Bond strength between root dentin and three glass-fiber post systems.

STATEMENT OF PROBLEM: Glass-fiber posts were introduced for use after endodontic therapy instead of metal alloy and ceramic posts. There are several new types of glass-fiber post systems available, but little is known about how well these posts bond to the root surface.

PURPOSE: The purpose of this in vitro study was to compare the bond strengths of 3 different types of glass-fiber post systems-opaque, translucent, and electrical glass-in 3 different locations of prepared post spaces.

MATERIAL AND METHODS: Sixty human intact single-rooted extracted teeth were used. The root canals were prepared using a step-back technique and obturated with gutta-percha using lateral condensation. The roots were divided into 3 experimental groups and further divided into 2 subgroups according to testing time (n=10). Roots were restored with 1 of the following post systems according to the manufacturer's instructions: opaque glass-fiber posts (Snowpost), translucent glass-fiber posts (FiberMaster), and electrical glass-fiber posts (Everstick). A self-etching primer (Clearfil Liner Bond) was applied to the walls of the post spaces, allowed to etch for 30 seconds, and gently air dried. A dual-polymerized bonding agent (Clearfil Liner Bond, Bond A and B) was then applied to the same walls. A dual-polymerizing resin luting agent (Panavia F) was mixed for 20 seconds and then placed in the post spaces using a lentulo spiral instrument. The roots were placed in light-protected cylinders; then the light source was placed directly on the flat cervical tooth surfaces and the cement was polymerized. Specimens were stored in light-proof boxes for 24 hours or 1 week after the polymerization procedure. Each root was cut horizontally, and six 1-mm-thick root segments (2 apical, 2 middle, and 2 cervical) were prepared. Using a push-out test, the bond strength between post and dentin was measured after 24 hours or 1 week using a universal testing machine. Statistical analysis was performed with 3-way ANOVA followed by independent t tests (alpha=.05) to detect differences between groups defined by the specific interacting variables. The different combinations of posts and luting material from the cervical segments were analyzed with SEM.

RESULTS: The 3-way ANOVA indicated that push-out test values varied significantly according to the post system used (opaque, electrical, and translucent) (P<.01); the root segments (cervical, middle, and apical) (P<.01), however, did not vary statistically according to the time of testing (24 hours and 1 week). Opaque and electrical glass-fiber posts showed higher bond strength values than translucent posts (P<.01). Push-out bond strength values of cervical segments were significantly higher than the middle and apical segments in translucent and electrical glass-fiber post groups (P<.01). In the opaque glass-fiber post group, there were no significant differences between cervical and middle segments. In SEM analysis, a distinct hybrid zone with long, numerous resin tags located between luting material and dentin was exhibited in all post systems.

CONCLUSION: The opaque and electrical glass-fiber posts exhibited similar bond strengths, and translucent posts exhibited the lowest bond strength. The highest bond strength was observed in the cervical third of the post spaces for translucent and electrical glass-fiber post groups.