Effect of a post-polymerization treatments on the flexural strength and Vickers hardness of reline and acrylic denture base resins

Abstract

This study evaluated the effect of water-bath and microwave post-polymerization treatments on the flexural strength and Vickers hardness of four autopolymerizing reline resins (Duraliner II-D, Kooliner-K, Tokuso Rebase Fast-TR and Ufi Gel Hard C-UGH) and one heat-polymerized acrylic resin (Lucitone 550-L), processed using two polymerization cycles (short cycle - 90 minutes at 73°C and 100°C for 30 minutes; and long cycle - 9 hours at 71°C). For each material, thirty specimens (64 x 10 x 3.3 mm) were made and divided into 3 groups (n=10). Specimens were tested after: processing (control group); water-bath at 55°C for 10 minutes (reline materials) or 60 minutes (L); and microwave irradiation. Flexural strength tests were performed at a crosshead speed of 5 mm/min using a three-point bending device with a span of 50 mm. The flexural strengths values were calculated in MPa. One fragment of each specimen was submitted to Vickers hardness test. Data were analyzed by 2-way ANOVA followed by Tukey's HSD test (α=0.05). L microwaved specimens (short cycle) exhibited significantly higher flexural strength means than its respective control group (p<0.05). Water-bath promoted a significant increase (p<0.05) in flexural strength of K and L (long cycle). The hardness of the tested materials was not influenced by the post-polymerization treatments. Post-polymerization treatments could be used to improve the flexural strength of some materials tested.

Impact strength, fracture toughness and hardness improvement of PMMA denture base through addition of nitrile rubber/ceramic fillers

“…6,34 The flexibility of the polymer chain may account for the relatively lower VH. 35 the surface hardness. This is due to fact that, a large particle size gives rise to greater stress concentrations and contributes to the formation of larger cavities and voids between these particles with the presence NBR micro-size particles in PMMA composite.…”

Effect of polymerization cycles on flexural strengths and microhardness of different denture base materials

“…Seo et al 23) noted that no significant difference was found between the heat-polymerized acrylic resin specimens polymerized with short or long cycles for microhardness (p>0.05). In contrast, in the present study, the microhardness for specimens polymerized with the F cycle were significantly higher than those polymerized with the A cycle (p<0.05).…”

“…Seo et al 23) reported that flexural strengths of heatpolymerized acrylic resin, when polymerized for 90 min at 73°C and then 100°C boiling water for 30 min (short cycle), were higher than when it was polymerized for 9 h at 71ºC (long cycle). This finding is in accordance with the present study in which the specimens polymerized with the F cycle (90 min at 74°C and then 100°C boiling water for 30 min) had higher flexural strengths than with the A cycle (9 h at 74°C).…”

The Influence of Polymerization Type and Reinforcement Method on Flexural Strength of Acrylic Resin

“…Heat-polymerized acrylics (HP) release less residual monomers than the SP ones once high temperatures promote higher degree of conversion and reduced powder (PMMA)/liquid (MMA) ratio in the mixture, affecting flexural strength [ 29 ]. Besides that, fiber reinforced resin can present voids and cracks (Figures 1(a) and 3(b) ).…”

“…Acrylic restorations reinforced with nonimpregnated fibers show lower fracture resistance than those reinforced with impregnated fibers [ 27 ]. However, the residual monomer release in autopolymerized or heat-polymerized acrylic resins [ 28 , 29 ] increases with the addition of preimpregnated fibers [ 27 ] and this could affect the strength of the reinforced material.…”