Effect of SiO2-ZrO2 slurry coating on shear bond strength of zirconia to resin cement

Abstract

Objective: To evaluate the effect of shear bond strength between resin cement and zirconia using SiO2-ZrO2 slurry coating. Methods: One hundred and forty pre-sintered zirconia discs were randomly divided into seven groups (n=20) according to the surface treatments: AS (as-sintered), SB (sand blasting with Al2O3), 2SiO2-1ZrO2 (2∶1 mole ratio SiO2-ZrO2 coating), 1SiO2-1ZrO2 (mole ratio 1∶1 SiO2-ZrO2 coating), 1SiO2-2ZrO2 (mole ratio 1∶2 SiO2-ZrO2 coating), 1SiO2-3ZrO2 (mole ratio 1∶3 SiO2-ZrO2 coating), 1SiO2-4ZrO2 (mole ratio 1∶4 SiO2-ZrO2 coating). Each zirconia disc was bonded to composite resin cylinder using resin cement. All specimens were stored in distilled water (37 ℃, 24 h). Each group was divided into two subgroups in which half specimens were tested using universal testing machine and another half specimens accepted artificial aging of 5 000 times thermocycling then tested. Scaning electron microscopy (SEM) was used to observe the micro-morphology of coating surface etched by hydrofluoric acid,then the coating thickness was measured. Results: Before artificial aging, 1SiO2-1ZrO2 showed a higher shear bond strength [(41.69±6.28) MPa] than all the other group (P<0.05). 1SiO2-2ZrO2 gained a higher strength than AS, SB, 1SiO2-3ZrO2 and 1SiO2-4ZrO2 (P<0.05). However, 1SiO2-2ZrO2 did not get a significant higher shear bond strength than 2SiO2-1ZrO2 (P>0.05). No significant differences were found among SB, 2SiO2-1ZrO2 and 1SiO2-3ZrO2 (P>0.05). After artificial aging, shear bond strength of all groups were decreased significantly besides 2SiO2-1ZrO2. 2SiO2-1ZrO2, 1SiO2-1ZrO2 and 1SiO2-2ZrO2 [(24.13±5.50), (22.28±4.40), (23.11±4.80) MPa] showed higher shear bond strength than SB and 1SiO2-3ZrO2 (P<0.05),no intergroup differences were observed (P>0.05). Shear bond strength of AS and 1SiO2-4ZrO2 fell to 0 MPa approximately. The SEM images of etched coating surface showed contraction fissure due to different thermal expansion coefficient between SiO2 and ZrO2 and intercrystal pores of zirconia. The thickness of coating was measured to be less than 30 μm. Conclusions: Mole ratio 1∶1 SiO2-1ZrO2 slurry coating showed the highest shear bond strength of resin cement to zirconia.