Alcides Gonini-Júnior

Impact of curing protocol on the selected properties of a model bis-GMA/TEGDMA dental resin composite

This study investigated the impact of different photo-activation protocols on selected properties of a model composite formulated using bis-GMA/TEGDMA (1:1 mass ratio), camphorquinone/amine (1:2 mass ratio) and 75% of fillers. The protocols tested were: high-intensity continuous (HIC-500 mW cm(-2) for 20 s), medium-intensity continuous (MIC-250 mW cm(-2) for 40 s), low-intensity continuous (LIC-100 mW cm(-2) for 100 s) and pulse-delay-1 min or 3 min (PD-1 min/3 min-100 mW cm(-2) for 5 s + 1 or 3 min interval + 500 mW cm(-2) for 19 s). Degree of conversion (DC) was evaluated using infrared spectroscopy. Flexural strength (FS) and modulus (FM) were measured in three-point bending mode. Cross-link density was estimated by calculating the swelling coefficient (alpha) after immersion in chloroform. All methods showed similar values for DC except for PD-1 min, which showed lower DC. HIC and MIC showed similar FS, but were both different than all of the other methods. All curing methods showed similar FM, except for HIC, which presented a different modulus. PD-3 min showed a different swelling than all of the remaining groups, while HIC showed the lowest swelling. A significant relationship was observed between swelling and both FS and FM. In conclusion, the HIC activation protocol generated polymers with properties at least similar, and sometimes improved, in comparison with the alternative protocols.

Effect of sodium hypochlorite and peracetic acid on the surface roughness of acrylic resin polymerized by heated water for short and long cycles.

Objective: To evaluate the surface roughness of acrylic resin submitted to chemical disinfection via 1% sodium hypochlorite (NaClO) or 1% peracetic acid (C 2 H 4 O 3 ). Materials and Methods: The disc-shaped resin specimens (30 mm diameter ×4 mm height) were polymerized by heated water using two cycles (short cycle: 1 h at 74°C and 30 min at 100°C; conventional long cycle: 9 h at 74°C). The release of substances by these specimens in water solution was also quantified. Specimens were fabricated, divided into four groups (n = 10) depending on the polymerization time and disinfectant. After polishing, the specimens were stored in distilled deionized water. Specimens were immersed in 1% NaClO or 1% C 2 H 4 O 3 for 30 min, and then were immersed in distilled deionized water for 20 min. The release of C 2 H 4 O 3 and NaClO was measured via visual colorimetric analysis. Roughness was measured before and after disinfection. Roughness data were subjected to two-way ANOVA and Tukey′s test. Results: There was no interaction between polymerization time and disinfectant in influencing the average surface roughness (Ra, P = 0.957). Considering these factors independently, there were significant differences between short and conventional long cycles (P = 0.012), but no significant difference between the disinfectants hypochlorite and C 2 H 4 O 3 (P = 0.366). Visual colorimetric analysis did not detect release of substances. Conclusion: It was concluded that there was the difference in surface roughness between short and conventional long cycles, and disinfection at acrylic resins polymerized by heated water using a short cycle modified the properties of roughness.

Influence of Surface Treatments and Adhesive Systems on Lithium Disilicate Microshear Bond Strength

The purpose of this study was to evaluate the microshear bond strength of ceramic prosthetic structures reinforced by lithium disilicate cemented with resin cement under conditions of different surface treatments and adhesive systems. Seventy-two rectangular blocks of lithium disilicate (6.5 mm long × 5 mm wide × 1 mm thick) were fabricated, air abraded with 50-μm Al2O3 particles and divided into six groups (n=12) depending on the surface pretreatments. The groups were as follows: 10HF/S/SBM: 10% hydrofluoric acid etched for 20 s (10HF) + silane (S) + Adper Scotchbond Multi-Purpose (SBM); 10HF/S/SB: 10HF + S + Single Bond Universal (SB); 10HF/SBM; 10HF/SB; S/SBM and S/SB. Two 1-mm-long plastic tubes were placed on the specimens, filled with RelyX ARC resin cement and cured for 20 s per tube. The plastic tube was removed, and the microshear bond strength was tested. Data were submitted to analysis of variance and Tukeys tests (α=0.05). Fractured specimens were observed under optical microscopy. For both adhesives, the bond strengths (MPa) of groups treated with acid-etching and silane (10HF/S/SB: 24.82, 10HF/S/SBM: 24.90) were higher (p<0.001) than those of groups treated with acid-etching (10HF/SB: 16.47, 10HF/SBM: 19.94) only or only silane (S/SB: 18.42, S/SBM: 13.24). All groups showed a predominance of failure adhesive. The silanization should be a clinical step in cementing ceramic structures reinforced by lithium disilicate, even with the application of universal adhesive that contains silane in its formulation.

Microtensile Bond Strength and Microhardness of Composite Resin Restorations Using a Sonic-Resin Placement System

The aim of this study was to evaluate the efficacy of applying sonic energy on microtensile bond strength and microhardness after the restoration process. A total of 40 human third molars were extracted. Class II cavities were prepared and restored with composite SonicFill or Filtek Z350 XT with and without the application of sonic energy. After the teeth were stored in water for 24 h, the teeth were sectioned into sticks (1.0 mm2) and subjected to tensile testing. For a depth Knoop hardness test, the samples were cut and indentations were made sequentially from the surface of the samples to the bottom of the samples in three intervals of 1 mm each. The samples were then subjected to a load of 50 g for 10 s. The results from the tensile (factors: placement system and composite) and hardness (factors: placement system, composite and depth) tests were subjected to the Kolmogorov-Smirnov normality test, followed by analysis of variance and Tukeys test (5% significance). For the placement system factor, higher bond strength was observed for the cavities that were restored with sonic energy (p < 0.001). For depth Knoop hardness, the hardness at 1 mm depth was significantly greater than that at 3 mm depth just for the restorations with Filtek Z350 XT composite without the application of sonic energy. Therefore, the use of sonic energy during the restorative process improved bonding, yet it did not markedly affect the depth hardness for both composites.