Studio degli effetti della mordenzatura con acido fluoridrico sul disilicato di litio utilizzato in odontoiatria

Purpose: The aim of this study was to evaluate the changes induced by different etching treatments on the surface morphology and microstructure of two lithium disilicate-based glass ceramic (IPS e.max® Press and IPS e.max® CAD) and examine the effects on the bond strength between ceramic and composite resin and on the biaxial flexural strength. Materials and methods: Seventy discs (12 mm diameter, 2 mm thickness) of each ceramic were prepared and divided in 5 groups: no treatment (G1), HF 5% 20s (G2), HF 5% 60s (G3), HF 9.6% 20s (G4), HF 9.6% 60s (G5). One specimen for each group was examined by optical profilometer and observed under scanning electron microscopy. On the other specimens was determined the shear bond strength (SBS) with a resin cement. After SBS test, specimens were loaded to failure using a piston-on-three-ball test to determine the biaxial flexural strength. Results: morphological analysis of treated specimens showed that different etching treatments produces changes in surface roughness but this changes are not directly related to an increasing adhesion value. The SEM analysis revealed that etching causes microstructural changes in lithium disilicate which are more relevant with the increasing of etching time and acid concentration. The mean bond strength values (MPa) for IPS e.max® CAD are statistically higher in G2 and G3 (21,28 +/- 4,9 and 19,55 +/- 5,41 respectively); for IPS e.max® Press, G3 has significant higher adhesion value (16,80 +/- 3,96). The mean biaxial flexural strength values (MPa) are significantly higher in IPS e.max® CAD (695 +/- 161) than in IPS e.max® Press (588 +/- 117). Etching with HF does not affect the flexural strength of the material. Conclusions: lithium disilicate has to be etched preferably with 5% HF. Etching produces several changes in surface and microstructure of the material, but does not compromise the flexural strength.