) were evaluated following exposure to nickel sulphate, potassium dichromate, silver nitrate, cobalt nitrate, copper sulphate, palladium chloride, platinum chloride and gold chloride. Nickel sulphate produced the most vigorous allergic response whereas gold chloride showed the least of all. The remaining solutions were ranked in decreasing order of severity as follows: potassium dichromate, cobalt nitrate, silver nitrate, copper sulphate, palladium chloride and platinum chloride. Patch testing is indicated in any patient with a history of allergy or sensitivity to a metal. The use of nickel containing alloys in such patients should also be avoided.

Evaluation of the biocompatibility of various dental alloys: Part I--Toxic potentials.

The biocompatibility of a high-gold alloy (Iropal W), two low-gold alloys (Argenco 9 and Gold EWL-G), one palladium alloy (Argipal), two palladium-silver alloys (Argenco 23 and EWL-G), one chrome-nickel alloy (Wiron-88), two chrome-cobalt alloys (Wironium and Wirocast) and a 22 carat gold alloy were evaluated histopathologically with the subcutaneous implantation technique. Cast discs of the materials were implanted for 15, 30 or 60 days in 111 rats. Mildest responses occurred to 22 carat gold alloy. The most vigorous responses were observed in the chrome-nickel alloy samples. The high-gold alloy and the palladium groups showed reactions quite similar to those of the 22 carat gold. However, the low-gold group and the palladium-silver alloys ranked between the basic metal alloy and the precious metal alloy groups.

[The biological compatibility of the new noble alloy Superpal for metal-ceramic dentures]. / Izuchenie biologicheskoi sovmestimosti novogo blagorodnogo splava "Superpal" dlia metallokeramicheskikh zubnykh protezov.

Toxic characteristics of Superpal, a dental palladium-based alloy for cermet dentures, were studied in a chronic experiment on 20 rats to which it was subcutaneously implanted. Analysis of histological findings, blood biochemistry, mast cell degranulation test, summarization of subthreshold pulses, and the micronucleus test showed that Superpal alloy is biologically inert, nontoxic, exerts no sensitizing and mutagenic effects, and may be used for making cement dentures.

Toxicity of copper-based dental alloys in cell culture.

The biocompatibility of three commercial copper-based dental casting alloys--Duracast MS, Goldent, and Trindium--three experimental copper alloys, and a control gold alloy, Modulay, were investigated. Trindium, Duracast MS, experimental alloys 1 and 2 are aluminum bronzes; Goldent is a hybrid aluminum-brass alloy; and experimental alloy #3 is a high zinc brass alloy. ASTM F813-83 Standard Practice for Direct Contact Cell Culture Evaluation of Materials for Medical Devices, a 3-day direct-contact cell culture regimen and atomic absorption spectroscopy were utilized for evaluating the biocompatibility of these alloys in both Waymouth's and RPMI 1640 complete media. Cellular proliferation assays, using 3H-thymidine uptake, were also conducted in Waymouth's media. In this investigation, only the experimental alloy #3 elicited alterations in morphology and viability of the fibroblast monolayer during the ASTM and 3-day culture tests in either media. Cell cultures exposed to experimental alloy #3 experienced copper concentrations greater than 16.0 ppm in Waymouth's and 10 ppm copper in RPMI 1640 media. Differences in the size of the cytotoxic zone around experimental alloy #3 were also observed, with the larger zone occurring in Waymouth's media. In contrast to the direct cell contact studies, all alloys caused decreases in 3H-thymidine uptake in Waymouth's media at much reduced metal ion concentrations as compared to the controls. Thus, adverse changes in DNA synthesis occurred at much lower copper and zinc concentrations than changes in morphology and viability. Consequently, the assessment of biocompatibility is dependent on the parameters evaluated, and several parameters must be analyzed before a material may be considered biocompatible.

Reaction of fibroblasts to various dental casting alloys.

The cytotoxicity of a series of dental casting alloys in the as-cast and polished condition was determined with cell culture techniques involving phase contrast microscopy to examine cell morphology and the succinic dehydrogenase histochemical reaction to measure any ring of inhibition of Balb/c 3T3 cellular respiration around alloys. Crown and bridge casting alloys and a nickel- and a cobalt-base alloy were biocompatible in the polished condition, but less so in the as-cast condition. The only two exceptions were casting alloys containing 50-60 wt% Cu. Porcelain-fused-to-metal alloys were biocompatible in either the as-cast or polished condition. This direct contact method appeared satisfactory for evaluating biocompatibility of dental casting alloys, especially since these materials are in contact with gingival tissues.