Development of new adhesive systems based on the characteristics of primary tooth dentin

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Primary dentin has significantly lower physical properties than permanent tooth dentin, and more susceptible to chemicals. The purpose of this study was to develop a new adhesive system with mild acid-etching ability, adequate penetration into the caries-affected dentin and simple and easy to clinical use.Materials, Methods and Results :Sun-Medicals 4-META one-step self-etch adhesives AQ Bond Plus (AQBP)or Hybrid Bond (HB, new product)was applied on the sound or caries-affected primary tooth dentin.#Test 1 : resin-dentin interfaces were measured with a nano-indentation tester and the hardness (H)and Young's modulus(Y)were calculated.#Test 2 : Ultrastructures of resin-dentin interfaces were observed with FE-SEM, SEM and TEM.(1)Only in the carious-HB group, the H and Y of the interfacial dentin were not significantly lower than those obtained from 10-70 μm beneath the interface.(2)Both in the sound-AQBP and sound-HB groups, the H of the interfacial dentin was significantly lower than those obtained from 10-70 μm beneath the interface.(3)Compared with sound primary tooth dentin, the H and Y values of adhesive layer of AQBP and HB were about 1/2 and 1/3, respectively.(4)The hybrid layer of both adhesives was about 1 μm thick.(5)In the sound dentin, silver nanoleakage was observed along the interface both in the AQBP and HB groups.(6)In the carious teeth, silver nanoleakage was not seen in the hybrid layer and many of the dentinal tubules were filled with mineral deposits that prevented silver nanoleakage. However, silver deposits were seen in the underlying porous caries-affected dentin.In both adhesive groups, silver nanoleakage was observed in these resin-dentin interfaces and porous caries-affected dentin. Those results might deteriorate effect of clinical prognosis of resin restorations. Further improvements of one-step self-etch adhesives are required to obtain stable adhesion