Effect of Cobalt and Chromium Ions on the Chlorhexidine Digluconate as Seen by Intermolecular Diffusion.

Metal ions such as cobalt (II) and chromium (III) might be present in the oral cavity, as a consequence of the corrosion of Co-Cr dental alloys. The diffusion of such metal ions into the organism, carried by saliva, can cause health problems as a consequence of their toxicity, enhanced by a cumulative effect in the body. The effect of the chlorhexidine digluconate, which is commonly used in mouthwash formulations, on the transport of these salts is evaluated in this paper by using the Taylor dispersion technique, which will allow an assessment of how the presence of chlorhexidine digluconate (either in aqueous solution or in a commercial formulation) may affect the diffusion of metal ions. The ternary mutual diffusion coefficients of metal ions (Co and Cr) in the presence of chlorhexidine digluconate, in an artificial saliva media, were measured. Significant coupled diffusion of CoCl2 (and CrCl3) and chlorhexidine digluconate is observed by analysis of the non-zero values of the cross-diffusion coefficients, D12 and D21. The observed interactions between metal ions and chlorhexidine digluconate suggest that the latter might be considered as an advantageous therapeutic agent, once they contribute to the reduction of the concentration of those ions inside the mouth.

Magnetic Nanoparticles Fishing for Biomarkers in Artificial Saliva.

Magnetic nanoparticles (MNPs) were synthesized using the colloidal co-precipitation method and further coated with silica using the Stöber process. These were functionalized with carboxylic and amine functionalities for further covalent immobilization of antibodies on these MNPs. The procedure for covalent immobilization of antibodies on MNPs was developed using 1-ethyl-3-(dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The evaluation of the efficiency of the coupling reaction was carried out by UV-vis spectrophotometry. The developed antibodies coupled to MNPs were tested for the pre-concentration of two biomarkers tumor necrosis factor alpha (TNF-α) and Interleukin-10 (IL-10). Both biomarkers were assessed in the matrix based on phosphate-buffered saline solution (PBS) and artificial saliva (AS) to carry out the demonstration of the format assay. Supernatants were used to determine the number of free biomarkers for both studies. Reduction of the nonspecific saliva protein adsorption on the surface of the complex antibodies-MNPs to levels low enough to allow the detection of biomarkers in complex media has been achieved.

Commercial Porcine Gastric Mucin Preparations, also Used as Artificial Saliva, are a Rich Source for the Lectin TFF2: In Vitro Binding Studies.

Mucous gels (mucus) cover internal body surfaces. The secretory mucins MUC5AC and MUC6 and the protective peptide TFF2 are characteristic constituents of gastric mucus; TFF2 is co-secreted with MUC6. Herein, we investigated two commercial mucin preparations by FPLC and proteomics, because they are model systems for studying the rheology of gastric mucins. One preparation is also used as a saliva substitute, for example, after radiation therapy. We show that both preparations contain TFF2 (≈0.6 to 1.1 %, w/w). The majority of TFF2 is strongly bound noncovalently to mucin in a manner that is resistant to boiling in SDS. First overlay assays with 125 I-labeled porcine TFF2 revealed that mucin binding is modulated by Ca2+ and can be blocked by the lectin GSA-II and the antibody HIK1083, both recognizing the peripheral GlcNAcα1→4Galß1→R moiety of MUC6. TFF2 binding was also inhibited in the presence of Me-ß-Gal but less so by the α anomer. TFF2 may play a role in the oligomerization and secretion of MUC6, the rheology of gastric mucus, and the adherence of gastric microbiota. TFF2 in artificial saliva may be of benefit. TFF2 might also interact with the sugar moiety of various receptors.

Electrooxidation of New Synthetic Cannabinoids: Voltammetric Determination of Drugs in Seized Street Samples and Artificial Saliva.

The electrochemical sensing of new psychoactive substances, synthetic cannabinoids (SCs), commonly marketed under the trade name "Spice" is explored for the first time. The electrooxidative transformations of 11 new indole and indazole SCs which are currently the predominant illicit smoking mixtures on the drug market is performed using cyclic and differential pulse voltammetry with various commercially available electrodes (Pt, GC, Bdd). It is found that SCs exhibit voltammetric responses that can be used for their detection in smoking mixtures and artificial saliva with limits of detection in the nanomolar range. The indole-based SCs exhibited an anodic peak at ∼1.5 V (vs Ag/Ag(+)) and ∼1.2 V (vs Ag/AgCl) in acetonitrile and artificial saliva, respectively, and the indazoles exhibited corresponding peaks at ∼1.7 V and ∼1.5 V. The voltammetric procedure was evaluated by prescreening of SCs in 12 confiscated street samples that were also independently analyzed by GC-MS and LC-MS techniques. A good agreement between the three analytical protocols was found. Voltammetry provides a tool for the prescreening of synthetic cannabinoid derivatives in seized materials and biological samples.

Validation of a human saliva model for the determination of leachable monomers and other chemicals from dental materials.

This study aimed to prove the validity of a mixture of chemicals, including salts, small organic molecules, mucin, and α-amylase, as saliva surrogate ("artificial saliva") for assessing leakage of methacrylate monomers and other constituents from dental materials. To achieve this, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), diurethane dimethacrylate (UDMA), bisphenol A glycerolate dimethacrylate (BisGMA), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), bisphenol A (BPA), and five homologues of ethoxylated bisphenol A dimethacrylate (BisEMA EO2-6) in unstimulated and artificial saliva, and compared their concentrations in the two saliva media following either spiking with a mixture of the compounds or incubation of test specimens of printed biomaterials. Test specimens were immersed in unstimulated/artificial saliva, incubated at 37 °C for 24 h, and saliva aliquots were extracted with methanol and subsequently analyzed by LC-MS/MS. The method was validated with regard to matrix effects, linearity, selectivity, lower limits of quantification (LLOQ), precision, bias and combined measurement uncertainty (u'). The performance characteristics of the method were comparable for unstimulated and artificial saliva samples. The combined u' for individual chemicals at a concentration of 10 × LLOQ were within the range of 5.3-14 % for unstimulated saliva and 6.9-16 % for artificial saliva, except for the BisEMA homologues. Combined u' for the latter were 27-74 % in unstimulated saliva, and 27-79 % in artificial saliva. There was no detectable release of BPA from the test specimens, and the TPO concentrations were mainly below the LLOQ. TEGDMA and UDMA were detected in the highest quantities, and at comparable concentrations in the unstimulated and artificial saliva. For all BisEMA homologues, the release was higher in unstimulated saliva than in artificial saliva. The study showed that the artificial saliva model can be a suitable replacement for native saliva, but might underestimate leakage of more lipophilic methacrylates.

Analysis of N-nitrosamines and N-nitrosatable substances from baby bottle rubber teats by liquid chromatography tandem mass spectrometry.

A simple and sensitive method based on liquid chromatography-atmospheric pressure chemical ionisation-tandem mass spectrometry (LC-APCI-MS/MS) was developed and validated to determine the levels of 13N-nitrosamines and N-nitrosatable substances migrated from rubber teats into artificial saliva. The migration test from rubber teats was conducted at 40 °C and for 24 h in artificial saliva, and the migrated artificial saliva solution was analysed by liquid chromatography tandem mass spectrometry (LC-MS/MS) without further extracting steps. The sensitivity of N-nitrosamines was examined by applying atmospheric chemical ionisation and electrospray ionisation to optimise the mass spectrometric conditions, and the atmospheric chemical ionisation (APCI) mode exhibited 1.6-19 times higher sensitivity. Method validation showed acceptable linearity, precision, and accuracy, and the detection and quantification limits were 0.07-0.35 and 0.24-1.1 µg kg-1, respectively. The developed liquid chromatography-atmospheric chemical ionisation-tandem mass spectrometry method was applied to 39 domestic and imported rubber teats. From 39 samples, N-nitrosamines [N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR), and N-nitroso n-methyl N-phenylamine (NMPhA)] were detected in 30 samples, with N-nitrosatable substances in 17 samples give rise to NDMA, NMOR, and N-nitrosodiethylamine. However, the levels were below the specific migration limit of Korean Standards and Specifications for Food Containers, Utensils, and Packages and EC Directive 93/11/EEC.

Chemical-physical characteristics of artificial saliva substitutes: rheological evaluation.

OBJECTIVE: We aimed at evaluating some chemical-physical properties of artificial saliva substitutes easily available on the E.U. market, such as viscosity, pH, buffering capacity, superficial tension, density and spinnbarkeit and to compare the results with human natural saliva bibliographic data. MATERIALS AND METHODS: Based on the easy availability on the market, twelve artificial saliva solutions in liquid formulation were analyzed. Kinematic viscosity (cSt) was determined using a micro-Ubbelohde model capillary viscosimeter (ViscoClock, SCHOOT-GERATE Mainz, Germany). Dynamic viscosity (mPas) was determined, through a simple multiplication between density (g/cm3) and kinematic viscosity of each solution. pH analyses were carried out at room temperature using a pH-meter (Mettler Toledo®- Five Easy, Columbus, OH, USA). Spinnbarkeit analysis was performed by a self-owned instrument built for the purpose. RESULTS: The median density value, obtained from the cohort of artificial saliva substitutes, was 1.036 g/cm3. The median value of the kinematic viscosity was 8.984 cSt. The median spinnbarkeit value was 3.2 mm and the median pH value was 6.29. In this study we found an almost linear correlation between the kinematic viscosity and spinnbarkeit values of the artificial saliva substitutes evaluated. CONCLUSIONS: Saliva substitutes should be as faithful as possible to the characteristics of human saliva, in order to completely replace its functions in the oral cavity. Nevertheless, despite several R&D efforts, it is difficult to reproduce all the different features that belongs to natural saliva in one device. Therefore, it would be desirable to create more products reproducing saliva with various rheological characteristics in respect of the main salivary functions such as: chewing, speaking and tissue coating.

Improved artificial saliva for studying the cariogenic effect of carbohydrates.

Saliva is a complex fluid that possesses many important functions regarding oral health. Many in vitro studies require relatively large quantities of saliva. While natural saliva would be the material of choice, it is difficult to obtain in sufficient quantities and varies in composition. Substitutes mimicking the physicochemical properties of saliva have been developed, but these are not appropriate to study the growth of mutans streptococci. Brain Heart Infusion (BHI) has been commonly used for this, but this medium is richer in nutrients than saliva. We therefore developed artificial saliva (AS) with nutrient levels resembling those in natural saliva as a substitute for natural human saliva (HS) to study the influence of different carbon sources on mutans streptococci growth. Growth of a wild-type Streptococcus mutans strain and S. mutans ATCC 15175 in BHI, HS, and AS was monitored anaerobically. Growth of S. mutans in the modified AS was very similar to the growth in HS, both in the absence and presence of different carbon sources. We therefore conclude that the developed AS is suitable for in vitro tests on S. mutans growth.

Effects of carboxymethyl cellulose-based saliva substitutes with varying degrees of saturation with respect to calcium phosphates on artificial enamel lesions.

The aim of the present study was to evaluate the effects of experimental saliva substitutes based on carboxymethyl cellulose (CMC) differing in degrees of saturation with respect to calcium phosphates on the mineral loss of enamel in vitro. Demineralized bovine specimens (subsurface lesions) were exposed to one of six experimental CMC-based solutions with theoretical degrees of saturation with respect to octacalcium phosphate (S(OCP)) of S0, S0.5, S1, S2, S4, and S8 for 10 weeks. A previously studied saliva substitute (Glandosane) and two aqueous solutions (C0 and C1) served as controls. Mineral losses and lesion depths before and after storage were evaluated from microradiographs. Free and bound calcium as well as phosphate and fluoride concentrations were determined. According to these measurements, S(OCP) of S2, S4, and S8 was 0.3, 1.1, and 3.4, respectively. Storage in Glandosane and both negative controls resulted in significant demineralization (p < 0.05). Only S2 significantly remineralized the specimens (p < 0.05). All other solutions showed neutral effects. No significant differences in mineralization between S0 and C0 as well as between S1 and C1 could be observed (p > 0.05). It can be concluded that a CMC-based solution actually unsaturated with respect to octacalcium phosphate (S2) shows most pronounced remineralization capability under the conditions chosen. This might be explained by a more favorable balance between calcium bound to CMC in an adsorbed layer at the enamel-liquid interface and heterogeneous nucleation of calcium phosphates within a solution compared to solutions either supersaturated or having lower levels of saturation.

Is bovine dentine an appropriate substitute in abrasion studies?

The study aimed to compare the wear behaviour of human and bovine dentine due to toothbrushing with different relative dentin abrasivity (RDA) toothpastes. Forty human and 40 bovine dentine samples were prepared from bovine lower incisors or human premolars roots, and baseline surface profiles were recorded. The samples were distributed to four groups (each group n = 10 human and 10 bovine samples) and brushed with fluoridated experimental toothpastes with different RDAs (group A: RDA 10, B: RDA 20, C: RDA 50, and D: RDA 100). Toothbrushing was performed in an automatic brushing machine with a brushing frequency of 60 strokes per minute and a brushing force of 2.5 N. After 2, 5, 10, and 25 min of toothbrushing, new surface profiles were recorded, and the dentine wear was calculated with a customized computer programme. The dentine wear of human and bovine dentine within the four groups was compared with unpaired t tests. No statistically significant difference was recorded for the dentine wear of human and bovine samples within the different groups.

The abrasive effect of a porcelain and a nickel-chromium alloy on the wear of human enamel and the influence of a carbonated beverage on the rate of wear.

PURPOSE: This study was conducted to determine the abrasive effect of a porcelain and an Ni-Cr alloy on the wear of human enamel, and the influence of a carbonated beverage on the rate of wear. MATERIALS AND METHODS: Tooth specimens were prepared by embedding 48 freshly extracted mandibular first premolars in acrylic. Twenty-four of these specimens were abraded against Ni-Cr, and the remaining 24 against porcelain in artificial saliva and carbonated beverage media, respectively (n = 12), on a specially designed abrasive testing machine at a constant load of 40 N with 6 mm amplitude for 15,000 cycles. The cusp heights of the tooth specimens were measured both before and after abrasion using a profile projector. The abraded cast specimens were subjected to profilometry for computing the surface roughness; the abrading media was subjected to atomic absorption spectrophotometry for analyzing Ni and Cr ion levels. Data obtained were statistically analyzed. RESULTS: Porcelain specimens in a medium of carbonated beverage caused the highest wear of tooth specimens. The lowest wear of tooth specimens was Ni-Cr specimens in artificial saliva medium. Carbonated beverage caused significantly higher wear of tooth specimens when abraded against Ni-Cr and porcelain specimens than did artificial saliva. The mean quantitative surface roughness of porcelain specimens was significantly higher than that of Ni-Cr specimens, irrespective of the medium in which abrasion testing was conducted. There was no statistically significant difference between the concentrations of Ni ions released in artificial saliva and carbonated beverage media. Also, there was no statistically significant difference between the concentrations of Cr ions released in artificial saliva and carbonated beverage media. CONCLUSIONS: The wear of human enamel was significantly higher in the presence of carbonated beverage than artificial saliva and against porcelain when compared with Ni-Cr. The surface roughness of porcelain in the presence of carbonated beverage was found to be highest, and the release of Ni and Cr was not affected by carbonated beverage.

Biodegradation of nickel and chromium from space maintainers: an in vitro study.

Band materials are often used in the practice of pediatric dentistry. Nickel and Chromium are the main ingredients of these materials. The potential health hazards of nickel and chromium and their compounds have been the focus of attention for more than 100 years. It has established that these metals could cause hypersensitivity. The study was undertaken to analyze in vitro biodegradation of space maintainers made out of stainless steel band materials from manufacturers Dentaurum and Unitek. The leaching effect simulating the use of one, two, three, and four space maintainers in clinical practice was studied by keeping the respective number of space maintainers in the artificial saliva incubating at 37 degrees C and analyzing for nickel and chromium release after 1,7,14,21 and 28 days using atomic absorption spectrophotometer. Results showed that there was measurable release of both nickel and chromium which reached maximum level at the end of 7 days which was statistically significant (P < 0.05) and was very much below the dietary average intake even for four bands used and was not capable of causing any toxicity.

Temperature-dependent erosivity of drinks in a model simulating oral fluid dynamics.

OBJECTIVES: Aim of this investigation was to study the temperature-dependent in vitro enamel erosion of five acidic drinks and citric acid under controlled conditions in an artificial mouth. METHODS: The erosive potential of Orange juice, Coca-Cola Zero, Sprite Zero, two fruit teas and citric acid (control) was investigated on bovine enamel specimens at temperatures between 5 °C and 55 °C. The pH values and total calcium content of all test drinks were determined. Specimens were immersed into an artificial mouth to imitate physiological oral conditions for 60 h. Cyclic de- and re-mineralization was performed, imitating the intake of six drinks in six h followed by a six-hour remineralization phase, where only artificial saliva ran over the specimens. Total erosive enamel loss was determined by contact profilometry. Differences in substance loss at different temperatures were tested for statistical significance (p-values ≤ 0.05) by means of ANOVA. RESULTS: Rising liquid temperature did not result in a considerable change of pH. Highest substance loss was observed for citric acid (33.6 ±â€¯6 µm to 38.7 ±â€¯6 µm), while only little erosion was induced by fruit tea (0.8 ±â€¯1 µm to 5.9 ±â€¯1 µm). Rising liquid temperature did not result in significantly increased substance loss for citric acid, orange juice and Coca-Cola Zero. Sprite Zero and both fruit teas, however, caused significantly (p < 0.001) more enamel loss at elevated temperature. CONCLUSIONS: Not all investigated drinks showed a temperature-induced change in erosivity. CLINICAL SIGNIFICANCE: For some erosive beverages it can be recommended to keep the consummation temperature as low as possible to decrease the risk of erosive tooth substance loss.

A polypyrrole-chitosan cryogel stir-bead micro-solid phase extractor for the determination of phthalate esters in contact lenses storage solutions and in artificial saliva in contact with baby teethers.

Phthalate esters (PAEs), especially dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), di-2-ethylhexyl phthalate (DEHP) are widely used as plasticizers in plastics and polymers. They are not chemically bound and can easily migrate into food and human tissue that comes into contact with these materials. The method developed in this work was applied for the preconcentration and determination of these four phthalate esters that might leach from contact lenses and baby teethers. A novel stir-bead micro-solid phase extractor of chitosan cryogel composited with polypyrrole with a steel wire core was evaluated for the extraction of DMP, DEP, DBP and DEHP before analysis by high performance liquid chromatography (HPLC). Scanning electron micrographs of the polypyrrole-chitosan cryogel beads revealed a high porosity with large surface area. Under the optimum conditions, the developed method provided a good linearity in a concentration range from 10 to 750 ng mL-1 for DMP and from 5.0 to 750 ng mL-1 for DEP, DBP and DEHP. The limits of detection (LOD) were 6.07 ± 0.22 ng mL-1, 4.358 ± 0.097 ng mL-1, 4.408 ± 0.099 ng mL-1 and 3.916 ± 0.053 ng mL-1 for DMP, DEP, DBP and DEHP, respectively, and the method reproducibility was good (n = 6, % RSD < 6.0). DBP and DEHP were detected in two original storage solutions of contact lenses from 13.2 ± 1.1 ng mL-1 to 15.4 ± 1.9 ng mL-1 and from 21.3 ± 1.6 ng mL-1 to 23.5 ± 1.5 ng mL-1, respectively. In the artificial saliva in contact with baby teether samples only DEHP was found, from 4.91 ± 0.31 ng mL-1 to 6.78 ± 0.23 ng mL-1, with good recoveries ranging from 81.3 ± 8.4% to 106.3 ± 5.2%.

Temperature-controlled ionic liquid-based ultrasound-assisted microextraction for preconcentration of trace quantity of cadmium and nickel by using organic ligand in artificial saliva extract of smokeless tobacco products.

A new approach was developed for the preconcentration of cadmium (Cd) and nickel (Ni) in artificial saliva extract of dry snuff (brown and black) products using temperature-controlled ionic liquid-based ultrasound-assisted dispersive liquid-liquid microextraction (TIL-UDLLµE) followed by electrothermal atomic absorption spectrometry (ETAAS). The Cd and Ni were complexed with ammonium pyrrolidinedithiocarbamate (APDC), extracted in ionic liquid drops, 1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]. The multivariate strategy was applied to estimate the optimum values of experimental variables influence the % recovery of analytes by TIL-UDLLµE method. At optimum experimental conditions, the limit of detection (3s) were 0.05 and 0.14µgL(-1) while relative standard deviations (% RSD) were 3.97 and 3.55 for Cd and Ni respectively. After extraction, the enhancement factors (EF) were 87 and 79 for Cd and Ni, respectively. The RSD for six replicates of 10µgL(-1) Cd and Ni were 3.97% and 3.55% respectively. To validate the proposed method, certified reference material (CRM) of Virginia tobacco leaves was analyzed, and the determined values of Cd and Ni were in good agreement with the certified values. The concentration of Cd and Ni in artificial saliva extracts corresponds to 39-52% and 21-32%, respectively, of the total contents of both elements in dry brown and black snuff products.

The effect of tin on the corrosion behavior of the Ag-Hg phase of dental amalgam and dissolution of mercury.

The anodic polarization behavior of the Ag-Hg matrix phase of dental amalgam (gamma 1) and the rate of mercury dissolution were examined as a function of the tin content. The objectives were to determine the effect of tin on the electrochemical behavior and dissolution of mercury and to provide evidence on whether tin dissolves in the gamma 1 phase or precipitates as a tin-rich phase. Anodic polarization curves were recorded for specimens of the gamma 1 phase containing 0-1.5% Sn and for the gamma 2 phase and a gamma 2-containing dental amalgam, in synthetic saliva. Mercury dissolved in synthetic saliva in 24 h was determined for the gamma 1 phase containing 0-1.0% Sn, with cold-vapor Atomic Absorption Spectrophotometry used for mercury analysis. Tin induced passive behavior of the gamma 1 phase and suppressed mercury dissolution. The passive gamma 1 phase did not exhibit a breakdown of passivity occurring at the gamma 2 phase. The results were consistent with the tin presence in gamma 1 in a solid solution, rather than in tin-rich precipitates, and indicated that at least 1.5% Sn can be dissolved in gamma 1 at 37 degrees C.

An in vitro stimulation of the effects of chewing sugar-free and sugar-containing chewing gums on pH changes in dental plaque.

The objective of these studies was to simulate the effect of chewing sugar-free and sucrose-containing chewing gums on the return of the pH to neutrality after exposure to sucrose of plaque located on the buccal (BLM) and lingual (LLM) surfaces of the lower molar teeth. In study 1, a 0.5-mm-deep artificial plaque containing Streptococcus oralis cells was exposed to 10% sucrose for one min, and a 0.1-mm-thick film of sucrose-free artificial saliva was then flowed over the plaque surface at the unstimulated salivary film velocities previously found at the BLM and LLM sites. At the time of the pH minimum (pH 4-5), one of three conditions was simulated: (a) a no-gum-chewing control, or chewing for 20 min on either (b) a sugar-free gum or (c) a sucrose-containing gum. The recovery of the plaque pH to resting values was rapid during simulation of chewing a sugar-free gum (SFG), much slower with the no-gum control, and even slower with simulation of chewing a sucrose-containing gum (SCG). The pH recovery was slower with the BLM than the LLM plaque. In study 2, the BLM plaque was exposed to a 2% sucrose solution for 20 min under stimulated salivary conditions, to simulate the consumption of a meal, followed by one of conditions (a), (b), or (c) described above. The pH recovery with simulation of chewing a SCG was faster than with the no-gum control, but much slower than with the SFG simulation.(ABSTRACT TRUNCATED AT 250 WORDS)

An electrochemical and multispectroscopic study of corrosion of Ag-Pd-Cu-Au alloys.

Corrosion of a multi-phase Ag-Pd-Cu-Au-based commercial dental casting alloy and a Cu-Pd-rich and Ag-rich single-phase alloy was studied by open-circuit potential measurements, atomic absorption spectrometry, and electron spectroscopy. The alloys were immersed in an artificial saliva solution for 24 hr while the open-circuit potentials of the alloys were measured. The potentials were found to stabilize at certain levels after a steep rise during the first hours of the experiment. Cu was found to dissolve considerably from the Cu-Pd-rich alloy, with simultaneous enrichment of Pd in the surface layer of the alloy. Ag dissolved slightly from the Ag-rich alloy, but both Cu and Ag were found to dissolve from the multi-phase alloy. Neither Pd nor Au dissolved from any of the alloys studied.

Filler leachability of composites stored in distilled water or artificial saliva.

Though dental composite materials leach filler elements when stored in distilled water, it is not known whether similar leaching occurs in saliva. The hypothesis to be tested was that due to ion exchange occurring at the filler surfaces, more filler elements leach from composites stored in a salt solution simulating saliva than from composites stored in distilled water. Another aim was to determine how matrix selection, filler composition, and filler silanization affect filler leachability of composites after storage in the simulated saliva and water media. We made 128 batches of experimental composites. Half of these used a bis-GMA/TEGDMA matrix and the other a UEDMA/TEGDMA matrix. Either silica or barium glass filler particles were incorporated into these matrices. Filler silanization was followed by a filler drying at 60 degrees C for 24 h. Half of the silanized particles received an additional heat treatment for 1 h at 110 degrees C in vacuum. One specimen per batch was stored in distilled water and the other in artificial saliva at 37 degrees C. After each 30-day interval for one year, the specimens were transferred to either freshly distilled water or newly mixed artificial saliva. The "old" solutions were analyzed by ICP for determination of the Si, Ba, and Al concentrations. Analysis of variance revealed that storage solution, filler composition, and total time in the storage solution had strong effects on the leachability (p < 0.0001 in all cases). The average monthly leakage of Si for quartz-filled composites was 0.22 +/- 0.20 microgram/mL (distilled water) and 2.80 +/- 1.20 microgram/mL (artificial saliva). For barium-glass-filled composites, the corresponding Si leaching values were 0.73 +/- 0.48 microgram/mL and 5.00 +/- 2.20 microgram/mL. The monthly means of the barium leaching values were 2.00 +/- 1.00 microgram/mL (distilled water) and 3.10 +/- 1.80 microgram/mL (artificial saliva). The large difference between leaching in artificial saliva and in distilled water, as well as the interaction between storage medium and filler, cast doubt on the clinical relevance of in vitro studies using distilled water.

A comparison of human dental plaque microcosm biofilms grown in an undefined medium and a chemically defined artificial saliva.

The growth and pathogenic properties of dental plaque result from interactions between the microbiota and the oral environment and have been studied in laboratory experimental systems ranging from single or a few species (such as in chemostats) to dental plaque microcosms. Microcosm plaque is an in vitro version of natural plaque and has been explored as a microflora model because it is sited a more manipulable and controllable environment. It is obtained as microcosm biofilms in an 'artificial mouth' plaque culture system by culturing the bacteria in natural plaque-enriched saliva (i.e. salivary bacteria where a whole-saliva donor has abstained from oral hygiene for 24 h to increase the plaque bacteria in the saliva). The aim here was to examine whether a new, chemically defined analogue of saliva (defined medium mucin, DMM) could substitute for a previously used, chemically undefined medium (basal medium mucin, BMM) as an analogue of saliva for large-scale biofilm culturing. DMM contains various ions, mucin, amino acids, vitamins and growth factors at concentrations generally similar to those in saliva, whereas BMM contains yeast extract, peptones and mucin. To model the nutrient functions of salivary proteins, amino acids equivalent to 5 g/l casein were also included in DMM. In earlier studies, BMM-grown plaques were similar to natural plaques in structure, composition, growth rate and pH response to substrates. Their doubling-time patterns over a 20-day period were similar, except that the DMM-grown plaques showed biphasic growth patterns that were more pronounced than with BMM. Variation in enzyme profiles between BMM- and DMM-grown plaque, measured using the API-ZYM technique, provided evidence of nutritional effects on plaque composition. It was concluded that realistic growth rates and patterns are generated in microcosm plaque biofilms by supplying both DMM and BMM. However, the use of DMM enables specific modifications to be made to nutrient conditions during large-scale culture in our 'artificial mouth' biofilm system.