Effect of nonthermal plasma treatment on surface roughness and bond strength between veneer ceramic and zirconia core

This in vitro study evaluated the effect of nonthermal plasma (NTP) treatment on the surface roughness (Ra) of the zirconia and the shear bond strength (SBS) between the veneer ceramic and the zirconia. Ninety zirconia specimens were divided into six groups according to the surface treatments applied: control with no treatment; sandblasting with 50-μm Al₂O₃ particles; oxygen plasma treated for 5 min; oxygen plasma treated for 10 min; argon plasma treated for 5 min; and argon plasma treated for 10 min. Ra values were measured using a profilometer. Specimens (n = 12) were then veneered with a nano-fluorapatite ceramic, and the SBS test was performed. Scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses were performed. The sandblasting procedure significantly increased the surface roughness; however, the plasma groups showed similar Ra values compared to the control group. NTP and sandblasting treatment significantly increased the bond strength and led to higher SBS values than the control. Plasma application did not induce phase transformation; however, sandblasting caused monoclinic phase transformation of the zirconia. NTP application (either oxygen or argon) can enhance the bond strength between the veneer ceramic and the zirconia core without altering the surface morphology or causing zirconia phase transformation.