Lithium Disilicate Adhesion and Biaxial Flexural Strength after Etching Duration

Objectives: To compare the effect of different hydrofluoric acid etching times on the resulting adhesion and resistance to fracture of two lithium disilicate pressable ceramics.
Methods: Ceramic cylinders from A2 MT LISI Press (LISI, GC America) and IPS e.max Press were formed according to manufacturer instructions to be 12 mm. Discs were cut with a slow speed diamond wafering saw and finished with 600 grit diamond discs. Test groups for shear bond strength (n=10, N=60) and biaxial flexural strength testing (n=10, N=60) included a 600-grit control, etching with a 5% HF etchant (IPS ceramic etchant gel, Ivoclar Vivadent, Inc.) for 20 seconds and 60 seconds.
Shear bond strength was performed according to ISO 29022:2013 methods using G-CEM LinkForce with G-Multi Primer on LISI press (LP, GC America), and Variolink Esthetic DC with Monobond Plus on IPS e.max Press (IEP, Ivoclar Vivadent, Inc.) and subjected to 5000 thermocycles. Biaxial flexural strength testing was performed according to ISO 6872:2015 methods. Data were analyzed by ANOVA and Fisher’s PLSD multiple comparison test was calculated at the 0.05 level of significance.
Results: Increased etching time had a significant improvement in bonding for the LP group between 600-grit, 20s and 60s etching, but with no significant difference in the IEP group between 20s and 60s etching. The LP group had higher mean bond strengths in all test groups. Biaxial flexural strength testing showed a small drop for LISI Press and e.max Press from 600-grit to 20 seconds of etching with no further significant change after 60 seconds.
Conclusions: Sixty seconds of etching of LISI Press resulted in a significant increase in adhesion without a loss of flexural strength compared to 20 seconds of etching.