Abstract
The objective of this study was to evaluate the influence of hydrofluoric acid (HF) concentration, etching time, and application of phosphoric acid (PA) followed by neutralization with sodium bicarbonate on the bond strength between a feldspar ceramic and resin cement. Thus, 80 blocks (10 x 12 x 2 mm) of glass ceramic (VM - Vita Mark II - Vita Zahnfabrik) were made and randomly assigned to eight groups (n = 10) according to the factors: HF concentration (5 and 10%), etching time (60 and 120 s), and use of phosphoric acid (PA) (with and without). According to the experimental group, 37% PA (Condac, FGM) was applied after HF etching for 60s. Afterwards, samples were immersed in sodium bicarbonate for 1 min then in an ultrasonic bath in distilled water (5 min) for cleaning. After surface bonding treatment, cylinders (Ø = 2 mm; h = 2 mm) of dual resin cement (AllCem / FGM) were made in the center of each block. The samples were then stored in water (37ºC) for 90 days and submitted to the shear bond test (50 KgF, 1 mm/min). Failure analysis was performed by stereomicroscope and scanning electron microscopy. Data (MPa) were analyzed with 3-way ANOVA and Tukey's test. Only the factor "HF concentration" was significant (p = 0.02). Most failures were of cohesive in ceramic (40%) and mixed types (42.5%). The 10% HF resulted in higher shear bond strength value than the 5% HF. Surface cleaning with phosphoric acid followed by sodium bicarbonate and HF time (60 or 120 seconds) did not influence the resin bond strength to feldspar ceramic.
Highlights
Glass-based dental ceramics have excellent aesthetic and mechanical properties in addition to biocompatibility and have broad clinical application for onlays, inlays,[1] veneers,[2] and crowns.[3]
Considering that 37% phosphoric acid (PA), air-water spray, ultrasonic bath and sodium bicarbonate solution are the techniques most commonly used by dentists, the present study aimed to evaluate the influence of hydrofluoric acid (HF)
According to Tukey’s test (p = 0.05), considering only the “HF concentration” factor, 10% HF (12.68 Mpa)A resulted in higher bond strength value than 5% HF (10.68 Mpa)B
Summary
Glass-based dental ceramics have excellent aesthetic and mechanical properties in addition to biocompatibility and have broad clinical application for onlays, inlays,[1] veneers,[2] and crowns.[3]. Time and use of phosphoric acid on the bond strength of feldspathic ceramics the acid dissolves the ceramic glass matrix, increasing free energy and surface porosity, and providing greater surface area for adhesion to resinous compounds.[6,7] HF etching exposes hydroxyl groups that are important for chemical bonding through coupling agents present in silane.[8] HF concentration and etching time may influence the size and shape of micro-retentions, and the bond strength with the substrate.[9,10] In addition, depending on acid exposure and concentration, the mechanical properties of ceramics may be negatively affected, causing decreased fatigue and flexural strength, and surface changes, which could increase the risk of fractures, especially if mechanical imbrication with the resin cement is incomplete.[11,12]
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