The safety of nanostructured synthetic amorphous silica (SAS) as a food additive (E 551)

KEY MESSAGES

Particle sizes of E 551 products are in the micrometre range. The typical external diameters of the constituent particles (aggregates) are greater than 100 nm. E 551 does not break down under acidic conditions such as in the stomach, but may release dissolved silica in environments with higher pH such as the intestinal tract. E 551 is one of the toxicologically most intensively studied substances and has not shown any relevant systemic or local toxicity after oral exposure. Synthetic amorphous silica (SAS) meeting the specifications for use as a food additive (E 551) is and has always been produced by the same two production methods: the thermal and the wet processes, resulting in E 551 products consisting of particles typically in the micrometre size range. The constituent particles (aggregates) are typically larger than 100 nm and do not contain discernible primary particles. Particle sizes above 100 nm are necessary for E 551 to fulfil its technical function as spacer between food particles, thus avoiding the caking of food particles. Based on an in-depth review of the available toxicological information and intake data, it is concluded that the SAS products specified for use as food additive E 551 do not cause adverse effects in oral repeated-dose studies including doses that exceed current OECD guideline recommendations. In particular, there is no evidence for liver toxicity after oral intake. No adverse effects have been found in oral fertility and developmental toxicity studies, nor are there any indications from in vivo studies for an immunotoxic or neurotoxic effect. SAS is neither mutagenic nor genotoxic in vivo. In intact cells, a direct interaction of unlabelled and unmodified SAS with DNA was never found. Differences in the magnitude of biological responses between pyrogenic and precipitated silica described in some in vitro studies with murine macrophages at exaggerated exposure levels seem to be related to interactions with cell culture proteins and cell membranes. The in vivo studies do not indicate that there is a toxicologically relevant difference between SAS products after oral exposure. It is noted that any silicon dioxide product not meeting established specifications, and/or produced to provide new functionality in food, requires its own specific safety and risk assessment.

Preparation and evaluation of candidate certified reference materials (CRMs) for nutrients in seawater

Certified reference materials (CRMs) are an essential part of the quality assurance (QA) necessary for the reliable analytical measurement of nutrients in seawater. The CRMs currently available for these analyses are not matrix matched to marine samples. QUASIMEME routinely produces test materials for the nutrients in seawater and nutrients in estuarine water and low-salinity open water Laboratory Performance Studies (LPS) that are both homogeneous and stable. QUASIMEME, in conjunction with Eurofins Scientific, Denmark have produced two reference materials (RMs). The homogeneity testing and preliminary stability studies were carried out by QUASIMEME, and the results are presented in this article. Participants of the QUASIMEME LPS who demonstrated satisfactory long-term performance for the analysis of nutrients in seawater and nutrients in estuarine water and low-salinity open water were invited to take part in the certification exercise. Twenty laboratories returned data, a summary of which is also presented. The certification and long-term stability testing and additional data analysis were carried out by Eurofins Scientific, Denmark, and are outwith the scope of this article and not reported here. Eurofins Scientific, Denmark have marketed these RMs as part of their range of VKI Reference Materials (further information is available from eurofins@eurofins.dk).

Effect of diode laser irradiation on the apical sealing of MTA retrofillings

Apical sealing is essential for the success of paraendodontic surgery, so any procedure that may favor an adequate sealing of the apical remainder should be performed. The purpose of this study was to evaluate the influence of diode laser irradiation on the apical sealing of root-end cavities with MTA retrofillings. Root canals in twenty extracted human teeth were shaped with K-files and filled with gutta-percha. The apexes were cut off and root-end preparations were performed. The roots were divided randomly in 2 groups. Group 1 (ten specimens) was retrofilled with MTA. Group 2 was irradiated with diode laser, with 1 W for 20 seconds, on the apical surface and root end cavity before retrofilling with MTA. The specimens had their external surfaces impermeabilized with cyanoacrylate, except for the apical surface, and were then immersed in 1% rhodamine B dye for 72 h and placed in plaster stone. After that, the specimens were submitted to longitudinal abrasion until half of the root remained. The linear dye leakage was observed in these mid-roots between the root canal wall and retrofilling. The linear dye leakage was measured with Image Lab software, and the results were statistically analyzed with Student's t test. There were no statistically significant differences between the two groups (p > 0.05). The diode laser irradiation did not improve the apical sealing of MTA retrofillings under the conditions of this in vitro study.

Effect of different dye solutions on the evaluation of the sealing ability of Mineral Trioxide Aggregate

Alkaline materials have shown incompatibility with methylene blue dye in leakage experiments. The goal of the present study was to analyze the effect of different dyes on the evaluation of the apical sealing ability of Mineral Trioxide Aggregate root-end fillings. Fifty-six extracted human canines were submitted to root canal instrumentation and obturation. After apical resection, retrograde cavities were prepared and teeth were randomly divided into four experimental (n = 13) and two control groups (n = 2). The following root-end filling materials were used: groups 1 and 2--Pro Root MTA (Dentsply), groups 3 and 4--zinc oxide-eugenol cement (ZOE). Teeth in groups 1 and 3 were immersed in 2% methylene blue solution, while teeth in groups 2 and 4 were immersed in 0.2% rhodamine B in a reduced pressure environment for 48 hours. Teeth were then longitudinally sectioned and leakage was evaluated. Results were submitted to statistical analysis (ANOVA and Tukey's test). Group 1 presented the least leakage (p < 0.05). It was concluded that the evaluation of the sealing ability of MTA is influenced by the dye used, since this material presented better sealing ability when evaluated with Methylene Blue, but was similar to ZOE when evaluated with rhodamine B.

Silicate antibodies in women with silicone breast implants: development of an assay for detection of humoral immunity

Silicon, in the form of sodium silicate (Na2SiO3), adsorbed onto bovine serum albumin (BSA)-precoated plates served as the solid-phase antigen in an enzyme immunoassay to detect silicate-reactive antibodies in the plasma of 40 symptomatic women with silicone breast implants, 91 asymptomatic women with silicone breast implants, 50 healthy control women, and 52 women with rheumatic diseases and without silicone breast implants, Silicate-reactive antibodies of immunoglobulin G (IgG) or IgM isotypes were detected in the plasma of 30% (12 of 40) of the symptomatic women with silicone breast implants; 9% (8 of 91) of the asymptomatic women with silicone breast implants; 5% (1 of 20) of the women without implants who had systemic lupus erythematosus; and 0% (0 of 32) of the women without implants who had either Sjögren syndrome, scleroderma, or rheumatoid arthritis. Only 2% (1 of 50) of the sera from the healthy control women contained silicate-reactive antibodies. Preincubation of sera with silicate and eight other metal compounds (including SiO2) demonstrated that the IgG and IgM antibodies bound specifically to silicate, because preincubation with Na2SiO3 inhibited more than 90% of the activity, whereas CrO3, Li2SO4, MgSO4, NiSO4, HgCl2, ZrOCl2, BeSO4, and SiO2 failed to inhibit the IgG or IgM antibody binding to the silicate-BSA plates. Furthermore, the F(ab')2 portion and not the Fc portion of the silicate-reactive IgG was reactive with BSA-bound silicate in the enzyme immunoassay. The assay for silicate-reactive antibodies was quantified by assigning arbitrary units to a standard curve composed of serial twofold dilutions of high-positive (ten times higher than the cutoff) silicate antibody sera. This novel assay is a useful method for detecting and quantifying humoral immune response to silicate.