Magnesium silicide nanoparticles as a deoxygenation agent for cancer starvation therapy.

A material that rapidly absorbs molecular oxygen (known as an oxygen scavenger or deoxygenation agent (DOA)) has various industrial applications, such as in food preservation, anticorrosion of metal and coal deoxidation. Given that oxygen is vital to cancer growth, to starve tumours through the consumption of intratumoral oxygen is a potentially useful strategy in fighting cancer. Here we show that an injectable polymer-modified magnesium silicide (Mg2Si) nanoparticle can act as a DOA by scavenging oxygen in tumours and form by-products that block tumour capillaries from being reoxygenated. The nanoparticles are prepared by a self-propagating high-temperature synthesis strategy. In the acidic tumour microenvironment, the Mg2Si releases silane, which efficiently reacts with both tissue-dissolved and haemoglobin-bound oxygen to form silicon oxide (SiO2) aggregates. This in situ formation of SiO2 blocks the tumour blood capillaries and prevents tumours from receiving new supplies of oxygen and nutrients.

Penetration of experimental infiltrants with different penetration coefficients and ethanol addition into natural caries lesions in primary molars.

This study evaluated the influence of the penetration coefficient (PC) and ethanol addition on the penetration depth (PD) of experimental infiltrants into proximal caries lesions in primary molars. Caries lesions (n = 45) were randomly treated with 1 of 4 experimental infiltrants (PC63; PC185; PC204; PC391) for 5 min. Lesion depths and PDs were analysed using dual fluorescence confocal microscopy. Lesions were almost completely infiltrated in all groups. Median PDs and percentage penetrations were not significantly different between groups (p > 0.05). When applied for 5 min, all tested infiltrants were able to infiltrate proximal caries in primary molars nearly completely.

Bisphenol A blood and saliva levels prior to and after dental sealant placement in adults.

PURPOSE: This study examined the effects of a widely used (Delton Pit & Fissure Sealant - Light Cure Opaque, DENTSPLY Professional, York, PA) pit and fissure sealant material on bisphenol A (BPA) levels in blood and saliva, among both low and high-dose groups over time. METHODS: A convenience sample of 30 adults from the Old Dominion University population were randomly and evenly divided into 2 independent variable groups: a low-dose group (1 occlusal sealant application) and high-dose group (4 occlusal sealant applications). A 2 group, time series design was used to examine the presence and concentration of BPA in serum and saliva after sealant placement. Differences comparing low-dose and high-dose groups were examined 1 hour prior (baseline), 1 hour post, 3 hours post and 24 hours after sealant placement, as measured by a direct-competitive BPA Enzyme Linked ImmunoSorbent Assay (ELISA). Hypothesized outcomes were evaluated by applying a parametric, 2 way ANOVA for repeated measures technique to data on the 30 participants ranging in age from 18 to 40 years, and were of mixed gender and ethnicity. RESULTS: BPA was detected in the saliva of all participants prior to sealant placement and ranged from 0.07 to 6.00 ng/ml at baseline. Salivary BPA concentration levels peaked over a 3 hour period following sealant placement and returned to baseline levels within 24 hours. BPA was significantly elevated at all post-sealant placement time periods for both the low-dose (1 occlusal sealant application) and high-dose (4 occlusal sealant applications) groups with peak levels of 3.98 ng/ml and 9.08 ng/ml, respectively. The blood serum did not contain BPA at any point in this investigation. CONCLUSIONS: Exposure to BPA from sources other than dental resins contributes to salivary baseline concentration levels and indicates environmental exposure and use of products containing BPA. Use of specific molecular formulations of dental sealant material determines the release of BPA, therefore, dental sealant materials should be reviewed independently when questioning the release of BPA from dental sealants. In addition, dosage amounts of the dental sealant material used in this study do not influence the serum concentration levels of BPA. Further research is needed to examine the cumulative estrogenic effects of BPA from dental sealants.

Biodegradation of resin-dentin interfaces increases bacterial microleakage.

Bis-GMA-containing resin composites and adhesives undergo biodegradation by human-saliva-derived esterases, yielding Bis-hydroxy-propoxy-phenyl-propane (Bis-HPPP). The hypothesis of this study is that the exposure of dental restorations to saliva-like esterase activities accelerates marginal bacterial microleakage. Resin composites (Scotchbond, Z250, 3M) bonded to human dentin were incubated in either buffer or dual-esterase media (pseudocholinesterase/cholesterol-esterase; PCE+CE), with activity levels simulating those of human saliva, for up to 90 days. Incubation solutions were analyzed for Bis-HPPP by high-performance liquid chromatography. Post-incubation, specimens were suspended in a chemostat-based biofilm fermentor cultivating Streptococcus mutans NG8, a primary species associated with dental caries, for 7 days. Bacterial microleakage was assessed by confocal laser scanning microscopy. Bis-HPPP production and depth and spatial volume of bacterial cell penetration within the interface increased with incubation time and were higher for 30- and 90-day PCE+CE vs. buffer-incubated groups, suggesting that biodegradation can contribute to the formation of recurrent decay.

Anti-biofilm effect of dental adhesive with cationic monomer.

The incorporation of polymerizable cationic monomers has been attempted to generate dental resinous materials with antibacterial activity. This study tested the hypothesis that a dental adhesive containing a cationic monomer, methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB), would influence biofilm formation and gtf gene expression of Streptococcus mutans. The effect of the photo-polymerized DMAE-CB-incorporated adhesive on in vitro biofilm accumulation was investigated with spectrophotometry and scanning electron microscopy. The relative level of gtf gene expression by Streptococcus mutans in the biofilm was quantified by real-time reverse-transcription polymerase chain-reaction. The DMAE-CB-incorporated adhesive significantly decreased bio-film accumulation on its surface (P < 0.05), and suppressed the expression of gtfB and gtfC of Streptococcus mutans in the biofilm (P < 0.05). The results suggest that the cured DMAE-CB-incorporated adhesive may hamper biofilm accumulation via selective down-regulation of the expression of gtf genes in Streptococcus mutans.

Excretion of dental resin monomers and metabolic intermediates via urine in guinea pigs.

OBJECTIVE: Monomers like BisGMA (Bisphenol-A-glycidyldimethacrylate) and comonomers like TEGDMA (triethyleneglycoldimethacrylate) are used in dental restorative materials in order to build up the three-dimensional network of filling materials. Since earlier investigations revealed uptake and subsequent metabolism of unpolymerized remainders of (co)monomers, the present experiment investigates the metabolic urine pattern of guinea pigs (n=4) after application of TEGDMA or BisGMA (each dose=0.02 mmol/kg body weight=100%), respectively. METHODS: For the investigations BisGMA was pre-dissolved in DMSO and subsequently diluted with 0.9% NaCl solution (final DMSO concentration 1%) and TEGDMA was dissolved in 0.9% NaCl solution. The solutions were administered with a gastric tube into the animals. Control animals received either 0.9% NaCl or 0.9% NaCl solution with 1% DMSO solution. RESULTS: After 24h in collected urine the following metabolites were identified. After administration of TEGDMA (mean relative concentration of administered substances)+/-s.d. [%]; n=4): unchanged TEGDMA: 12+/-1.5%, MA: 2.4+/-0.8%, and triethyleneglycol: 35+/-2.2%. After administration of BisGMA (mean+/-s.d. [%]; n=4): unchanged BisGMA: 11.4+/-2.7%, MA: 2.2+/-0.6%, and bisphenol-A-bis(2,3-dihydroxypropyl)ether: 60.1+/-5.2%). CONCLUSION: No further metabolites like the previously identified intermediate 2,3-epoxymethacrylic acid and derived reaction products were identified in the urine, indicating that these metabolites must have reacted further.

The effect of in-office in combination with intracoronal bleaching on enamel and dentin bond strength and dentin morphology.

AIM: The aim of this study was to evaluate in vitro effects of the combination of in-office and intracoronal bleaching on enamel and dentin bond strength and on dentin morphology. METHODS AND MATERIALS: Bleaching treatment was performed on 128 bovine teeth for three weeks. Intracoronal bleaching was performed in groups G1 to G3, and in the other groups a combination of in-office and intracoronal bleaching was performed. The following agents and materials were used (n=16): G1- sodium perborate and water (SP); G2- 37% carbamide peroxide (CP); G3- 35% hydrogen peroxide (HP); G4- HP + cotton pellet soaked in water (CPW); G5- HP + SP; G6- HP + CP; G7- HP + HP; and G8- CPW (control). Seven days after bleaching treatment the teeth were sectioned into two halves. One half of each tooth was ground to obtain a flat dentin surface. Dentin and enamel fragments were treated with a dentin/enamel resin adhesive. Resin composite was inserted in two increments and polymerized for 20 seconds. Following the restorative procedures, specimens were sectioned into beams with a rectangular cross-sectional area of approximately 1 mm2. Microtensile testing was performed in a universal testing machine. Bond strengths (in MPa) were calculated and the data were submitted to an analysis of variance (ANOVA) and the Tukey test (a=0.05). For the scanning electron microscopy (SEM) observation, the exposed pulp chambers (n=5) were fixed, dehydrated, dried in a Critical Point dryer, and gold-sputter coated for analysis at standardized magnifications (500X, 1000X, and 2000X). RESULTS: None of the bleaching techniques reduced the enamel bond strength, the best results observed were with the intracoronal treatments with SP and HP. In dentin all bleaching techniques reduced the bond strength with the exception of the in-office HP application technique. The SEM results demonstrated similar dentin surfaces for the G1, G3, G6, and G7 groups with more open dentin tubules found than in the other groups. CONCLUSION: None of the bleaching techniques tested reduced the bond strength of enamel, but they all reduced the bond strength of dentin with the exception of the group only treated with in-office bleaching using 35% HP. The worst bond strength results to dentin were observed in groups that received intracoronal bleaching with SP.

Distribution and excretion of BisGMA in guinea pigs.

Bisphenol-A-glycidyldimethacrylate (BisGMA) is used in many resin-based dental materials. It was shown in vitro that BisGMA was released into the adjacent biophase from such materials during the first days after placement. In this study, the uptake, distribution, and excretion of [(14)C]BisGMA applied via gastric and intravenous administration (at dose levels well above those encountered in dental care) were examined in vivo in guinea pigs to test the hypothesis that BisGMA reaches cytotoxic levels in mammalian tissues. [(14)C]BisGMA was taken up rapidly from the stomach and intestine after gastric administration and was widely distributed in the body following administration by each route. Most [(14)C] was excreted within one day as (14)CO(2). The peak equivalent BisGMA levels in guinea pig tissues examined were at least 1000-fold less than known toxic levels. The peak urine level in guinea pigs that received well in excess of the body-weight-adjusted dose expected in humans was also below known toxic levels. The study therefore did not support the hypothesis.

Effect of bacterial collagenase on resin-dentin bonds degradation.

The objective of this study is to evaluate the effect of a bacterial collagenase on the degradation of resin-dentin bonds. Human dentin surfaces were bonded with: an etch-&-rinse self-priming adhesive (SB), a two-step self-etching primer/adhesive (SEB), and a 1-step self-etching adhesive (OUB). Composite build-ups were constructed. The bonded teeth were stored (24 h, 3 months, 1 year) in distilled water or in a buffered bacterial collagenase solution. Half of the specimens were stored as intact bonded teeth (Indirect Exposure/IE). The other half were sectioned into beams prior to storage (Direct Exposure/DE). After storage the intact teeth were sectioned into beams and all specimens were tested for microtensile bond strengths (MTBS). ANOVA and multiple comparisons tests were performed. Fractographic analysis was performed by scanning electron microscopy. The inclusion of bacterial collagenase in the storing solution did not lower the MTBS values over those seen in specimens stored in water. SB and SEB bonds strength were equal, and were superior to OUB. After 3 months of DE, SB and OUB bonded specimens showed decreases in MTBS; similar reductions required 1 year for SEB/DE. MTBS did not decrease in IE specimens except for OUB. Resin and collagen dissolution were evident in DE groups after storing.

Detection of acid diffusion through bovine dentine after adhesive application.

AIM: Acidic diffusion through bovine dentine was investigated by measuring pH changes on dentine surfaces after applying three adhesive systems. METHODOLOGY: Coronal incisor bovine dentine discs, 0.5 mm thick, were prepared from dentine close to the pulp chamber. A single-bottle adhesive system-Single Bond, a self-etching primer system-Clearfil SE Bond and an 'all-in-one' adhesive system-AQ Bond were used. The labial dentine surfaces were conditioned as follows: Single Bond groups: (SB-1) 35% phosphoric acid etchant was applied and left in place; (SB-2) the etchant was applied for 15 s and rinsed off for 10 s; (SB-3) application of adhesive agent and light curing following step SB-2; Clearfil SE Bond groups: (SE-1) SE primer was applied for 20 s and dried; (SE-2) application of adhesive agent and light curing following step SE-1; AQ Bond groups: (AQ-1) AQ Bond adhesive was applied for 20 s and dried, applied for additional 5 s and dried again; (AQ-2) light curing following step AQ-1. The pH change on the pulpal dentine surface was measured using a pH-imaging microscope. RESULTS: All the Single Bond groups revealed a lower pH on the pulpal surface (pH 6.25, 6.59 and 6.64 for SB-1, SB-2 and SB-3, respectively) compared with intact dentine. Clearfil SE Bond and AQ Bond groups showed no significant deference in pH value from intact dentine. CONCLUSIONS: Acid diffusion from phosphoric acid etching was observed when placed on 0.5 mm-thick dentine discs; however, there was only limited evidence of acid diffusion from SE primer and AQ Bond.

Tensile strength and microhardness of treated human dentin.

OBJECTIVES: To determine the ultimate tensile strength and Knoop hardness of mineralized, EDTA-treated, sodium hypochlorite (NaOCl)-treated, EDTA-treated resin-infiltrated, and NaOCl-treated resin-infiltrated dentin. METHODS: Dumbell-shaped specimens with a cross-sectional area of 0.5 mm2 were prepared from the crowns of extracted human third molars. Specimens were randomly assigned to the following experimental groups: (1) mineralized dentin; (2) 0.5 M EDTA-demineralized dentin, pH 7/5 days; (3) 5% NaOCl-deproteinized dentin/2 days; (4) EDTA-treated, Single Bond resin-infiltrated dentin; (5) NaOCl-treated, Single Bond resin-infiltrated dentin. All specimens were tested in tension in a Vitrodyne testing machine at 0.6 mm/min. Knoop microhardness was measured on the fractured edges of specimens in groups 1, 3, 4, and 5. Results were analyzed by ANOVA and SNK tests (p < 0.05). RESULTS: Both EDTA and NaOCl treatments caused significant reductions in the tensile strength and microhardness of mineralized dentin (p < 0.05) with the largest reductions observed after NaOCl treatment (p < 0.05) Resin infiltration of treated dentin resulted in moderate increase of its tensile strength and microhardness, however, the original mineralized values were not recovered (p < 0.05). SIGNIFICANCE: Whenever dentin surfaces are treated with EDTA or NaOCl prior to a clinical bonding procedure, clinicians must be aware that a weak layer may be present at the interface, which may lead to premature failures of resin/dentin bonds.

Effect of dental adhesives on the exudative phase of the inflammatory process in subcutaneous tissue of rats.

The vascular changes in the subcutaneous connective tissue of rats induced by dentin bonding systems (one step) was studied and compared to those induced by saline solution (negative control) and Furacin (positive control), during the exudative phase of the inflammatory process. Twenty mg/kg of Evan's blue were injected intravenously in the vein of the rats' penises; 0.1 ml of each substance tested was inoculated in the subcutaneous tissue. After a 3 hour period the animals were sacrificed and their skins were excised and punched out with a standard steel 2.5 cm in diameter. The specimens were immediately immersed in 8 ml of formamide and taken to a double boiler for 72 hours at 37 C, to remove the dye. The liquid containing the overflowed dye was filtered, analyzed in the spectrophotometer (620 nm) and classified according to the criteria established by Nagem-Filho, Pereira (1976). After statistical analysis, the irritative potential of the substances was ranked as follows: Furacin (severe) > Single Bond and Bond 1 (moderate - no significant differences between the dentin bonding systems tested) > saline solution (not significant as regards the irritation degree).

Effect of dental adhesives on the exudative phase of the inflammatory process in subcutaneous tissue of rats

The vascular changes in the subcutaneous connective tissue of rats induced by dentin bonding systems (one step) was studied and compared to those induced by saline solution (negative control) and Furacin (positive control), during the exudative phase of the inflammatory process. Twenty mg/kg of Evan's blue were injected intravenously in the vein of the rats' penises; 0.1 ml of each substance tested was inoculated in the subcutaneous tissue. After a 3 hour period the animals were sacrificed and their skins were excised and punched out with a standard steel 2.5 cm in diameter. The specimens were immediately immersed in 8 ml of formamide and taken to a double boiler for 72 hours at 37ºC, to remove the dye. The liquid containing the overflowed dye was filtered, analyzed in the spectrophotometer (620 nm) and classified according to the criteria established by Nagem-Filho, Pereira (1976). After statistical analysis, the irritative potential of the substances was ranked as follows: Furacin (severe) > Single Bond and Bond 1 (moderate - no significant differences between the dentin bonding systems tested) > saline solution (not significant as regards the irritation degree)

Biocompatibility of hydroxylated metabolites of BISGMA and BFDGE.

Unpolymerized dental monomers can leach out into the oral biophase and are bioavailable for metabolism. We hypothesize that metabolites would be less toxic than parent monomers. We first identified the formation of metabolites from bisphenol F diglycidyl ether (BFDGE) and Bisphenol A glycidyl methacrylate (BISGMA) after their exposure to liver S9 fractions. Then, the metabolites and parent compounds were subjected to in vitro cytotoxicity, mutagenicity, and estrogenicity studies. Bisphenol A bis(2,3-dihydroxypropyl) ether and bisphenol F bis(2,3-dihydroxypropyl) ether were the hydroxylated metabolites of BISGMA and BFDGE, respectively. Cytotoxicity against L929 cells showed that the metabolites were significantly (p < 0.05) less cytotoxic than the parent monomers. Only BFDGE was mutagenic in the Ames assay with strain TA100 of Salmonella typhimurium. Parent and metabolite compounds did not stimulate estrogen-dependent MCF-7 cell proliferation above solvent controls. These results indicated that the hydroxylated metabolites were non-mutagenic, non-estrogenic, and less cytotoxic than their parent monomers.

Penetration of an antibacterial dentine-bonding system into demineralized human root dentine in vitro.

In this study, the penetration of three proprietary dentine-bonding agents (Prime & Bond 2.1, Single Bond, Liner Bond 2) and experimental dentine-bonding systems incorporating an antibacterial monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), into artificial root caries lesions was evaluated, and the bactericidal activity of each material against Streptococcus mutans or Lactobacillus casei impregnated into demineralized dentine blocks was assessed. All of the commercial dentine-bonding agents were capable of penetrating into the artificial carious lesions to more than 150 microm. The depth of penetration of the experimental systems, which were based on Liner Bond 2, was not significantly different from that of their parent product. Liner Bond 2 primer exhibited the greatest bactericidal effects among the three proprietary dentine-bonding agents tested. Bactericidal activities of experimental primers containing MDPB were greater than those of any other products, and the application of 4% MDPB-containing primer resulted in complete killing of bacteria in demineralized dentine. The results indicate that the penetration of dentine-bonding agents into extensively demineralized root dentine is possible in vitro, and the experimental dentine-bonding systems containing the antibacterial monomer MDPB are capable of killing bacteria within demineralized dentine. This could be of benefit when managing root caries lesions.

[Hormone dysregulators. Pseudo-estrogens in dental composite resins and sealanta?]. / Hormoonontregelaars. Pseudo-oestrogenen in tandheelkundige composieten en sealants?

A number of polluting chemicals in the ecosystems must be characterized as hormone disruptors. Among others, male animals appear to become feminized by the action of the so-called pseudo-estrogens and under their influence mens' fertility is said to decrease. Composites and sealants based on Bis-GMA resin may contain bisphenol-A as an impurity and Bis-DMA, from which in saliva bisphenol-A will be formed by hydrolytic degradation. Therefore, in extreme circumstances a weak estrogenic effect is not impossible on the short-term. However, the amounts of these probably not very potent estrogenic compounds are small, thereby resulting in a tolerable risk on the short term. Long-term-effects and synergism with pseudo-estrogens from other sources prompt further studies in order to verify the safety of the Bis-GMA containing products.

Effect of filler content on the profile of released biodegradation products in micro-filled bis-GMA/TEGDMA dental composite resins.

This study assesses the effect of the filler content, in a micro-filled composite (0.04 microm), on the liberation of biodegradation products derived from two model composite systems. The materials were based on bis-phenyl glycidyl dimethacrylate (bis-GMA) and triethylenene glycol dimethacrylate (TEGDMA) monomers. The composites were produced using silica filler concentrations of 20 and 40%) by weight. Samples were incubated with either cholesterol esterase (CE) or phosphate buffer solutions (PBS) for 8, 16 and 32 days. Products were isolated by high-performance liquid chromatography (HPLC) and identified by mass spectrometry. The identified products included TEGDMA, 2,2-bis[4(2,3-hydroxypropoxy)-phenyl]propane (bis-HPPP) and triethylene glycol methacrylate (TEGMA). Bis-HPPP was only produced in the presence of enzyme. The amount of isolated TEGMA, in both composite systems, was shown to be significantly higher for materials incubated with enzyme than their buffer counterparts (P < 0.05). Between 0 and 8 days incubation with enzyme, significantly higher amounts of Bis-HPPP and TEGMA were generated with the lower filler model material (composite-20) than the higher filled composite (composite-40), while the opposite effect was observed between 8 and 16 days. The data indicate that biodegradation product release profiles are dependent on the filler/resin ratios, and suggests that this parameter should be considered when assessing product release for biocompatibility issues pertaining to dental composite systems.

Extractable free monomers from self-cured dental sealants resulting from dispensing errors.

High performance liquid chromatography (HPLC) experiments were performed on a series of commercially available self-curing dental sealant materials that were deliberately mismixed. The goal of the experiments was to measure the amount of extractable sealant under conditions of nonideal processing as might happen clinically. The stoichiometry of the two component resins ranged from a 2/1 to a 1/2 catalyst to base mixture using a commercially available self-cure sealant that was to be mixed 1/1 based on the manufacturer's recommendations. Following fabrication the samples were immersed in an ethanol/water mixture as an extraction fluid that was then analyzed using HPLC. Values other than the 1-1 stoichiometry led to a statistically larger extractable content of bis-glycidyl methacrylate relative to the control. The extractable fraction of triethylene glycol dimethacrylate also increased with mismixing, although statistical differences varied somewhat more. Given the increased concerns about the effects of extractable monomers on the endocrine system, there may be an increased need to maintain proper stoichiometry in a clinical setting.

BIS-GMA--based resins in dentistry: are they safe?

BACKGROUND: The authors critically surveyed research dealing with the release of resin components from dental composites and the potential of these agents to mimic or disrupt estrogenic cell responses. TYPES OF STUDIES REVIEWED: The studies reviewed included those on synthetic methods used to make bisphenol A glycidyl methacrylate, or BIS-GMA, and the biological effects of this resin in cell culture and animals. The estrogenic effect of bisphenol A was targeted because bisphenol A is present as an impurity in some resins (BIS-GMA) and as a degradation product from other resins (bisphenol A dimethacrylate, or BIS-DMA). RESULTS: The outcomes of this review revealed that short-term administration of BIS-GMA and/or bisphenol A in animals or cell cultures can induce changes in estrogen-sensitive organs or cells. However, considering the dosages and routes of administration and the modest response of estrogen-sensitive target organs, the authors conclude that the short-term risk of estrogenic effects from treatments using bisphenol A-based resins is insignificant. Long-term effects need to be investigated further. CLINICAL IMPLICATIONS: Commonly used dental resins should not be of concern to the general public; however, pharmacological evaluation of dental materials is needed to ensure biologically safe and therapeutically effective substances.

Bioavailability of components of resin-based materials which are applied to teeth.

Chemical components of many materials used in dental practice can move into the local biophase, where they can have beneficial or adverse effects. The strongest indirect evidence that components of resin-based materials used in dentistry can move into the biophase are the many reports of allergic dermatitis in dental personnel. Direct measurement of component release has shown that triethylene glycol dimethacrylate (TEGDMA), hydroxyethyl methacrylate (HEMA), and, in the case of some orthodontic cements, bis-glycidyl methacrylate and benzoyl peroxide can move into an aqueous medium from a range of resin-based materials which are applied to teeth as part of oral care. In the case of resin composite restorations, HEMA and TEGDMA are available in microgram quantities via the salivary surface in the minutes and hours after clinical placement and via dentin and pulp in the hours and days after placement. Fortunately, moderate thickness of dentin protects pulp tissue against local toxicity. There are no data which suggest that systemic toxicity is a risk with any of these materials. There are some case reports of allergic responses to the monomers in patients, but the incidence of such responses appears at present to be much lower than that in dental personnel.