Residual acrylic monomer content of denture base resins with different fiber systems

The conversion of monomer to its polymer may not be complete and residual monomer is left over in the polymeric matrix; this, in turn, affects the properties of the polymeric matrix. In this study, we wanted to compare residual monomer content of the unreinforced conventional heat-polymerized and microwave-polymerized acrylic resins with those of fiber-reinforced ones. High performance liquid chromatography was used for the determination of the residual monomer content. Statistical analysis of the results was carried out with a confidence level of 95%. It was observed that conventional heat-polymerized denture base resin resulted in a relatively higher residual monomer content than the microwaved one. Conventional heat-polymerized denture base resin with fiber reinforcement caused an increase in the residual monomer content. Furthermore, the change in the residual monomer content of microwave-polymerized denture base resin with fiber reinforcement was not statistically significant compared with no fiber reinforcement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of mechanical roughening and chemical treatment on shear bond strength of urethane dimethacrylate denture base resin

Relining of ill-fitting denture is often required to establish the fit of denture base, hence better retention and stability of the prostheses. However clinical success depends on the ability of reline resin to bond with denture base. The effect of surface preparations of urethane dimethacrylate (UDMA) denture base resin (Eclipse) on the shear bond strength (SBS) to auto-polymerizing polyethyl methacrylate reline material was evaluated. Eclipse specimens were mechanically prepared using two different tungsten carbide burs and submitted to chemical treatments either with dichloromethane (Secure adhesive) or methyl acetate (Eclipse Bonding Agent). Reline resin was then applied to the prepared surface and shear bond strength was tested after 24 h. Data was analyzed using two-way ANOVA and post-hoc Tukey HSD test at p=0.05. The morphological changes of Eclipse surfaces after preparations were also observed under SEM. The results showed that SBS was significantly affected by mechanical roughening, chemical treatment and their interactions. Higher reline SBS values were observed for Eclipse specimens without mechanical roughening compared to those with roughening. Both chemical agents improved reline SBS with the highest bond strength shown when chemically treated using Secure adhesive. For mechanically roughened specimens, Eclipse Bonding Agent (BA) resulted in significantly higher reline bond strength than Secure adhesive. SEM showed different surface appearance of Eclipse resin with various mechanical and chemical preparations.     

Toughening effect of comonomer on acrylic denture base resin prepared via suspension copolymerization

In this article, three copolymers used as denture base resins were prepared via suspension copolymerization using butyl acrylate (BA), butyl methacrylate (BMA), or methyl acrylate (MA) with methyl methacrylate (MMA), respectively. The homopolymers and copolymers were characterized by ¹³C nuclear magnetic resonance (¹³C NMR). The influence of the three comonomers on the mechanical property was investigated in details and the fracture surfaces of copolymer specimens were examined using scanning electron microscopy (SEM). Meanwhile, the T_g values of three copolymers were examined by differential scanning calorimetry (DSC). The results indicate that, poly(methyl methacrylate) (PMMA) copolymers with BA, BMA, or MA have been successfully prepared via suspension copolymerization. The presence of BA, BMA, or MA could improve the mechanical property especially the impact strength, the toughness of the materials was remarkably improved. The toughening effect of BMA monomer is most significant. When the content of BA is 2 wt %, the flexural strength improves by 51% and the impact strength improves by 81.3%. The T_g values of three copolymers all decrease. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of temperature on the monomer reactivity ratios of 2-hydroxypropyl methacrylate with methyl acrylate and methyl methacrylate

Summary 2-Hydroxypropyl methacrylate (2-HPMA) has been copolymerized with methyl acrylate (MA) and methyl methacrylate (MMA) in bulk at temperatures between 60 and 100°C using benzoyl peroxide as initiator. The compositions of copolymers have been determined by hydroxyl content; the reactivity ratios have been calculated by Kelen Tüdös method. The intrinsic viscosities and thermal behaviour of the copolymers were also studied.     

The transport of methyl methacrylate monomer in poly(methyl methacrylate)

The absorption kinetics and equlibria of methyl methacrylate monomer into poly(methyl methacrylate) were studied over a range of penetrant activities. The interval sorption kinetics at elevated activities were determined, compared, and contrasted with the integral sorption experiments in previously unpenetrated film samples. The sorption kinetics in previously unpenetrated films were predominantly case II or relaxation controlled at high activities. A Fickian contribution to the overall kinetics was apparent at lower activities. In contrast, interval sorption, at elevated activities in previously equilibrated and plasticized samples, followed Fickian kinetics rather closely, whereas resorption, over an activity range which involved a traversal of the effective T_g, was characterized by more complicated kinetics involving a super case II mechanism at long times. These composite results reinforce the notion that the kinetics describing penetration of a single penetrant into a single polymer are extremely sensitive to the boundary condition imposed upon the polymeric sorbent.     

自交联丙烯酸酯乳液粘合剂的合成

作为粘合剂的丙烯酸酯中引入自交联单体如N－羟甲基丙烯酰胺及醚,可提高胶粘剂的性能,如耐磨牢度、耐水、耐寒性和改善柔软性。     

Fiber‐reinforced nanopigmented poly(methyl methacrylate) as improved denture base

Nanopigmented and fiber‐reinforced poly (methyl methacrylate) (PMMA) were synthesized for denture bases, by incorporating E‐glass fibers, flock fibers, or polyethylene fibers into the PMMA powder formulation to improve the flexural behavior and porosity; decreasing the Candida albicans adherence and being noncytotoxic. The commercial acrylic resin, Lucitone 199 was used as a control group. Scanning electron microscopy analysis was performed to the PMMA particles and the reinforcing fibers. Flexural strength increased by adding E‐glass fibers in the PMMA powder as compared to flock and polyethylene fibers. The reinforced PMMA with flock fibers showed the lower porosity even smaller than Lucitone 199. The synthesized PMMA and the fiber reinforced nanopigmented PMMA groups reduced significantly the C. albicans adherence when compared to the commercial acrylic resin. All the tested groups were found to be nontoxic materials after being in contact with mouse fibroblast culture during 24 h, showing that these novel nanostructured composites are suitable for producing adequate and nontoxic reinforced materials with antimicrobial properties for dentistry applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of hot-etching treatment on shear bond strength of zirconia to resin cement

ABSTRACT

The purpose of this study was to evaluate the effect of hot-etching surface treatment on the shear bond strength between zirconia ceramics and resin cement. Ceramic cylinders were divided randomly into 10 groups (n?=?10) according to different surface treatments (blank control; airborne particle abrasion; hot-etching for 10?min; hot-etching for 30?min; hot-etching for 60?min) and whether or not performed thermal cycling fatigue test. Flat enamel surfaces, were prepared from human permanent incisors and were bonded to the zirconia discs. All specimens were subjected to shear bond strength test by a universal testing machine. All data were statistically analysed using one-way analysis of variance and multiple comparison least significant difference tests (α?=?0.05). Hot-etching for 60?min treatment produced higher bond strengths than the other treatment. Surface treatment of zirconia with a hot-etching solution might enhance surface roughness and bond strength between zirconia and resin cement.     

Radiation grafting of methyl methacrylate monomer on natural rubber latex

A method of radiation grafting of methyl methacrylate (MMA) monomer on natural rubber (NR) latex has been studied. The irradiation dose in radiation emulsion polymerization of MMA monomer was lower compared to the irradiation dose for grafting of MMA monomer on NR latex, in order to obtain the same degree of conversion. This is due to the size of the rubber particles which are quite large and, hence, not sufficient to ensure an ideal emulsion polymerization. The irradiation dose for radiation grafting of MMA monomer on latex was around 300 krad to obtain a 75% degree of conversion. However, this irradiation dose was lower compared to the irradation dose for bulk polymerization of MMA monomer, in order to obtain the same degree of conversion. This is due to the gel effect in the viscous media. Radiation grafting of MMA monomer on NR latex does not influence the pH of the latex, but influences the viscosity significantly. The viscosity of the NR latex increased with an increase in irradiation dose, due to the increase of the total solid content in the latex. The MMA monomer converted to P-MMA in NR latex was largely grafted on the NR, or at least insoluble in a solvent for P-MMA, such as acetone or toluene. The hardness of the pure gum vulcanizate with an increase in the degree of grafting or P-MMA content, but the other physical properties, such as tensile strength, modulus, elongation at break, and thermal stability, were not greatly influenced by the degree of grafting.     

Effect of free monomer content on the drawing behavior of poly(methyl methacrylate)

Cold drawing has been used to produce oriented samples of various molecular weight grades of poly(methyl methacrylate), all of which exhibited marked strain hardening characteristics over a range of drawing temperatures. The differences between the yield and drawing behavior of the grades did not correlate with molecular weight but could instead be attributed to the plasticizing effect of additional free monomer, generated by degradation during melt processing of the polymer.     

Evaluation of thermal conductivity and esthetic quality of denture base resin composites with acrylic polymer and nanodiamonds

The effect on the thermal conductivity and esthetic quality of acrylic denture base resins due to the addition of surface-carboxylated nanodiamonds (NDs) was evaluated using direct heat flux measurement and spectrophotometric measurement, respectively. The addition of NDs to the denture resin improved its thermal conductivity, which was highly depended on the ND content. The thermal conductivity increased significantly upon the addition of a small amount of NDs, followed by a gradual decrease with increasing ND content. The influence of the ND content on the thermal conductivity of the ND-impregnated resins was explained via experimental results and the theory of phonon scattering. Furthermore, changes in the appearance of the denture base resins caused by ND impregnation were observed to assess their esthetic qualities. The color changes in the resins with low ND contents were found to be minor. Therefore, the improved thermal conductivity and the retention of appearance of the resin can be simultaneously achieved by the addition of a small amount of NDs.     

Microtensile bond strength testing of resin cements

To investigate the microtensile bond strength (μTBS) and failure mode of resin cements bonded to ceramic blocks following various surface treatments.Seventy-two Ceramco II (Ceramco lnc., Burlington, NJ) ceramic discs 10 mm in diameter and 4 mm thick were prepared. The ceramic specimens received 8 different surface conditions treatments before the application of resin cement. These surface treatments were sanding with 600-grit silicon carbide paper, microetching with aluminum oxide, sanding followed by silane application, microetching followed by silane application, hydrofluoric acid etching, hydrofluoric acid etching followed by silane application, application of adhesive resin, and combination of the previous two treatments (HF+S+Adh). Seventy-two extracted molars were ground flat at 90° to the long axis of the tooth until a sufficient circular area of dentin was exposed (at least 5 mm in diameter). Three resin cements were applied to these surfaces. After 24 h storage at 37 °C, the non-trimming version of μTBS test was used to produce 1 mm² microbars. The microbars were subjected to a tensile load using a modified testing device.Data were analyzed with 2-way analysis of variance. The interaction between the substrate surface treatment and cement type is significant (p<0.001).The results of this in vitro study suggest that when the tested ceramic restoration is cemented with a resin cement system, the ceramic should be etched with hydrofluoric acid, silane and adhesive should be applied prior to cementation. The results also suggest that an auto- or light-polymerizing cement should be considered instead of a dual-polymerizing cement.     

Heat treatment of silanized feldspathic ceramic: Effect on the bond strength to resin after thermocycling

PurposeThis study aimed to evaluate the effect of heat treatment (at 77 °C) of a silanized feldspathic ceramic on microtensile bond strength (μTBS) with a resin cement before and after being aged by thermocycling.Material and methodsTwenty-four blocks (12×10×4 mm³) of a CAD/CAM feldspathic ceramic (Vitablocks Mark II, Vita) were obtained and randomly divided into three groups, according to the surface treatment prior to the cementation: Group AS – hydrofluoric acid 10%+silane; Group S77 – silane+heating at 77 °C for 60 s; and Group AS77 – hydrofluoric acid 10%+silane+heating at 77 °C for 60 s. Ceramic blocks were cemented to composite resin blocks with a resin cement. The sets were subsequently cross-sectioned into 1 mm² beams for μTBS testing. The beams of each group were randomly divided into two subgroups: aging (thermocycling, 12,000 cycles between 5 °C and 55 °C) and non-aging (tested immediately). One-way ANOVA and Tukey's test (α=0.05) and Weibull analysis (95% CI) were used to analyze the data.ResultsGroup AS77 had the lowest pre-test failure number during the cutting among the groups. There was no significant difference (p=0.255) between the μTBS mean values of the non-aged groups. After aging, the mean value of S77 was significantly lower than those of AS77 and AS (p=0.005). There was no difference in the Weibull modulus (m) and characteristic strength (σ₀) of the aged and non-aged groups for all comparisons. Before aging, heat treatment of silanized feldspathic ceramic (non acid-etched surface) demonstrated bond strength similar to that achieved with hydrofluoric-acid-etching treatment however, it had lower bond strength after aging.ConclusionThe combination of hydrofluoric-acid-etching treatment with heat treatment silanized feldspathic ceramic did not improve the bond strength of the interface.     

w(MMA)对MMA乳液聚合成核的影响

以甲基丙烯酸甲酯(MMA)为单体,在c(乳化剂)=2mmol/L下制备乳液,研究不同w(MMA)对MMA乳液聚合成核的影响,并分析了不同w(MMA)对乳胶粒粒径的影响规律。实验结果表明:当w(MMA)≤10%,随着w(MMA)的增加转化率逐渐增大,乳胶粒的生成速率也逐渐增大;当w(MMA)≥10%时,转化率可以达到70%以上,w(MMA)对乳胶粒的生成速率的影响不大,多余的单体用于乳胶粒粒径的增长;在w(MMA)=10%时基本能够满足c(乳化剂)=2mmol/L时的成核要求。当5%≤w(MMA)≤30%,在乳化剂的自调节作用下,使得最终形成的乳胶粒数目相差不大。     

Effect of acrylic acid and hydroxyethyl methacrylate modified nano-SiO2 particles on poly(methyl methacrylate-hydroxyethyl methacrylate) soap-free emulsion polymerization

Nano-SiO₂ powder was modified with acrylic acid (AA) and hydroxyethyl methacrylate (HEMA), respectively. The kinetics of the soap-free emulsion polymerization of methyl methacrylate (MMA) and HEMA in the presence of unmodified or modified nano-SiO₂ particles was investigated. The structure of the nano-SiO₂ particles and the Poly(MMA-HEMA) composite emulsion was characterized by Fourier transform infrared spectroscope (FT-IR). The particle size and size distribution of the emulsion, the morphology of emulsion particle, the surface tension, and ionic conductivity of these systems before and after polymerization were determined. The IR spectra showed that the organic modifiers were incorporated onto the surface of the nano-particles. In addition, the solid content and monomer conversion of the Poly(MMA-HEMA) composite emulsion with modified nano-SiO₂ are higher than that with original inorganic particles. The particle size became smaller and the particle distribution narrowed after applying the modified nano-SiO₂ particles. The SEM observation demonstrated that the shapes of these emulsion particles were uniform sphere. The surface tension and ionic conductivity increased significantly after polymerization.     

Synthesis of new imidazole-based monomer and copolymerization studies with methyl methacrylate

In this study, copolymers were synthesized using methyl methacrylate (MMA) and 2-allyloxymethyl-1-methylimidazole (AOMMI) monomers at various ratios. For this purpose, hydroxyl end-functionalized imidazole was initially prepared with 1-methylimidazole and then it was used to prepare allyl-derived imidazole monomers. Finally, the synthesis of copolymers (poly(MMA-co-AOMMI)) was carried out using different proportions of commercial MMA and AOMMI monomers. Photopolymerization method was preferred as polymerization technique. The polymerization was carried out in solvent-free medium and benzophenone was used as the initiator. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR) and elemental analysis were used for the structural characterization of the obtained copolymers. Molecular weights and the thermal behaviour of the synthesized copolymers were analysed with gel permeation chromatography (GPC) and thermogravimetry (TG) techniques, respectively. The surface of the products was tried to be illuminated using scanning electron microscopy (SEM). According to the obtained FTIR, NMR and elemental analysis results, the copolymers were successfully synthesized. A number average molecular weights of poly(MMA-co-AOMMI) samples were found 13,500 (MMA:2/AOMMI:1), 16,600 (MMA:1/AOMMI:2) and 17,300 (MMA:1/AOMMI:1) according to the mixing ratios. When the thermal stabilities of the synthesized copolymers were observed, it has been seen that those containing imidazole had higher stability than the neat PMMA.     

Graft copolymerization of acrylonitrile and methyl methacrylate monomer mixtures on crumb natural rubber

Graft copolymerization of mixtures of acrylonitrile and methyl methacylate on crumb natural rubber was carried out in toluene at 60°C. The nitrogen content of the grafted copolymer was determined by elemental analysis and used to estimate the composition of the copolymer samples. It was found that the amount of acrylonitrile monomeric units incorporated into the polymer was disproportionately lower than the acylonitrile content of the feed and explanations in terms of the e‐value of the monomers and the inherent heterogenous nature of the polymerization mixture were offered. The miscibility of the natural rubber‐g‐polyacrylonitrile‐co‐poly(methyl methacrylate) with poly(vinyl chloride) was studied by viscometry, differential scanning calorimetry, and phase contrast microscopy. It was found that the natural rubber‐g‐polyacrylonitrile‐co‐poly(methyl methacrylate) formed semimiscible blends with poly(vinyl chloride). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1872–1877, 2002; DOI 10.1002/app.10474     

Effect of metallic flask closure and investment materials on the stability of the denture base resin

This study evaluated the dimensional stability of the poly‐methylmethacrylate (PMMA) denture bases under the effect of different metallic flask closure techniques (FCT) and investment materials (IM). Sixty stone cast maxillary‐wax base plate sets were randomly assigned to six groups (n = 10) for the following treatments: 1 and 4—stone or silicone investments and flask closure with clamp; 2 and 5—stone or silicone investments and flask closure with RS system; 3 and 6—stone or silicone investments and flask closure with screws. PMMA denture bases were polymerized in a water bath at 74°C for 9 h. PMMA base‐stone cast sets were sectioned at regions (R) of the canines, first molars, and posterior palatal zone. Gap discrepancies were measured at five points: right and left ridge crests, palatal midline, and right and left marginal limits of the flanges. An optical micrometer with accuracy of 0.0005 mm was used for measurement purposes. Data were submitted to ANOVA and Tukey's test (α = 0.05). Silicone showed an adaptation mean (0.177 mm) significantly different when compared with stone (0.207 mm). The RS system presented a statistically different adaptation mean (0.166 mm) in relation to the traditional clamp (0.200 mm) and flask with screws (0.211 mm). Adaptation values for the regions of the canines (0.141 mm), first molars (0.185 mm), and posterior palatal (0.250 mm) were statistically different. For all flask closure techniques, better adaptation was shown with the RS system and silicone investment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of residual monomer content on some properties of a poly(methyl methacrylate)-based bone cement

Through this article, the degree of polymerization attainable in a commercial acrylic bone cement based on poly(methyl methacrylate) (PMMA) was investigated by differential scanning calorimetry (DSC) and gas chromatography (GC). The results obtained revealed a marked dependence between the maximum monomer conversion and the cure temperature. Specimens for the mechanical evaluation of the cement were subjected to two different cure conditions: one set of samples was allowed to cure at room temperature and an additional set was also postcured at 140°C for 2 h. The latter thermal treatment permitted one to discard the presence of the unreacted monomer in the hardened material. The effect of the unreacted monomer on the mechanical behavior was evaluated by measuring the flexural modulus (E), the compressive yield stress (σ_y), and the fracture toughness (K_IC). Samples prepared at room temperature for mechanical evaluation contained residual monomer which acts as a plasticizer of the matrix, increasing K_IC and decreasing E and σ_y. The cure temperature and mold di-mensions influence the amount of the residual monomer in the hardened material. Thus, differences in the values of the mechanical properties measured for the same commercial formulation may be attributed to a different mold dimension used in the test. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1367–1383, 1998