Bonding to enamel using alternative Enamel Conditioner/etchants

[Display omitted] •Enamel Conditioner and ZON etchant etched enamel as affective as phosphoric acid.•EC, ZON and phosphoric acid resulted in comparable bond strength to enamel.•Multi Etchant dissolved hydroxyapatite rods least, as revealed by TEM. Enamel bond durability of three new alternative etchants combined with three representative adhesives was determined. The ‘immediate’ and ‘aged’ micro-tensile bond strength (μTBS) of the 3-step etch&rinse adhesive OptiBond FL (‘O-FL’, Kerr), 2-step self-etch (SE) adhesive Clearfil SE Bond 2 (‘C-SE2’, Kuraray Noritake) and universal adhesive Adhese Universal (‘ADU’, Ivoclar Vivadent) were measured when bonded to enamel following either a proprietary organic acid-containing Enamel Conditioner (‘EC’, Shofu), a phosphoric-acid monomer-containing Multi Etchant (‘ME’, Yamakin: 10-methacryloyloxy tetraethylene glycol dihydrogenphosphate or MTEGP), or a metal salt-based ZON etchant (‘ZON’, Ivoclar Vivadent: ZrO(NO3)2). All alternative etchants were used in replacement of phosphoric acid, the latter (K-Etchant, Kuraray Noritake) also used with O-FL and ADU, in addition to C-SE2 that was solely used in SE mode (controls). The enamel-etching patterns and de-bonded fracture surfaces were examined by SEM, while the interfaces with enamel were ultra-morphologically characterized by TEM. No statistically significant difference in immediate and aged μTBS, obtained by combining the three alternative etchants with the three adhesives, was recorded as compared with the respective controls, except for ME combined with O-FL. Upon aging, significant reduction in μTBS was recorded for the ME/C-SE2 and ME/ADU combinations. The percentage of adhesive failures increased with aging. SEM revealed similar etching patterns produced by EC and ZON as by classic phosphoric-acid etching, for which also numerous micro-resin tags at the adhesive-enamel interface were disclosed. Durable bonding to enamel was generally obtained for all etchant/adhesive combinations with the exception of the ME/O-FL combination.