Increasing Acid Concentration, Time and Using a Two-Part Silane Potentiates Bond Strength of Lithium Disilicate–Reinforced Glass Ceramic to Resin Composite: An Exploratory Laboratory Study

Abstract

There is still a lack of consensus concerning the recommended etching concentration, application time and type of silane when bonding lithium disilicate-reinforced glass ceramics manufactured by CAD/CAM. The purpose of this study was thus to conduct an in vitro study which investigates the influence of hydrofluoric acid (HF) concentration, etching time and silane type on the microtensile bond strength (μTBS) of lithium disilicate to resin composites. Thirty-nine IPS e.max CAD blocks were randomly divided between thirteen groups (n = 3). The variables were HF concentration (9.5 or 4.9%), etching time (20 or 60 s) and silane type (Bis-Silane, Monobond Plus and ESPE Sil Silane). The blocks were cut into beams, aged for 10,000 cycles in a thermocycler and submitted to tensile stress to determine μTBS. A control group featuring the Monobond Etch & Prime (MEP) agent that combines etching/silanisation into a simultaneous process was also added. This group was discarded from the analysis due to only having pre-test failures. The data were analysed using a three-way ANOVA (α = 0.05). The HF concentration, etching time and silane type significantly influenced μTBS (p < 0.001). Significant interactions between time and silane type (p = 0.004), HF concentration and silane type (p < 0.001) and among the three factors (p < 0.001) were noted. Etching lithium disilicate with 9.5% HF (60 s), followed by the application of Bis-Silane, resulted in the highest μTBS (16.6 ± 9.0 MPa). The highest concentration and etching time under study, combined with a two-part silane, resulted in the highest bond strength, while the application of MEP showed a complete pre-test failure.

Effect of Different Etching Times with Hydrofluoric Acid on the Bond Strength of CAD/CAM Ceramic Material

“…It was observed that with the increase in of the crystallization rate of CAD/CAM dental restoration materials, the solubility level decreased [ 40 ]. Additionally, there were substantial differences in the proportion of chemical components among the products from diverse manufacturers, which led to various etching-time procedures [ 41 ]. The recommended conditioning practice comprised etching with 5% to 10% hydrofluoric acid (HF), with etching time varying from 15 s to 90 s [ 42 , 43 ].…”

“…The authors were also concerned that over-etching the ceramic might reduce the strength of the material [ 46 ]. Other studies have also raised the aspect of the weakening effect that HF acid produces, regardless of the action time or concentration [ 41 , 45 ].…”

“…Some studies confirmed that the HF etching time and concentration for ceramic materials should be increased to over 60 s to produce a sufficient material displacement for adequate retention and bond strength. Superficial roughness was obtained for etching times of 20 s and 60 s, which might not provide an appropriate mechanical interlocking effect [ 37 , 41 , 43 , 45 , 46 ].…”

Chemical surface modification of lithium disilicate needles of a silica-based ceramic after HF-etching and ultrasonic bath cleaning: Impact on the chemical bonding with silane

“…Figure 1 localizes the resin-ceramic interfaces of interest for a schematic bonding system in dental restoration when the ceramic surface is prepared by hydrofl uoric acid (HF-etching) followed by a silane treatment and fi nished with the adhesive resin cement layer. In the literature, it is well known that ceramic surface pre-treatment helps to improve the bonding properties at the resin-ceramic interface [1][2][3][4][5][6][7][8][9][10][11]. Silanes are hybrid functional monomers able to form chemical bonds with organic and inorganic surfaces.…”

“…chemical bonding). The stability and effectiveness of this adhesion are also supposed to be improved by heat treatment [11][12][13][14][15][16][17]. Bruzi, et al [16] based on the evaluation of the shear bond strength of composite resin to CAD/CAM lithium disilicate ceramics recommends a regular application of silane.…”