Flexural strength of acrylic resins polymerized by different cycles

Abstract

Despite the large number of studies addressing the effect of microwave polymerization on the properties of acrylic resin, this method has received limited clinical acceptance. This study evaluated the influence of microwave polymerization on the flexural strength of a denture base resin. A conventional heat-polymerized (Clássico), a microwave-polymerized (Onda-Cryl) and a autopolymerizing acrylic (Jet) resins were used. Five groups were established, according to polymerization cycles: A, B and C (Onda-Cryl, short cycle – 500W/3 min, long – 90W/13 min + 500W/90 sec, and manufacturing microwave cycle - 320W/ 3 min + 0W/3 min + 720W/3 min); T (Clássico, water bath cycle – 74°C/9h) and Q (Jet, press chamber cycle – 50°C/15 min at 2 bar). Ten specimens (65 x 10 x 3.3mm) were prepared for each cycle. The flexural strength of the five groups was measured using a three-point bending test at a cross-head speed of 5 mm/min. Flexural strength values were analyzed by one-way ANOVA and the Tukey's test was performed to identify the groups that were significantly different at 5% level. The microwave-polymerized groups showed the highest means (p<0.05) for flexural strength (MPa) (A = 106.97 ± 5.31; B = 107.57 ± 3.99; C = 109.63 ± 5.19), and there were no significant differences among them. The heat-polymerized group (T) showed the lowest flexural strength means (84.40 ± 1.68), and differ significantly from all groups. The specimens of a microwavable denture base resin could be polymerized by different microwave cycles without risk of decreasing the flexural strength.

Effect of different solutions on color stability of acrylic resin-based dentures

“…The color change of LU may be due to its molecular structure, which favors water absorption and has a greater porosity due to the release of residual monomer. 27,28 Moreover, the components used for chemical activation in addition to thermal activation, contained in the short-cycle resins, may be responsible for the results shown by the QC resin. 29 These results are in agreement with those by Hersek et al, 20 who evaluated the color stability of acrylic resins in three colorants used in food and verified that LU followed by QC presented the greatest color changes.…”

Color Stability, Surface Roughness and Flexural Strength of an Acrylic Resin Submitted to Simulated Overnight Immersion in Denture Cleansers

“…Connecting these points in an area on the polished surface of the specimen, roughness was measured. After the markings, the specimens were stored in distilled water at 37°C for 50 ± 2 h, to eliminate the residual monomer (14). Sixty disc-shaped samples were obtained for color alteration analyses and 80 rectangular specimens for surface roughness and flexural strength assays.…”

“…Color changes and flexural strength of acrylic resins have been investigated (9,14,15), as well as the surface roughness (16), but in short periods of immersion. Paranhos et al (17) did not find alterations in color, roughness and flexural strength of microwave acrylic resins after immersion in denture cleansers (NaOCl 0.5% and 1%, Clorox/Calgon and water) for 20 min daily for 180 days.…”

Effect of conventional water-bath and experimental microwave polymerization cycles on the flexural properties of denture base acrylic resins

“…As this heating occurs rapidly and homogeneously, it eliminates the time required to transfer the heat from the water bath until the resin is inside the flask 10) . Despite the advantages of microwave polymerization, this method has still received limited clinical acceptance 11) . The total removable denture bases can fracture or crack during clinical use, occurring most frequently in the midline region of superior prostheses 12) .…”