Residual Methyl Methacrylate Monomer 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.

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.

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.

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.

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.

Fibre-reinforced composite implant: in vitro mechanical interlocking with bone model material and residual monomer analysis

The aim of this study was to examine in vitro the mechanical interlocking of an experimental implant made of E-glass fibre-reinforced polymethyl methacrylate (PMMA)-based composite (FRC) to dental stone. FRC implants with a porous surface were embedded into the dental stone, which was chosen to simulate bone ingrowth into the porous surface of the implant, after which push-out tests were performed. PMMA cylinders with smooth and grooved surface were used as controls. In addition, the release of residual methyl methacrylate monomer (MMA) into water from FRC and control implants with different compositions and fabrication methods was determined using high performance liquid chromatography (HPLC). The highest push-out force (2149 ± 263 N) was measured for the implants with grooved surface and the lowest value for the implants with smooth surface (194 ± 68 N). The push-out forces were over five times higher for FRC implants with a porous surface (958 ± 217 N) than for implants with smooth surface. During the first day of testing, the MMA release into water was 1.4–2.8 times higher from the FRC implants than from the control PMMA implants, depending on fabrication method. With time, the difference between the implants diminished.

Evaluation of two matrix materials intended for fiber‐reinforced polymers

Two matrix resins for fiber composites that remain in a fluid state during storage and handling before polymerization were evaluated. The resin mixtures, based on methyl methacrylate (MMA), were produced with two different cross-linking agent systems: 1,4-butanediol dimethacrylate and ethylene glycol dimethacrylate or diethylene glycol dimethacrylate. Water sorption, water solubility, water uptake and residual MMA monomer were determined. Thermomechanical analysis was used to determine linear dimensional changes as a function of temperature. Flexural strength and modulus as well as fracture work and the maximum stress intensity factor were determined. The results revealed similar values for both matrix polymers regarding water sorption, water solubility, water uptake, residual MMA monomer (0.5 wt% (+/- 0.03)) and coefficient of linear thermal expansion. Flexural strength for polymer B was 68.7 MPa (+/- 9.8) compared to 56.0 MPa (+/- 13.3) for polymer A when tested dry and 64 MPa (+/- 6.1) compared to (54 MPa (+/- 3.3) when water-saturated. Fracture toughness tests showed higher maximum stress intensity factor values for polymer B (0.75 +/- 0.17) MPa x m1/2 than for polymer A (0.55 +/- 0.12) MPa x m1/2. The resin binders showed an appropriate consistency while remaining in a fluid state during storage and manipulation.

Flexural strength and moduli of hypoallergenic denture base materials

Hypoallergenic denture base materials show no residual methyl methacrylate (MMA) or significantly lower residual MMA monomer content compared to polymethyl methacrylate-based (PMMA) heat-polymerizing acrylic resin. There is insufficient knowledge of the mechanical properties of hypoallergenic denture base materials to warrant their use in place of PMMA-based acrylic resins for patients with allergic reaction to MMA. This in vitro study compared flexural strength and flexural modulus of 4 hypoallergenic denture base materials with flexural strength/modulus of a PMMA heat-polymerizing acrylic resin. The following denture base resins were examined: Sinomer (heat-polymerized, modified methacrylate), Polyan (thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), Microbase (microwave-polymerized, polyurethane-based), and Paladon 65 (heat-polymerized, methacrylate, control group). Specimens of each material were tested for flexural strength and flexural modulus (MPa, n = 5) according to ISO 1567:1999. The data were analyzed with 1-way analysis of variance and the Bonferroni-Dunn multiple comparisons post hoc analysis for each test variable (alpha=.05). Flexural strength of Microbase (67.2 +/- 5.3 MPa) was significantly lower than Paladon 65 (78.6 +/- 5.5 MPa, P <.0001). Flexural strength of Polyan (79.7 +/- 4.2 MPa, P =.599), Promysan (83.5 +/- 3.8 MPa, P =.412), and Sinomer (72.3 +/- 2.1 MPa, P =.015) did not differ significantly from the control group. Significantly lower flexural modulus was obtained from Sinomer (1720 +/- 30 MPa, P =.0007) compared to the PMMA control group (2050 +/- 40 MPa), whereas the flexural modulus of Promysan (2350 +/- 170 MPa, P =.0005) was significantly higher than the PMMA material. Microbase (2100 +/- 210 MPa, P =.373) and Polyan (2070 +/- 60 MPa, P =.577) exhibited flexural modulus similar to the PMMA material. The tested denture base materials fulfilled the requirements regarding flexural strength (>65 MPa). With the exception of Sinomer, the tested denture base resins passed the requirements of ISO 1567 regarding flexural modulus (>2000 MPa). Flexural modulus of Promysan was significantly higher than the PMMA material. Microbase and Sinomer exhibited significantly lower flexural strength and flexural modulus, respectively, than PMMA. The other groups did not differ significantly from the control group.

Determination of Residual Methylmethacrylate Monomer in Denture Base Resins by Gas Chromatography

Acrylic base resins are widely used in orthopedics and dental surgery. It is generally accepted that due to the incomplete conversion of methyl methacrylate (MMA) monomer to the polymer form during polymerization of the resin, some MMA monomers remain in the hardened material. MMA monomer has been reported to cause abnormalities or lesions in several organs of animals. Study of the literatures showed that there are no perfect and valid methods for analysis of MMA. The aim of this study was to develop a simple and valid method for determination of MMA residual monomer in the denture base resins. We have developed and validated an analytical procedure employing gas chromatography with flame ionization detector (GC-FID), with temperature programming, and a close analogue internal standard for fast and repeatable analysis of MMA residual monomer contents in denture base polymers. For quantification of monomer, two calibration curves were used by two different methods of solution preparation and they were compared to each other. The assay was linear over the range of 0.03-0.6 mg/ml MMA with correlation coefficients (r 2 ) of greater than 0.99. Accuracy, intra-day (Error<9.1%) and inter-day (Error<6.6%) , precision (RSD<5.5% and RSD<6.5%, respectively) were in acceptable values over the examined concentration range. Limit of detection (LOD) and limit of Quantification (LOQ) for MMA were 0.01 and 0.02 mg/ml, respectively. In conclusion, the proposed method was a simple and fast assay for MMA residual monomer in denture base resins.

Residual methyl methacrylate monomer, water sorption, and water solubility of hypoallergenic denture base materials

Statement of problem Denture base materials have the potential to cause irritation and allergic reaction to the oral mucosa. Water sorption and water solubility of denture base resins affect dimensional behavior and denture stability. A correlation between residual monomer and water sorption exists. Purpose This in vitro study compared the amount of residual monomer, quantity of water sorption, and solubility of 4 denture base materials purported to be hypoallergenic with those of a polymethyl methacrylate–based (PMMA) heat-polymerizing acrylic resin. Material and methods The denture base resins Sinomer (heat-polymerized, modified methacrylate), Polyan (thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), and Microbase (microwave polymerized, polyurethane-based), which are purported to be hypoallergenic, and Paladon 65 (heat-polymerized, methacrylate, control group) were examined. Specimens of each material were tested for residual methyl methacrylate (MMA) monomer (% wt, n=3), amount of water sorption (μg/mm 3, n=5) and water solubility (μg/mm 3, n=5), according to ISO 1567:2000. The residual MMA monomer concentrations were determined by gas chromatography (GC). The data were analyzed with 1-way ANOVA and the Bonferroni-Dunn multiple comparisons post hoc analysis for each test variable (α=.05). Results Significantly lower residual MMA monomer was shown for Sinomer and Polyan compared to the PMMA control group (0.90 ± 0.20% wt, P<.05). Sinomer contained 0.31% ± 0.00% wt MMA monomer, and Polyan exhibited residual MMA monomer content of 0.44% ± 0.01% wt. Promysan and Microbase did not contain detectable residual MMA. Water sorption of Promysan (16.21 ± 0.96 μg/mm 3) was significantly lower than Paladon 65 (23.04 ± 3.13 μg/mm 3, P<.0001), whereas water solubility of the hypoallergenic denture base materials (0.34-0.84 ± 0.05-0.09 μg/mm 3) was not significantly lower than the PMMA material (0.40 ± 0.06 μg/mm 3, P>.05). Except for Sinomer, the tested denture base resins passed the requirements of ISO 1567 regarding residual MMA monomer (<2.2% wt). Sinomer failed to comply with the requirements for residual MMA monomer because the manufacturer claimed that the material did not contain any MMA. The tested denture base materials fulfilled the requirements regarding water sorption (<32 μg/mm 3) and solubility (<1.6 μg/mm 3). Conclusion The tested hypoallergenic denture base materials exhibited significantly lower residual monomer content than PMMA. Promysan and Microbase showed no detectable residual MMA.

The influence of vacuum mixing on methylmethacrylate liberation from acrylic cement powder

Polymethylmethacrylate (PMMA) bone cement is a biomaterial used to anchor prostheses during joint replacement surgery. Residual methylmethacrylate monomer (MMA) may be related with the cytotoxic effect of PMMA. The aim of the present paper was to investigate the effect of two different cement mixing methods: hand stirring at atmospheric pressure and under partial vacuum (0.330 and 0.154 bar) on residual monomer liberation in phosphate buffer saline solution from acrylic cement powder. Residual MMA content was determined by high-performance liquid chromatography. Mathematical models were applied to experimental dissolution data revealing that monomer release was significantly reduced in bone cement powder obtained at 0.154 bar vacuum pressure compared to the other mixing conditions. The kinetic models applied are consistent with a simple diffusion mechanism of the monomer from the polymer matrix.