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.
Highlights
Due to their optimal mechanical/optical properties, chemical durability and survival rates,[1,2] dental glass-ceramics are one of the most adopted indirect restorative materials for reestablishing function, shape and esthetics of affected dentition
Hydrofluoric acid etching of IPS e.max Press A person that was not involved in the study and blinded to the groups randomly divided the EMX blocks into 3 groups according to the hydrofluoric acid (HF) concentrations: 1%, 5% and 10% (Fórmula & Ação, São Paulo, Brazil) (n=21)
In the present study, the different HF concentrations only affected the μTBS for the groups luted with resin cement type 1 (BisGMA/tri-ethylene glycol dimethacrylate (TEGDMA)), a condition that was not confirmed for resin cement type 2 (BisGMA/TEGDMA/urethane dimethacrylate (UDMA)), with the three HF concentrations (1%, 5% and 10%) demonstrating statistically similar μTBS values
Summary
Due to their optimal mechanical/optical properties, chemical durability and survival rates,[1,2] dental glass-ceramics are one of the most adopted indirect restorative materials for reestablishing function, shape and esthetics of affected dentition. The lithium disilicate glass-ceramic is noteworthy among glass-ceramics due to its outstanding natural look-like,[3] translucency and high mechanical strength.[1,4]. The effect of hydrof luoric acid and resin cement formulation on the bond strength to lithium disilicate ceramic. As lithium disilicate glass-ceramic is suitable to be adhesively bonded to dental tissues, the bond between glass-ceramics and resin cements is one of the key factors for long-term clinical success.[5] hydrofluoric acid (HF) etching followed by silane application is recognized as the most widely accepted procedure before luting glass-ceramic with resin cements,[3,5,6,7,8] the ideal etching protocol is still not clear.[4] The manufacturer of IPS e.max Press (EMX) (Ivoclar Vivadent, Schaan, Liechtenstein), a pressable lithium disilicate glass-ceramic, recommends etching EMX with 4.8% HF for 20 seconds. In vitro studies and clinical case reports have demonstrated concentrations of up to 10%.3,6,7,8
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