Residual Methyl Methacrylate Research Articles

Material extrusion of thermoplastic acrylic for intraoral devices: Technical feasibility and evaluation

With global demand for 3D printed medical devices on the rise, the search for safer, inexpensive, and sustainable methods is timely. Herein, we assessed the practicality of the material extrusion process for acrylic denture bases of which successful outcomes can be extended to implant surgical guides, orthodontic splints, impression trays, record bases and obturators for cleft palates or other maxillary defects. Representative materials comprising denture prototypes and test samples were designed and built with in-house polymethylmethacrylate filaments using varying print directions (PDs), layer heights (LHs) and reinforcements (RFs) with short glass fiber. The study undertook a comprehensive evaluation of the materials to determine their flexural, fracture, and thermal properties. Additional analyses for tensile and compressive properties, chemical composition, residual monomer, and surface roughness (Ra) were completed for parts with optimum parameters. Micrographic analysis of the acrylic composites revealed adequate fiber-matrix compatibility and predictably, their mechanical properties improved simultaneously with RFs and decreased LHs. Fiber reinforcement also improved the overall thermal conductivity of the materials. Ra, on the other hand, improved visibly with decreased RFs and LHs and the prototypes were effortlessly polished and characterized with veneering composites to mimic gingival tissues. In terms of chemical stability, the residual methyl methacrylate monomer contents are well below standards threshold for biological reactions. Notably, 5 vol% acrylic composites built with 0.05 mm LH in 0° on z-axis produced optimum properties that are superior to those of conventional acrylic, milled acrylic and 3D printed photopolymers. Finite element modeling successfully replicated the tensile properties of the prototypes. It may well be argued that the material extrusion process is cost-effective; however, the speed of manufacturing could be longer than that of established methods. Although the mean Ra is within an acceptable range, mandatory manual finishing and aesthetic pigmentation are required for long-term intraoral use. At a proof-of-concept level, it is evident that the material extrusion process can be applied to build inexpensive, safe, and robust thermoplastic acrylic devices. The broad outcomes of this novel study are equally worthy of academic reflection, and further translation to the clinic.

Water temperature for fabrication of autopolymerizing polymethyl methacrylate (PMMA) interim fixed restoration affects cytotoxicity and residual methyl methacrylate (MMA)

Background/purposeClinically, dentists are suggested to immerse autopolymerizing interim fixed restorations in hot water during fabrication. However, this suggestion, without including the best temperature, mostly comes from clinical experience instead of scientific evidence. This in vitro study evaluated the effect of water temperature on the cytotoxicity of interim partial fixed dental prostheses (FDPs) and examined its correlation with residual MMA. Materials and methodsTempron was chosen as the autopolymerizing polymethyl methacrylate material. Tempron was mixed and then soaked in water at different temperatures, except control group (Controlair) was not being soaking in water. The specimens were incubated with conditioned medium. The concentration of residual MMA was determined by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The cell viability of human gingival fibroblasts (HGFs) was evaluated by MTT assay. ResultsThe 60 °C and 80 °C groups exhibited significantly higher cell viabilities than those of the other groups (P < 0.05) at 48 and 72 h. The concentration of residual MMA was highly correlated with this outcome: the higher the concentration of residual MMA detected in the eluates, the poorer the cell viability was; the longer the incubation time was, the stronger the correlation was between the concentration of residual MMA and the cell viability. ConclusionAutopolymerizing PMMA interim FDPs that are polymerized in water up to at least 60 °C could reduce cell toxicity. Higher water temperature could certainly decrease the amount of residual MMA, which is closely correlated with the outcome of cell viability.

Effect of acidic saliva on monomer leaching and surface roughness of 3D-printed and milled denture-base materials

The study evaluated the effect of different acidic salivary pH values on monomer leaching and surface roughness of conventional and CAD/CAM processed (milled and 3D-printed) denture base materials. High-performance liquid chromatography was used to determine the quantity of residual methyl methacrylate monomer leaching after 30 days of immersion in acidic saliva. The surface roughness (Ra) before and after incubation was recorded using a non-contact optical profilometer. The monomer leaching and the surface roughness of the tested materials depended on the pH value of the saliva. The conventional denture framework material exhibited the highest and lowest leaching rates at pH=4.5 and pH=3.5, respectively, regardless of the treatment method. Among the CAD/CAM processed materials, the 3D-printed material showed the highest and lowest leaching at pH=5.5 and pH=3.5, respectively. Regardless of the pH, roughness after incubation was the lowest for conventional materials, and the highest for 3D printing.

Purification Process of Poly Methyl Methacrylate Products Made with Suspension Polymerization Techniques

Poly Methyl Methacrylate (PMMA) is a commodity polymer produced from Methyl Methacrylate (MMA) monomer. This applied in various industries such as automotive and in the manufacture of artificial bones. Suspension polymerization techniques are able to produce polymer powders in micron size, uniform molecular weight and desired particle size distribution. This research was initiated by conducting polymerization process by heating Polyvinyl Alcohol (PVA, dispersant)/aqua dest (H2O) mixture accompanied by nitrogen gas purging and stirring, then MMA and Benzoyl Peroxide (BPO, initiator) was added. The results of the polymerization process produce PMMA products in the form of powders which are suspected to still contain MMA, BPO, and PVA so that the washing process is required for PMMA products. Therefore, PMMA products resulting from the polymerization process are washed with water solvent with stirring, then the results of washing PMMA products are filtered and dried. The results of final PMMA products in the form of white powder which are then analyzed using Fourier Transform Infrared Spectroscopy (FTIR) analysis showed that product there is still a residual MMA. Scanning Electron Microscopy (SEM) analysis which results produce spheres of varying size and average particle size of 64.45 µm. Particle Size Analyzer result presents the average size of 62.05 µm.

A GAS CHROMATOGRAPHY STUDY ON THE EFFECT OF TWO DIFFERENT CURING CYCLES ON THE RESIDUAL MONOMER CONTENT OF TWO DIFFERENT HEAT CURE DENTURE BASE RESINS.

The conversion of monomer to polymer is not complete in denture base resins and residual monomer left can cause mucosal irritation, inflammation, and allergic reactions in tissues adjacent to dentures. The mechanical properties of denture base resins have been found to be lacking with increased residual monomer content. Therefore, it is desirable to reduce the residual monomer content in the processed denture. In the present study Gas chromatography method was used to determine the levels of residual methyl methacrylate monomer of two different brands of heat cure denture base resins processed by two different polymerization cycles. The study concluded that while processing the denture sufficient length of boiling phase should be given and for each brand, manufacturer’s instructions should be strictly followed while selecting polymerization cycle.

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.

Chemical characterization of additively manufactured methacrylates for dental devices

Despite the potential benefits of photopolymerization-based additive manufacturing, photochemical reactions in free-radical polymerization rarely proceed to completion, leading to the accumulation of residual monomer in polymer networks. In this novel study, we examined an array of methacrylate polymers for denture bases (>60 % Bis-EMA and 15–25 % proprietary methacrylic oligomer), orthodontic appliances (>70 % proprietary methacrylic oligomer, <20 % glycol methacrylate and <5 % pentamethyl-piperidyl sebucate) and implant surgical guides (≥75 % Bis-EMA and 30–50 % diurethane dimethacrylate, mixture of isomers) using headspace gas chromatography-mass spectrometry. Experimental data reported herein show that a substantial proportion of chemical compounds observed in the methacrylates decreased with post-illumination and the applied ethanol treatment. In the absence of residual methyl methacrylate, other potentially toxic acrylic esters were observed thus emphasizing the need to thoroughly scrutinize additively manufactured dental devices prior to their use. In the long term, standards for medical devices in dentistry could be revised to reflect the current trends in biomaterials and precursors they are generated from.

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.

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.

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.

Poly(methyl methacrylate) denture base materials modified with ditetrahydrofurfuryl itaconate: Significant applicative properties

The aim of this work was to examine the possibility of modification of commercial denture base materials with itaconic acid esters, in order to obtain material with less toxicity and higher biocompatibility. Despite their relatively higher price compared to methacrylates, itaconic acid and itaconates are materials of choice for environmentally friendly applications, because they are not produced from petrochemical sources, but from plants. Commercial system based on poly(methyl methacrylate) was modified using ditetrahydrofurfuryl itaconate (DTHFI), wherein the ratio of DTHFI was varied from 2.5 to 10% by weight. Copolymerization was confirmed using FTIR spectroscopy, while SEM analysis showed the absence of micro defects and pores in the structure. The effect of the itaconate content on the absorption of fluids, the residual monomer content, thermal, dynamic-mechanical and mechanical properties (hardness, toughness, stress and elongation at break) was investigated. It was found that the addition of DTHFI significantly reduced the amount of residual methyl methacrylate, what made these materials less toxic. It was shown that the increase in DTHFI content gave materials with decreased glass transition temperature, as well as with decreased storage modulus, ultimate tensile strength and impact fracture resistance, however mechanical properties were in the rang prescribed by ADA standards, and can be used in practice. The deterioration of mechanical properties was therefore worth losing in order to gain lesser toxicity of the leached monomer.

Processing behavior and mechanical properties of autopolymerizing hypoallergenic denture base polymers

ABSTRACTDriven by the phenomenon of increasing irritations and allergic reactions of dental prosthesis carriers preferably due to residual methyl methacrylate monomer in conventional dental materials, autopolymerizing hypoallergenic denture base polymers were prepared as two‐component materials in the shape of paste/paste‐ or powder/liquid systems. The processing behavior of these materials was investigated regarding the processing and solidification times also in dependence on the polymerization catalyst concentration, whereas the whole processing and curing characteristics and the final polymer properties were evaluated by dynamic mechanical analysis in shear mode in the temperature range from −145°C to 200°C. The mechanical properties of the hypoallergenic denture base polymers were validated regarding stiffness (flexural modulus E') and fracture toughness (maximum factor of loading intensity , total work of fracture ) and the effects of monomer composition, kind of resin powder, impact modification by the liquid component, and water immersion on these properties were investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41378.

High Performance Liquid Chromatographic Determination of Residual Monomer Released from Heat‐Cured Acrylic Resin. An In Vivo Study

Heat-polymerized acrylic resins are used in dentistry for complete denture fabrication. Despite the polymerization method, conversion of monomer into polymer is often incomplete with free or unreacted residual monomer remaining in the polymerized resin. The aim of this study was to determine the amount of residual monomeric methyl methacrylate (MMA) leaching in the saliva of patients wearing complete dentures in their postinsertion period. Thirty edentulous participants as first-time complete denture wearers (age 60 to 65 years) were selected. All the prostheses were fabricated using a similar standard technique with a heat-cured acrylic resin denture base material. Saliva samples were collected at time intervals of 1 hour, 1 day, and 3 days postdenture insertion. Participants were asked to discharge saliva every 30 seconds into a pre-weighed screw-capped container for a 5-minute period. MMA levels were measured using high performance liquid chromatography. Data were analyzed by ANOVA and Tukey-HSD. The maximum concentration of monomer released into saliva peaked 1 day after insertion of the complete dentures. The mean (SD) MMA content was 0.04 ± 0.01 (μg/ml) 1 hour after insertion, and 0.3 ± 0.09 (μg/ml), and 0.05 ± 0.01 (μg/ml) on the first and third days postinsertion, respectively. Although the released monomeric MMA was not at toxic levels, it could potentially sensitize complete denture patients or elicit an allergic reaction. The risk of the residual material as a primary irritant for a sensitizing reaction could be minimized by immersion of the denture in water for 24 hours before insertion.

Influence of Acrylic Resin Polymerization Methods on Residual Monomer Release

The aim of this study was to quantify and compare the amount of methyl methacrylate (MMA) monomer released from three different denture base acrylic material processed by different polymerization methods and storage conditions. Microwave-cured, conventional heat and injection-technique acrylic polymerized materials were stored in neutral (pH = 7) and acidic (pH = 4.5) artificial saliva for 24 hours at the room temperature, separately. The residual MMA content was determined by high performance liquid chromatography (HPLC). The MMA leaching from resins showed that microwave-cured material has lower residual MMA leach compared both conventional and injection-technique on neutral saliva storage conditions. The all data's exhibited higher MMA release into an acidic saliva environment than neutral artificial saliva and there were no significant differences between the materials groups on acidic saliva storage conditions. Microwave polymerization method might has some advantages on reducing release of MMA concentration and may contributory effect upon polymerization reaction on neutral pH storage condition, therefore methods of polymerization should be considered as amount of monomer release.

Diffusion and solubility of commercial poly(methyl methacrylate) denture base material modified with dimethyl itaconate and di‐n‐butyl itaconate during water absorption/desorption cycles

AbstractThis study evaluated the water absorption, solubility, kinetics of water diffusion and residual monomer content of commercial poly(methyl methacrylate) (PMMA) denture base material modified with dimethyl itaconate (DMI) and di‐n‐butyl itaconate (DBI). Water absorption and solubility were measured gravimetrically while the residual monomer content was analysed using high‐performance liquid chromatography with ultraviolet detection. It was found that the addition of di‐n‐alkyl itaconates significantly decreases the residual methyl methacrylate (MMA) content in the polymerized material. Maximum uptake (M∞) and loss (M′∞), and diffusion coefficients for absorption (Da) and desorption (Dd) of water through all materials were established. M∞ shows a linear decrease with increasing amount of itaconate in the system while Da shows a linear increase with increasing amount of itaconate, both of these effects being more pronounced when DBI is present compared to DMI. M∞ is a linear function of the value of Hoy's solubility parameter. The reduction in residual MMA promoted by addition of a small amount of di‐n‐alkyl itaconates can improve the applicative properties and biocompatibility of the PMMA denture base material. Also, it is shown that modification of the denture base material with di‐n‐alkyl itaconates can enable precise control of water absorption in the system. Copyright © 2012 Society of Chemical Industry

Effect of post-polymerization heat-treatments on degree of conversion, leaching residual MMA and in vitro cytotoxicity of autopolymerizing acrylic repair resin

Objectives This study evaluated the effect of post-polymerization heat-treatments on degree of conversion (DC), residual methyl methacrylate concentration (MMA r) and in vitro cytotoxicity of autopolymerizing acrylic repair resin. Methods A total of 336 specimens were prepared by bench- and hydroflask-curing and subjected to post-polymerization heat-treatments: a) water immersion at 60 °C for 30 min, b) microwaving at 500 W for 3 min, c) combined use of water immersion and microwaving d) no treatment (as control). Specimens were eluted in cell culture medium for 1, 2, 5 and 7 days. DC and MMA r in eluates were measured by FTIR spectrometry and HPLC, respectively. In vitro cytotoxicity of eluates on L-929 fibroblasts was determined by XTT assay. Data were statistically analyzed with Dunn's multiple comparison and Pearson correlation tests ( p ≤ 0.05). Results DC was highest (99.9%) in bench- and hydroflask-cured groups which were subjected to water immersion. At all elution periods, MMA r was detected in eluates of all treatment groups and were higher in bench-cured groups than hydro-flask cured groups. Cell proliferation values indicated slightly cytotoxic effect throughout 7 days; regardless of the curing method or post-polymerization treatment. The correlation between MMA r and cell proliferation was negative after elution of 1, 2, 5 days and was only statistically significant ( p < 0.05) at 5 days. At elution of 7 days, the correlation was positive with no significance. Significance Post-polymerization heat-treatment of autopolymerizing acrylic repair resin by immersion in water at 60 °C for 30 min is clinically recommended to improve the DC while reducing the leaching residual MMA.

Effect of leaching residual methyl methacrylate concentrations on in vitro cytotoxicity of heat polymerized denture base acrylic resin processed with different polymerization cycles

ObjectivesResidual methyl methacrylate (MMA) may leach from the acrylic resin denture bases and have adverse effects on the oral mucosa. This in vitro study evaluated and correlated the effect of the leaching residual MMA concentrations ([MMA]r) on in vitro cytotoxicity of L-929 fibroblasts. Material and MethodsA total of 144 heat-polymerized acrylic resin specimens were fabricated using 4 different polymerization cycles: (1) at 74ºC for 9 h, (2) at 74ºC for 9 h and terminal boiling (at 100ºC) for 30 min, (3) at 74ºC for 9 h and terminal boiling for 3 h, (4) at 74ºC for 30 min and terminal boiling for 30 min. Specimens were eluted in a complete cell culture medium at 37ºC for 1, 2, 5 and 7 days. [MMA]r in eluates was measured using high-performance liquid chromatography. In vitro cytotoxicity of eluates on L-929 fibroblasts was evaluated by means of cell proliferation using a tetrazolium salt XTT (sodium 3´-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzenesulphonic acid) assay. Differences in [MMA]r of eluates and cell proliferation values between polymerization cycles were statistically analyzed by Kruskal-Wallis, Friedman and Dunn's multiple comparison tests. The correlation between [MMA]r of eluates and cell proliferation was analyzed by Pearson's correlation test (p<0.05). Results[MMA]r was significantly (p≤0.001) higher in eluates of specimens polymerized with cycle without terminal boiling after elution of 1 and 2 days. Cell proliferation values for all cycles were significantly (p<0.01) lower in eluates of 1 day than those of 2 days. The correlation between [MMA]r and cell proliferation values was negative after all elution periods, showing significance (p<0.05) for elution of 1 and 2 days. MMA continued to leach from acrylic resin throughout 7 days and leaching concentrations markedly reduced after elution of 1 and 2 days. ConclusionDue to reduction of leaching residual MMA concentrations, use of terminal boiling in the polymerization process for at least 30 min and water storage of the heat-polymerized denture bases for at least 1 to 2 days before denture delivery is clinically recommended for minimizing the residual MMA and possible cytotoxic effects.

Effect of polymerisation techniques on residual monomer amount released from different acrylic resins

The purpose of this study was to investigate the influence of different polymerisation methods (heat, auto-, injection moulding and microwave) with curing processes (conventional, short- and long-term terminal boiled heat polymerisation and room temperature polymerisation) in combination with varied water storage periods (24 h, 7 and 30 days) on the residual methyl methacrylate (MMA) contents of different dental acrylic resins. Twelve discs were fabricated for each denture base material. Specimens were immersed immediately in separate light proof glass bottles containing 20 mL 75% ethanol and 25% deionised water. Residual monomer (MMA) which eluted from acrylic resins was analysed with high performance liquid chromatography. Data were analysed by two-way analysis of variance and Tukey honestly significant difference tests. The MMA monomer amount eluted from autopolymerised acrylic resin groups (p<0·01) was higher than that from the other groups. Microwave polymerised acrylic resin showed the lowest residual monomer amount compared to the other acrylic resins (p<.01).

Identification and quantification of leachable substances from polymer-based orthodontic base-plate materials

The aim of this study was to analyse leachable monomers, additives, and degradation products from polymer-based orthodontic base-plate materials. One heat-cured resin (Orthocryl), one light-cured (Triad VLC), and three thermoplastic materials (Biocryl C, Essix A+, and Essix Embrace) were investigated. Elution was performed in water at 37°C for 10 days. The extract medium was changed and analysed daily. Chromatographic methods were used to identify and quantify the leachables. In addition, the content of residual methyl methacrylate (MMA) was quantified in the poly(methyl methacrylate) (PMMA)-based materials. Statistical analysis of the quantitative results was performed using a t-test for comparison of two independent samples. Monomers and additives leached from the materials polymerized in situ and from the thermoplastic PMMA-based material. No leachable substances were found in the extracts from the other thermoplastic materials. Accumulated over 10 days, a larger amount of MMA leached from the powder-and-liquid material, Orthocryl (42 μg/cm(2)), than from the thermoplastic material, Biocryl C (0.49 μg/cm(2)). The accumulated amounts of monomers leached from Triad VLC were 91 μg/cm(2) of urethane dimethacrylate and 2.2 μg/cm(2) of 2-hydroxyethyl methacrylate. Formaldehyde was found to leach from methacrylate-based materials: 3.2 μg/cm(2) from Orthocryl and 0.16 μg/cm(2) from Triad VLC. However, formaldehyde was not detectable in extracts from Biocryl C. Residual MMA was 5.4 wt % in Orthocryl and 0.4 wt % in Biocryl C. No phthalates were detected in the tested materials. In this in vitro study, minimal leaching was found from the thermoplastic materials, while leaching of methacrylates and formaldehyde was observed from the powder-and-liquid type and the paste material. Within the limitations of this study, the results suggest that prefabricated thermoplastic plates should be preferred for patients with an allergy to methacrylates.

Effect of polymerization methods on the residual monomer level of acrylic resin denture base polymers

AbstractWearing dental acrylic prosthesis causes adverse reactions to oral tissues due to bioactive leachables from resins such as residual methyl methacrylate (MMA). The aim of this study is to apply the high performance liquid chromatography (HPLC) method to quantify and compare the amount of MMA monomers released from denture base resin polymers processed by the conventional compression molding method (Paladent), microwave polymerization (Acron MC), and injection molding technique (PalaXpress). Six specimens of 10 ± 0.2 mm in diameter and 2.0 ± 0.2 mm in thickness of each material were prepared according to manufacturer's instructions. Specimens were stored in nanopure water at room temperature (23 ± 2°C) for 4 hr, 48 hr, 8 days, and 15 days separately. Residual MMA released into water was determined with HPLC for all time intervals. Data for all time intervals were analyzed among each group using the Friedman test and differences were found to be statistically significant for all time intervals for Acron MC, Paladent, and PalaXpress (p &gt; 0.05). Kruskal–Wallis test was used to compare changes of residual MMA within time intervals among denture base resin groups and statistically significant differences were found between all time intervals (p &gt; 0.05). Acron MC exhibited significantly lower residual MMA leach compared both to Paladent and PalaXpress, and Paladent showed more residual MMA leach compared to PalaXpress. Residual MMA leach for Acron MC, PalaXpress, and Paladent showed statistically significant leach in the first 48 hr of immersion in water followed by gradual longer‐lasting moderate increase until the 15 day interval which was not statistically significant (p &lt; 0.05). Copyright © 2007 John Wiley &amp; Sons, Ltd.