Marcia Margarete Meier

Subcritical crack growth and in vitro lifetime prediction of resin composites with different filler distributions

OBJECTIVES Verify the influence of different filler distributions on the subcritical crack growth (SCG) susceptibility, Weibull parameters (m and σ(0)) and longevity estimated by the strength-probability-time (SPT) diagram of experimental resin composites. METHODS Four composites were prepared, each one containing 59 vol% of glass powder with different filler sizes (d(50)=0.5; 0.9; 1.2 and 1.9 μm) and distributions. Granulometric analyses of glass powders were done by a laser diffraction particle size analyzer (Sald-7001, Shimadzu, USA). SCG parameters (n and σ(f0)) were determined by dynamic fatigue (10(-2) to 10(2) MPa/s) using a biaxial flexural device (12 × 1.2 mm; n=10). Twenty extra specimens of each composite were tested at 10(0) MPa/s to determine m and σ(0). Specimens were stored in water at 37°C for 24 h. Fracture surfaces were analyzed under SEM. RESULTS In general, the composites with broader filler distribution (C0.5 and C1.9) presented better results in terms of SCG susceptibility and longevity. C0.5 and C1.9 presented higher n values (respectively, 31.2 ± 6.2(a) and 34.7 ± 7.4(a)). C1.2 (166.42 ± 0.01(a)) showed the highest and C0.5 (158.40 ± 0.02(d)) the lowest σ(f0) value (in MPa). Weibull parameters did not vary significantly (m: 6.6 to 10.6 and σ(0):170.6 to 176.4 MPa). Predicted reductions in failure stress (P(f)=5%) for a lifetime of 10 years were approximately 45% for C0.5 and C1.9 and 65% for C0.9 and C1.2. Crack propagation occurred through the polymeric matrix around the fillers and all the fracture surfaces showed brittle fracture features. SIGNIFICANCE Composites with broader granulometric distribution showed higher resistance to SCG and, consequently, higher longevity in vitro.

Adhesives Doped with Bioactive Niobophosphate Micro-Filler: Degree of Conversion and Microtensile Bond Strength

To evaluate the effect of incorporating niobium phosphate bioactive glass (NbG) into commercial etch-and-rinse adhesive systems, with and without silane, on their degree of conversion (DC) (%) and microtensile bond strength (μTBS). The NbG micro-filler was added to two etch-and-rinse adhesive systems: One Step (OS) and Prime & Bond (PB) at 40% concentration. The following groups were formed: control without glass addition OS; addition of unsilanized NbG (OSNbG); addition of silanized NbG (OSNbGS); control without glass PB; addition of unsilanized NbG (PBNbG); addition of silanized NbG (PBNbGS). The DC was determined using total Fourier spectroscopy reflection (FTIR/ATR). For μTBS testing, 48 human third molars (n=8) were restored and sliced to obtain specimens (0.8 mm2) and they were tested at two different time intervals: immediately and after 6 months. The fracture mode was evaluated with a stereoscopic loupe (40×) and by scanning electron microscopy (SEM). The data were subjected to ANOVA and Tukey tests (a=0.05). NbG addition did not compromise the adhesive system DC values (p>0.05). Furthermore, the NbG added to the adhesive systems did not affect μTBS values (p>0.05). Fracture occurred predominantly at the dentin-adhesive interface. NbG bioactive glass did not affect the DC or microtensile bond strength results.

Ion-releasing dental restorative composites containing functionalized brushite nanoparticles for improved mechanical strength

OBJECTIVES This study describes the synthesis of brushite nanoparticles (CaHPO4·2H2O) functionalized with triethylene glycol dimethacrylate (TEGDMA) and their application in dental restorative composites with remineralizing capabilities. METHODS Nanoparticles were synthesized, with TEGDMA being added to one of the precursor solutions at three different molar ratios (0:1, 0.5:1 and 1:1, in relation to the ammonium phosphate precursor). Then, they were added (10 vol%) to a photocurable dimethacrylate matrix containing 50 vol% of reinforcing glass particles. The resulting composites were tested for degree of conversion, biaxial flexural strength and elastic modulus (after 24h and 28days in water), and ion release (over a 28-day period). Commercial composites (one microhybrid and one microfilled) were tested as controls. RESULTS The final TEGDMA content in the functionalizing layer was modulated by the molar ratio added to the precursor solution. Functionalization reduced nanoparticle size, but did not reduce agglomeration. Improved mechanical properties were found for the composite containing nanoparticles with higher TEGDMA level in comparison to the composite containing non-functionalized nanoparticles or those with a low TEGDMA level. All brushite composites presented statistically significant reductions in strength after 28 days in water, but only the material with high-TEGDMA nanoparticles retained strength similar to the microhybrid commercial control. Overall, ion release was not affected by functionalization and presented steady levels for 28 days. SIGNIFICANCE Though agglomeration was not reduced by functionalization, the improvement in the matrix-nanoparticle interface allowed for a stronger material, without compromising its remineralizing potential.

Bioactivity and properties of an adhesive system functionalized with an experimental niobium-based glass

OBJECTIVE This study evaluated the incorporation of niobophosphate bioactive glass (NbG) fillers into a commercial adhesive resin. MATERIALS AND METHODS The silanized (NbGs) or non-silanized (NbG) NbG was added to the commercial adhesive system One Step (OS) at 30% by weight; unfilled adhesive served as control. The bioactivity of adhesives was analyzed by SEM and FTIR/ATR after 28 days in PBS. The adhesives were evaluated as regards microtensile bond strength immediately and after six months (n = 6); degree of conversion (n = 3), microhardness (n = 5); and radiopacity (n = 3). Data from each test were submitted to ANOVA and Tukey tests (P <0.05). RESULTS FTIR/ATR analysis showed phosphate and carbonate precipitates on the NbG adhesive specimen surface. Statistical analysis of microtensile bond strength values showed that material x time interaction was not significant, but NbG group values were similar to those of unfilled adhesive (p <0.05). Addition of NbG did not alter the degree of conversion, but did increase microhardness and radiopacity values of the adhesive systems compared with those of the control group (OS). Incorporation of NbG into the adhesive system did not compromise the properties of the adhesive. CONCLUSION A smart adhesive system with bioactive properties, high radiopacity, microhardness, and similar bond strength and degree of conversion was obtained by incorporating 30% by weight of NbG.

Development of calcium phosphate/ethylene glycol dimethacrylate particles for dental applications: DEVELOPMENT OF CaP/ETHYLENE GLYCOL DIMETHACRYLATE PARTICLES

This study describes the synthesis of dicalcium phosphate dihydrate (DCPD) particles in the presence of different ethylene glycol dimethacrylates (EGDMA, ethylene glycol/EG units: 1, 2, 3 or 4) at two monomer-to-ammonium phosphate molar ratios (1:1 and 2:1), as a strategy to develop CaP-monomer particles with improved interaction with resin matrices. Particles displaying high surface areas and organic contents were added to a photocurable BisGMA-TEGDMA resin and the resulting materials were tested for degree of conversion (DC), biaxial flexural strength (BFS), flexural modulus, and ion release. Data were subjected to one-way ANOVA or Kruskal-Wallis/Dunn test (alpha: 0.05). Functionalization with EGDMA derivatives was dependent upon the length of the spacer group and monomer concentration in the synthesis. No differences in DC were observed among materials (p > 0.05). A 39% increase in BFS was obtained with the use of particles with the highest functionalization level compared to non-functionalized particles (p < 0.001). The use of functionalized DCPD reduced flexural modulus in comparison to non-functionalized particles (p < 0.001). Calcium release was similar among materials and remained constant during the experiment, while phosphate release was higher at 7 days in comparison to the remaining weeks (p < 0.001). In conclusion, diethylene glycol dimethacrylate resulted in the highest functionalization levels and the highest BFS among DCPD-containing materials. Ion release was not affected by functionalization.

Microencapsulação do pesticida cipermetrina em blendas de P(3HB/PCL): caracterização e ensaio de liberação in vitro

A aplicacao de polimeros biodegradaveis para encapsular pesticidas e uma estrategia que permite, a partir de diferentes proporcoes entre os polimeros, modificar o perfil de liberacao do agente. Este trabalho avaliou a liberacao controlada do pesticida cipermetrina encapsulado em microesferas de blendas de P(3HB)/PCL (100/0, 0/100, 97/03, 95/05, 90/10, 80/20 e 70/30) obtidas pelo metodo de emulsificacao-evaporacao do solvente. As imagens de microscopia eletronica de varredura revelam a forte influencia da PCL na porosidade das microesferas. As analises de infravermelho mostraram a presenca do pesticida em todas as composicoes de polimeros avaliadas. O ensaio de liberacao de cipermetrina sugere que, no intervalo de 4 horas, o teor de cipermetrina liberada e dependente da composicao das blendas utilizadas. As microesferas de PHB e blendas com menores teores de PCL, 97/03 e 95/05 liberaram 75% a 85% enquanto a composicao 70/30 liberou 100% de cipermetrina.