Hardness, elasticity and ultrastructure of primary tooth dentin bonded with a self-reinforcing one-step self-etch adhesive

Objective: This study evaluated the interfacial quality of sound and caries-affected primary tooth dentin bonded with a self-reinforcing one-step self-etch adhesive. Methods: Non-carious, sound dentin was prepared with water-cooled high-speed diamond burs. Caries-infected dentin was removed with water-cooled low-speed round steel burs and hand instrument. Dentin was bonded with Bond Force (Tokuyama Dental). A nano-indentation tester was employed for determination of hardness (H) and Young's modulus (Y) of resin-dentin interface. Similar resin-dentin interfaces were examined with a SEM/EDX, and with a TEM using ammoniacal silver nitrate tracer for nanoleakage. Results: In the comparison of the H and Y values between the interfacial dentin and the underlying mineralized dentin, no significant difference was seen in caries-affected dentin, however, the values of the interfacial dentin were significantly lower in sound dentin. The H value of the interfacial dentin of sound dentin was significantly lower than that of caries-affected dentin with significantly higher Ca content. No significant difference was observed in the Y values of the interfacial dentin of the two substrates. For both sound and caries-affected dentin, TEM revealed silver deposits in the interfacial dentin and adhesive layer, and smear layer remained within the resin-dentin interface. However, Ca and P contents of the adhesive layer at 10 μm above the dentin surface were the same as those present in the interfacial dentin. Conclusions: Both for sound teeth and caries teeth, Bond Force does not prevent the nanoleakage along the resin-dentin interface.