Influence of dowel type on push-out bond strength to regional root canal dentin.

Purpose: To compare the laboratory bond strengths of three different types of fiber-reinforced composite dowel systems in three different locations of prepared root canal dentin.

Methods: 60 human extracted intact upper central incisors were selected. The coronal aspect of each tooth was removed, and the remaining root received endodontic therapy. The roots were divided into three experimental groups (n = 20). Roots were restored with one of the following dowel systems according to the manufacturers' instructions: carbon fiber (C-Posts), quartz (Aestheti-Plus), glass fiber (FibreKor). A single bond adhesive (OptiBond Solo Plus) was applied to the walls of the dowel spaces, excess carefully removed with paper points, and then light cured for 10 seconds. A dual-polymerizing resin luting agent (Variolink II) was mixed and then placed in the dowel 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. Each root was cut horizontally, and three 1 mm-thick root segments (one apical, one middle, and one cervical) were prepared. Using a push-out test, the bond strength between dowel and dentin was measured using a universal testing machine. The data were analyzed with 2-way analysis of variance and Tukey's Honestly Significant Difference (HSD) test (alpha = 0.05).

Results: Dowel type and regional root canal dentin resulted in significant differences for push-out bond strength (P < 0.001). Glass fiber dowels (FibreKor) had significantly higher mean bond strength values (SD) for all dowel space regions: coronal (13.6 [1.5] MPa), middle (10.8 [1.8] MPa), and apical (8.9 [1.1] MPa). The carbon fiber dowels (C-Posts) had significantly lower bond strength values in all dowel space regions: coronal [8.6 (1.1) MPa], middle (4.7 [1.0] MPa), and apical (4.1 [1.1] MPa). Quartz dowels (Aestheti-Plus) had intermediate bond strength values: coronal (10.9 [1.1] MPa), middle (9.6 [1.1] MPa), and apical (7.7 [1.1] MPa). Also, there were differences in bond strength between regional root canal dentin, with a reduction in values from the coronal to middle and apical thirds for all experimental groups (P < 0.001).