Influence of different surface treatments on the short-term bond strength and durability between a zirconia post and a composite resin core material.

STATEMENT OF PROBLEM: Reliable bonding between zirconia posts and composite resin core materials is difficult to achieve because of the smooth surface texture and lack of silica content of zirconia posts.
PURPOSE: The purpose of this study was to evaluate the effect of different surface treatments on the short-term bond strength and durability between a zirconia post and a composite resin core material.
MATERIAL AND METHODS: Eighty zirconia posts were divided into 4 groups (n=20). Specimens received 1 of 4 different surface treatments: group AIRB, airborne-particle abrasion; group TSC-SIL, tribochemical silica coating (CoJet system) and silanization (ESPE Sil); group AIRB-BSIL, airborne-particle abrasion and MDP-containing primer (Clearfil SE Bond Primer)/silane coupling agent (Clearfil Porcelain Bond Activator) mixture application; and group TSC-BSIL, tribochemical silica coating and MDP-containing primer/silane coupling agent mixture application. Average surface roughness (Ra) of zirconia posts produced by airborne-particle abrasion or silica coating was measured using an optical profilometer. Composite resin core foundations (Build-it FR) were formed using transparent acrylic resin tubes (12mm in length and 7mm in diameter). Each group was further divided into 2 subgroups of 10 specimens and stored in distilled water at 37 degrees C, either for 24 hours or for 150 days with 37,500 thermal cycles between 5 degrees C and 55 degrees C, with a dwell time of 30 seconds. Following water storage, the specimens were sectioned perpendicular to the bonded interface into 2-mm-thick post-and-core specimens under water cooling. Push-out tests were performed with a universal testing machine at a crosshead speed of 0.5mm/min. Debonded post surfaces were examined with SEM. Data were analyzed with 1- and 2-way ANOVA and Tukey multiple comparison tests (alpha=0.05).
RESULTS: No significant differences were detected between the Ra values of airborne-particle-abraded and silica-coated specimens (P=.781). The short-term mean bond strengths for group TSC-BSIL (27.1 +/- 3.2 MPa) and TSC-SIL (25.2 +/- 2.4 MPa) were statistically higher (P<.001) than AIRB-BSIL (23.3 +/- 2.2 MPa). The relatively high bond strengths for groups TSC-BSIL and TSC-SIL decreased significantly after 150 days of water storage to 13.5 +/- 1.6 and 11.8 +/- 1.2 MPa, respectively (P<.001). Durable bonding was obtained only in group AIRB-BSIL (21.8 +/- 2.7 MPa), which was also the only group demonstrating predominantly cohesive failures in the core material after long-term water storage.
CONCLUSIONS: Data suggest that the short-term high bond strength obtained with a silane coupling agent or MPD-containing primer/silane coupling agent mixture to silica-coated zirconia posts was decreased with water storage and thermal cycling, whereas a durable bond could be obtained when an MPD-containing primer/silane coupling agent mixture was applied to the airborne-particle-abraded post surface.