Residual Monomer Content Research Articles

Acrylic Bone Cement Incorporated with Low Chitosan Loadings

Despite the potential of acrylic bone cement (ABC) loaded with chitosan (CS) for orthopedic applications, there are only a few in vitro studies of this composite with CS loading ≤ 15 wt.% evaluated in bioactivity tests in simulated body fluid (SBF) for duration > 30 days. The purpose of the present work was to address this shortcoming of the literature. In addition to bioactivity, a wide range of cement properties were determined for composites with CS loading ranging from 0 to 20 wt.%. These properties included maximum exotherm temperature (Tmax), setting time (tset), water contact angle, residual monomer content, flexural strength, bending modulus, glass transition temperature, and water uptake. For cement with CS loading ≥ 15 wt.%, there was an increase in bioactivity, increase in biocompatibility, decrease in Tmax, increase in tset, all of which are desirable trends, but increase in residual monomer content and decrease in each of the mechanical properties, with each of these trends, were undesirable. Thus, a composite with CS loading of 15 wt.% should be further characterized to explore its suitability for use in low-weight-bearing applications, such as bone void filler and balloon kyphoplasty.

Influence of polymerization method on the cytotoxicity of three different denture base acrylic resins polymerized in different methods.

Statement of ProblemAcrylic plastics are used for over 80 years for the manufacture of prostheses. This kind of material has some limitations, one of them is a residual monomer, that remains after the polymerization has been terminated, which can influence the biological properties of the final medical device.The purposeThe aim of this investigations was a comparison of the residual monomer concentration and cytotoxic effect of three various acrylic materials which differ in the polymerization method (hot-cured, polymerized under pressure and at lower temperatures).Material and methodsThe cytotoxicity of three different acrylic resins from the same producer were tested on the in vitro model (VERO CCL-81) by MTT assay. The residual monomer of acrylic materials was detected by gas chromatography.ResultsThe Superacryl Plus material polymerized in hot water has a residual monomer concentration of 0.67 ± 0.05%, Superpont C + B hardened under pressure of 2.61 ± 0.208%, and Premacryl Plus after cold curing process has 3.53 ± 0.27% of uncured MMA. The results revealed that the least cytotoxic effect were observed in case of a thermally polymerized material.ConclusionMaterial polymerized in high temperatures has lower residual monomer concentration and not affect cell cultures. Self-curing materials polymerized in lower temperature have a higher concentration of residual monomer, which reduces the number of living cells by 20%, which can cause allergic reaction shortly after new denture was prepared.

Effect of nano silica coating concentration on reducing acrylic resin denture cytotoxicity

Acrylic resin is a denture base material mostly used in the fabrication of removable partial denture and complete denture because it is easy to process, economical and aesthetically satisfying. However, the acrylic resin has a weakness i.e. residual monomer content which causes cytotoxic effect to human cells. Nano-silica coating could be used on the acrylic resin to reduce residual monomer content. The purpose of this study was to determine the effect of nano-silica coating concentration on the cytotoxicity of acrylic resin denture base material. Twenty-four acrylic resin disc-shaped specimens (5 mm in diameter and 2 mm in thickness) were divided into 4 groups (n=6), i.e. control, group with application of 0.5%,1%, and 2% nano silica coating. The specimens on the silica coating groups were silica coated using dip-coating method. After the coating was completed, the specimens were added into cell fibroblast culture (vero cell line). Cytotoxicity testswere done by MTT assay. The optical density was measured using ELISA plate reader to determine the percentage of cell viability. The highest mean of cell viability was shown in 0.5% concentration (96.78 ± 1.71) and the lowest mean was shown in the control group (80.32 ± 6.53). One-way ANOVA showed that there were significant differences among these groups. LSD tests showed that there was significant difference among all of the groups. This study concluded that nano silica coating concentration has a significant effect on the cytotoxicity of acrylic resin denture base materials.

How subtle differences in polymer molecular weight affect doxorubicin-loaded PLGA nanoparticles degradation and drug release

Aims: To evaluate the influence of minor differences in molecular weights of commercially available low molecular weight PLGA grades on the kinetics of doxorubicin release from the nanoparticles.Methods: Three low-molecular weight 50/50 PLGA polymers were thoroughly characterised concerning intrinsic viscosity, molecular weight (Mw), acid value, and residual monomer content. The doxorubicin-loaded nanoparticles prepared using these polymers were evaluated concerning the kinetics of drug release and hydrolytic degradation.Results: The Mw of the polymers were slightly different: 10.2, 10.3, and 4.7 kDa. The nanoparticles obtained from the polymer with Mw of 4.7 kDa exhibited considerably higher rates of drug release and polymer degradation.Conclusion: In the case of low molecular weight PLGA grades even a few kilodaltons could be important for the batch-to-batch reproducibility of the nanoformulation parameters. These results bring forward the importance of in-house characterisation of the polymers to be used for the nanoparticle preparation.

Effect of Acrylic Polymerization on Cytotoxicity, Residual Monomer Content and Mechanical Properties

Introduction: The aim of this study was to test and find connection between three different parameters of acrylic resins: cytotoxicity, residual monomer content in the material and flexural strength. Materials and Methods: Superacryl Plus (SpofaDental, Czech Rep.) acrylic material has been polymerized in three different ways, short-time polymerization (45 minutes), normal time (90 minutes) and long-time (7 hours 30 minutes). Flexural strength was tested in compressive instrument Shimadzu for 65 × 10 × 3.3 mm samples. Then after 24 hours the samples were broken. In 50 mm diameter and 1 mm thick samples, residual monomer was determined by gas chromatography (according to ISO standard), and the last series of the sample was used to perform cytotoxicity tests (5 mm diameter). Statistical analysis: Data were analyzed by two-way ANOVA (in GraphPad Software Inc., San Diego, CA, USA), with p-value < 0.05 as statistically significant. Results: The results from the tests show that the greatest inhibition in the development of cell cultures (VERO CCL-81) by MTT assay), was observed for the sample polymerized in the first short-time method (73.49±10%). The material also had the largest content of residual monomer 2.02±0.08% (p-value < 0.01) and lowest flexural strength 71.53±2.26 MPa. Hardened acrylic resins over 60 minutes do not adversely affect cell cultures (undisturbed growth 83.18±10.72%). The residual monomer content was below 1% (p-value < 0.01) and the mechanical resistance to fracture was over 80 MPa (p-value < 0.01). Conclusion: The use of a short polymerization method of acrylic materials can adversely affect both the mechanical properties of the prosthesis itself and its biocompatibility. From a clinical point of view, it is important to take care about the polymerization times of acrylic. Dentures for allergic patients should be carried out in long-term polymerization when the content of residual monomer is as low as possible.

Determination of residual monomer content in dental acrylic polymers and effect after tissues implantation

The aim of the present study was to determine the content of residual monomer methyl methacrylate (MMA) in cold and hot polymerized poly(methyl methacrylate) (PMMA), both widely applicable in dentistry, by using MHE-GC-MS (multiple headspace extraction analysis by gas chromatography-mass spectrometry) in combination with GC-FID (gas chromatography with flame-ionization detection). The samples of PMMA were obtained by free-radical polymerization of MMA at room temperature (cold polymerized PMMA) and at 100 °C (hot polymerized PMMA), according to the manufacturer’s instructions. The MHE-GC-MS method consisted of ten successive extractions of MMA from the polymerized samples. According to the constructed calibration curve, the content of residual MMA in PMMA samples (mgMMA/gPMMA) was determined. Intramuscular implantation of sample materials was performed in experimental animals (rats) in order to demonstrate potential adverse effects of the unpolymerized residual reactants to the tissue in direct contact with polymeric implants. The content of residual monomer in cold polymerized PMMA was higher (15.75 mgMMA/gPMMA) in comparison to hot polymerized PMMA (10.96 mgMMA/gPMMA). The implanted samples of cold-polymerized acrylic resin showed intense inflammatory response of the surrounding tissue. According to the obtained results, hot polymerized PMMA is safer for use in dentistry.

The Effect of the Parameters of T-RTM on the Properties of Polyamide 6 Prepared by in Situ Polymerization.

With the rapid development of the automotive industry, there is also a significant need to improve the raw materials used. Therefore, the demand is increasing for polymer composites with a focus on mass reduction and recyclability. Thermoplastic polymers are preferred because of their recyclability. As the automotive industry requires mass production, they require a thermoplastic raw material that can impregnate the reinforcement in a short cycle time. The most suitable monomer for this purpose is caprolactam. It can be most efficiently processed with T-RTM (thermoplastic resin transfer molding) technology, during which polyamide 6 is produced from the low-viscosity monomer by anionic ring-opening (in situ) polymerization in a tempered mold with a sufficiently short cycle time. Manufacturing parameters, such as polymerization time and mold temperature, highly influence the morphological and mechanical properties of the product. In this paper, the properties of polyamide 6 produced by T-RTM are analyzed as a function of the production parameters. We determine the crystallinity and the residual monomer content of the samples and their effect on mechanical properties.

Characterization of Aerosol Release during Spraying of Isocyanate Products.

The aerosol release during the professional application of two different isocyanate based two component spray systems was identified and the physicochemical properties of the released airborne aerosols were characterized. For this purpose, aerosol release fractions were measured using a mass balance method described by Schwarz and Koch. Besides the release of total aerosol mass special emphasis was directed to the content of free monomeric MDI (4,4'- and 2,4'-diphenylmethane diisocyanate) in three particle size fractions relevant for inhalation uptake: inhalable, thoracic, and respirable size fraction. Two products were investigated: a two component PUR (polyurethane) spray foam (Elastopor) and a polyurea spray coating (Elastocoat). The mass fraction of the applied products released with the overspray as inhalable aerosol is 6.3 × 10-4 (Elastopor) and 4.0 × 10-4 (Elastocoat). Of the released total overspray aerosol 75 or 80% were in the thoracic size range, and 26 or 47% in the respirable regime for the PUR spray foam or the polyurea spray coating, respectively. At the time point of release the content of monomeric MDI in the aerosol corresponds to the composition of the bulk product. However, analysis of air samples indicates that <1% of the spray foam aerosol mass release fraction is attributed to free monomeric 4,4'- and 2,4'-MDI. For the Spray Coating the monomeric MDI fraction is <0.1%. Higher oligomers of MDI and prereacted oligomeric reaction products make up a few percent of the aerosol. This results in a total fraction of 0.0023% (spray foam) and 0.00015% (spray coating), respectively, of the sprayed monomeric MDI that is transferred into an inhalable aged aerosol. This data demonstrates, that during professional spraying only a small fraction of the total applied mass is released as airborne aerosol. The potential distribution of the theoretically inhalable aerosol in the respiratory tract and a low residual monomer content is described, significantly contributing to a refined safety assessment of the spray applications at the workplaces.

Flocculant Based on Acrylamide and Acrylic Acid Grafted on Sodium Alginate by Electron Beam Irradiation

The paper presents the obtaining, characterization and testing of a new type of polyelectrolyte based on acrylamide (2.63 mol/L), acrylic acid (1.73 mol/L) and sodium alginate (4.63x10-3 and 9.26x10-3 mol/L), for flocculation purposes. Two types of monomeric solutions were irradiated in electron beam at room temperature and in atmospheric conditions with doses between 0.5 and 2 kGy using ALID 7 linear electron accelerator of 5.5 MeV. The potassium persulfate (9.25x10-4 mol/L) was used as reaction initiator in both types of solutions. The flocculants thus obtained were characterized using various physical and chemical methods in order to determine conversion coefficient, residual monomer content, intrinsic viscosity, grafting ratio and grafting efficiency. The flocculation efficiency was evaluated in 0.1 and 0.2 wt % blue kaolin suspension at room temperature using a standard Jar test apparatus.

Residual Monomer Content Affects the Interpretation of Plastic Degradation

Plastic degradation rates in the marine environment are essential to understand. This study demonstrates that in plastic-microbial interaction experiments, residual monomeric and oligomeric content of PA6 significantly influences the development of dissolved organic carbon. While it is well recognized that additives in plastics should be considered during the inception of plastic-exposure experiments, residual monomers have yet to be prominently considered in the same light. As such, in degradation studies where residual contents of monomers and/or oligomers are not considered, degradation of synthetic polymers could be significantly overestimated. The substantial conversion of these monomeric and oligomeric leachates also has implications for plastic-biofilm development studies and microplastic-biota-based ingestion experiments.

Radical scavenging of poly(methyl methacrylate) bone cement by rifampin and clinically relevant properties of the rifampin-loaded cement.

ObjectivesThe objective of this study was to characterize the effect of rifampin incorporation into poly(methyl methacrylate) (PMMA) bone cement. While incompatibilities between the two materials have been previously noted, we sought to identify and quantify the cause of rifampin’s effects, including alterations in curing properties, mechanical strength, and residual monomer content.MethodsFour cement groups were prepared using commercial PMMA bone cement: a control; one with 1 g of rifampin; and one each with equimolar amounts of ascorbic acid or hydroquinone relative to the amount of rifampin added. The handling properties, setting time, exothermic output, and monomer loss were measured throughout curing. The mechanical strength of each group was tested over 14 days. A radical scavenging assay was used to assess the scavenging abilities of rifampin and its individual moieties.ResultsCompared with control, the rifampin-incorporated cement had a prolonged setting time and a reduction in exothermic output during polymerization. The rifampin cement showed significantly reduced strength and was below the orthopaedic weight-bearing threshold of 70 MPa. Based on the radical scavenging assay and strength tests, the hydroquinone structure within rifampin was identified as the polymerization inhibitor.ConclusionThe incorporation of rifampin into PMMA bone cement interferes with the cement’s radical polymerization. This interference is due to the hydroquinone moiety within rifampin. This combination alters the cement’s handling and curing properties, and lowers the strength below the threshold for weight-bearing applications. Additionally, the incomplete polymerization leads to increased toxic monomer output, which discourages its use even in non-weight-bearing applications.Cite this article: G. A. Funk, E. M. Menuey, K. A. Cole, T. P. Schuman, K. V. Kilway, T. E. McIff. Radical scavenging of poly(methyl methacrylate) bone cement by rifampin and clinically relevant properties of the rifampin-loaded cement. Bone Joint Res 2019;8:81–89. DOI: 10.1302/2046-3758.82.BJR-2018-0170.R2.

ИССЛЕДОВАНИЕ ПРОЧНОСТНЫХ И УСТАЛОСТНЫХ ХАРАКТЕРИСТИК АРМИРОВАННОГО ЧАСТИЦАМИ ДИОКСИДА ТИТАНА ПОЛИМЕРНОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА ДЛЯ БАЗИСОВ СЪЕМНЫХ ЗУБНЫХ ПРОТЕЗОВ

Background. Removable designs are used in orthopedic dentistry for prosthetics of patients. The most used materials for the manufacture of bases of removable dental prosthesis currently are acrylate-based plastics. More than 90 % of removable dental prosthesis designs are produced with using of this material. The affordable cost of acrylate-based plastics prosthesis makes this material attractive for different groups of population. But this material has a number of well-known disadvantages: at first, the high concentration of residual monomer, which has a toxic effect, may cause allergic reaction and impossibility of using prosthesis; secondly, the porous structure of material contributes to the microbial seeding of the prosthesis; also, material shrinkage is up to 8 %. In connection with above, the certified in Russia Vertex ThermoSens (Vertex-Dental B.V., the Netherlands; ISO-Certificate 9001:2008) polyamide construction material deserves attention. This material has no residual monomer in its composition; the prostheses has an ability to be corrected in laboratory; shrinkage in the process of manufacturing designs is minimal. It is important to note such advantages as the high density of thermoplastics in combination with low specific weight and minimal porosity, which significantly reduces the formation of a microbial film on prostheses. Objectives. The aim of the research is to enhance the strength and fatigue characteristics of material based on Vertex ThermoSens, reinforced with titanium dioxide particles, for prosthetics of patients with complex clinical situations. Methods. In this work, the mechanical characteristics of reinforced with titanium dioxide powder (5 and 10 % by weight) polyamide material have been investigated. Tests on a static three-point bend at room temperature and temperature of 40 ºC and tests on fatigue of samples of this material were performed. Results. The analysis of changes of characteristics of material at different mass fractions of filler was carried out. Higher mechanical characteristics of the material with 10 % filling were noted, in particular, greater resistance to elevated temperatures and greater fatigue life. Conclusions. On the basis of research results it is possible to make a conclusion that using 1st group material is more effective for dental prosthesis production than using 2nd group material. The research results will be relevant for working out of dentures for patients with various clinical situation.

Rheokinetic study of acrylic reactive mixtures dedicated to fast processing of fiber‐reinforced thermoplastic composites

ABSTRACTThis study focuses on the characterization of acrylic reactive mixtures designed for liquid composite molding (LCM) and yielding thermoplastic matrices for composite applications. Conversion degree, complex viscosity, and cure exothermicity are tracked during the radical polymerization. Results show that these systems suffer from Trommsdorff's effect, that is, the polymerization is highly exothermic. The rheological study also highlights a limit of injectability for LCM processes around a conversion degree of 10%. The vitrification curve, which correlates conversion degree to glass‐transition temperature, has been established for methyl methacrylate/poly(methyl methacrylate) mixtures. It constitutes a useful tool to identify the thermal conditions required to reach a full monomer conversion and thus, to manage the residual monomer content. The use of such acrylic‐based reactive solutions for fast LCM processing appears appropriate as fully polymerized matrices were obtained in less than 5 min at 90 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47391.

Vicker’s-Hardness Evaluation of Light Cured Resin Impregnated Fiber Glass Reinforced Complete Denture

Background: Hardness could found to be sensitive to the residual monomer content in the polymerized resins; the hardness is an effective method to evaluate the polymerization depth of resin materials. In addition, hardness had used to predict the wear resistance of dental materials. Materials and Methods: Acrylic resin specimens had divided into two groups according to the type of material tested (group I: conventional heat cured acrylic resin, group II: resin impregnated fiberglass reinforced complete denture base). Vicker`s micro hardness tester was used to measure Vicker`s hardness number (VH) of the acrylic specimens in which diamond indenter was applied under 25 g load for 10 seconds time evaluated by 20 x objective lens. Results: The VH values of resin impregnated fiberglass reinforced acrylic resin showed statistically insignificant lower values (as P < 0.05) than conventional heat cured acrylic resin. Conclusion: Unreacted monomer would act as a plasticizer and weaken the matrix. Heat cured PMMA could perform better in this aspect that the residual monomer content was less when compared to PMMA reinforced through other mechanisms. Key words: Hardness, Fiber, Reinforce, Denture.

Toxicological assessment of additively manufactured methacrylates for medical devices in dentistry

The paucity of information on the biological risks of photopolymers in additive manufacturing is a major challenge for the uptake of the technology in the construction of medical devices in dentistry. In this paper, the biocompatibility of methacrylates for denture bases, splints, retainers and surgical guides were evaluated using the innovative zebrafish embryo model, which is providing a high potential for toxicity profiling of photopolymers and has high genetic similarity to humans. Toxicological data obtained confirmed gradations of toxicity influenced by ethanol treatment, exposure scenarios and extraction vehicles. In direct exposure tests, juvenile fish exposed to non-treated methacrylates in ultrapure water showed accelerated toxicity endpoints compared to fish in transparent E3 medium. Similarly, toxic extracts induced mostly acute responses (embryonic mortality) in contrast to cumulative chronic (sublethal and teratogenic effects) in direct exposure. Methacrylates composed of >60% Ethoxylated bisphenol A dimethacrylate produced a relatively lower conversion rate in FTIR spectroscopy, but were safe in zebrafish bioassays after ethanol treatment. The study affirms that biocompatibility was influenced primarily by physico-chemical characteristics of the materials, which subsequently influenced their residual monomer content before and after immersion in ethanol. Given the precautionary implications of the study, we propose a 3-tiered approach i.e. using approved materials, apposite manufacturing parameters and post-processing techniques that together guarantee optimal results for medical devices. Statement of SignificanceThis study is timely and relevant since there is limited published literature that precisely describes the toxicological properties of additively manufactured methacrylates despite their increased popularity for medical devices. While it is generally accepted that the zebrafish excels as a model system for developmental toxicity, a further examination of its utility in this study using different protocols provides basis for its consideration and adoption at a crucial time when there is a lack of consensus regarding the most suited biological assessment methods for medical devices.

EVALUATION OF THE MECHANICAL PROPERTIES AND RESIDUAL MONOMER CONTENT OF COPOLYMER ACRYLIC RESINS POLYMERIZED BY DIFFERENT METHODS

Background:The aim of this study was to evaluate the effect of adding four different monomers on the flexural strength, elastic modulus, impact strength and residual monomer content of denture base resins polymerized by copolymerization mechanism.Methods:Butyl methacrylate (BMA), Isobutyl mathacrylate (IBMA), 2-hydroxyethyl methacrylate (HEMA) and methacryl-polyhedral silsesquioxane (POSS-MA) were added to monomers of conventional heat (HP) and microwave polymerized (MP) polymethyl methacrylate (PMMA) resin at the concentrations of 2%, 5% and 10% per volume. The flexural strength, elastic modulus and impact strength of specimens were measured with an universal testing machine and Charpy-type impact tester. Residual monomer contents were determined by high performance liquid chromatography (HPLC) method. Results:10% IBMA and 10% HEMA enhanced the flexural strength of HP resin. For the elastic modulus of MP resin, significant differences observed between the control group and 2 and 5% IBMA, 5 and 10% HEMA, and 5% POSS-MA groups (P&amp;lt;.05). Copolymerization mechanism had no positive effect on the impact strength of denture base resins. Significant differences were observed between the residual monomer of control group and 10% IBMA, 10% BMA, 10% POSS-MA groups of HP resin (P&amp;lt;.05). In MP resin group significant differences were observed between control group and 5% IBMA, 2-5-10% HEMA groups (P&amp;lt;.05).Conclusions: Copolymerization process was effective on the flexural strength of HP denture base resin with 10% IBMA and 10 % HEMA. However the process caused an increase in the residual monomer content of some resin groups. Keywords: Denture base resin, copolymer, flexural strength, impact strength, residual monomer.

A critical review of the application of polymer of low concern and regulatory criteria to fluoropolymers.

Per- and polyfluoroalkyl substances (PFAS) are a group of fluorinated substances that are in the focus of researchers and regulators due to widespread presence in the environment and biota, including humans, of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). Fluoropolymers, high molecular weight polymers, have unique properties that constitute a distinct class within the PFAS group. Fluoropolymers have thermal, chemical, photochemical, hydrolytic, oxidative, and biological stability. They have negligible residual monomer and oligomer content and low to no leachables. Fluoropolymers are practically insoluble in water and not subject to long-range transport. With a molecular weight well over 100 000 Da, fluoropolymers cannot cross the cell membrane. Fluoropolymers are not bioavailable or bioaccumulative, as evidenced by toxicology studies on polytetrafluoroethylene (PTFE): acute and subchronic systemic toxicity, irritation, sensitization, local toxicity on implantation, cytotoxicity, in vitro and in vivo genotoxicity, hemolysis, complement activation, and thrombogenicity. Clinical studies of patients receiving permanently implanted PTFE cardiovascular medical devices demonstrate no chronic toxicity or carcinogenicity and no reproductive, developmental, or endocrine toxicity. This paper brings together fluoropolymer toxicity data, human clinical data, and physical, chemical, thermal, and biological data for review and assessment to show that fluoropolymers satisfy widely accepted assessment criteria to be considered as "polymers of low concern" (PLC). This review concludes that fluoropolymers are distinctly different from other polymeric and nonpolymeric PFAS and should be separated from them for hazard assessment or regulatory purposes. Grouping fluoropolymers with all classes of PFAS for "read across" or structure-activity relationship assessment is not scientifically appropriate. Integr Environ Assess Manag 2018;14:316-334. © 2018 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Comparative evaluation of the amount of the residual monomer in conventional and deep-frozen heat cure polymethylmethacrylate acrylic resin: An in vitro study.

Statement of Problem:Heat cure acrylic resin material with reduced monomer content is generally recommended for clinical usage as it leads to improved mechanical, physical, and biocompatibility properties.Aims and Objective:The purpose of the present study was to evaluate and compare the amount of the residual monomer in the conventional and three different groups of deep-frozen heat cure polymethylmethacrylate (PMMA) acrylic resin.Materials and Methods:Totally 40 Specimens of heat cure PMMA acrylic resin (DPI India) (10 conventional heat cure and 30 deep frozen) were made using two disc-shaped stainless steel molds and invested into type II dental stone using compression molding technique. Each group contained 10 specimens (n = 10). Group 1: Control group of conventional polished PMMA specimen stored in water for 24 h at +37°C (10 specimens), Group 2: Deep frozen unpolished PMMA (10 specimens), Group 3: Deep frozen polished PMMA (10 specimens), and Group 4: Deep frozen polished PMMA specimen stored in water for 24 h at +37°C (10 specimens). Amount of the residual monomer content in all the specimens was measured using high-performance liquid chromatography. Data were analyzed using One-Way Analysis of Variance and multiple comparison Tukey's post hoc test (α = 0.05).Results:Least residual monomer content was found in Group 4 (0.12 wt%) followed by Group 3 (0.19 wt%), Group 2 (0.23 wt%), and Group 1 (0.26 wt%). Statistically significant difference (P < 0.05) was found in residual monomer content for all the four groups tested. Post hoc test for intergroup comparison also showed a significant difference between groups.Conclusion:The amount of the residual monomer was found to be least in deep-frozen polished PMMA specimen stored in water for 24 h at +37°C (Group 4). Thus, it can be concluded that deep freezing, polishing, and storing in water can reduce the residual monomer content.

Synthesis and Properties of Adhesive Polymer-Methylmethacrylate Materials

Kinetics of emulsion polymerization of hydrophilic vinyl monomers in the presence of polyvinylpyrrolidone and technological principles of their synthesis are determined. Reasonable technological parameters in the synthesis of copolymers are determined. Physicochemical properties of the synthesized copolymers (surface tension, the size of latex particles, and pH) are determined. Synthesized graft copolymers were used to create high-adhesion polymer-monomer compositions. These compositions have high reactivity at room temperature. It can be regulated by the nature of the polymer matrix and the introduction of comonomers and fillers due to the influence of physicochemical factors on the process of polymer formation. The rate of polymerization and the degree of monomer conversion largely depend on the nature of the polymer matrix. The highest polymerization rate and the maximum degree of conversion are observed when using a copolymer of polyvinylpyrrolidone and polymethylmethacrylate. Materials based on the developed compositions are characterized by a low residual monomer content and high operational properties, such as surface hardness, Vicat softening temperature, and adhesive bond strength to supports of different nature.

The residual monomer content and mechanical properties of CAD\CAM resins used in the fabrication of complete dentures as compared to heat cured resins.

BackgroundThe utilization of computer-assisted designing and computer-assisted milling CAD\\CAM resins in the fabrication of removable prostheses is a modern-day concept that offers many advantages over the use of the traditional polymethylmethacrylate (PMMA).AimThis study instigated some of the mechanical properties of CAD\\CAM denture base resin including the amount of residual monomer.MethodsThis study was conducted at the Faculty of Dentistry, King Abdulaziz University from October 2016 to February 2017. A total of seventy rectangular specimens were fabricated (group A: 35 heat-cured PMMA and group B: 35 CAD/CAM pre-polymerized acrylic resin blocks). The flexural strength and surface hardness were tested while the residual monomer content at baseline, two-day and seven-day intervals was estimated using gas chromatography (GC). Means and standard deviations were determined for each group as well as independent-samples t-test and ANOVA with repeated measures for comparison between the groups and subgroups of varying time intervals.ResultsHeat cured PMMA (A), displayed higher flexural strength and low value flexural modulus compared to CAD/CAM acrylic resin denture base material (B). Student t-test indicated highly significant differences (p<0.001) of the flexural strength (t=37.911) and flexural modulus (t=88.559). The surface hardness of group (B) was significantly higher compared to group (A) as indicated by the t-test (t=20.430). Higher release of the monomer content was detected by GC in group (A) at different time intervals with a statistically significant difference (p<0.001) in residual monomer content.ConclusionCAD/CAM resin may be considered suitable for use in the construction of denture bases.