The effect of hydrofluoric acid and resin cement formulation on the bond strength to lithium disilicate ceramic

Abstract To investigate how the hydrofluoric acid (HF) concentrations applied to a lithium disilicate glass-ceramic (EMX) affects the surface morphology and microtensile bond strength (μTBS) of ceramics to dentin, using light-cured resin cements with or without UDMA. Sixty-three EMX square ceramic blocks were etched for 20 seconds using different HF concentrations (1%, 5% and 10%) and luted to dentin using two types of resin cement combinations: BisGMA/TEGDMA and BisGMA/TEGDMA/UDMA (n = 10). Each bonded EMX-dentin block was sectioned to obtain 1 mm2 sticks for μTBS evaluation. Half of the sticks were tested after 24 hours and the other half was assessed after 6 months of water storage. Data were statistically assessed using split-plot three-way ANOVA and multiple comparisons were performed using the Tukey's post hoc test (α = 0.05). One EMX sample from each HF concentration was analyzed using field-emission scanning electron microscope (FE-SEM) to characterize the etching pattern. According to the FE-SEM images, increasing the concentration of HF from 1 to 5 and then to 10% led to increased removal of glassy matrix and greater exposure of lithium disilicate crystals. The 10% HF concentration yielded higher μTBS when compared to 1% for BisGMA/TEGDMA formulation (p < 0.05); whereas HF 1% and 5% showed similar μTBS values when compared to 10% HF for BisGMA/TEGDMA/UDMA resin matrix (p > 0.05) at both storage times. Water aging decreased the μTBS values (p < 0.05), except when 10% HF was associated with BisGMA/TEGDMA resin cement. Resin cement formulation and hydrofluoric acid concentrations can interfere with the immediate and long-term glass-ceramic bond strength to dentin.

Characterization of water sorption, solubility and filler particles of light-cured composite resins

The goals of this study were to measure the water sorption (WS) and solubility (SO) of 3 composite resins containing different filler contents. Additionally, the size, shape, type and other characteristics of fillers were analyzed by scanning electron microscopy (SEM). Three composites, classified according to filler size, were selected: Filtek Supreme nanofill (3M/ESPE), Esthet-X minifill (Dentsply/Caulk) and Renamel microfill (Cosmedent Inc.). Ten disk-shaped specimens of each resin composite were made and stored in desiccators until constant mass was achieved. Specimens were then stored in water for 7 days, and the mass of each specimen was measured. The specimens were dried again and dried specimen mass determined. The WS and SO were calculated from these measurements. Data analyzed by one-way ANOVA and Tukey's post-hoc test (?=0.05). Composite filler particles were observed under SEM after removal of resin matrix by organic solvents. WS values were not significantly different among the resins; however, SO values were lower for Filtek Supreme. The materials presented differences in filler contents (e.g. particle size and shape). The composite resins had similar WS, while the SO was lower for the nanofill than for mini and microfill resins. The filler characteristics varied and were different among the materials.

Os objetivos deste estudo foram determinar a sorção de água (SA) e solubilidade (SO) de 3 resinas compostas que contêm diferentes conteúdos de partículas de carga. Adicionalmente, o tamanho, formato, tipo e outras características das partículas foram analisados em microscopia eletrônica de varredura (MEV). As resinas foram selecionadas de acordo com o tamanho das partículas: Filtek Supreme nanoparticulado (3M ESPE), Esthet-X microhíbrido (Dentsply Caulk) e Renamel microparticulado (Cosmedent Inc.). Dez espécimes com formato de disco de cada compósito foram confeccionados e armazenados em dessecador até obtenção de massa constante. Em seguida, os espécimes foram armazenados em água por 7 dias e a massa mensurada novamente. Os espécimes foram desidratados novamente e a massa final mensurada. A SA e a SO foram calculados a partir destas medidas. As partículas de carga dos compósitos foram observadas em MEV, após a remoção da matriz orgânica com solventes orgânicos. Os dados foram analisados por ANOVA e teste de Tukey (?=0.05). As médias de SA das resinas compostas foram semelhantes. A SO foi menor para o compósito Filtek Supreme. Os materiais contêm diferentes conteúdos de carga, em termos de formato e tamanho das partículas. As resinas compostas mostraram similar SA, enquanto o compósito nanoparticulado apresentou a menor SO. As características das partículas de carga foram diferentes entre os compósitos estudados.