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

Abstract 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.

Resumo Avaliar o efeito da incorporação de vidro niobofosfato bioativo (NbG, 40% em peso) em dois sistemas adesivos simplificados convencionais (One Step [OS] e Prime & Bond {PB}) com e sem silano, no grau de conversão (%) e resistência de união (RU) após 6 meses. Os seguintes grupos foram testados: Controle OS: sem adição de partículas; OS e adição de NbG sem silano (OSNbG); OS e adição de partículas silanizadas NbG (OSNbGS); Controle PB: sem adição de partículas; PB e adição de partículas de NbG sem silano (PBNbG); PB e adição de partículas silanizadas NbG (PBNbGS). O grau de conversão (GC) foi determinado utilizando espectroscopia de Fourier (FTIR/ATR). Para RU, 48 terceiros molares humanos (n=8) foram restaurados e cortados para obter corpos-de-prova (0,8 mm2) e, em seguida, testados em dois momentos: imediato e após seis meses. O padrão de fratura foi avaliado com lupa estereoscópica (40×) e microscópio eletrônico de varredura (MEV). Os dados foram submetidos à análise de variância e Tukey (a=0,05). NbG não comprometeu valores de GC dos sistemas adesivos (p>0,05). Além disso, a adição de NbG aos sistemas adesivos não afetou os valores de RU (p>0,05). O padrão de fratura ocorreu predominantemente na interface dentina-adesivo. NbG não afetou os resultados de GC e RU.

Influence of silane content and filler distribution on chemical-mechanical properties of resin composites

This study investigated the influence of silane concentration and filler size distribution on the chemical-mechanical properties of experimental composites. Experimental composites with silane contents of 0%, 1% and 3% (in relation to filler mass) and composites with mixtures of barium glass particles (median size = 0.4, 1 and 2 μm) and nanometric silica were prepared for silane and filler analyses, respectively. The degree of conversion (DC) was analyzed by FTIR. Biaxial flexural strength (BFS) was tested after 24-h or 90-d storage in water, and fracture toughness, after 24 h. The data were subjected to ANOVA and Tukey’s test (p = 0.05). The DC was not significantly affected by the silane content or filler distribution. The 0% silane group had the lowest immediate BFS, and the 90-d storage time reduced the strength of the 0% and 3% groups. BFS was not affected by filler distribution, and aging decreased the BFS of all the groups. Silanization increased the fracture toughness of both the 1% and 3% groups, similarly. Significantly higher fracture toughness was observed for mixtures with 2 μm glass particles. Based on the results, 3% silane content boosted the initial strength, but was more prone to degradation after water storage. Variations in the filler distribution did not affect BFS, but fracture toughness was significantly improved by increasing the filler size.

Effects of zirconia nanoparticles addition to experimental adhesives on radiopacity and microhardness

AIM: To evaluate the radiopacity and microhardness (KHN) of experimental dental adhesives (EX). The experimental adhesive resins of the present study were formulated based on the simplified adhesive system Ambar (FGM). METHODS: Five EX with different concentrations of zirconia nanoparticles [0(EX0), 15(EX15), 25(EX25), 30(EX30) e 50%(EX50)] were incorporated in a UDMA/HEMA adhesive (control). Adper Single BondTM 2 (SB, 3M ESPE) was used as a commercial reference. For the radiopacity (n=5), KHN (n=5), adhesive specimens were fabricated using a stainless steel mold. Data were submitted to one-way ANOVA and Tukey's test (α=0.05). RESULTS: The filler addition on the EX showed radiopacity similar to enamel and higher than SB. The EX25, EX35 and EX50 showed higher KHN values when compared to the commercial SB. EX25, EX35 and EX50 showed higher KHN values when compared to the commercial SB. CONCLUSIONS: The results of the present investigation suggest that the addition of zirconia nanoparticles seems to be a good alternative to produce radiopaque adhesives with increased microhardness.