Effect of surface treatment on damage and reliability of Y-TZP

OBJECTIVE:

To test the effect of different intaglio surface treatments on mouth-motion step-stress fatigue and failure modes of Y-TZP core/composite bilayers.

METHODS:

CAD/CAM zirconia Y-TZP plates (12x12x0.5 mm) (IPS e.max ZirCAD, Ivoclar Vivadent) were subjected to two kinds of intaglio surface treatments before adhesive bonding (Panavia 21, Kuraray) to resin-based composite blocks (12x12x4 mm) (Z-100, 3M/ESPE). Resin blocks were previously aged in water for 60 days. Bonded samples were stored in water at least 7 days prior to fatigue testing. In Group G (n=24) the bottom surface of the Y-TZP plates was ground with 600 grit silicon carbide paper (Buehler Ltd., Lake Bluff) under water cooling. Prior to cementation, the ground intaglio surface was treated with NaOH (0.1 molar) for 10 sec, rinsed and dried prior to the metal primer (Alloy Primer, Kuraray) application. In Group SB (n=24) the intaglio surface of the Y-TZP plates was sandblasted with 50 µm Al2O3 (5 sec, 0.5 MPa, 10 mm distance) prior to application of the metal primer (Alloy Primer) and cementation. Samples (n=21 per group) were mouth-motion step-stressed using 3 profiles at 1.5-2 Hz (El-3300, Bose/Enduratec), with a WC indenter (r=3.18 mm) until radial fractures were observed at the intaglio surface (polarized reflection light microscopy). Step-stress profiles were determined from single-cycle load-to-failure tests (n=3) from Group G.

RESULTS:

Weibull stress level probability curves were calculated (Alta Pro, Reliasoft) and reliability (2 side @ 90% confidence bounds) at 100,000 cycles and 200 N load was determined.

Reliability 600 grit Sandblasted

Upper 90% CB 0.75 0.91

Value 0.59 0.80

Lowe 90% CB 0.42 0.58

CONCLUSION:

The step-stress fatigue reliability of sandblasted and 600 grit ground Y-TZP ceramics was comparable. Irrespective of surface treatments, Y-TZP cores failed from intaglio surface radial fractures with near-contact induced cone fractures present. Supported by NIDCR P01-DE10976 and Ivoclar Vivadent.