Acrylic Discs Research Articles

Complete dechlorination of pentachlorophenol using palladized bacterial cellulose in a rotating catalyst contact reactor

A rotating catalyst contact reactor (RCCR) was developed which consisted of palladized bacterial cellulose immobilized on acrylic discs for hydrodechlorination of pentachlorophenol (PCP). More than 99% of 40 mg L −1 PCP was dechlorinated to phenol in the presence of hydrogen in batch mode at initial pH values of 5.5 and 6.5 within 2 h of reaction with stoichiometric release of free chloride. The rate of PCP dechlorination was found to be independent of rotational speed of discs. PCP (40 mg L −1) hydrodechlorination experiments were also conducted using RCCR in continuous flow mode at hydraulic retention times of 1 and 2 h. The average outlet PCP concentrations revealed that liquid phase in RCCR closely resembled that of a continuous flow complete mix reactor (CFMR). Approximately 12 and 11 L of 40 mg L −1 PCP (pH 6.5) could be treated in RCCR with 99 and 80% efficiencies in batch and continuous flow modes, respectively without any appreciable loss of the catalytic activity. These results suggested reusability of palladized bacterial cellulose which in turn is expected to substantially reduce the cost of treatment process. Thus RCCR seems to have high potential for treatment of ground water contaminated with chlorinated organic compounds. Dried palladized bacterial cellulose has been used as a material for electrodes in a fuel cell. However, its application as a hydrodechlorination catalyst in a reactor operating under room temperature and atmospheric pressure has not been reported to the best of our knowledge. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analyses suggested the irreversible deposition of palladium (Pd 0) particles on the bacterial cellulose fibrils.

In vitro candidacidal activity of a synthetic killer decapeptide (KP) against Candida albicans cells adhered to resin acrylic discs

Oral Candida spp., and C. albicans in particular, are considered as important aetiological agents in the pathogenesis of denture-induced stomatitis. Several studies have reported that C. albicans is able to easily adhere to different medical devices, such as vascular and urinary catheters or acrylic denture surfaces, and that adhesion is a fundamental step in the initial pathogenic process of colonization and further possible infection. Recently, a synthetic decapeptide (KP) derived from the sequence of a single-chain recombinant anti-idiotypic antibody, acting as a functional internal image of a microbicidal, broad spectrum yeast killer toxin, has been reported to kill in vitro C. albicans cells and to exert a therapeutic activity against experimental mucosal and systemic candidiasis. The aim of this study was to evaluate, through a CFU assay, the candidacidal activity of KP on sanded acrylic resin discs, previously colonized by C. albicans cells. At 100 microg/ml KP showed over 90% of killing activity on C. albicans cells adhered to resin discs, when compared with a scramble peptide used as control. The results of this study suggest a potential effect of KP on C. albicans cells adhered on the surface of resin materials, such as prosthetic dentures.

Noncontact transportation in water using ultrasonic traveling waves

A noncontact transport experiment in water using ultrasonic traveling waves was investigated. Acrylic, aluminum, and brass discs were used as test objects. Traveling waves were generated using two ultrasonic transducers attached at the ends of a vibrating plate. One side was used as the wave-source side and the other side was used as the wave-receiving side. Acrylic plates cemented to the sides of the vibrating plate formed a tank to hold water. Object transportation was accomplished by adding a small amount of water to the vibrating structure. The transport velocity of floating objects in water is faster than for floating transport in air because of buoyancy. The transport velocity of an object depends on water height. The minimum value of the velocity occurs when the disc thickness is equal to the water height. The transport velocity increases as the height of water increases. For very shallow depths, the largest velocity is obtained when cavitation-induced streaming occurs.

Removable acrylic resin disk as a sampling system for the study of denture biofilms in vivo

The adhesion of microorganisms to a denture surface can result in denture stomatitis. The purpose of this study was to evaluate denture biofilm in vivo using a new sampling system to gain a better understanding of plaque organization in Candida-induced denture stomatitis. Removable acrylic resin disks were used with self-adhesive paper disks to compare biofilm formation and retention efficacy of both sampling systems. Twenty-one subjects with a complete maxillary denture were recruited, 12 with a clinical diagnosis of chronic denture stomatitis and 9 with a clinically healthy palatal mucosa. A custom-made autopolymerized 3.0-mm-diameter acrylic resin disk inlay was inserted in a cavity prepared within the intaglio surface of the maxillary denture in contact with either normal or inflamed mucosa. Next to the acrylic resin disk, a self-adhesive paper disk was placed for comparison of the 2 sampling techniques. Denture biofilms were collected within variable time periods of 1 hour to several months, and descriptive data were provided by means of scanning electron microscopy analyses. The method of retention and recovery of specimen disks were evaluated between both sampling techniques using a chi-square test to assess significant differences (alpha=.05). Early event features of denture biofilms showed differences in biofilm organization between the 2 sampling techniques but became subtler with increased time periods. Regardless of the sampling technique, interparticipant variations could be observed as to rate, microorganism density, and architectural pattern. In general, denture biofilm formation was increased when the sampling disks were localized in areas affected by denture stomatitis. The new sampling technique provides reliable information with controlled formation time of denture biofilm in its natural environment.

Effects of Mica and Glass on Surface Hardness of Acrylic Tooth Material

The purpose of this study was to evaluate the effects of four different ratios of silanized mica filler and milled glass fiber on the surface hardness of an acrylic denture tooth material. Acrylic resin disks made of polymethyl methacrylate (PMMA) used in fabrication of denture teeth were used as the control group. Eight test groups were prepared by adding a ratio of 5%, 10%, 15%, or 20% by weight of silane-treated mica filler or milled glass fibers to the PMMA resin of denture teeth. Surface hardness test was performed for each group. There were statistically significant differences in surface hardness between the control group and 5%, 10%, and 15% mica- and glass-containing test groups (p<0.05). It was determined that addition of 5%, 10%, and 15% of silane-treated mica filler or silane-treated milled glass fiber to the PMMA resin of denture teeth resulted in significantly improved surface hardness.

The effect of two fibre impregnation methods on the cytotoxicity of a glass and carbon fibre‐reinforced acrylic resin denture base material on oral epithelial cells and fibroblasts

Acrylic resin dentures may have cytotoxic effects on oral soft tissues. However, there is sparse data about the cytotoxic effect of fibre-reinforced acrylic resin denture base materials. The purpose of this in vitro study was to determine the effect of two fibre impregnation methods on the cytotoxicity of a glass and carbon fibre-reinforced heat-polymerized acrylic resin denture base material on oral epithelial cells and fibroblasts. One hundred acrylic resin discs were assigned to five experimental groups (n = 20). One of the groups did not include any fibre. Two groups consisted of silane and monomer treated glass fibres (Vetrolex) impregnated into acrylic resin (QC-20) discs. The other two groups consisted of silane and monomer treated carbon fibres (Type Tenox J, HTA). Untreated cell culture was used as positive control. The human oral epithelial cell line and buccal fibroblast cultures were exposed to test specimens. The cytotoxicity of the test materials was determined by succinic dehydrogenase activity (MTT method) after 24 and 72 h exposures. Data were analysed with a statistical software program (SPSSFW, 9.0). A one-way analysis of variance (anova) test and Bonferroni test were used for the comparisons between the groups. All statistical tests were performed at the 0.95 confidence level (P < 0.05). After 24 and 72 h incubation, cell viability percentages of all experimental groups showed significant decrease according to the positive control cell culture. Fibroblastic cell viability percentages of silane and monomer treated fibre-reinforced groups were lower than the unreinforced group. Cell viability of monomer-treated groups displayed the lowest percentages. Elapsed incubation time decreased epithelial cell viability in silane-treated groups. Fibroblastic cell viability was not influenced by elapsed time except the unreinforced group.

TH‐E‐330A‐02: A Local Fourier Description of Artifacts in Circular Cone Beam Computed Tomography

Purpose: Circular cone‐beam computed tomography is challenged by a lack of plane sums resulting in incomplete inversion of the radon transform. These missing plane sums have been identified by theory, and may be represented as a shift‐variant cone of missing frequencies in the Fourier domain. The aim was to verify the presence of this cone in real data, and to show the dependency of resulting image artifacts on the frequency distribution of the imaged object. Method and Materials: A mini disk phantom (mylar/foam) was constructed to probe the local frequency response at various locations in the reconstruction space. Projections obtained using an experimental CBCT benchtop were reconstructed with 120 μm3 voxel size using a modified Feldkamp filtered backprojection routine. Local Fourier transforms of the mini disks were analyzed for missing frequency data and compared with theory. Large disk phantoms of acrylic and cellular polyurethane were also imaged for further demonstration of the effect of varying the frequency content of the imaged object. Results: The cone of missing frequency was successfully identified in the mini disk phantom and agreed well with theory. Image artifact was found to have dependency on the local distribution of the object's frequency power spectrum relative to the cone of missing frequency information. Decreased resolution of the disks occurred when their dominant spatial frequency components were directionally aligned to coincide with the predicted null cone, as expected. Image reconstructions of large disk phantoms showed good detail in cellular disks even at locations that showed strong artifacts in the acrylic disk. Conclusion: The predicted null cone is observable in Fourier transforms of localized objects. Resolution in reconstruction is dependent on the relative frequency distribution of the imaged object; features that are most poorly resolved will be those with strong frequency components directed in the expected null space.

In vitro antiseptic properties of an ammonium compound combined with denture base acrylic resin

Denture base acrylic resin is easily colonised by oral endogenous bacteria and Candida spp., and eventually by extra-oral species such as Staphylococcus spp., Pseudomonadaceae or members of Enterobacteriaceae. This microbial reservoir can be responsive for denture related stomatitis and aspiration pneumonia, a life-threatening infection especially in geriatric patients. However, the oral and denture hygiene of dependent elderly individuals is extremely poor. This in vitro study aimed to determine the per cent of a quaternary ammonium compound heat-polymerised in acrylic resin necessary to obtain denture base displaying antiseptic properties. Acrylic resin discs containing 2-50% ammonium polymer (Poly 202063A; 0% control) were soaked in artificial saliva for 4 weeks. Resin discs were incubated for 24 hours with Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa [37 degrees C, brain-heart infusion (BHI) broth and phosphate-buffered saline (PBS) buffer] and Candida albicans (30 degrees C, Schaedler broth), in 15 ml (168 discs) and 600 microl (168 discs) of inoculum. Microbial growth was verified at t 0 hours and t 24 hours. Data were recorded as the mean of three colony forming unit (CFU) numerations. The borderline of antimicrobial effect was determined at 0.1% viable cells. In 600 microl of PBS inoculum, resin specimens had a bactericidal effect (E. coli and S. aureus: 2%; P. aeruginosa: 10%) and a fungicidal effect (C. albicans: 50%). Long-term stability and toxicity in vivo studies are now required. A 2% quaternary ammonium compound polymerised with a denture acrylic resin displayed antiseptic properties after a 4-week soaking period in artificial saliva. Such antiseptic denture base could help geriatric patients to improve their oral health.

Effect of Mica and Glass on Acrylic Teeth Material's Color

The purpose of this study was to evaluate the effect of two different ratios of silanized mica filler and milled glass fiber reinforcement on the color of acrylic denture teeth materials. Ten acrylic resin discs made of acrylic denture teeth material (PMMA) obtained from the manufacturer were used as the control group. Four experimental groups were modified from the control group's PMMA material by adding a ratio of 5% or 10% by weight of silane-treated mica filler or milled glass fibers. Each group consisted of 10 specimens. Measurements were performed using a spectrophotometer CM-2600d, and the color changes were characterized in the Commission Internationale d'Eclairage L*a*b* color space. deltaE* values of 5% mica-, 10% mica-, 5% glass-, and 10% glass-containing sample groups were 2.46, 3.03, 2.16, and 2.59 respectively. There were statistically significant differences in L*, a*, and b* values between the control group and each test group. It was shown that when PMMA denture teeth material was modified with silane-treated mica filler or silane-treated milled glass fibers for the purpose of reinforcement, it would also cause significant changes to the original color of the material.

Development and application of methods for determination of residual monomer in dental acrylic resins using high performance liquid chromatography

Two high-performance liquid chromatographic methods for determination of residual monomer in dental acrylic resins are described. Monomers were detected by their UV absorbance at 230 nm, on a Nucleosil C18 (5 microm particle size, 100 A pore size, 15 x 0.46 cm i.d.) column. The separation was performed using acetonitrile-water (55:45 v/v) containing 0.01% triethylamine (TEA) for methyl methacrylate and butyl methacrylate, and acetonitrile-water (60:40 v/v) containing 0.01% TEA for isobutyl methacrylate and 1,6-hexanediol dimethacrylate as mobile phases, at a flow rate of 0.8 mL/min. Good linear relationships were obtained in the concentration range 5.0-80.0 microg/mL for methyl methacrylate, 10.0-160.0 microg/mL for butyl methacrylate, 50.0-500.0 microg/mL for isobutyl methacrylate and 2.5-180.0 microg/mL for 1,6-hexanediol dimethacrylate. Adequate assay for intra- and inter-day precision and accuracy was observed during the validation process. An extraction procedure to remove residual monomer from the acrylic resins was also established. Residual monomer was obtained from broken specimens of acrylic disks using methanol as extraction solvent for 2 h in an ice-bath. The developed methods and the extraction procedure were applied to dental acrylic resins, tested with or without post-polymerization treatments, and proved to be accurate and precise for the determination of residual monomer content of the materials evaluated.

A noncontact transportation in water using ultrasonic traveling waves

A noncontact transport experiment in water using a traveling‐wave‐type linear motor was investigated. Acrylic disks were used as the floating objects. A vibrating plate was enclosed in acrylic plates, and a water tank was made that would allow the vibrating plate to be placed on the bottom. In order to propagate the traveling wave, two ultrasonic transducers were attached at both ends to the bottom of the vibrating plate. One side was used as the wave‐sending side and the other side was used as the wave‐receiving side. Comparing the transport experiments conducted in water with those conducted in air, the transport velocity becomes faster for floating transport in water than for floating transport in air. The occurrence of cavitation bubbles acts as a resistive force on the movement of the object being transported, and causes the transport velocity to be reduced. Transport velocity depends on the height of the water. If the height of the water surface is too shallow, the water surface freely deforms and the water surface forms bumpy standing waves, making it difficult for the object to be transported.

Evaluating radiographic parameters for mobile chest computed radiography: Phantoms, image quality and effective dose

Conventional chest radiography is technically difficult because of wide variations in tissue attenuations in the chest and limitations of screen-film systems. Mobile chest radiography, performed bedside on hospital inpatients, presents additional difficulties due to geometric and equipment limitations inherent in mobile x-ray procedures and the severity of illness in the patients. Computed radiography (CR) offers a different approach for mobile chest radiography by utilizing a photostimulable phosphor. Photostimulable phosphors overcome some image quality limitations of mobile chest imaging, particularly because of the inherent latitude. Because they are more efficient in absorbing lower-energy x-rays than rare-earth intensifying screens, this study evaluated changes in kVp for improving mobile chest CR. Three commercially available systems were tested, with the goal of implementing the findings clinically. Exposure conditions (kVp and grid use) were assessed with two acrylic-and-aluminum chest phantoms which simulated x-ray attenuation for average-sized and large-sized adult chests. These phantoms contained regions representing the lungs, heart and subdiaphragm to allow proper CR processing. Signal-to-noise ratio (SNR) measurements using different techniques were obtained for acrylic and aluminum disks (1.9 cm diameter) superimposed in the lung and heart regions of the phantoms, where the disk thicknesses (contrast) were determined from disk visibility. Effective doses to the phantoms were also measured for these techniques. The results indicated that using an 8:1, 33 lines/cm antiscatter grid improved the SNR by 60-300 % compared with nongrid images, depending on phantom and region; however, the dose to the phantom also increased by 400-600%. Lowering x-ray tube potential from 80 to 60 kVp improved the SNR by 30-40%, with a corresponding increase in phantom dose of 40-50%. Increasing the potential from 80 to 100 kVp reduced both the SNR and the phantom dose by approximately 10%. The most promising changes in technique for trial in clinical implementation include using an antiscatter grid, especially for large patients, and potentially increasing kVp.

A novel rodent mammary window of orthotopic breast cancer for intravital microscopy

Orthotopic and ectopic organ environments differentially influence tumor growth, metastasis, and sensitivity to therapy. In this study we present a novel rodent mammary window of orthotopic breast cancer, which is amenable to study of microvascular function and angiogenesis in this orthotopic site. The skin around the nipple of selected mammary glands of female Fischer 344 rats was removed and the nipple was cut at its base. R3230Ac tumor fragments or cells in Gelfoam were aseptically implanted into the nipple sinus. An acrylic disk was placed on top of the implant and was sutured in place. Histology showed that tumors were well established within 5 days. Similar techniques were also applied to BALB/c mice transplanted with 4T1 murine mammary carcinoma cells. With GFP-expressing tumor cells and serial observations, we demonstrated unique patterns of tumor cell proliferation and vascularization in both tumor models. The images obtained were comparable to those from the dorsal skinfold window chambers. This model will allow for study of tumor microcirculatory function, angiogenesis, tumor cell–host interactions, and evaluation of effects of various treatments.

412 超音波振動面近傍で浮揚するアクリル円板の保持力

412 超音波振動面近傍で浮揚するアクリル円板の保持力

1/f Fluctuation and a Many-Body Disk Model of Slip Phenomena

A many-body disk system was investigated as a model of slip phenomena. A two-dimensional many-body disk system was used as a model of the boundary layer between slip surfaces. Frustrated states occurred in this system depending on the disk configuration. Experiments with this were carried out using a random packing configuration (packing fraction: 0.74 ∼0.76). Acrylic resin disks were packed between a co-axial outer rotating cylinder and an inner fixed cylinder. The outer cylinder was rotated by a motor and the torque at the fixed inner cylinder was measured in a time series. Stick-slip and 1/ f fluctuation were observed in the time series.

Development of a scattering probability method for accurate vapor fraction measurements by neutron radiography

Recent test results indicated drawbacks associated with the simple exponential attenuation method (SEAM) as currently applied to neutron radiography measurements to determine vapor fractions in a hydrogenous two-phase flow in a metallic conduit. The scattering component of the neutron beam intensity exiting the flow system is not adequately accounted for by SEAM, and this leads to inaccurate results. To properly account for the scattering effect, a neutron scattering probability method (SPM) is developed. The method applies a neutron-hydrogen scattering kernel to scattered thermal neutrons that leave the incident beam in narrow conduits but eventually show up elsewhere in the measurements. The SPM has been tested with known vapor (void) distributions within an acrylic disk and a water/vapor channel. The vapor (void) fractions deduced by SPM are in good agreement with the known exact values. Details of the scattering correction method and the test results are discussed.

Comparison of chemical analysis of residual monomer in a chemical-cured dental acrylic material to an FTIR method

Objective The purpose of this work was to perform quantitative analysis of residual monomer in chemical-cured acrylic using an infrared spectroscopic method and to compare it to an accepted form of quantitative chemical analysis. Identical samples of acrylic were analyzed and compared using Fourier transform infrared (FTIR) spectroscopy with multiple standard additions vs. “wet” chemical analysis of bromination followed by titration. Methods Two 6 g disks from a single mix of cold-cured acrylic (Lang Dental Mfg. Co., Inc.) were prepared and cured in room air for 1 hr using a ratio of 12 g of powder to 8 mL of liquid. One of the cold-cured acrylic disks was dissolved in glacial acetic acid and analyzed according to the “wet” technique described by Smith and Bains (Smith and Bains,1956). The other disk was dissolved in methyl isobutyrate (MIBT). Five aliquots, zero plus four incremental additions of pure methyl methacrylate (MMA), were prepared from the MIBT solution. Absorption spectra were collected for all five aliquots. The data were plotted with the ratio of the mass of methyl methacrylate added to the mass of aliquot of MIBT solution as the independent variable, and the absorption, corrected for dilution, as the dependent variable. Least squares fit of the data yielded the slope and intercept. The ratio of intercept to slope divided by the weight fraction of the acrylic disk dissolved in MIBT yielded the concentration of methyl methacrylate in the disk. Results The plot of absorbance as a function of mass ratio of MMA added to MIBT solution was linear over the concentration range covered (r = 0.999). Analysis of the spectroscopic data revealed a concentration of residual C=C double bonds of 0.32 ± 0.01 mol/kg. “Wet” chemical analysis of the acrylic yielded a concentration of residual C=C double bonds of 0.288 ± 0.003 mol/kg. There was significant difference (students Mest, 99% confidence level) between the two techniques with respect to the amount of residual monomer calculated. Significance The multiple standard additions technique works well for the quantitative analysis of small amounts of residual double bonds in the poly(methyl methacrylate) chemical-cured acrylic polymer system, eliminating the need for an internal standard or external calibration.

Persistence of bacteria on antibiotic loaded acrylic depots. A reason for caution.

Bacterial growth on the surface of antibiotic loaded acrylic cement was examined in an in vitro model. Tobramycin or vancomycin impregnated discs were incubated in broth containing either Staphylococcus epidermidis or Staphylococcus aureus organisms. At 24, 48, and 96 hours, the broth and the surface of the acrylic discs were examined for viable organisms. In the broth, only 6% (8 of 136) of samples contained viable organisms at 24 hours, and all samples were sterile by 96 hours. This is in contrast to the surface of the discs, which revealed the presence of viable organisms at all study time periods. Growth was noted in 99% and 30% of the Staphylococcus epidermidis and Staphylococcus aureus discs, respectively, at 24 hours. Viable organisms were found on both types of discs through 96 hours (20% of Staphylococcus epidermidis and 15% of Staphylococcus aureus). The surface of bone cement is therefore a suitable substrate for bacterial growth, even in the presence of antibiotics. In clinical practice, antibiotic loaded acrylic cement should therefore be used with caution and clear indications.

Velocity and amplitude of P-waves transmitted through fractured zones composed of multiple thin low-velocity layers

Fractured zones and faults in rock masses influence the velocity and amplitude of P-waves propagated through them. In the frequency range of seismic exploration, wavelengths of P-waves are comparable to or longer than the thickness of fractures or faults. Fractures can be modeled as thin low-velocity layers in homogeneous high velocity material. We carried out model experiments on P-wave propagation through a low-velocity zone composed of many thin low-velocity layers, with the direction of P-wave propagation normal to the layers. The experimental models were made of aluminum rods and acrylic resin disks: they correspond, respectively, to rock and materials filling fractures such as clay. Next, we numerically simulated one-dimensional wave propagation through the low-velocity zone by using the communication matrix method. Waveforms obtained by this model calculation show good agreement with those obtained by the model experiments. The waveform and the amplitude of the transmitted P-waves vary with the number and the thickness of low-velocity layers. The time-average equation does not provide a good velocity estimation, because the velocity decreases with the increase in the number of low-velocity layers in spite that the total thickness of layers remaining the same. The distribution of low-velocity layers has little effect on velocity and waveform. Effects of low-velocity zones on waveform, amplitude and velocity of the transmitted P-wave vary with frequency of the incident P-wave. We concluded that the wave transmitted through the low-velocity zone was formed by the superposition of the direct wave and the many waves having multiple reflections at the interfaces of the layers in their path.

Retentive ability of various denture adhesive materials: An in vitro study

This in vitro investigation of the retentive ability of various commercially available denture adhesives was performed by measuring the adhesion and cohesion that developed between a glass surface and an acrylic resin disk surface when some liquids, adhesive materials, or both were placed between them. Student's paired t-test, repeated measures, and two-factor design analysis of variance were performed to determine the significance among mean values. The adhesive materials studied exhibited a significantly greater retentive ability than that of saliva, and their retentive ability increased significantly when they were used in combination with artificial saliva. Highly significant differences of the retentive ability among the different brands of denture adhesives were observed.