Micromorphology of the fiber post–resin core unit: a scanning electron microscopy evaluation

Objectives. To microscopically evaluate the structural characteristics of post-and-core units made with a fiber post and different types of composite resins used as build-up materials. Materials and methods. Forty endodontically treated human maxillary incisors were prepared for receiving a fiber post (Aesthetic Post Plus, RTD). One-Step (Bisco) was used as a bonding material, and C&B resin cement (Bisco) for luting the post. The posted roots were randomly divided into eight groups. In each group a different material or technique was applied to build up the abutment. The materials on trial were Z100 (3M-ESPE), Lumiglass (RTD), Gradia (GC), Build-it! (Jeneric Pentron). On the specimens of Groups 5–8, the same materials were used for build-ups, with the addition of a preshaped plastic shell (Composipost, Core Form, RTD). All the post-and-core specimens were cut perpendicular to their long axis and processed for SEM observation. The objective was to detect the presence of voids/bubbles within the resin abutment, and of gaps at the interface between the post surface and the core material. These aspects were quantified with reference to indexes. The differences among the scores were tested for statistical significance (p<0.05). Results. In the absence of any matrix, cores built up with Gradia showed the highest integrity, and those made with Z100 the best adaptation onto the post. In the presence of shells, Build-it! provided the most satisfactory result. Build-it! was the only material to perform better when used in combination with a shell. Significance. When hybrid composites are used to build up a core onto a fiber post, a higher homogeneity of the abutment and a better post–core integration are achieved if the build up is done in the absence of any matrix.