Long-term microwaving of denture base materials: effects on dimensional, color and translucency stability.

INTRODUCTION: While the combined effect of microwave irradiation with cleansing solutions on denture base materials has been investigated, the effects of only using microwave irradiation and, more importantly, in a long-term basis, was not studied yet. OBJECTIVE: The purpose of this study was to evaluate the effect of a long-term repeated microwaving on the dimensional, color and translucency stability of acrylic and polyamide denture base materials. MATERIAL AND METHODS: Thirty two specimens (32 mm x 10 mm x 2.5 mm) from polyamide (Valplast) and PMMA (Vertex Rapid Simplified) denture base materials were made. Eight specimens from each material were immersed in distilled water (control) and 8 were subjected to microwave exposure at 450 W for 3 minutes for a period simulating 224 days of daily disinfection. Linear dimension, color change (ΔE*) and translucency parameter (TP) were measured at baseline and after certain intervals up to 224 cycles of immersion, using a digital calliper and a portable colorimeter. The results were analysed using two-way repeated measures ANOVA to estimate possible differences among predetermined cycles and material type. Regression analysis was also performed to estimate the trend of changes with time. Statistical evaluations performed at a significance level of 5%. RESULTS: Data analysis showed significant changes in length at baseline with an increasing number of cycles (p<0.05) and a significant interaction of cycle-material (p<0.001). The ΔΕ* parameter was significantly higher with a higher number of cycles (p<0.001), but it did not vary between materials (p>0.05). TP decreased similarly in both materials following microwave action but in a significantly higher level for Valplast (p<0.001). CONCLUSIONS: The results indicated that long-term repeated microwaving affects linear dimensional, color and translucency changes of both materials. Differences between PMMA and polyamide material were noted only in dimension and translucency changes.

Long-term microwaving of denture base materials: effects on dimensional, color and translucency stability

Abstract While the combined effect of microwave irradiation with cleansing solutions on denture base materials has been investigated, the effects of only using microwave irradiation and, more importantly, in a long-term basis, was not studied yet. Objective The purpose of this study was to evaluate the effect of a long-term repeated microwaving on the dimensional, color and translucency stability of acrylic and polyamide denture base materials. Material and Methods Thirty two specimens (32 mm x 10 mm x 2.5 mm) from polyamide (Valplast) and PMMA (Vertex Rapid Simplified) denture base materials were made. Eight specimens from each material were immersed in distilled water (control) and 8 were subjected to microwave exposure at 450 W for 3 minutes for a period simulating 224 days of daily disinfection. Linear dimension, color change (ΔE*) and translucency parameter (TP) were measured at baseline and after certain intervals up to 224 cycles of immersion, using a digital calliper and a portable colorimeter. The results were analysed using two-way repeated measures ANOVA to estimate possible differences among predetermined cycles and material type. Regression analysis was also performed to estimate the trend of changes with time. Statistical evaluations performed at a significance level of 5%. Results Data analysis showed significant changes in length at baseline with an increasing number of cycles (p<0.05) and a significant interaction of cycle-material (p<0.001). The ΔΕ* parameter was significantly higher with a higher number of cycles (p<0.001), but it did not vary between materials (p>0.05). TP decreased similarly in both materials following microwave action but in a significantly higher level for Valplast (p<0.001). Conclusions The results indicated that long-term repeated microwaving affects linear dimensional, color and translucency changes of both materials. Differences between PMMA and polyamide material were noted only in dimension and translucency changes.

Melt processing and property testing of a model system of plastics contained in waste from electrical and electronic equipment.

In the present research, blending of polymers used in electrical and electronic equipment, i.e. acrylonitrile-butadiene-styrene terpolymer, polycarbonate and polypropylene, was performed in a twin-screw extruder, in order to explore the effect process parameters on the mixture properties, in an attempt to determine some characteristics of a fast and economical procedure for waste management. The addition of polycarbonate in acrylonitrile-butadiene-styrene terpolymer seemed to increase its thermal stability. Also, the addition of polypropylene in acrylonitrile-butadiene-styrene terpolymer facilitates its melt processing, whereas the addition of acrylonitrile-butadiene-styrene terpolymer in polypropylene improves its mechanical performance. Moreover, the upgrading of the above blends by incorporating 2 phr organically modified montmorillonite was investigated. The prepared nanocomposites exhibit greater tensile strength, elastic modulus and storage modulus, as well as higher melt viscosity, compared with the unreinforced blends. The incorporation of montmorillonite nanoplatelets in polycarbonate-rich acrylonitrile-butadiene-styrene terpolymer/polycarbonate blends turns the thermal degradation mechanism into a two-stage process. Alternatively to mechanical recycling, the energy recovery from the combustion of acrylonitrile-butadiene-styrene terpolymer/polycarbonate and acrylonitrile-butadiene-styrene terpolymer/polypropylene blends was recorded by measuring the gross calorific value. Comparing the investigated polymers, polypropylene presents the higher gross calorific value, followed by acrylonitrile-butadiene-styrene terpolymer and then polycarbonate. The above study allows a rough comparative evaluation of various methodologies for treating plastics from waste from electrical and electronic equipment.

Local treatment of experimental Pseudomonas aeruginosa osteomyelitis with a biodegradable dilactide polymer releasing ciprofloxacin.

A biodegradable system of poly-D,L-dilactide releasing ciprofloxacin was assessed in a Pseudomonas aeruginosa osteomyelitis model after inoculation of the test pathogen into the left tibia of 76 New Zealand White rabbits; 31 were controls (group A), and 45 were implanted with the polymer at the infection site (group B). The rabbits were killed on a weekly basis, and cancellous bone was harvested for histopathology and for estimation of bacterial growth and the concentrations of ciprofloxacin. Tibial X ray was performed immediately before the animals were killed. The total number of fistulas with purulent discharge that developed after inoculation of the pathogen was counted, and fistulas with purulent discharge were found in 16 animals in group A (51.6%) and 3 animals in group B (6.7%) (P < 0.0001). The animals in group A had a profound loss of body weight compared to the animals in group B. The main radiological finding was the presence of sequestra in 25 animals (80.6%) in group A and 6 animals in group B (13.3%) (P < 0.0001). The bacterial load in group B was significantly reduced compared to that in group A, possibly due to the prolonged local antibiotic release at concentrations exceeding even 80 times the MIC for the test pathogen. The histology of animals killed after week 49 revealed a mild inflammatory reaction accompanied by diffuse fibrosis and new bone formation in group A animals and the presence of small polymer particles in group B animals. It is concluded that the system described achieved eradication of the pathogen, accompanied by clinical and radiologically confirmed benefits, so this treatment may be a candidate for the management of difficult orthopedic infections.

Bonding of silicone extra-oral elastomers to acrylic resin: the effect of primer composition.

Silicone elastomer is bonded to acrylic resin in many facial or oro-facial prostheses. The silicone elastomer/acrylic resin bond has been reported to be insufficient and primers have been used to enhance the bond. This study investigated the bond strength of silicone elastomer to acrylic resin using different types of primers. The extra-oral silicone elastomers studied were Cosmesil and Ideal. The "overlap-joint" model was used to evaluate the bond strength and the samples were stretched until fracture. The bonding surfaces were treated with a primer. The control primer was Cosmesil and the others a mixture of Cosmesil/Z-6020 and Cosmesil/A-174 in 50/50 v/v ratio. The bond strength ranged from 0.026 MPa to 0.219 MPa. The results obtained in this work led to the conclusion that the most critical parameter allowing the efficient performance of a primer is the compatibility and affinity of its composition with the selected silicone elastomer.

Evaluation of porosity in microwave-processed acrylic resin using a photographic method.

STATEMENT OF PROBLEM: The effect of microwave polymerization on the porosity of denture base resin has not been fully determined. PURPOSE: This study investigated the effect of microwave energy on the porosity of 2 heat-activated denture base resins. MATERIAL AND METHODS: Two heat-activated denture base resins, one conventional (Paladon 65) and one designed for microwave polymerization (Acron MC), were used to prepare 50 test specimens. Five groups of 10 specimens each were established: Group A (Paladon 65, water bath); Group B(1) (Paladon 65, short microwave cycle); Group B(2) (Paladon 65, long microwave cycle); Group C(1) (Acron MC, short microwave cycle); and Group C(2) (Acron MC, long microwave cycle). Half of the specimens in each group were 3 mm thick, the other half 6 mm thick. After being polymerized, specimens were cut so that 3 cross-sectional areas were formed (S(1), S(2), and S(3)). These surfaces were polished and photographed under a microscope at x100 magnification. On the developed photographs, the area of each pore was measured with a digital planimeter, and the total area of pores per surface was calculated in percentage form. The total number of pores on each surface and the topographical distribution of the pores also were recorded. A 3-factor repeated-measures analysis of variance was used to compare porosity data, and a 1-way analysis of variance was performed to determine possible interactions between groups based on material and specimen thickness (P<.05). The effect of surface area on porosity data was analyzed with the use of contrasts. RESULTS: Group A specimens exhibited no pores. In the thicker specimens of Groups B(1) and B(2), giant pores (area as great as 3.69 mm(2)) and small, gaseous pores of almost uniform shape and size were found. In Groups C(1) and C(2), only the smaller pores were found; these were not clinically significant. Of the observed surfaces, 75.3% were free of pores and 24.7% contained at least one pore. In a selected group of pore-bearing surfaces, the majority (81%) had pores located near the center. The thicker specimens in Group B exhibited the greatest amount of porosity (P<.0001); Group C specimens exhibited the least porosity. Repeated-measures analysis of variance showed that polymerization cycle had no effect on porosity (P=.19). The 3 other factors (material, specimen thickness, and surface) and all possible interactions among them were significant (P<.05). Among the surfaces, S(1) and S(2) exhibited the highest total mean value of porosity (0.71% and 0.74%, respectively) and S(3) the lowest (0.025%). S(3) showed a different pattern of porosity than S(1) and S(2). CONCLUSION: Within the limitations of this in vitro study, minor porosity was identified in thin and more severe porosity in thicker areas of conventional resin specimens that underwent microwave polymerization. The resin designed specifically for microwave polymerization exhibited no clinically significant porosity.