The effect of dowel space on the bond strengths of fiber posts

Purpose: The purpose of this study was to evaluate the effect of the degree of mismatch between post space and post diameters on the bond strength of a fiber-reinforced resin post. Materials and Methods: Thirty-two extracted human maxillary central incisors and canines were endodontically treated and assigned to four groups: Group 1 - Canal prepared with a D.T. Light Post 1 drill (control); Group 2 - Canal prepared with a D.T. Light Post 2 drill; Group 3 - Canal prepared with a D.T. Light Post 3 drill; Group 4 - Canal prepared with a Gates Glidden 6 drill. A D.T. Light Post size 1 was then luted into the canal using One-Step Adhesive and Post Cement Hi-X. A push-out test was performed on three sections of each root to measure push-out bond strengths. Data were analyzed with ANOVA and Bonferroni's test at p < 0.05. Two extra teeth for each group were restored in the same fashion and processed for SEM observation. Results: (in MPa): Group 1: 15.7 ± 6.9; Group 2: 14.7 ± 6.5; Group 3: 14.0 ± 5.0; Group 4: 14.0 ± 5.1. The variable "post space" resulted in no statistically significant difference in mean bond strengths (p > 0.05). For the variable "root region," the coronal third (17.5 ± 6.0) resulted in statistically greater mean bond strengths than the apical third (12.3 ± 6.0) at p < 0.008. The middle third (14.0 ± 5.3) resulted in no statistically significant different mean bond strengths from the coronal third at p > 0.119 and from the apical third at p > 0.999. Under the SEM, some areas of the canal system still displayed residual gutta-percha, which resulted in debonding of the interface between the resin cement and dentin. Areas with incomplete dentin hybridization were observed in localized areas of all groups. Conclusions: The diameter of the post space did not affect the push-out bond strengths. Bonding at the coronal level of the root canal is more reliable than bonding at the apical level. The presence of residual gutta-percha and the deficient dentin hybridization may result in deficient seal of the resin-dentin interface.