Effects of C-factor and resin volume on the bonding to root canal with and without fibre post insertion

The aim of this study was to evaluate the effects of C-factor and resin volume on the regional bond strength of dual-cure luting resin to root canal dentine.

Twelve single-root human premolars were decoronated and post space prepared to a depth of 8 mm, with a diameter of 1.5 mm for six roots and 1.75 mm for the other six. Root canal dentine was treated with a dual-cure bonding system and light-cured for 20 s. Specimens were filled with a dual-cure resin composite with or without insertion of 1.4-mm-diameter light-transmitting glass fibre posts, followed by light-curing for 60s from the coronal direction. After 24 h water storage, each specimen was serially sliced into eight 0.6 mm × 0.6 mm thick beams for a microtensile bond strength test. Failure modes were observed using SEM. Bond strength data were divided into coronal and apical regions and statistically analysed.

For both sizes of post space, bond strengths dramatically decreased when fibre posts were inserted. There were no significant differences in microtensile bond strength between 1.5 mm and 1.75 mm canal width, regardless of fibre post insertion. Regional differences in bond strength were found only in the resin-filled canals.

The increase of C-factor of the root canal system by insertion of a fibre post had a detrimental effect on the bond strength to root canal dentine. On the other hand, the change of resin volume had no significant effect on bonding.