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.