Antimicrobial dental composites with K18-methyl methacrylate and K18-filler.

OBJECTIVE: To determine the effects of using K18-methyl methacrylate (K18-MMA) and K18-Filler on composite cure, esthetic, mechanical, polymerization shrinkage, and antimicrobial properties. METHODS: K18-MMA (0-20% w/w) was used to replace TEGDMA in a 70:30 Bis-GMA:TEGDMA composite filled to 70% w/w with barium glass or K18-Filler. Composite degree of cure (Rockwell15T hardness and near Infrared FTIR), hydrophilicity (contact angle measurements), translucency (transparency parameter measurements, TP), mechanical (3-point bend test), polymerization shrinkage (volumetric shrinkage and shrinkage stress), and antimicrobial properties (colony counting assay) against Streptococcus mutans, Streptococcus sanguinis, and Candida albicans were determined. RESULTS: All experimental groups had comparable degrees of cure (near Infrared FTIR and Rockwell15T Hardness), TP, moduli, polymerization volumetric shrinkages and shrinkage stresses to those of controls (Bonferroni corrected p > 0.0018). Only one group (15% K18-MMA+K18-Filler) had significantly different (lower) contact angles as compared to that of controls (Bonferroni corrected p < 0.0018). Most of the K18-Filler-containing composites had significantly lower ultimate transverse strengths (UTS) than controls (Bonferroni corrected p < 0.0018). Controls had significantly greater S mutans colony counts than 15% and 20% w/w K18-MMA+K18-Filler groups, and greater S sanguinis and C albicans colony counts than K18-containing groups. Of the composites with that provided significant antimicrobial properties against S. mutans, S. sanguinis, and C. albicans, only the 20% K18-MMA+K18-Filler group had significantly lower UTS than controls. SIGNIFICANCE: Composites with K18-MMA and K18-Filler with comparable physical properties to control composites and significant antimicrobial properties have been developed. K18-MMA and K18-Filler seem to be suitable for incorporation into commercial dental resins.

Is methyl methacrylate fixator reliable for the treatment of gartland type IV supracondylar fractures?

Background: In childhood supracondylar fractures of the humerus, fixation with percutaneous Kirschner wire is the standard treatment. In the case of irreducible-unstable fractures, these can be defined as fractures in which reduction is not well-achieved or in which fixation cannot be achieved with the K-wire. Intraoperative management of these types of fractures may be difficult. Treatment with a methyl methacrylate fixator consisting of K-wire and methyl methacrylate cement, as defined by the senior author of the article, may be a good option for Gartland type IV supracondylar humeral fractures where the fracture is unstable in flexion and extension due to complete periosteal tearing. Materials and Methods: The short-term and mid-term results of 27 patients between the ages of 4-12 with Gartland type IV supracondylar fracture of the humerus treated with methyl methacrylate fixation were reviewed. The patients were scored in terms of function and cosmetic satisfaction. Results: A total of 19 of the 27 patients treated with the methyl methacrylate fixator had full elbow motion function and rated the outcome of the treatment as excellent, which was judged by orthopedic surgeons on the basis of Flynn's criteria. Six patients had nearly full elbow motion and evaluated their recovery outcome as good. Two patients reported nearly full range of motion (ROM) and evaluated the method as moderate in terms of treatment. Discussion: Treatment with the methyl methacrylate fixation method is an inexpensive method that allows early joint mobilization, provides strong biomechanical stability, ensures good outcomes, and should be considered in the treatment of irreducible and unstable supracondylar fractures of the humerus.

Poly-Ether Ether-Ketone Post Conditioned with Sulfuric Acid, Rose Bengal Activated by Photodynamic Therapy and Sandblasting on Pushout Bond Strength to Radicular Dentin Luted with Methyl Methacrylate and Composite-Based Cement.

Objective: Assessment of post surface conditioners [sulfuric acid (SA), Rose Bengal (RB), and sandblasting (SB)] and different luting cements [methyl methacrylate (MMA)-based cement and composite-based cement] on pushout bond strength (PBS) of poly-ether ether-ketone (PEEK) post bonded to canal dentin. Materials and methods: Endodontic treatment was performed on 120 single-rooted human premolar teeth. The preparation of the post space was performed and 4 mm of gutta-percha was retained in the apical region of the root. One hundred and twenty PEEK posts were fabricated from a PEEK blank utilizing a Computer aided design-Computer aided manufacture (CAD-CAM) system. The PEEK posts were allocated randomly into four groups based on post surface conditioning (n = 30). Group A: SA, Group B: RB, Group C: SB, and Group D: No conditioning (NC). Each group was further divided into two subgroups based on the luting cement used for bonding (n = 15). Group A1, B1, C1, and D1 specimens were cemented using composite-based resin cement. However, Group A2, B2, C2, and D2 posts were luted with MMA-based resin cement. PBS assessment using a universal testing machine was performed. Failure modes were analyzed under a stereomicroscope. The data relating to the effects of surface treatment and luting types of cement were analyzed using one-way analysis of variance (ANOVA) and Tukey's post hoc test (p = 0.05). Results: Coronal section of Group B2: RB+Super-Bond C&B [9.61 ± 0.75 megapascals (MPa)] displayed the highest bond scores of PEEK after root dentin. Whereas it was also discovered that Group D1: NC+Panavia®V5 (2.05 ± 0.72 MPa) presented the lowest PBS scores. Intergroup comparison analysis revealed that Group A2: SA+Super-Bond C&B and Group B2: RB+Super-Bond C&B displayed no significant difference in their bond scores. Conclusions: RB and SA possess the potential to be used as a PEEK post conditioner. MMA-based cement displayed better performance than composite-based cement.

Study on the poly(methyl methacrylate-acrylic acid)/calcium phosphate cement composite bound by chelation with enhanced water absorption and biomechanical properties.

Polymethylmethacrylate (PMMA) bone cement has been widely used as a critical material for fixing prostheses and filling bone defects. The shrinkage of PMMA bone cement was addressed by the additives, however, the uneven integral water absorption and expansion performance as well as the deteriorated mechanical properties of the modified bone cement after immersion in phosphate buffered saline (PBS) and simulation body fluid (SBF) affected the long-term stability after implantation. Calcium phosphate cement (CPC) is a biomaterial with promising applications in orthopedics, whose hydration reaction provides an important driving force for the transfer of water. Besides, the mechanical properties of CPC can be enhanced with the curing process. In this study, CPC was utilized to modify the poly(methyl methacrylate-acrylic acid) [P(MMA-AA)] bone cement. The results demonstrated the successful construction of interconnected CPC water delivery networks in the P(MMA-AA)/CPC composite, the water absorption ratio and expansion ratio of the composite were up to 131.18 ± 9.14% and 168.19 ± 5.44%, respectively. Meanwhile, the transformation of CPC water delivery networks into rigid mechanical support networks as well as the chelation interaction between organic-inorganic enhanced the mechanical properties of the composite after immersion, the compressive strength after immersion reached 62.97 ± 0.97 MPa, which was 27.65% higher than that before immersion. The degradation ratio of the composite was up to 13.76 ± 0.23% after 9 days of immersion, which was 16.4% higher than that of CPC. Furthermore, composites exhibited superior biocompatibility as the release of Ca2+. Therefore, P(MMA-AA)/CPC composite serves as a promising medical filling material for clinical use.

The Bone Cement Hypercoagulation Syndrome: Pathophysiology, Mortality, and Prevention.

Since Charnley introduced acrylic cement to seal metallic hip prostheses in the 1950s, reports of perioperative fatal cardiorespiratory and vascular dysfunctions have been published. Studies on humans and animals have shown neurogenic stimulation and substantial local and systemic activation of coagulation are caused by surgical bone marrow damage and chemical cell destruction by toxic monomeric methyl methacrylate from the implanted cement and other tissue-released substances. Venous blood-borne cell fragments and conjugates of activated cells from the surgical site are sequestered and trapped in the pulmonary microcirculation. A substantial hypercoagulation occurs in the lung circulation. Hypercoagulable blood is passed over to the arterial side and may cause vessel obliteration and organ damage. This process may affect the brain, heart, and kidneys and, through the release of vasoactive substances, introduce hemodynamic imbalances that can lead to fatal outcomes in susceptible populations such as elderly patients with hip fractures. The main underlying pathophysiologic processes leading to these occasionally devastating outcomes are a substantial activation of coagulation and cell destruction caused by the toxic substance released by curing bone cement and several vasoactive substances.

Proliferation and differentiation of MC3T3-E1 cells on polymethyl methacrylate cements containing Fe3O4 and TiO2 for hyperthermic treatment of metastatic bone tumors.

Polymethyl methacrylate (PMMA) bone cement is widely used to relieve pain caused by metastatic bone tumors. We previously found that PMMA bone cement containing 15 mass% or more of TiO2 showed good apatite-forming ability, and 25 mass% or more of Fe3O4 generated sufficient heat for hyperthermia under an alternating current (AC) magnetic field. In this study, the cytocompatibility of PMMA bone cement with Fe3O4:TiO2 weight ratios of 25:15 (F25T15-3/2-42) and 30:15 (F30T15-3/2-42) was evaluated using osteoblastic cells (MC3T3-E1). The proliferation and differentiation of MC3T3-E1 cells were suppressed for F25T15-3/2-42 and F30T15-3/2-42 compared to PMMA bone cement without Fe3O4 and TiO2 (F0T0-3/2-42). The release of methyl methacrylate (MMA) monomers from F25T15-3/2-42 and F30T15-3/2-42 at 7 days was about 33 and 50 times higher than that from F0T0-3/2-42, respectively. The remarkable release of MMA monomers from F25T15-3/2-42 and F30T15-3/2-42 may be responsible for the suppressed proliferation and differentiation of MC3T3-E1 cells. The release of MMA monomers was not reduced when the MMA/PMMA weight ratio was decreased from 3/2 to 1/1, however, it was significantly reduced by increasing the content of benzoyl peroxide (BPO) and N, N-dimethyl-p-toluidine (DMPT) to 8 and 4 mass% against MMA, respectively. Proliferation and differentiation of MC3T3-E1 cells on PMMA-type cements containing Fe3O4 and TiO2 with increased BPO and DMPT contents need to be investigated in the future; however, our findings will be useful for designing PMMA cements for the hyperthermic treatment of metastatic bone tumors.

Comparison of the acceptable surface limits derived from the skin sensitization potency for workers and swab residue limits determined from the permitted daily exposure derived from the systemic effects.

Allergic contact dermatitis is a common occupational and environmental health problem and setting of health-based exposure limits (HBELs) to prevent induction of skin sensitization is strongly desired. When manufacturing pharmaceuticals in a shared facility, cleaning validation using surface residue levels (SRLs) derived from permitted daily exposures (PDEs) is conducted to avoid cross-contamination from the perspective of protecting patients; however, it is unclear whether the SRLs are sufficient to prevent induction of skin sensitization for workers as well. In this study, we compared acceptable surface limits (ASLs) derived from acceptable exposure levels (AELs) based on EC1.6 obtained from local lymph node assay (LLNA): BrdU-ELISA for occupational risk management of skin sensitizers with PDE-based SRLs. ASLs for 1,4-phenylenediamine (GHS skin sensitization sub-category 1A), isoeugenol (sub-category 1A), and methyl methacrylate (sub-category 1B) were compared with SRLs based on the PDEs derived from their systemic effects. The results yielded an SRL for 1,4-phenylenediamine (PDE: 0.8 mg/day) of 30 mg/100 cm2, almost 1,000 times higher than ASL (0.031 mg/100 cm2) derived from its skin sensitization potency. SRL for isoeugenol (PDE: 3.1 mg/day) was 130 mg/100 cm2, over 500 times higher than ASL (0.18 mg/100 cm2). For methyl methacrylate (PDE: 5 mg/day) as well, SRL (200 mg/100 cm2) was higher, but it was within 20 times the ASL (10 mg/100 cm2). These results showed that ASL-based risk management is extremely important especially for strong sensitizers classified as GHS sub-category 1A for occupational skin sensitization risk management.

Bone Cement Fumes Generated in Laminar Airflow Versus Conventionally Ventilated Operating Rooms: Does the Mixing System Matter?

BACKGROUND: Bone cement is commonly utilized in a variety of orthopaedic procedures and contains methylmethacrylate (MMA) monomer. MMA is a colorless, clear, flammable liquid of intense odor. Its vapor concentration in the immediate breathing zone can vary considerably in the operative setting and, in higher concentrations, can become an occupational health hazard. Therefore, reducing MMA vapor is desirable. The aim of this study was to compare the MMA vapor levels emitted during mixing among 5 commercially available cement-mixing systems across 2 operative settings: an operating room (OR) with conventional ventilation (CV) and an OR with laminar airflow (LAF). METHODS: A prospective, in vitro study was conducted at a single hospital in an OR with LAF and in an OR with CV. MMA vapor release during the cement preparation of a SAWBONES femoral canal was measured with use of a calibrated MiniRAE 3000. A total of 5 different vacuum cement-mixing systems were utilized to mix the same cement type according to the manufacturer instructions of each system. MMA vapor concentrations were measured during 5 phases of mixing, and each mixing system was randomly utilized 10 times in each OR. RESULTS: When comparing the MMA concentration levels of each system between the 2 settings, emissions remained generally higher in the CV setting for every system and in nearly every phase. Among the 5 systems analyzed, System #5, the only entirely closed system, had the lowest overall emissions for each of the 5 phases in the CV setting. CONCLUSIONS: This study demonstrated that an operative environment with LAF is conducive to clearing the fumes of MMA during mixing as well as limiting the amount of time that residual fumes linger after mixing. Additionally, the entirely closed cement-mixing system was the most effective in minimizing fume levels within the CV setting. Utilizing this closed system, especially in an OR with CV, may reduce exposure to MMA fumes from bone cement, potentially creating a more favorable working environment. CLINICAL RELEVANCE: This study provides evidence that a closed cement-mixing system utilized under vacuum in both an OR with CV and an OR with LAF is effective in keeping MMA fume levels below those considered harmful by the U.S. Occupational Safety and Health Administration.

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.

Can we do better at measuring patient-reported outcomes after cranioplasty? A systematic review.

Measuring quality of life (QOL) after cranioplasty is increasingly evident as a necessary component of patient-centered care. For data to be useful in clinical decision-making and approval of new therapies, studies must utilize valid and reliable instruments. Our objective was to critically appraise studies evaluating QOL in adult cranioplasty patients and determine validity and relevance of the patient-reported outcome measures (PROMs) used. Electronic databases of PubMed, Embase, CINAHL, and PsychINFO were used to identify PROMs measuring QOL in adult patients with cranioplasty. The methodological approach, cranioplasty outcomes, and domains measured by the PROMs were extracted and summarized descriptively. A content analysis of the identified PROMs was completed to identify the concepts measured. From 2236 articles identified, 17 articles containing eight QOL PROMs met the inclusion criteria. None of the PROMs was specifically validated or developed for adults undergoing cranioplasty. The QOL domains included physical health, psychological health, social health, and general QOL. These four domains encompassed 216 total items among the PROMs. Appearance was only assessed in two PROMs. To our knowledge, there are currently no validated PROMs that comprehensively measure appearance, facial function, and adverse effects in adults undergoing cranioplasty. There is an urgent need to develop PROMs to measure QOL outcomes rigorously and comprehensively in this patient population to inform clinical care, research, and quality improvement initiatives. Findings from this systematic review will be used to derive an outcome instrument containing important concepts related to QOL in patients who undergo cranioplasty.

Tailoring Polymerization Controllability and Dispersity Through a Photoswitchable Catalyst Strategy.

Modulating on-demand polymerization is a challenge in synthetic macromolecules. Herein, tailoring polymerization controllability and dispersity during single-electron transfer mediated living radical polymerization (SET-LRP) of methyl methacrylate (MMA) is achieved. Hexaarylbiimidazole (HABI) is employed as a photoswitchable catalyst, allowing reversible control of catalytic activity between an active and inactive state. In the presence of HABI and with the light on (active state), control SET-LRP of MMA follows first-order kinetics, resulting in polymers with a narrow molecular weight distribution. In contrast, polymerization responds to light and reverts to their original uncontrolled state with light off (inactive state). Therefore, repeatable resetting polymerization can be easily performed. The key to photomodulating dispersity is to use an efficient molecular switch to tailor the breadths of dispersity. Besides, the mechanism of HABI-mediated SET-LRP with switchable ability is proposed.

Effects of methacryloyloxydecyl dihydrogen phosphate on bonding of tri-n-butylborane-initiated resin to human enamel.

This study investigated the effect of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) in methyl methacrylate (MMA) monomer on the adhesion of tri-n-butylborane (TBB)-initiated resins (MDP/MMA-TBB resins) to human enamel. Enamel surface conditions were either polished only or phosphatized surfaces. The 1.0, 1.7, and 2.0 mol% MDP/MMA-TBB resins, 4-methacryloxyethyl trimellitate anhydride (4-META)/MMA-TBB resin and MMA-TBB resin were prepared as luting materials. The shear bond strength was determined before and after thermocycles, and the results were compared using non-parametric statistical analyses (each, n=15). The MDP/MMA-TBB resins showed significantly better bond durability to enamel than other resins with or without etching. The 1.7 and 2.0 mol% MDP/MMA-TBB resins were suggested to be the optimum MDP concentrations from pre- and post-thermocycling results for the non-etched specimens. The TBB initiator resin including MDP was shown to be effective in bonding to human enamel, and this effect was enhanced in combination with phosphate treatment.

dl-Methionine-Mediated Reversible Deactivation Radical Polymerization of Styrene and Methyl Methacrylate.

Reversible deactivation radical polymerization (RDRP) is a facile and highly efficient technique for the synthesis of well-defined polymer with precise structure. dl-Methionine (Met) as a RDRP control agent is described and assessed for RDRP of styrene (St) and methyl methacrylate (MMA) with AIBN as radical initiator at 75 °C, which enables excellent control of this polymerization. The addition of dl-Methionine significantly decreased the dispersity (D) of the polymers for both monomers and first-order linear kinetic plots of polymethyl methacrylate (PMMA) are observed in DMSO. Considering the heat resistance of dl-Methionine, kinetic studies indicate that polymerization develops at a faster rate at higher reaction temperature (100 °C) with the same dl-Methionine content. Well-defined polymethyl methacrylate-block-polystyrene (PMMA-block-PSt) is successfully achieved by the chain extension reaction that demonstrates the high end fidelities of this polymerization approach. The system allows the use of dl-Methionine, a rich source and easily synthesized agent, to mediate RDRP strategy.

The effects of different surface treatments applied to milled PMMA denture base material on repair bond strength.

The high cost of CAD/CAM systems and materials is a severe economic burden. Therefore, repair of CAD/CAM PMMA, selecting appropriate repair materials, and surface modifications are clinically important. This study aims to evaluate the shear bond strength of PMMA repair materials after various surface treatments on CAD/CAM PMMA denture base material. For this purpose, a total of 480 CAD/CAM PMMA denture base test specimens were manufactured. Then all test specimens were divided into 6 groups, and different surface treatments were applied. Group A: sandblasting, Group B: 4% hydro fluoric acid, Group C: tungsten carbide bur, Group D: dichloromethane + methyl methacrylate mixture, Group E: dichloromethane and methyl methacrylate, Group F: no surface treatment. Each group is then divided into 4 different subcategories; repair processes were performed using; heat-cured acrylic resin (n:20), auto-polymerized acrylic resin (n:20), gingiva composite (n:20), and CAD/CAM PMMA tooth material (n:20). After repairs, thermal aging was applied to half of the test specimens in each subcategory. The shear bond strength value was measured with a universal test device. Sandblasting group showed the highest surface roughness value in all test specimens (p < 0.001). Heat-cured acrylic resin with sandblasting exhibited the highest bond strength, while the untreated gingiva composite resin exhibited the lowest value. Thermal aging decreased bond strength in all repair materials (p < 0.001). Among the surface treatment groups, sandblasting with Al2O3 particles exhibited the highest surface roughness value and repair bond strength. The application of organic solvents to the surface increased the surface roughness and repair bond strength. Applying dichloromethane and methyl methacrylate monomer separately is more effective than applying it as a mixture. The ideal bonding among repair materials was obtained with heat-cured acrylic resin.

Proteinosomes via Self-Assembly of Thermoresponsive Miktoarm Polymer Protein Bioconjugates.

To fabricate nanoscale proteinosomes, thermoresponsive miktoarm polymer protein bioconjugates were prepared through highly efficient molecular recognition between the ß-cyclodextrin modified BSA (CD-BSA) and the adamantyl group anchored at the junction point of the thermoresponsive block copolymer poly(ethylene glycol)-b-poly(di(ethylene glycol) methyl ether methacrylate) (PEG-b-PDEGMA). PEG-b-PDEGMA was synthesized by the Passerini reaction of benzaldehyde-modified PEG, 2-bromo-2-methylpropionic acid, and 1-isocyanoadamantane, followed by the atom transfer radical polymerization of DEGMA. Two block copolymers with different chain lengths of PDEGMA were prepared, and both self-assembled into polymersomes at a temperature above their lower critical solution temperatures (LCST). The two copolymers can undergo molecular recognition with the CD-BSA and form miktoarm star-like bioconjugates. The bioconjugates self-assembled into ∼160 nm proteinosomes at a temperature above their LCSTs, and the miktoarm star-like structure has a great effect on the formation of the proteinosomes. Most of the secondary structure and esterase activity of BSA in the proteinosomes were maintained. The proteinosomes exhibited low toxicity to the 4T1 cells and could deliver model drug doxorubicin into the 4T1 cells.

Preparation and water erosion resistance properties of tara gum-g-poly (acrylic acid-co-methyl methacrylate) emulsion.

The main purpose of this paper is to synthesize a new kind of green and environmental protection emulsion, which can be used as water erosion resistant materials. Here, a non-toxic polymer was prepared by grafting acrylic acid (AA) and methyl methacrylate (MMA) onto the long chains of tara gum (TG) to synthesize a copolymer emulsion (TG-g-P (AA-co-MMA)). The structure, thermal stability, morphology and wettability of the polymer were characterized by conventional methods, and the effects of key synthesis conditions on the performance of the emulsion (viscosity) were optimized. The erosion resistance and compressive strength of polymer-treated loess and laterite soils were evaluated under laboratory conditions. The results showed that the successful grafting of AA and MMA monomers onto TG improved its thermal stability and viscosity. In soil performance tests with low amounts of polymer additive, a 0.3 wt% application of TG-g-P (AA-co-MMA) to loess could resist continuous precipitation for >30 h with an erosion rate of 2.0 %. The compressive strength of the laterite treated with 0.4 % TG-g-P (AA-co-MMA) was 3.7 MPa, which was about three times that of the untreated soil. The results from this study suggest that TG-g-P (AA-co-MMA) emulsions have good potential for soil remediation applications.

Recycled PMMA prepared directly from crude MMA obtained from thermal depolymerization of mixed PMMA waste.

Recycled PMMA was prepared by directly polymerizing crude pyrolysis oils from lab-scale pyrolysis of collected industrial waste PMMA. The pyrolysis oils consisted mainly of methyl methacrylate (MMA, >85%), while the type and number of by-products from the thermal process were assigned through GC-MS analysis showing a clear correlation to the pyrolysis temperature. By-products can be removed by distillation; however, directly employing the crude oils to prepare PMMA through solution, suspension, emulsion, or casting polymerization was investigated to assess the potential for omitting this costly step. It was found that the crude pyrolysis oils could be polymerized efficiently via solution, emulsion, and casting polymerization to produce a polymer similar to the PMMA prepared from a pristine monomer. The impurities in the PMMAs prepared from the crude mixtures were investigated by extraction analyses followed by screening by GC-MS. In the case of casting polymerization, the GC-MS analysis, as expected, revealed various residual by-products, while solution and emulsion polymerization showed only very few impurities, mainly originating from the polymerization and not the feed material. Additional purification of the crude pyrolysis oils would be required for applications in casting polymerization. In contrast, direct polymerization by emulsion or solution polymerization is considered applicable for producing pristine PMMA from crude waste PMMA pyrolysis oil.

Inherently Antimicrobial P(MMA-ran-DMAEMA) Copolymers Sensitive to Photodynamic Therapy: A Double Bactericidal Effect for Active Wound Dressing.

In this work, two compounds belonging to the BODIPY family, and previously investigated for their photosensitizing properties, have been bound to the amino-pendant groups of three random copolymers, with different amounts of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in the backbone. The P(MMA-ran-DMAEMA) copolymers have inherently bactericidal activity, due to the amino groups of DMAEMA and to the quaternized nitrogens bounded to BODIPY. Systems consisting of filter paper discs coated with copolymers conjugated to BODIPY were tested on two model microorganisms, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). On solid medium, irradiation with green light induced an antimicrobial effect, visible as a clear inhibition area around the coated disks. The system based on the copolymer with 43% DMAEMA and circa 0.70 wt/wt% of BODIPY was the most efficient in both bacterial species, and a selectivity for the Gram-positive model was observed, independently of the conjugated BODIPY. A residual antimicrobial activity was also observed after dark incubation, attributed to the inherently bactericidal properties of copolymers.

Evidential requirements for the regulatory hazard and risk assessment of respiratory sensitisers: methyl methacrylate as an example.

This review addresses the need for a framework to increase the consistency, objectivity and transparency in the regulatory assessment of respiratory sensitisers and associated uncertainties. Principal issues are considered and illustrated through a case study (with methyl methacrylate). In the absence of test methods validated for regulatory use, formal documentation of the weight-of-evidence for hazard classification both at the level of integration of individual studies within lines of evidence and across a broad range of data streams was agreed to be critical for such a framework. An integrated approach is proposed to include not only occupational studies and clinical evidence for the regulatory assessment of respiratory sensitisers, but also information on structure and physical and chemical factors, predictive approaches such as structure activity analysis and in vitro and in vivo mechanistic and toxicokinetic findings. A weight-of-evidence protocol, incorporating integration of these sources of data based on predefined considerations, would contribute to transparency and consistency in the outcome of the assessment. In those cases where a decision may need to be taken on the basis of occupational findings alone, conclusions should be based on transparent weighting of relevant data on the observed prevalence of occupational asthma in various studies taking into account all relevant information including the range and nature of workplace exposures to the substance of interest, co-exposure to other chemicals and study quality.

Evaluation of Shear Bond Strength Between Denture Teeth and 3D-Printed Denture Base Resin.

PURPOSE: The aim of this study was to evaluate the bond strength between two types of artificial teeth with a 3D-printed denture base resin using different bonding agents. MATERIALS AND METHODS: Two types of artificial teeth were evaluated: 3D-printed (Cosmos TEMP) and prefabricated polymethylmethacrylate (Biotone) bonded to cylinders (2.5 mm in height and 5 mm in diameter) of 3D-printed denture bases (Cosmos Denture designing by Meshmixer and printed by Flashforge Hunter DLP Resin 3D Printer). Two combinations between denture base and artificial teeth were eveluated: Cosmos Denture - Biotone, n = 30, and Cosmos Denture - Cosmos TEMP, n = 30. For each combination, the specimens were randomly distributed according to the bonding agent: (1) autopolymerized acrylic resin-Duralay, n = 10; (2) 3D-printed resin Cosmos TEMP, n = 10; and (3) methylmethacrylate monomer (MMA) + 3D-printed resin Cosmos TEMP, n = 10, totaling 60 specimens. The application of MMA was done conditioning the tooth surface for 180 seconds; the other agents were applied on the same surface. The virtual design of the 3D-printed resin teeth was obtained by scanning the first maxillary molar of the prefabricated teeth as the same protocol of cylinders. The control group (n = 10) was a conventional heat-polymerized denture base resin (Lucitone 550) bonded to the prefabricated resin teeth (Biotone). The shear bond tests were performed by applying a perpendicular force to the artificial tooth - denture base resin, through a chisel at 1 mm/min until failure. Two-way ANOVA and Bonferroni post hoc tests (α = 0.05) were used for multiple comparisons. RESULTS: For the Biotone tooth, the bond strength was significantly higher using MMA + Cosmos TEMP (10.04 MPa), and similar to the control (11.84 MPa, p = 0.484). For the 3D-printed tooth (Cosmos TEMP), the bond strength using the agents Cosmos TEMP (9.57 MPa) and MMA + Cosmos TEMP (12.72 MPa) were similar to the control (11.84 MPa, p = 0.169 and p = 1, respectively), but different from each other (p = 0.016). CONCLUSIONS: From the results, it is recommended to use: MMA + Cosmos TEMP bonding agent for the Biotone tooth; and Cosmos TEMP or MMA + Cosmos TEMP bonding agents for the Cosmos TEMP tooth, both attached to the 3D-printed denture resin Cosmos Denture.