OBJECTIVETo observe the influence of different bonding process and three different root canal sealing materials on microstructure of root canal dentin bonding interface after fiber post and resin bonding, so as to improve clinical operation steps and to optimize fiber post resin bonding effect.

METHODSFifteen human single mandibular first premolars were selected. Three were bonded with fiber posts through Relyx Unicem conventional bonding steps after filled with root canal sealing materials of zinc oxide eugenol paste (Group A), and another three were bonded through the same steps after filled with sealing materials of Vitapex (Group B). The other nine were filled with sealing materials of AH Plus, randomly divided into three groups and bonded through different steps as follows: conventional bonding steps only (Group C), etching with 35% phosphoric acid before conventional bonding steps (Group D), and etching and coating with Singlebond 2 adhesive before conventional bonding steps (Group E). After immersed in saline solution for one week, all the roots were cut into three sections of 3 mm in thickness with emery chip and numbered as crown section, middle section and tip section respectively. The samples were observed the resin protrusion in mixed layer of dentin interface and dentinal tubules by scanning electron microscopy.

RESULTSWe observed the resin protrusion in microstructures of the roots bonded through Relyx Unicem after filled with three different root canal sealing materials (Group A, B, C, E): most obvious in the root crown sections, middle in the root middle sections and least in the root tip sections. Differences were observed in roots filled with different sealing materials: little resin protrusion were observed in crown sections only in Group A and B, but large number of resin protrusion were found in crown and middle sections in Group C-E. Compared with Group C, no more resin protrusion were found in Group D. More and elongated resin protrusions were found in Group E.

CONCLUSIONSWe recommend using AH Plus as root canal sealing materials for residual crown and root needed to strengthen by fiber post. It is no need to etch before Relyx Unicem conventional bonding steps. However, coating Singlebond 2 adhesive after acid etching has the potential to increase fiber post cementation.