A novel chemical aging method for evaluating degradation of resin-dentin bond: a preliminary study

Abstract

Purpose: to investigate the use of NaOH solution as storage medium on dentin micro-tensile bond strengths (MTBS) and the micromorphology of resin–dentin interfaces. Materials and Methods: mid-coronal dentin was exposed for 45 human third molars. One of five dentin adhesives investigated was applied to each dentin surface, followed by placement of a resin composite from the same manufacturer (Clearfil S3 Bond + Clearfil Majesty, Clearfil SE Bond + Clearfil Majesty, Kuraray Co. Ltd; Adper Easy One + Z250, Adper Single Bond 2 + Z250, 3M ESPE; Gluma Comfort Bond + Charisma, Heraeus Kulzer). Bonded specimens were sectioned through resin–dentin interfaces into multiple beams with a cross-sectional area of about 1 mm2. The beams were kept in 10 wt% NaOH solution at 37 °C for 0, 2, 4, 6, 8, 10, or 12 h respectively prior to MTBS evaluation. The MTBS data were analyzed statistically. Failure modes were determined by stereomicroscopy. Representative fractured surfaces and resin–dentin interfaces were examined by scanning electron microscopy. Resin–dentin interfaces were also analyzed by transmission electron microscopy (TEM). Results: dentin MTBS decreased significantly with increased storage time in NaOH. Micro-gaps appeared along the resin–dentin interfaces after NaOH treatment and became wider over time. An electron-dense hybrid layer was observed by TEM in the control group, while an electron-lucent band was detected at the resin–dentin interfaces of specimens treated with NaOH for 8 h. Conclusion: aging of resin–dentin bonds in NaOH solution may be used as an expedited chemical aging method for evaluating degradation of dentin bond.