Hardness and elasticity of caries-affected and sound primary tooth dentin bonded with 4-META one-step self-etch adhesives

Purpose: To evaluate the quality of the interface of sound and carious primary tooth dentin bonded with two 4-META one-step self-etch adhesives. Methods: 12 sound and 12 carious primary molars were bonded with AQ Bond Plus (AQBP; Sun Medical) or Hybrid Bond (HB; Sun Medical) and restored with Clearfil Protect Liner F (Kuraray Medical Inc.). After 24 hours of water immersion, the teeth were sectioned and polished. Resin-dentin interfaces were measured with a nano-indentation tester and hardness and Young's modulus were calculated. Data were analyzed using one-way or two-way ANOVA and Fisher's PLSD test with α=0.05. Resin-dentin interfaces were also observed with SEM and TEM. Ammoniacal silver nitrate was used as a tracer for TEM observation. Results: Hardness and Young's modulus of the interfacial dentin were significantly lower than the underlying intact dentin except for the carious-AQBP group. However, there was no significant difference of hardness and Young's moduli of the interfacial dentin among all groups. TEM revealed extensive interfacial nanoleakage in sound dentin bonded with either AQBP or HB. For the carious teeth, nanoleakage was absent in the hybrid layers bonded with the two adhesives. However, extensive silver deposits were identified from the subsurface, porous caries-affected dentin.