Amount Of Residual Monomer Research Articles

Assessing the impact of dental restorative materials on fibroblast cells: an immunohistochemical and ELISA analysis.

In this study, our aim was to investigate the effects of restorative materials such as composite, compomer and high viscosity glass ionomer, which are frequently used in dentistry, on L929 fibroblast cells by evaluating the oxidative stress parameters, pro- and anti-inflammatory cytokines, and apoptosis markers. L929 fibroblast cells were cultured, and dental filling materials were applied in two doses (50 and 100µl). Immunohistochemical staining was performed for experimental groups with Anti-Bax and Anti-Caspase 9 antibodies. Then, ELISA technique was used to detect the level of TNF-alpha, TGF-beta, IL-1-beta, IL-6, IL-10, LPO and CAT. In the light of the data, the examined dental filling materials were effective on increasing the TGF-beta, IL-10, LPO and CAT levels, and decreasing the TNF-alpha, IL-1-beta, and IL-6 levels. The histological micrographs were also support the issues. When the levels of H-score in Caspase 9 labeled micrographs were evaluated, the mean of the control group was lower than the mean of the experimental groups. Biocompatibility varies according to the content of the material, the amount of residual monomer, and its solubility. Although all the experimental groups have cytotoxic effects, the least effect is seen in the Omnichroma group.

Evaluation of residual monomer release after polymerization of different restorative materials used in pediatric dentistry

BackgroundThe choice of the restorative resin material to be used in pediatric dentistry is of a great importance due to the cytotoxic effects caused by residual monomers. In this study, it was aimed to investigate the amount of residual monomer released over time from different resin-based restorative materials, which are widely used in pediatric dentistry, by using high performance liquid chromatography with photodiode array detector (HPLC–PDA).MethodsThe compomers in all colors (Twinky Star and Glasiositte A2), two composites with different hybrid properties (Arabesk-GrandioSO), and RMGIC (Ionolux) samples with 2 × 5 mm diameters were prepared. The samples were polymerized with an LED light unit (CELALUX 2, VOCO, Cuxhaven, Germany) and then finishing-polishing procedures were applied. A total of 156 samples were obtained, 13 samples in each of the 12 groups. The amount of residual monomer (BIS-GMA; HEMA, TEGDMA, UDMA) (µg/mL) released into the 75% ethanol solution was determined at different times, (1st hour, 1st, 7th, 14th, and 21st day) by using HPLC–PDA.ResultsThe residual monomer release continued on day 21 and BIS-GMA was the most released monomer in all groups. HEMA release showed a maximum increase in all the materials at day 7. The highest amount of residual monomer was detected in the gold-colored compomer. HEMA and BIS-GMA release from RMGIC was less than others in all time frames.ConclusionsThe color and composition of resin-based restorative materials affect the amount of residual monomer. Pediatric dentists should prefer gold-colored compomers less than others as a restorative material, especially in deep cavities. More studies are needed about the subject.

Preparation of expandable polystyrene by multi-stage initiator dosing/ styrene-butadiene-styrene blends with application of artificial neural networks

Expandable Polystyrene (EPS) is one of the most used polymers. Preparation of this polymer by conventional method has some problems which causes the synthesis process to be difficult and quality of the prepared EPS to decrease. In this study, Styrene-Butadiene-Styrene (SBS) has been added to improve some properties of prepared polymer and Multi-stage Initiator Dosing (MID) method has been used to reduce the time of the polymerization which increases the polymer’s production capacity. SBS has been added to EPS in shares of 2%wt, 4%wt and 6%wt. Polydispersity index (PDI) test and the amount of the tension in yield point of the polymer has been checked. The amount of absorbed pentane on the polymer studied. The amount of residual monomer on the polymer has been investigated. All of the studies happened in different conditions like: different percentages of initiator, different number of dosings and different time periods of first stage of the polymerization. Experimental data has been simulated by Multi-Layer Perceptron (MLP) and Radial Basis Function (RBF) methods of Artificial Neural Networks (ANN). The performance of simulation for RBF method was better than MLP method due to having strong scientific foundation and also the ability of filtering noises. The experimental data show that the increase in SBS causes improvement in properties like: elongation at break, better pentane absorption and PDI amount has improved, which show better distribution of molecular weight and decrease in residual monomer in products.

Effects of molecular aggregation on photostability of protoporphyrin-IX/halloysite nanotube composites

This article presents a successfully development of hybrid functional nanomaterials composed of Protoporphyrin-IX/Halloysite nanotubes (PpIX/HNTs), in which the PpIX molecules were adsorbed on the surface of the HNTs at different degree of aggregation. This article also presents a possible explanation for the PpIX adsorption by the HNTs surface and, moreover, the results show that the PpIX molecules adsorption on the HNTs surfaces, and its degree of aggregation, can be controlled by changing the ratio between PpIX and HNTs concentrations. Interestingly, from photodegradation experiments, it is observed that, after the photodegradadion of isolated monomers, the PL spectra and the photodegradation curves show that there is a ratio between the amount of residual monomers and dimers in which the PpIX/HNTs photodegradation decreases significantly, leading to a more photostable system. Therefore, these PpIX/HNTs systems can lead to the development of more efficient porphyrin-based devices and processes, and help to understand the processes of aggregation and formation of porphyrin supramolecular structures.

Silica coating application on heat-cured acrylic resin plates towards the surface hardness and the amount of residual monomers

Introduction: Silica has been used as a coating material on acrylic resin denture plates to reduce the attachment of C. albicans, and acrylic resin denture coating application has been shown to increase the resistance. Acrylic resin as denture plate has many advantages, including good aesthetical aspect, easy to be manipulated, and relatively low costs. Acrylic resin also has disadvantages, namely the presence of residual monomers, low abrasion resistance, and broken easily. Residual monomers have poor biocompatibility and can weaken the mechanical strength of acrylic resin dentures. The purpose of this study was to analyse the silica coating application on heat-cured acrylic resin plates towards the surface hardness and the amount of residual monomers. Methods: This study used as much as 40 rod-shaped heat-cured acrylic resin specimens measured 13 x 13 x 2 mm. Specimens were divided into 2 groups (n = 20), namely the control group and the acrylic resin plate group applied with silica coating. Specimens in the treatment group applied with silica coating material using the dip-coating method. The surface hardness was tested using the Vickers hardness tester, and the amount of residual monomers was tested using gas chromatography. All data were analysed using an independent t-test. Results: Surface hardness in the group applied with silica coating was significantly higher than the control group (p < 0.05), while the remaining monomers of acrylic resin plate specimens in the group applied with silica coating were significantly lower than the control group (p < 0.05). Conclusion: Silica coating increases the surface hardness and decreases the amount of residual monomer of heat-cured acrylic resin.Keywords: Silica coating, surface hardness, residual monomer, acrylic resin

Study to determine and estimate residual monomer leached out in heat cure polymethylmethacrylate Resins of commonly used brands using different polymerization cycles: (An invitro study)

Introduction: To study the residual monomer leached out in heat cure poly methylmethacrylate Resins of commonly used brands using different polymerization cycles. Aims and Objectives: To compare the amount of leachable residual monomer in Poly methylmethacrylate of heat cure brands available in market at different time interval that are polymerized by short and long curing cycle. Results: Results from the study shows that following short curing cycle denture has to be kept in water for 48 hours whereas following long curing cycle denture has to be kept in water for minimum for 24 hours in order to deliver denture with least leachable residual monomer. Conclusion: From the results of this study it was concluded higher level of residual methylmethacrylate was leached from short curing cycle than long curing cycle, suggesting that long curing cycle causes greater degree of polymerization as compared to the short curing cycle, resulting in the reduction of amount of residual monomer in long curing cycle. It was observed that by keeping immersed regular resin denture of short curing cycle for 48 hours duration, the leaching of monomer has significantly decreased, whereas long curing cycle requires resin denture to be immersed for 24 hours duration only which showed significant reduction in leaching of monomer. Keywords: Short curing cycle, long curing cycle, Heat cure acrylic resin.

The effect of UDMA and Bis-GMA irradiation period on residual monomers in resin packable composite

Background: Residual monomers are non-polymerized monomers which can cause clinical harm, for example inflammation, to oral cavity tissue while the remaining monomers can potentially be carcinogenic. The more residual monomers that remain due to an imperfect polymerization processes, the lower the compressive strength level and the higher the number of micro slits that can cause secondary caries and tooth sensitivity. Urethane dimethacrylate (UDMA) and bisphenol A glycol dimethacrylate (Bis-GMA) constitute two of the resins most frequently used in packable composites. During the short irradiaton period forming part of the polymerization process, UDMA and Bis-GMA have the potential to produce residual monomers. Purpose: This study aimed to compare the number of residual monomers in packable composite resin following irradiation lasting 1x20 seconds and 2x20 seconds. Methods: 28 samples of cylindrical packable composite with a thickness of 2 mm and a diameter of 5 mm were divided into four groups. Groups 1 and 2 were irradiated for 1x20 seconds, and groups 3 and 4 for 2x20 seconds with the composite subsequently being immersed in ethanol solution for 24 hours. The number of residual monomers using high-performance liquid chromatography (HPLC) devices was calculated and the results statistically analyzed using a Mann-Whitney Test. Results: Repeated irradiation had no effect on the amount of residual monomers in packable composite resins. However, there were differences in the number of residual monomers in the material contained in packable composite resins Bis-GMA and UDMA, while the remaining monomers in UDMA outnumbered those in Bis-GMA. Conclusion: The number of residual monomers in Bis-GMA is lower than in the remaining UDMA after 1x20 seconds irradiation, while the number of residual monomers in Bis-GMA and UDMA following 2x20 seconds irradiation was no different to that after irradiation of 1x20 seconds duration.

Properties of PMMA Bone Cement Modified with Nano-hydroxyapatite and Acetone

Fracture in the adjacent levels is one of the consequences to the use of commercial poly methylmethacrylate (PMMA) bone cement. Modified PMMA with a reduced Young’s modulus was found to be safer for cancellous bone augmentation procedures. The aim of this research was to study the effect of adding hydroxyapatite (HA) nano-particles and acetone on different properties of PMMA cement. A commercial PMMA cement was used as a model for bone cement. Three groups of modified PMMA/nano-HA were investigated by adding 2, 4 and 6 wt. % of HA. Acetone as a porogen mixed with distilled water in different amounts (A/W: 1:1, 2:1.5 and 2:1g) was used to produce porous PMMA cement. The residual monomer, polymerization and mechanical properties under tension and compression tests were investigated. Young’s modulus detected from compression test decreased from 826.5±10 to 728±66 MPa by adding 6wt.% HA. Adding acetone to PMMA with 2:1.5g (A/W) has decreased the compressive Young’s modulus to 753±38 MPa. High Performance Liquid Chromatography (HPLC) measurements were carried out with intervals of 2 hours, 6 hours and 24 hours to evaluate the residual monomer for all groups. The amount of residual monomer has decreased after 24 hours of curing by adding acetone and nano-HA. Modifying PMMA by HA and acetone have inconsistent effect on the polymerization temperature. It was concluded that HA and acetone can be used to reduce the stiffness and residual monomer with enhanced biocompatibility of the commercial PMMA bone cement.

The difference between residual monomer dentin bonding HEMA and UDMA with acetone and ethanol solvent after binding to type I collagen

Background: In caries and non-caries lesions involving dentine, it is necessary to provide dentine-bonding material to help improve retention between the composite resin and the tooth surface. Composite resin attachment to dentine is influenced by bonding polymerization reactions. In several studies, researchers found that polymerized monomers will experience volume shrinkage because not all will fully polymerize but, rather, become residual monomers that can cause post-operative pain. Purpose: This study aimed to identify the difference in the amount of residual monomers between HEMA- and UDMA-based dentin bonding materials with acetone and ethanol solvents after binding to type I collagen. Methods: Four groups featured in this study: HEMA with acetone solvent and type I collagen , HEMA with ethanol solvent and type I collagen , UDMA with acetone solvent and type I collagen and UDMA with ethanol solvent and type I collagen . All groups were checked by high performance liquid chromatography (HPLC) to quantify the remaining amount of monomers. Results: The percentage of residual monomers of dentine bonding HEMA with acetone solvent and type I collagen was 10.69%, HEMA with ethanol solvent and type I collagen was 13.93%, UDMA with acetone solvent and type I collagen was 2.89% and UDMA with ethanol solvent and type I collagen was 7.48%. Conclusion: HEMA with ethanol solvent has the highest number of residual monomers, while UDMA with acetone solvent has the lowest.

HPLC analysis of eluted monomers released from dental composites containing bioactive glass

Objectives: The aim of the present study is to evaluate the released residual monomers from composite resins that contain different proportions of bioactive glass (BAG). Methods: Experimental resin composites were prepared by a resin matrix (50% BisGMA and 50% TEGDMA) and inorganic filler with BAG (5, 10 and 30%). Each resin composite was placed in the tooth cavity (n = 5). After polymerisation, samples were immediately immersed in 75% ethanol and 25% deionised water (6 ml) at 37 °C. Residual monomers (Bis-GMA, TEGDMA, HEMA and UDMA) that were eluted from the composites for 10 m, 1 h, 1 d, 7 d and 30 d were analysed by high-performance liquid chromatography (HPLC). The data were analysed with one-way ANOVA and Tukey HSD at a p < 0.05 significance level. Results: Among the time periods, the fastest released residual monomer was observed in the 10 m elution. The highest amount of released residual monomer from all groups (except the control group) was TEGDMA, whereas this was HEMA for the control group. The amounts of residual monomers eluted from BAG30 were significantly higher than other groups (p < 0.05). Conclusions: The release of the monomer increases in accordance with the increased BAG addition to the composite resins.

Influence of Heating Rates and Residual Monomer on Dimensional Changes of Acrylic Resin Denture Base

Background: Most of spaces between the denture base and master cast produced by shrinkage of the base material during polymerization and by the difference in coefficient of thermal expansion of the cast and acrylic resin. The aim of this study is to evaluate the effect of the different heating rates and the presence of residual monomer on the accuracy different curing denture base by recording the gap space between the cast and the dentureMaterials and methods: 18 maxillary edentulous stone cast were prepared then divided into three main groups, denture bases were constructed. In Group A, using Biostar plates (free of monomer) in the pressure champers. In group B, using short curing cycle while group C, using long curing cycle . The gap space between the cast and denture base was recorded using traveling microscope measuring device.Results: Biostar curing resin (group A) showed significantly the highest dimensional changes among groups (short and long curing resins). There was no significant difference between group B ( short curing resin) and group C (long curing resin). The lowest gap space values were obtained in long curing resin. All samples showed maximum discrepancy in mid palatal reign and minimum dimensional changes at the crest of ridge. Minimum gap space values were shown in the canine reign for record bases cured with short and long curing cycles, while minimum gap space values were shown in the posterior palatal seal for record base cured with Biostar machine.Conclusion: The dimensional changes of record bases mainly depend on the amount of heat applied during processing rather than the amount of residual monomer. Greater distortion was shown in record base processed by Biostar machine (Free of monomer), while the least distortion in record base processed by long curing cycle. All samples showed maximum discrepancy in the mid palatal region and minimum dimensional changes at the crest of ridge.

Fabrication of a fast‐swelling superabsorbent resin by inverse suspension polymerization

ABSTRACTA novel, fast‐swelling superabsorbent polymer (SAP2) was fabricated with an anionic–nonionic surfactant [poly(oxy‐1,2‐ethanediyl)–(3‐carboxy‐1‐oxo‐3‐sulfopropyl)–(nonylphenoxy) sodium salt] as the stabilizer by inverse suspension polymerization. The microstructure, chemical structure, and gel strength of the superabsorbent polymers (SAPs) were characterized by scanning electron microscopy, porosity, and specific surface area analysis, Fourier transform infrared spectroscopy, and rheometry. The results show that SAP2 had irregularly shaped particles with a large number of pores and presented a greater specific surface area, pore volume, and gel strength than the prepared SAP1 with a nonionic surfactant (Span 60) as the stabilizer. The amount of residual monomer and the gel fraction of SAP2 were 202 mg/kg and 80.6%, respectively. Meanwhile, SAP2 demonstrated a faster swelling and deswelling rate as well as greater water absorbency than SAP1. The fast swelling rate mainly resulted from the capillary effect of the pores in the irregularly shaped particles. Superfast swelling SAPs should possess outstanding potential for healthcare products, communication cables, and the biomedical field. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46142.

Effect of polymerization temperature on the properties of autopolymerizing resin

Statement of problemThe polymerization conditions of an autopolymerizing resin affect its physical properties, and at chairside, 3 different methods are commonly used: cooling in cold water, warming in warm water, and heating in hot water. However, the effects of polymerization temperature on the physicomechanical properties of autopolymerizing resin are unclear. PurposeThe purpose of this in vitro study was to determine the effect of polymerization temperature on the physicomechanical properties of autopolymerizing resin, including shrinkage, water absorption, surface roughness, amount of residual monomer, and flexural strength. Material and methodsThe experiment was designed to simulate a direct technique commonly used for the fabrication of interim crowns. Autopolymerizing resin specimens were made according to the powder-to-liquid ratio recommended by the manufacturer and soaked in water at 13°C, 37°C, or 60°C for 2 minutes to mold the resin until polymerization was completed 4 minutes after mixing. Shrinkage, water absorption rate, surface roughness, residual monomer, and flexural strength were measured immediately after polymerization and after 1, 3, and 7 days in distilled water at 37°C. Differences among these properties among the 3 different temperatures groups were statistically analyzed by using 1-way ANOVA and the Tukey honest significant difference test (α=.05). ResultsShrinkage tests showed that the 13°C group had significantly lower shrinkage (P=.004 for 37°C and P<.001 for 60°C) than the other groups immediately after specimen preparation. The 13°C group had significantly higher surface roughness after 0 (P<.001 for 37°C and P<.001 for 60°C), 1 (P=.025 for 37°C and P=.012 for 60°C), 3 (P<.001 for 37°C and P<.001 for 60°C), and 7 days (P<.001 for 37°C and P<.001 for 60°C) than those in the other groups and significantly higher water absorption rates (P=.033 for 37°C and P<.001 for 60°C) than the other groups during the 7 days after fabrication. However, the 13°C group showed significantly higher weight percentage of residual monomers than the 60°C group at 0 (P<.001) and 1 day (P<.001). Finally, 3-point bend tests showed that the 13°C group had significantly lower flexural strength at 0 (P<.001), 1 (P<.001), 3 (P<.001), and 7 days (P<.001) than the other groups. ConclusionsThe temperature environment during dental chairside polymerization of the autopolymerizing resin affected the physicomechanical properties of shrinkage, water absorption rate, surface roughness, residual monomer, and flexural strength.

Ultrasonic cleaning reduces the residual monomer in acrylic resins

Background/purposeThe residual monomer remaining in acrylic resin can cause an allergic reaction and is toxic to oral soft tissue. This study determined the effect of the duration of ultrasonic cleaning on the amount of residual methyl methacrylate monomer in one heat-polymerized acrylic resin, Meliodent, and three autopolymerized acrylic resins, Unifast Trad Ivory, Unifast Trad Pink, and Unifast III. Materials and methodsThirty-six disc-shaped specimens of each brand were prepared and randomly divided into six groups: control (no treatment), positive control, and ultrasonic treatment in 50°C water for 3 minutes, 5 minutes, 10 minutes, or 15 minutes. The residual monomer was extracted and analyzed using high performance liquid chromatography. ResultsThere were no significant differences in the residual monomer amount in the Meliodent groups. The amounts of residual monomer in the autopolymerized acrylic resin positive control group and ultrasonic treatment groups were significantly lower than those of the control group for the Unifast Trad Ivory, Unifast Trad Pink, and Unifast III groups (P<0.05). The amount of residual monomer was not significantly different between the ultrasonic treatment in 50°C water (3 minutes for Unifast Trad Pink and 5 minutes for Unifast Trad Ivory and Unifast III) groups and the positive control group (P>0.05). ConclusionUltrasonic treatment with 50°C water for 3–5 minutes for autopolymerized resin and 3 minutes for heat-polymerized acrylic resin reduced the amount of residual monomer similarly to previously recommended methods, using shorter treatment times.

Influence of chemical polymer composition on integrated waveguide formation induced by excimer laser surface irradiation

We show that the chemical composition and the amount of residual monomers in polymethylmethacrylate significantly affect the evolution of optical waveguide formation induced by UV surface irradiation. We employ an interferometric approach in Mach-Zehnder configuration to determine the refractive index depth profile in different planar polymethylmethacrylate materials. Our results reveal a distinctive different surface and buried waveguide formation for materials having different monomer content. In particular, we find that for smaller residual monomer content buried waveguide formation is less pronounced, which is in turn preferential for a selective light guidance in planar polymer structures. Attenuation measurements confirm a difference in attenuation coefficient of 0.5dB/cm.

The effect of various frequencies of ultrasonic cleaner in reducing residual monomer in acrylic resin

Monomer remaining in denture base acrylic can be a major problem because it may cause adverse effects on oral tissue and on the properties of the material. The purpose of this study was to compare the effect of various ultrasonic cleaner frequencies on the amount of residual monomer in acrylic resin after curing. Forty-two specimens each of Meliodent heat-polymerized acrylic resin (M) and Unifast Trad Ivory auto-polymerized acrylic resin (U) were prepared according to their manufacturer’s instructions and randomly divided into seven groups: Negative control (NC); Positive control (PC); and five ultrasonic treatment groups: 28kHz (F1), 40kHz (F2), 60kHz (F3) (M=10min, U=5min), and 28kHz followed by 60kHz (F4: M=5min per frequency, U=2.5min per frequency, and F5: M=10min followed by 5min per frequency, U=5min followed by 2.5min per frequency). Residual monomer was determined by HPLC following ISO 20795-1. The data were analyzed by One-way ANOVA and Tukey HSD. There was significantly less residual monomer in the auto-polymerized acrylic resin in all ultrasonic treatment groups and the PC group than that of the NC group (p<0.05). However, the amount of residual monomer in group F3 was significantly higher than that of the F1, F4, and PC groups (p<0.05). In contrast, ultrasonic treatment did not reduce the amount of residual monomer in heat-polymerized acrylic resin (p>0.05). The amount of residual monomer in heat-polymerized acrylic resin was significantly lower than that of auto-polymerized acrylic resin. In conclusion, ultrasonic treatment at low frequencies is recommended to reduce the residual monomer in auto-polymerized acrylic resin and this method is more practical in a clinical situation than previously recommended methods because of reduced chairside time.

Effect of increased exposure times on amount of residual monomer released from single-step self-etch adhesives.

The aim of this study was to evaluate the effect of increased exposure times on the amount of residual Bis-GMA, TEGDMA, HEMA and UDMA released from single-step self-etch adhesive systems. Two adhesive systems were used. The adhesives were applied to bovine dentin surface according to the manufacturer's instructions and were polymerized using an LED curing unit for 10, 20 and 40 seconds (n = 5). After polymerization, the specimens were stored in 75% ethanol-water solution (6 mL). Residual monomers (Bis-GMA, TEGDMA, UDMA and HEMA) that were eluted from the adhesives (after 10 minutes, 1 hour, 1 day, 7 days and 30 days) were analyzed by high-performance liquid chromatography (HPLC). The data were analyzed using 1-way analysis of variance and Tukey HSD tests. Among the time periods, the highest amount of released residual monomers from adhesives was observed in the 10th minute. There were statistically significant differences regarding released Bis-GMA, UDMA, HEMA and TEGDMA between the adhesive systems (p&lt;0.05). There were no significant differences among the 10, 20 and 40 second polymerization times according to their effect on residual monomer release from adhesives (p&gt;0.05). Increasing the polymerization time did not have an effect on residual monomer release from single-step self-etch adhesives.

Evaluation Amount of Residual Monomer in Two Types of Denture Base Materials Heat and Light Cure Acrylic Reinforced with Silainated Glass Fiber

Background: Residual monomer is one of the undesirable factors affecting the properties of acrylic resin denture bases this study compared the influence of addition silanated glass fiber(SGF) to two types of acrylic (heat &light cured resin) on the amount of residual monomer methyl methacrylate (MMA) at different periods of time. Materials and Methods: specimens of heat and light cured denture base materials reinforced with(2mm length, 2wt%)(SGF) were measured for their amount of residual monomer (MMA)by using high-performance liquid chromatography (HPLC) after(3days, 7days, 14days, and 30days). Results: The amount of residual monomer in reinforced groups with (SGF) either heat or light cured resin was less than non reinforced groups. The amount of residual monomer in heat cured resin was higher significance than light-cured resin and the amount of residual monomer of both types of acrylic decreased with time increased. conclusion: The addition of 2% silainated glass fiber to the both heat cured & light cured resin slightly decrease the amount of residual monomer.

Comparison of residual monomer loss from cold-cure orthodontic acrylic resins processed by different polymerization techniques

This investigation aimed to assess and compare the amount of residual monomer (RM) released from removable orthodontic appliances constructed by sprinkle-on and dough techniques. One hundred and twenty acrylic samples were prepared from orthodontic autopolymerized acrylic resins and divided into three groups, according to the processing method: sprinkle-on with polyclave, sprinkle-on without polyclave and dough technique. After polymerization, the specimens of each group were immersed in distilled water for 24 h, 48 h, 72 h and 1 week. High-performances liquid chromatography (HPLC) was utilized to measure residual monomer content. Maximum observed RM was 1284·91±129·07 ppm measured for sprinkle-on technique without polyclave after 24 h of water immersion. At this time, the level of RM was significantly different among the three applied techniques (P<0·05). In all soaking time groups, sprinkle-on technique with polyclave released the least amount of RM. Within each group, the maximum monomer releasing was observed after the first 24 h and decreases were observed in subsequent time groups. The reduction over the time was not significant in the polyclave groups (P>0·05). The sprinkle-on technique with polyclave and longer water immersion reduced residual monomer released from acrylic orthodontic appliances.

Analysis of optimal operation of a fed-batch emulsion copolymerization reactor used for production of particles with core–shell morphology

In this paper dynamic optimization of a lab-scale semi-batch emulsion copolymerization reactor for styrene and butyl acrylate in the presence of a chain transfer agent (CTA) is studied. The mathematical model of the process, previously developed and experimentally validated, is used to predict the glass transition temperature of produced polymer, the number and weight average molecular weights, the monomers global conversion, the particle size distribution, and the amount of residual monomers. The model is implemented within gPROMS environment for modeling and optimization. It is desired to compute feed rate profiles of pre-emulsioned monomers, inhibitor and CTA that will allow the production of polymer particles with prescribed core–shell morphology with high productivity. The results obtained for different operating conditions and various additional product specifications are presented. The resulting feeding profiles are analyzed from the perspective of the nature of emulsion polymerization process and some interesting conclusions are drawn.