An SEM evaluation of several adhesive systems used for bonding fiber posts under clinical conditions

The objective of this investigation was to evaluate the effectiveness of three 'one-bottle' and two 'three step' adhesive systems (as controls) in the formation of resin tags, adhesive lateral branches and a resin dentin interdiffusion zone (RDIZ) when used to bond fiber posts under clinical conditions. This study was performed using standardized SEM observations and scoring resin tag formation and density.

Fifty root canal treated teeth, already scheduled for extraction for endodontic or periodontal reasons, were selected for this study. The patients were informed and their written consent was obtained. The samples were randomly allocated to five groups of ten samples each. Group 1: All Bond 2 with C & B (Bisco); Group 2: Scotchbond Multipurpose Plus with Opal Luting Composite (3M); Group 3: Scotchbond 1 in combination with Rely X ARC resin cement (3M); Group 4: One-step with C & B resin cement (Bisco); Group 5: All Bond Experimental with Post Cement HI-X (Bisco). The adhesive systems and resin cements were used strictly according to the manufacturers' instructions. The priming-adhesive solution of each 'one-bottle' system was light-cured before placing the resin cement and the post. Fifty Aestheti-Plus posts (white quartz fiber posts, RTD, France) were used. A week later, the roots were extracted and processed for SEM observations.

All the adhesive systems showed a RDIZ and resin tag and adhesive lateral branch formation. Microscopic examination of the restored interfaces of Groups 1 and 2 showed a higher percent of RDIZ than those found in samples of Groups 3, 4 and 5. RDIZ morphology was easily detectable and uniform in the first two thirds of the root canals, whilst in the apical third the RDIZ was not uniformly present. Resin tag morphology and formation were significantly more detectable in the cervical and middle areas than in the apical zone. No statistically significant differences were found among the five groups coronally, while in the apical and middle thirds two 'one-bottle' systems (Groups 3 and 4) showed significantly less resin tags than the control Groups 1, 2 and the experimental Group 5. No statistically significant differences were found among the three 'one-bottle' systems in the three evaluated areas. The standardization of SEM observations and scoring resin tag formation allowed statistical evaluation.

The 'three step' adhesive systems can create a wider micromechanical interlocking between adhesive materials and etched dentin than 'one-step' systems.