Structural Analysis of Acid-base Resistant Zone Using Self-etching Primer Systems

Objectives: The aim of this study was to examine the ultra-structure of acid-base resistant zone (ABRZ) using a field emission scanning electron microscope (FESEM) in combination with Energy Dispersive X-Ray Spectroscopic (EDS) analysis.

Methods: Dentin disks were ground with #600 SiC. One of three self-etching primer adhesive systems, Clearfil SE Bond (SE, Kuraray Medical, Japan), FL-Bond (FL) and FL-BondII(FLII)(Shofu, Japan) was applied to the dentin surface according to the manufacturers' instructions. A resin composite (BeautifilIIfor FL-Bond and FL-BondII, Clearfil AP-X for Clearfil SE Bond) was put between two dentin disks and light-cured to make a dentin disk sandwich. Each specimen was stored in a demineralizing solution (pH 4.5) for 90 min to create artificial secondary caries, and then immersed in 5% NaClO for 20 min to remove the demineralized dentin collagen. Following this, they were vertically sectioned, polished and etched with an argon-ion beam for 6 min to observe under a FESEM (S-4500, Hitachi). An EDS line scan analysis was performed for the elements of calcium (Ca) and fluoride (F) at the adhesive-dentin interface (EMAX-7000, Horiba).

Results: The ABRZ was observed beneath the hybrid layer (HA) for each group. In the cases of SE and FL, the ABRZ was parallel and homogeneous to HA, while the ABRZ of FLII sloped and increased from the top to the end of outer lesion. Ca was detected in ABRZ in all the groups, however, higher contents of Ca were detected in the ABRZ of FLII than those in SE and FL. However, F was only detected around the S-PRG filler contained in FLII.

Conclusion: The ultra-structures of the ABRZ were material dependent. The ABRZ formed by the self-etching primer systems demonstrated good resistance against artificial secondary caries formation.