Fig. 1

Preparation of dentin/resin slices and shear bond testing using a universal testing machine. a The crowns of the primary molars were cut at the level of cemento-enamel junction, sectioned in to 1.5 mm-thick slices, embedded into self-curing epoxy resin, ground and polished with 800 mesh waterproof abrasive paper. b Dental resin composite was filled into the cavity, piled up into blocks and light-cured, and cut into slices (4 mm × 4 mm × 2 mm) using a low-speed cutting machine and polished by 400–600-grit silicon carbide paper. c The resin slice was bounded to the dentin surface. d The shear bond strength was calculated by dividing the maximum load required to fail the bond by the bond area