Polymerization shrinkage stress, internal adaptation, and dentin bond strength of bulk-fill restorative materials

Purpose: To evaluate polymerization shrinkage stress (PSS), internal gap formation (IGF), and dentin bond strength (DBS) of one conventional resin composite and five bulk-fill restorative materials. Materials and methods: One conventional resin composite (Filtek Supreme Ultra/SU) and five bulk-fill restorative materials: two regular paste-consistency composites (Tetric EvoCeram Bulk Fill/TE and Opus Bulk Fill/OP), one low-viscosity dual-cure composite (Fill-Up!/FI), one bioactive material (Activa BioActive Restorative/AC), and one high-viscosity glass ionomer (Equia Forte Fil/EQ) were tested. PSS was determined with a tensiometer attached to a universal testing machine (n = 5). For IGF, Class I cavities prepared in the occlusal surface of extracted third molars (n = 5) were filled up, cross-sectioned, and analyzed in scanning electron microscopy. The DBS was evaluated with microtensile bond strength test measured after 24 h or one-year storage. Data were statistically analyzed by one and two-way ANOVA and Tukey post-hoc test (α = 0.05). Results: FI, SU, and OP presented higher PPS values and EQ showed the lowest ones. IGF was lower for OP and AC. SU showed the greatest DBS values and OP and FI the lowest after one-year storage. Conclusions: No correlation between PSS and IGF was found. Little difference in DBS among the restorative materials was detected, and its stability was material dependent.