Surface characterisation and bonding of Y-TZP following non-thermal plasma treatment

Objectives: (1) To chemically characterise Y-TZP surface via X-ray photoelectron spectroscopy (XPS) and evaluate the surface energy levels (SE) after non-thermal plasma (NTP). (2) To test the microtensile bond strength (MTBS) of Y-TZP bonded to cured composite disks, after a combination of different surface conditioning methods. Methods: Twenty-four Y-TZP discs (13.5 mm × 4 mm) were obtained from the manufacturer and composite resin (Z-100) discs with similar dimensions were prepared. All discs were polished to 600 grit and divided into 8 groups (n = 3 disks each), four control (non-NTP treated) and four experimental (NTP treated for 10 s) groups. All groups received one of the four following treatments prior to cementation with Rely × Unicem cement: sand-blasting (SB), a Clearfil ceramic primer (MDP), sand-blasting + MDP (SBMDP), or baseline (B), no treatment. SE readings and surface roughness parameters were statistically analysed (ANOVA, Tukey's, p < 0.05). Mixed model and paired samples t-tests were used to compare groups on MTBS. Results: XPS showed increase in O and decrease in C elements after NTP. The polar component increased for BP (42.20 mN/m) and SBP (43.77 mN/m). MTBS values for groups BP (21.3 MPa), SBP (31 MPa), MDPP (30.1 MPa) and SBMDPP (32.3 MPa) were significantly higher in specimens treated with NTP than their untreated counterparts B (9.1 MPa), SB (14.4 MPa), MDP (17.8 MPa) and SBMDP (24.1 MPa). Conclusions: (1) Increase of O and decrease of C led to higher surface energy levels dictated by the polar component after NTP; (2) NTP application increased MTBS values of Y-TZP surfaces.