Biomedical subjects

J C Wataha

Publications and source records attributed to J C Wataha.

At least 55 records · Page 3Linked to original sources

PubMed1999

Cytotoxicity of dental casting alloys pretreated with biologic solutions.

STATEMENT OF PROBLEM: Short-term (72-168 hours) in vitro tests are used to evaluate the cytotoxicity of dental casting alloys. The ability of these short-term tests to predict long-term in vivo cytotoxicity has been questioned. A procedure to accelerate the testing of casting alloys would be useful in predicting longer-term alloy cytotoxicity. PURPOSE: This study hypothesized that preconditioning casting alloys by soaking in a biologic liquid would change subsequent cytotoxicity by removing some elements. Preconditioning may be 1 method of accelerating short-term in vitro tests. MATERIAL AND METHODS: Dental casting alloys were exposed to either saline, cell culture medium, or a saline/bovine serum albumin (BSA) solution for 72 hours before standard in vitro cytotoxicity testing. Six types of alloys were tested (n = 6): 5 Au-Ag-Cu-Pd alloys (single phase) and 1 Ag-Pd-Cu alloy (multiple phase). Teflon (Tf) samples served as a control. After preconditioning, alloys were placed in direct contact with Balb/c fibroblasts for 72 hours, after which cell viability was measured by succinic dehydrogenase activity (MTT method) relative to Tf controls (100% = no toxicity). Elements released into the preconditioning solutions were measured by atomic absorption spectroscopy. Cytotoxicities of preconditioned alloys and amounts of elemental release were compared with unconditioned alloys. RESULTS: A preconditioning time of 72 hours was sufficient to change the cytotoxicity of the tested alloys. The alloys that were more cytotoxic initially became less cytotoxic after preconditioning. For all the alloys tested, except the Ag-Pd-Cu multiphase alloy, preconditioning with either the saline or the saline/BSA solution caused an increase in cellular activity, therefore the preconditioned alloys were less cytotoxic. The cell culture medium preconditioning solution had a variable effect, causing increased or decreased cellular activity depending on the alloy treated. CONCLUSION: Preconditioning of casting alloys decreased subsequent cytotoxicity. However, not all preconditioning solutions are equivalent. A preconditioning strategy may be useful in accelerating the short-term cytotoxicity test toward a longer-term result.

3T3 Cells↗

PubMed1999

Effect of dentin bonding agents on the secretion of inflammatory mediators from macrophages.

Dentin bonding agents (DBAs) have been proposed as substitutes for amalgam as root-end filling materials. The current study tested the hypothesis that certain components of DBAs could alter the secretion of cytokines from macrophages. Such alteration would likely be undesirable for healing of the periapical tissues. Human THP-1 macrophages were exposed to 2-hydroxyethyl methacrylate, 4-methacryloxyethyl trimelliate anhydride, bisphenol-gycidylmethacrylate, and urethane dimethacrylate. The secretion of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) were measured with or without challenge by lipopolysaccharide (LPS). Results showed that all DBA components completely suppressed LPS-induced IL-1 beta and TNF-alpha secretion at concentrations that suppressed mitochondrial activity by 50%. In addition, 4-methacryloxyethyl trimelliate anhydride induced secretion of IL-1 beta, but not TNF-alpha, without the LPS challenge. These results indicate that DBA components may alter normal macrophage-directed inflammatory responses if the macrophages are exposed to sufficiently high concentrations of these components.

Acrylic Resins↗

PubMed1999

In vitro cytotoxicity of dental casting alloys over 8 months.

Although in vitro cytotoxicity tests have been a valuable part of the biological testing of dental casting alloys, these tests are generally limited by their short-term nature ( < 168 h). The objective of the current study was to measure the in vitro cytotoxicity of representative types of dental casting alloys over a relatively long-term interval (months) and compare longer-term cytotoxicity with that seen initially. Polished casting alloy samples were exposed to cell-culture medium for 30-day intervals. During the last 3 days of each interval, the medium was changed to provide a 3-day extract which was then placed on fibroblast or macrophage cultures for 48 h. The mitochondrial activity of the cells was measured and compared to control cultures to assess the cytotoxic effect of the alloys. The cytotoxic effect was plotted versus time of medium exposure. The total time of exposure was 8 months. For most alloys, the mitochondrial response was constant over the 8 months, indicating that the cytotoxic effect of the alloys did not change significantly after extended exposure to the medium. A trend of improving biological response was suspect for a reduced-gold alloy, but this trend was not statistically significant. The mitochondrial activity of the macrophages was less sensitive to the alloy extracts than the activity of the fibroblasts, which was significantly suppressed for several alloy types. However, mitochondrial activity of the macrophages was significantly increased for several alloys in the early time intervals. The total noble metal content of the alloys was not necessarily predictive of the biological response. Thus, it appears that in this indirect test of in vitro cytotoxicity, the short-term cytotoxicity is predictive of the longer-term for many types of dental casting alloys.

Analysis of Variance↗

PubMed1999

Initial versus subsequent release of elements from dental casting alloys.

The release of elements from dental casting alloys is directly related to adverse biological effects they may have. Longer-term (>1 month) studies of elemental release have suggested that release decreases significantly after a higher initial release of elements. The aim of the current study was to measure the release of elements from a variety of clinically relevant dental casting alloys and compare the release at weekly intervals through 4 weeks. The hypothesis was that the release during the initial week should be higher than in subsequent weeks, and that cytotoxicity should decrease as elemental release decreases. Alloy samples were exposed to cell-culture medium which was changed at weekly intervals and assessed for elemental release by means of atomic absorption spectrometry. The cytotoxicity of the medium was also measured. The results showed that for single phase alloys, initial release was often significantly higher in the first weeks than in subsequent weeks, but not for all elements in an alloy. Multiple phase alloys showed steady or increasing release relative to the first week. Cytotoxicity relationships were complex depending on which elements were released and the ratios of elements released. This study suggests that short-term tests (<1 week) may not be appropriate to evaluate longer-term elemental release or cytotoxicity because of changing rates of elemental release.

Animals↗

PubMed1999

Effect of toothbrushing on elemental release from dental casting alloys.

PURPOSE: This study assessed the effect of toothbrushing on the elemental release from common dental casting alloys. MATERIALS AND METHODS: A Au-Pt high-noble alloy, a Au-Pd high-noble alloy, a Pd-Cu-Ga noble alloy, and a Ni-Cr base-metal alloy were placed into a biological medium for 1 week to allow equilibration of elemental release, then brushed for 30 minutes at 90 strokes/min under 200 g of force with a soft toothbrush. The brushing was performed in neutral saline or lactic acid at pH 4 with or without toothpaste. The alloys were then transferred back into a biological medium for 1 week. Atomic absorption spectroscopy was used to measure the mass lost from each alloy during and in the week after brushing. Mass loss was expressed as micrograms per square centimeter of alloy surface, and the various brushing conditions were compared by analysis of variance and Tukey multiple comparison intervals (alpha = 0.05). RESULTS: During brushing, element release increased significantly over nonbrushed controls for all alloys except the Ni-Cr. Toothpastes, acidic solutions, or combinations of these conditions with toothbrushing further enhanced elemental release, but Ni release from the Ni-Cr alloy increased the most (30-fold). In the week after brushing, brushing alone increased elemental release only from the Ni-Cr alloy. However, toothpastes and acidic solutions increased elemental release for all alloys significantly, except for the Au-Pd alloy. In general, elemental release during brushing was far greater than in the week after brushing. CONCLUSIONS: Under the conditions of this study, toothbrushing increased the elemental release from dental casting alloys.

Analysis of Variance↗

PubMed1999

Effects of long-term sub-lethal concentrations of dental monomers on THP-1 human monocytes.

Studies have shown that monomers from dental resins are acutely cytotoxic, but little is known of their long-term effects at sub-lethal concentrations. The current study determined the long-term effects of sub-lethal concentrations of TEGDMA (triethyleneglycol dimethacrylate) and Bis-GMA (bisphenol-glycidylinethacrylate), two common dental monomers, on the in vitro cellular proliferation, succinic dehydrogenase activity, and total cellular protein production of monocytes. Human THP-1 monocytes were exposed to concentrations of 100, 200, and 400 micromol l(-1) of TEGDMA or 1, 5, and 25 micromol l(-1) Bis-GMA for 5 weeks. Controls received only vehicle solutions of ethanol. Each week cellular proliferation (hemocytometer), succinic dehydrogenase (SDH) activity (MTT) and total cellular protein (bicinchoninic acid) were assessed. The results were compared with ANOVA and Tukey intervals (alpha = 0.05). TEDGMA had no proliferative or cellular protein effects, but increased SDH activity 20-60% in week 1 (p < 0.05). SDH activity then decreased 40% in week 2, followed by a gradual increase of 30-40% over week 3-5 (p < 0.05). Bis-GMA reduced proliferation by 40-60% from 1-5 weeks exposure (p < 0.05). However, SDH activity and total protein per cell were not affected. There was some indication of increased SDH activity after 5 weeks (20-30%, p < 0.05). Sub-lethal concentrations of TEGDMA and Bis-GMA have significant long-term effects on monocytes at low-dose 5-week exposures in vitro. Each monomer acted differently.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1998

Effect of pH on element release from dental casting alloys.

STATEMENT OF PROBLEM: Dental casting alloys are subjected to transient acidity in the oral environment, yet most studies have not investigated the effects of these transient environments on elemental release from alloys. Elemental release is important because it plays a significant role in alloy biocompatibility. PURPOSE: It was hypothesized that acidic environments would increase elemental release from dental alloys during exposure and after the acidic environment was removed. This hypothesis was based on the known increase in release of nickel from nickel-based alloys in an acidic environment. MATERIAL AND METHODS: High-noble, noble, and base metal casting alloys were exposed for 30 minutes to solutions with pH ranging from 1 to 7. Elemental release of representative elements was measured by means of atomic absorption spectrometry during the exposure and in the week after the exposure. This release was compared with elemental release in the week before the exposure. RESULTS: High-noble and noble alloys were resistant to acidic environments. A pH of 4 did not increase elemental release during or after exposure. A pH 1 environment slightly elevated release of Ag, Cu, and Pd in some alloys. However, a Ni-based alloy released large amounts of Ni during the acidic exposure of pH 1 or 4, and more importantly, in the week after the exposure as well. Increased time of exposure to acid did not alter elemental release from noble or high-noble alloys, but markedly increased release from the Ni-based alloy. CONCLUSIONS: Transient exposure of casting alloys to an acidic oral environment is likely to significantly increase elemental release from Ni-based alloys, but not from high-noble or noble alloys.

Analysis of Variance↗

PubMed1998

Effects of dentin bonding agents on macrophage mitochondrial activity.

Dentin bonding agents (DBA) have been considered for use as root-end fillings. Previous studies have documented the release of DBA components in vivo and in vitro, but the biological implications are not clear. The macrophage is important in wound healing, and likely to be important in any inflammatory response. Therefore, this study determined the concentrations of the components of DBAs that suppress the mitochondrial activity of human macrophages in vitro. THP-1 macrophages were cultured in the presence of four DBA components (2-hydroxyethyl methacrylate (HEMA), 4-methacryloxyethyl trimellitate anhydride (4-META), bisphenol-glycidylmethacrylate (Bis-GMA), and urethane dimethacrylate (UDMA)) at various concentrations and for varying durations. Residual effects were also measured after the resins were removed. Controls received only the vehicle solution, ethanol or water. THP-1 mitochondrial activity was estimated using the MTT assay, and the 50% toxicity concentrations (TC50) were determined graphically. Resin components suppressed the mitochondrial activity of macrophages at different concentrations (TC50 values for HEMA (10,000 mumol/L), 4-META (3,800 mumol/L), Bis-GMA (130 mumol/L), and UDMA (110 mumol/L) at 24 h, and the effect was time-dependent. Residual effects were observed for all resins.

Acrylic Resins↗

PubMed1998

Release of elements from dental casting alloys into cell-culture medium over 10 months.

OBJECTIVE: The release of elements from eight types of commonly used dental casting alloys into cell-culture medium was measured over a 10-month period. The release of elements was determined to provide information about the long-term biological risk these alloys may pose to the oral tissues. The current work extends previous studies of shorter time periods, and is more relevant to the in vivo situation, where dental alloys are present intraorally for years. METHOD: The alloys were Au-, Ag-, Pd-, and Ni-based with nobilities ranging from 0 to 95 at.%. Alloy samples (n = 12) were exposed to cell-culture medium. The medium was changed every 30 days for 10 months. Elemental release into the medium was measured by means of atomic absorption spectrophotometry. Differences in mass release were determined using ANOVA and Tukey multiple comparison intervals (alpha = 0.05). RESULTS: The release of elements continued through 10 months, and it appeared that the release was constant throughout most of the experiment. Higher initial rates were suspected but not verified. Most alloys reached a constant rate after < 100 days of exposure to the medium. Long-term element release was not generally intuitive based on the amount of an element in an alloy or the overall nobility of the alloy. Total mass lost over the 10-month period ranged from < 2 micrograms/cm2 for the Au-Pd alloy to 55 micrograms/cm2 for the Au-Ag-Cu alloy (Tukey interval at alpha = 0.05 was 0.8 microgram/cm2). By comparison, pure Cu lost 4500 micrograms/cm2 during this period. SIGNIFICANCE: Tests which assess biological risk from elemental release must consider longer-term release because elemental release continues for extended periods. Longer-term mass loss from a given alloy is often not intuitive based on its overall composition or noble metal content.

Analysis of Variance↗

PubMed1998

Uptake and reversibility of uptake of nickel by human macrophages.

The use of nickel-containing alloys in dentistry has been questioned because of the biological liabilities of nickel and the release of nickel ions from dental appliances into the oral cavity. The uptake of nickel by cells in the oral tissues is a critical factor in assessing the biological liabilities of nickel. Nickel uptake by macrophages may be particularly important because of the central role of macrophages in the inflammatory process and the known role of the macrophage in orchestrating the response to biomaterials. The aims of the current study were to assess the reversibility of the uptake of nickel from human macrophages and determine the portion of the nickel which reaches the nuclei as a function of time. Cellular nickel content was measured by means of atomic absorption spectrometry. Nuclear nickel content was assessed after fractionating cells. The results showed that nickel was rapidly taken up by macrophages and that the nickel accumulated in the nucleus in as little as 8 h. After 48 h, over 60% of the cellular nickel was in the nucleus. Once taken up, the nickel was lost at a lower rate. The rate of loss decreased as the initial exposure time to the nickel increased. Thus, the results indicated that macrophages may accumulate nickel if the time between exposures is insufficient to reverse the uptake. Further studies are necessary to correlate the retention of nickel with impaired function of macrophages and to further define the biological risks of using nickel in dental alloys.

Biological Availability↗

PubMed1998

Cloned 3T6 cell line from CD-1 mouse fetal molar dental papillae.

Only primary pulpal cell cultures and one virally transformed mouse cell culture have been formally reported in the literature to synthesize proteins such as phosphophoryn which are unique to dentin matrix. In the present study, a mixed culture was derived from dental papilla cells of 18-19 fetal day CD-1 mouse mandibular first molars, maintained on a 3T6 plating regimen, and subsequently cloned after 28 passages. This cloned cell line (MDPC-23) exhibited several unique features, some of which were characteristic of odontoblasts in vivo. The features of this cell line included (1) epithelioid morphology of all cells with multiple cell membrane processes, (2) high alkaline phosphatase activity in all cells, (3) formation of multilayered nodules and multilayered cultures when maintained in ascorbic acid and beta-glycerophosphate, and (4) expression of two markers for odontoblast differentiation, i.e. dentin phosphoprotein and dentin sialoprotein.

Animals↗

PubMed1998

Expression of dentin sialoprotein (DSP) and other molecular determinants by a new cell line from dental papillae, MDPC-23.

The purpose of this study was to characterize the molecular expression of a spontaneously immortalized and cloned cell line (MDPC-23) derived from 18-19 day CD-I fetal mouse molar dental papillae to determine if these cells were odontoblast-like. Western blots showed that a protein band, at approximately 105 kDa, reacting positively with anti-DSP antibodies and co-migrating with mouse DSP, was present in lysates of cells from passages 7, 37 and 77, in serum-free conditioned medium from passage 37 cells, and in mouse dentin extract. A minor band at 55 kDa was also apparent in cell lysates. Using a cDNA probe for a 486bp mouse DSP coding sequence, DSP or DSP-PP mRNA expression was detected by Northern analysis as well as Southern analysis after RT-PCR in all three passages. It was also shown that in these cells 1,25 (OH)2 vitamin D3 upregulated both osteopontin and osteocalcin mRNA, and dexamethasone downregulated alkaline phosphatase and alpha2(I) collagen mRNA. Thus, MDPC-23 cells express proteins which are common to mineralizing tissue. The expression of DSP and DSP-PP strongly suggests that this cell line is from the odontoblast lineage.

Animals↗

PubMed1997

Effects of metal ions on osteoblast-like cell metabolism and differentiation.

The objective of this study was to evaluate the effects of metal ions, which may be released from orthopedic or dental implants, on osteoblast metabolism and differentiation. ROS 17/2.8 cells were cultured in F-12 medium for 7 days. Then Al+3, Co+2, Cr+3, Ni+2, Ti+4, and V+3 were added at concentrations less than their cytotoxic concentrations. After 3 days, DNA synthesis, succinate dehydrogenase activity, alkaline phosphatase (ALP) activity, and culture calcification were assessed. Northern blots were performed for ALP, osteocalcin (OCN), and osteopontin (OPN) mRNA transcription. The data indicated that Cr+3 and A1+3 had few inhibitory effects on ROS cell metabolism below their cytotoxic concentrations, Ni+2, Co+2, Ti+4, and V+3 affected all these parameters of ROS cell metabolism at concentrations below cytotoxic levels. For RNA analysis, A1+3 significantly suppressed the expression of ALP, OCN, and OPN at both cytotoxic and noncytoxic concentrations. Co+2 specifically suppressed ALP expression at cytotoxic concentrations. Cr+3 and Ni+2 inhibited OCN, OPN, and ALP gene expression only at cytotoxic concentrations. For Ti+4 and V+3 ions, gene expression at cytotoxic levels was not significantly affected as compared with the effects at noncytotoxic level. These results show that metal ions may alter osteoblast behavior even at subtoxic concentrations, but do not always affect the expression of all genes similarly.

Blotting, Northern↗

PubMed1997

In vitro cytotoxicity of amalgams made with binary Hg-In liquid alloys.

OBJECTIVE: Mercury vapor release from amalgams during setting significantly decreases when the amalgams are prepared with binary Hg-In liquid alloys. The objective of this study was to compare the cytotoxicity of amalgams made with experimental Hg-In alloys with that of amalgam without In and a commercial In-containing amalgam. METHODS: Amalgam specimens were prepared by triturating a high-Cu alloy powder (Tytin, Kerr) with pure Hg or Hg-In liquid alloy containing 5, 20 or 50% In and also by triturating an In-containing high-copper alloy powder (Indiloy, Shofu) with pure Hg. After the specimens were aged for 2 wk, a cylindrical specimen of each amalgam was immersed consecutively in cell culture medium for 0-8, 8-48 and 48-72 h. The cytotoxicity of the extracts was determined by placing them in contact with Balb/c 3T3 mouse fibroblasts for 24 h, after which the succinic dehydrogenase (SDH) activity was measured and expressed as a percentage of the Teflon negative controls. The results were statistically compared using ANOVA and Tukey's test (alpha = 0.05). The concentration of elements released into the extracts was determined by atomic absorption spectrophotometry and evaluated by Kruskal-Wallis and nonparametric multiple comparisons. RESULTS: For the 0-8 h and 8-48 h intervals, the 20% In amalgam was significantly (p < 0.05) less toxic than the other amalgams, and not different from the Teflon control. Results for the other amalgams were only slightly depressed compared to the Teflon control. For the 48-72 h interval, all amalgams were essentially no different from the control. Copper was the element dominantly released into the medium from all the amalgams tested. SIGNIFICANCE: For amalgam tested after aging, alloying indium to mercury did not deleteriously affect the cytotoxicity of the resultant amalgam compared to the amalgam without indium.

3T3 Cells↗

PubMed1996

In vitro cytotoxicity and dentin permeability of HEMA.

An in vitro diffusion chamber was used to measure the diffusion of 2-hydroxyethyl methacrylate (HEMA) through etched human dentin disks. Concentrations of HEMA, which diffused through dentin, were measured by ultraviolet spectroscopy, and the effect of initial HEMA concentration, dentin thickness, and back pressure on diffusion were assessed. The cytotoxicity of HEMA was determined using BALB/c 3T3 mouse fibroblasts in direct contact with HEMA for 12 or 24 h. HEMA diffused rapidly through dentin under all conditions, but increased thickness, back pressure, or decreased initial concentration all reduced diffusion. The permeability coefficient of HEMA was approximately 0.0003 cm/min, and diffusion through 0.5 mm of dentin reduced the HEMA concentration by a factor of approximately 6,000 (with 10 cm of H2O back pressure). It was concluded that the risk of acute cytotoxicity to HEMA through dentin was probably low, but that decreased dentin thickness, lack of polymerization, or extended exposure times might increase the risk significantly.

3T3 Cells↗

PubMed1996

In vitro models of biocompatibility: a review.

The objectives of this paper were to define in vitro biocompatibility of materials, to discuss some of the issues concerning why conclusions from tissue culture are sometimes different from in vivo biocompatibility, to give highlights of the sequence of the development of these in vitro assays from the early 1950s to their present state of development, and to discuss possible future trends for in vitro testing. In vitro biocompatibility tests were developed to simulate and predict biological reactions to materials when placed into or on tissues in the body. Traditional assays have measured cytotoxicity by means of either an end-stage event, (i.e., permeability of cytoplasmic membranes of dead and dying cells, or some metabolic parameter such as cell division or an enzymatic reaction). In vitro assays for initiation of inflammatory and immune reactions to materials have also begun to appear in the literature. More recently, the concept of dentin barrier tests has been introduced for dental restorative materials. Four models which measure both permeability and biological effects of materials are compared and discussed. Future efforts may be directed toward development of materials which will allow or promote function and differentiation of tissues associated with materials. New analytical procedures and understanding of optimal characteristics of materials should improve our ability to develop more biocompatible materials. Both molecular biology techniques, and altered design of material surfaces may make the materials either more or less reactive to the biological milieu. These trends suggest a greater future role of the biological sciences in the development of biomaterials.

Animals↗

PubMed1996

In vitro IL-1 beta and TNF-alpha release from THP-1 monocytes in response to metal ions.

OBJECTIVES: Previous studies have shown that biomaterials can activate macrophages to produce cytokines and promote an inflammatory response. Although the toxicity of many metal ions has been extensively investigated, little is known about the ability of these ions to alter cytokine release from macrophages. Yet the release of these ions from biomaterials has been well documented. Previous studies indicated that alterations in cytokine release might be expected because metal ions alter protein production in macrophages at sub-toxic concentrations. Thus, the hypothesis of this study was that metal ions can alter the secretion of cytokines from macrophages at sub-toxic concentrations. METHODS: The release of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) from macrophages was investigated when the macrophages were exposed to metal ions, with or without lipopolysaccharide (LPS), a component of dental plaque. Human THP-1 macrophages were exposed to ions of Ag, Au, Cu, Hg, and Ni for 24 h. In half of the cultures, LPS was added for the last 4 h. The release of IL-1 beta and TNF-alpha into the medium was measured using enzyme-linked immunosorbent assays. ANOVA and Tukey multiple comparison intervals were used to compare the various experimental conditions. RESULTS: None of the metal ions elevated the IL-1 beta or TNF-alpha levels after 24 h, but Ni ions significantly elevated the IL-1 beta and TNF-alpha levels after 72 h. With LPS added, Ag, Cu, and Ni significantly amplified the LPS-induced production of IL-1 beta but only Ni amplified the TNF-alpha response. These alterations in cytokine response occurred with metal ion concentrations which have been previously shown to be released from dental alloys in vitro and in vivo. SIGNIFICANCE: It appeared plausible that macrophage-cytokine mediated inflammatory responses may be altered by the presence of some metal ions in tissues, particularly Ni.

Analysis of Variance↗

PubMed1996

Effect of alloy surface composition on release of elements from dental casting alloys.

The release of elements from dental casting alloys is a continuing concern because of the potentially harmful biological effects the elements may have on local tissues. The surfaces of the alloys appear to be most important in controlling the release of these elements. In the current study, the surfaces of high-, reduced-, and no-gold dental alloys were analysed by X-ray photoelectron spectroscopy before and after they were exposed to a biological medium for up to 96 h. The goal was to relate the release of elements from these alloys to their surface composition, and to determine the depth of the effect of the medium. The depth of the effect of the exposure was determined by argon milling of the alloy surface after exposure to the medium. Elements that were released into the medium were measured by means of atomic absorption spectroscopy. The release of elements from alloys was greater when the atomic ratio of noble to non-noble elements at the surface was less than 1. The depth of the effect of the medium varied with the alloy, but was always less than 100 A. The surface composition was significantly different from layers only 5 A below. It was concluded that the surface concentration of noble elements is important in controlling the release of non-noble elements from these alloys, and the surface composition appeared to be only one or two atomic layers thick. Of the three types of alloys, the high-gold alloy appeared to develop the most stable surface composition which released the lowest levels of elements.

Dental Alloys↗