Minerva Stomatologica 2020 Mar 16

DOI: 10.23736/S0026-4970.20.04330-7

Copyright © 2020 EDIZIONI MINERVA MEDICA

lingua: Inglese

Effect of neutralization and hydrofluoric acid precipitate remotion on the compressive strength of monolithic lithium disilicate crowns

Lucas V. ZOGHEIB ¹, Guilherme R. LOPES ² ✉, Jefferson D. MATOS ², Daniel S. CASTRO ³, Marco A. BOTTINO ², John McCABE ⁴, Estevão T. KIMPARA ²

¹ Department of Dentistry, University of Fortaleza (UNIFOR), Fortaleza, Brazil; ² Department of Prosthodontics and Dental Materials, São Paulo State University (Unesp), Institute of Science and Technology, São José dos Campos, Brazil; ³ Department of Dentistry, University Center Christus (UNICHRISTUS), Fortaleza, Brazil; ⁴ Dental Materials Science, School of Dental Science, Newcastle University, Newcastle, UK

BACKGROUND: The cleaning protocol for the ceramic surface after acid etching resulted in a decrease in bond strength and flexural strength of a glass ceramic. This study aims to evaluate the effect of different ceramic surface treatments after hydrofluoric acid etching (HF) on the compressive strength of monolithic lithium disilicate crowns.
METHODS: Forty (40) human third molars received conventional full coverage preparation. After performing digital impressions of teeth preparations, ceramic blocks were machined using a CAD/CAM system in order to obtain the crowns. The crowns were distributed in 4 groups as ceramic surface treatment (n=10): (HF) - 4.9% HF for 20s + air-water spray for 30s; (HFN) - HF + neutralizing agent for 5 min (N); (HFU) - HF + ultrasonic bath for 5 min (U); e (HFNU) - HF + N + U. SEM and EDS analysis was performed in each group in order to characterize the ceramic surface and to verify the chemical element distribution after HF cleaning protocols. A silane layer was applied (for 60s), and crowns were then cemented with dual resin cement. A compressive load was applied on the middle of the occlusal crown surface with a crosshead speed of 1 mm/min until fracture. Data were analysed using ANOVA and Tukey test (α=0.05).
RESULTS: Fluoride ions were found in samples of all post-etching cleaning protocols. The mean value (Kgf) was: HF = 169.92 ± 21.37; HFN = 187.34 ± 34.79; HFU = 166.63 ± 40.22 and HFNU = 175.26 ± 40.22. The ceramic surface treatment after HF etching did not significantly influence (p>0.05) the compressive strength of the tested ceramic crowns.
CONCLUSIONS: Surface treatments with neutralizing agent associated with the ultrasonic bath as the pre-cementation protocol was the most efficient protocol in eliminating the precipitate deposited on the porosities created by acid etching.

KEY WORDS: Hydrofluoric acid; Dental stress analysis; Tooth crown; Ceramics; Compressive strength