Evaluation of a new universal primer for ceramics and alloys

To evaluate in vitro the effect of using a universal primer on the resin bond strength to ceramics (silicate and zirconia) and two noble alloys for metal-ceramic restorations.

Disk-like specimens made of four dental restoration materials (silicate ceramic, zirconia ceramic, gold-based alloy and palladium-based alloy) were ground with abrasive paper, prepared for bonding (silicate ceramic: etching with 5% hydrofluoric acid for 60 s; the other materials: air abrasion with 50-µm Al2O3 at 2.5 bar) and ultrasonically cleaned in 96% isopropanol. Eight specimens of each material were primed with a universal primer, 8 specimens were primed with a well-established material-specific method (silicate ceramic: silanization; zirconia ceramic: phosphate monomer-containing primer; alloys: sulfuric monomer-containing primer). Plexiglas tubes filled with a composite resin were bonded to the specimens using an alignment apparatus and a composite luting resin. After storage in 37°C tap water for three days, or 167 days with additional thermocycling, tensile bond strength (TBS) was measured in a universal testing machine at a crosshead speed of 2 mm/min.

After 167 days of storage, median TBS values for each material were (well-established method/universal primer) 40 MPa/37 MPa (silicate ceramic), 41 MPa/41 MPa (zirconia ceramic), 20 MPa/17 MPa (gold-based alloy), and 20 MPa/19 MPa (palladium-based alloy). Statistical analysis revealed no statistically significant differences among control groups and test groups.

The universal primer seems to be a promising alternative compared to using three different primers for alloys, silicate and zirconia ceramics.