Is a "flexible" glass fiber-bundle dowel system as retentive as a "rigid" quartz fiber dowel system?<||||>This study had two aims: (1) to compare the retention of a flexible directly placed fiber-bundle dowel system with that of a rigid prefabricated fiber-reinforced composite (FRC) dowel system, and (2) to determine the effect of decreasing the volume of luting cement around the flexible fiber-bundle dowels on the axial retention of the restorations. Single-canal premolars (n = 36) were decoronated, cleaned, shaped, and prepared for both flexible and rigid dowels to a depth of 10 mm using a size 2 drill. The roots were then randomly allocated into three groups: Ia, Ib, and II (n = 12). Flexible fiber-bundle dowels were placed in groups Ia and Ib. These were available in three fiber-bundle diameters: small (0.9 mm), medium (1.2 mm), and large (1.5 mm). These bundles were luted in the root canals with Variolink II. The differences between Ia and Ib were in the ratio of the volume of fiber-bundles to the volume of luting cement and in the mode of application. Medium fiber-bundles were placed to the end of the preparation in groups Ia and Ib; however, in group Ia, a small diameter auxiliary bundle was placed, whereas in group Ib, a large-diameter auxiliary bundle was cut axially into strips of circa 0.2-mm thickness before being sequentially overlapped in placement. Roots in group II were restored with size 2 rigid prefabricated fiber dowels and luted with the light-cured cement provided by the manufacturer. After 24 hours of storage, axial tensile forces were applied to all luted dowels progressively to failure at 0.5 mm/min. Data were analyzed using a one-way analysis of variance (ANOVA) and the Bonferonni test. The mean axial resistance forces (standard deviation [SD]) for groups Ia, Ib, and II were not statistically different at 166 (49), 157 (36), and 151 (44) N, respectively (p>0.05).
There was no significant difference between the retention of the flexible fiber-bundle dowel system and that of the rigid prefabricated fiber dowel system. Decreasing the volume of luting cement around the flexible dowels did not have a significant effect on the axial retention of the restorations.