Abstract:

Objective To evaluate the effect of two different acid etching agents on the bonding strength between deciduous enamel and composite resin at different etching times. Methods Seventy primary incisors were made into test specimens and randomly divided into 7 groups(n=10), 6 experimental groups, and 1 blank control group. The specimens were divided into groups and etchedwith two different acid etching agents(35% H₃PO₄, 15% HCl) for different durations(15, 30, 60 s). After bonding with the composite resin, shear force testing was performed. Additionally, two deciduous molar dental crowns were cut vertically along the gingival axis, with each tooth divided into seven sections and randomly assigned to seven groups. Enamel acid etched specimens were produced and the surface morphology was observed using scanning electron microscopy. Finally, 24 deciduous molars were randomly divided into 3 groups(n=8) according to the etching time(15, 30, 60 s), and each tooth was vertically cut into 2 pieces along the buccal lingual direction, namely the phosphoric acid group and the hydrochloric acid group, and etched for the same time(n=8), for a total of 6 groups. They were bonded with resin and made into specimens. The specimen was cut vertically to the bonding surface into 2 parts. One measurement point was selected for each part, and each group had a total of 16 measurement values. Resin protrusion length was measured under scanning electron microscopy and was statistically analyzed. Results When comparing acid etching for 15, 30, and 60 s, the bonding strength of the phosphate group was higher than that of the hydrochloric acid group. Under scanning electron microscopy, there was no significant difference in the acid etching mode between the two groups, both of which were type 2 acid etching modes dissolved along the glaze column direction. At 15 seconds of acid etching, the enamel surface was uneven, and continuous and uniform dissolution appeared at 30 seconds. The length of resin protrusion increased with the increase of acid etching time, and the phosphoric acid group was greater than the hydrochloric acid group at 15, 30, and 60 s compared between groups. Conclusion The etching time is positively correlated with the shear bonding strength. The best bonding effect is achieved when deciduous teeth are etched with 35% H₃PO₄for 60 seconds, and the effect of 35% phosphoric acid etching on deciduous tooth enamel is better than that of 15% hydrochloric acid.

Key words: shear bonding strength, deciduous enamel, scanning electron microscope, hydrochloric acid