A Comparative Study of the Effect of Water Storage on Conventional, Self-etching, and Adhesive Liquid Resins

Objective: A variety of liquid resins is currently available composed of conventional (non-adhesive) methacrylate monomers or mixtures of conventional monomers and polar-group functionalized monomers to facilitate demineralization and infiltration of hard dental tissues. As crosslinked methacrylate networks are susceptible to hydrolytic degradation, doubts have been expressed on the stability of adhesive resin components in an aqueous environment. The aim of the present study was to comparatively assess the effect of water on a conventional bonding resin (Heliobond/HB), three adhesive resins of two-step self-etching systems (SE Bond/SE, KBF/KB,UniFil Bond/UF) and a single-step self-etching system (One Up Bond F/OB). Methods: Two series of specimens (n=5, d:7mm, h:1mm) were produced; the 1st (D) was kept in dark and dry conditions, whereas the 2nd (W) was immersed in water (2wk,37 degrees centigrade). The flat specimen surfaces were subjected to Vickers microhardness measurements (200g load, 15s period) and micro-internal reflectance FTIR spectroscopy. Results: The results of microhardness were: [HVD]: HB:22.13(0.28),SE:31.44(0.29), KB:26.03(0.27), UF:28,85(0.13), OB:28.26(0.46); [HVW]: HB:17.36(0.47),SE:14.83(0.35),KB:16.44(0.36), UF:13.38(0.29), OB:11.43(0.25). A significant HV reduction was noted in all products after water storage(p<0.05, t-test), but the %ÄH(D-W) in the adhesive resins was much higher (37-60%) than in the conventional resin (21%). FTIR revealed increased amount of H-bonded –OH groups in all water stored specimens, reduction in the extent of –COOH (UF,OB) and P-OH (SE,KB). Conclusion: The results of the present study demonstrate that the adhesive resins tested are subjected to greater extent of water plasticization than the conventional resin, due to ionization of the acidic groups immobilized in the network and increased water hydrogen bonding, that may induce network degradation.