FESEM and TEM observations of dentin-adhesive interface after acid challenge

Objective: This study examined the in vitro caries inhibiting potential of five dentin adhesives. Materials and Methods: Fifteen human premolars were divided into five groups (three teeth each). Occlusal enamel was removed to expose underlying coronal dentin by using a slow speed diamond blade. The dentin surface was treated with one of the following dentin adhesives; Clearfil Protect Bond (PB), Clearfil SE Bond (CB), Clearfil Tri-S Bond (TB) (Kuraray Medical, Japan), G-Bond (GB, GC, Japan) and Single Bond (SB, 3M-ESPE, USA) according to the manufacturers' recommendations. Each specimen was longitudinally sectioned in the mid coronal plane mesio-distally into two halves and stored in an artificial demineralization solution (pH 4.5) for 90 min. The demineralized each half was then sectioned along the bonding interface mesio-distally into 2 x 3 x 5 mm slabs. 90 nm thick sections were prepared for transmission electron microscopic (TEM) observation. After TEM examination (H-7100, Hitachi, Japan), the grids were coated with carbon and observed under a field emission scanning electron microscope (FESEM, 4500S, Hitachi-Japan) equipped with energy dispersive X-ray analysis (EDS). Results: FESEM showed the outer lesion (depth of 15-20 ìm) after acid challenge in all groups. TEM of dentin side of outer lesions showed a gradual dissolution of hydroxy apatite crystals. The self-etch adhesives of PB, CB, TB and GB formed a 1-2ìm thick acid-resistant zone (ARZ) adjacent to the hybrid layer. EDS confirmed higher density of calcium and phosphorus in the ARZ than the adjacent hybrid layer. However, no ARZ was observed in SB. In the ARZ, more densely arranged crystallites were observed in PB and CB than in TB and GB. Hydroxy apatite crystallites of PB were larger compared to CB. Conclusion: The ultrastructure of dentin-adhesive interface after acid challenge was material dependent. The self-etch adhesives demonstrated anticariogenic potential at the interface.