Bond Strength to Cubic Zirconia and Lithium-disilicate. A Preliminary Study

Objectives: Bonding to polycrystalline ceramics is a concern in fixed prosthodontics. Aim of this study was to determine the micro-SBS of two MDP-based cements to cubic-zirconia (ZIR) and lithium-disilicate (L-DIS). The null hypothesis was that mean micro-SBS did not vary among tested groups. Methods: Twenty plates 12x12x2mm of Katana-UTML, (Kuraray-Noritake), and 20 of IPS e.max CAD LT, (Ivoclar-Vivadent) were used as substrates. They were assigned to 4 groups (n=40) according to the combination with two resin-cements: PanaviaV5 (PV5) + Clearfil-Ceramic-Primer-Plus, (groups PV5/ZIR and PV5/L-DIS); PanaviaSA (PSA) self-adhesive cement, (groups PSA/ZIR and PSA/L-DIS). The ceramics were pre-treated following the cements manufacturer instructions: ZIR-tablets were sandblusted (Al2O3 powder, 50mm); L-DIS-tablets were conditioned (35% H3PO4, K-Etchant Syringe). Four cylinders (1.7mm diameter, 2mm height) of resin-cement were applied on each plate with vertical load (1Kg) and light-cured (20sec). All samples were stored in water (37°C, 24h) and tested for micro-SBS (Instron-machine). Failed surfaces were analyzed under optical-microscope and failure pattern was determined (adhesive, cohesive or mixed). Percentage of actual-failed/total adhesive surface was calculated with dedicated software (Zeiss ZEN). Mean micro-SBS values were measured (MPa) and statistically analyzed (Kruskall-Wallis-test, Dunn’s test, a=0.05). Results: The null hypothesis that micro-SBS did not vary among the groups was rejected, (p<0.05). Mean values varied from 7.7±1.9MPa (PSA/L-DIS) to 19.6±1.7MPa (PV5/ZIR). All groups were statistically different, except PSA/ZIR vs PV5/L-DIS, (p>0.05). Both cements presented significantly higher bond strength to ZIR than L-DIS substrate. For each substrate, PV5 showed higher bond strength than PSA. Adhesive failures were mostly observed in all groups. Mean percentage of actual-failed adhesive surface varied from 69.5% (PSA/ZIR) to 85.1% (PV5/L-DIS). Conclusions: ZIR treatment with MDP-based primer helped obtaining improved adhesion. L-DIS treatment with H3PO4 should be further investigated and compared with the conventional HF treatment. Micro-SBS measurements after longer aging conditions are needed to evaluate the bonding stability