The specimens were subjected to shear bond strength testing with a universal testing machine (Instron 5965; Instron, England) with a load cell of 5 kN operated by a single operator. A knife‐edged rod with a width of 0.5 mm was applied at the interface of the resin composite disk with the enamel/dentin at a crosshead speed of 0.5 mm/min. Modes of bond failure were determined by viewing the fracture sites along the enamel/dentin–composite disk interface under a stereomicroscope (Nikon Stereomicroscope 100 m Microscope, SMZ 1000, SMZ800, Swift, CA, USA) with a digital camera (Nikon digital camera DXM1200F). Failure modes were classified as adhesive, cohesive, or mixed and were defined as follows: adhesive failure showed no sign of dentin/enamel fracture or remnants of composite resin on the tooth; cohesive fractures showed complete fracture of dentin or resin; and mixed samples showed both adhesive and cohesive failures.