Effects of Selective Phosphoric Acid Etching on Enamel Using "No-wait" Self-etching Adhesives

Purpose: To evaluate the effect of selective phosphoric acid etching on enamel using "no-wait" self-etching adhesives. Materials and Methods: Clearfil Universal Bond Quick (UBQ, Kuraray Noritake) or G-Premio BOND (GPB, GC) was applied to ground human enamel surfaces. The adhesives were used in 3 modes: no-waiting self-etching mode (UBQ-0 or GPB-0), 10-s self-etching mode (UBQ-10 or GPB-10), and the selective-etch mode with phosphoric acid etching (UBQ-PA or GPB-PA). After an acid-base challenge, the morphological attributes of the interface were examined using scanning electron microscopy (SEM) to characterize the acid-base resistant zone (ABRZ). Microshear bond strength (µSBS) testing to enamel and ultimate tensile strength (UTS) of the adhesive resin were carried out. Results: ABRZ formation was confirmed in all groups. UBQ-PA and GPB-PA created thicker ABRZ with no funnel-shaped erosion beneath the adhesive-enamel interface. µSBS of UBQ-PA was significantly higher than UBQ-0 and UBQ-10 (p 0.05). However, there were no statistically signficant differences in µSBS among GPB-0, GPB-10, and GPB-PA. For the UTS, UBQ was significantly higher than GPB. Conclusion: Selective phosphoric acid etching created a stable adhesive-enamel interface. The no-waiting self-etching concept adhesive led to a thinner ABRZ. The results of µSBS suggest that phosphoric acid etching effects on enamel are material dependent. Keywords: enamel, multimode, no-waiting self-etching concept, phosphoric acid, acid-base resistant zone, microshear bond strength test