Influence of Lactic Acid Aging on Bond Strength of Bracket

Objective: Lactic acid has an etching effect on both enamel and dentin and the possibility of substituting lactic acid for phosphoric acid as an enamel and dentin conditioner might be considered. This study was to determine the effect of lactic acid at various  concentrations and etching times on the shear bond strength of brackets before and after aging bonded with the resin orthodontic adhesive system Transbond XT.

Method: 100 extracted human premolars were divided into 5 groups of 20 teeth each according to enamel surface treatment. Group I 37% phosphoric acid - 30 sec., Group II 10% lactic acid - 30 sec., Group III 20% lactic acid - 30 sec., Group IV 20% lactic acid - 10 sec., and Group V 20% lactic acid - 20 sec. Random samples were prepared for observation by scanning electron microscopy. Brackets were bonded to the teeth in each test group with Transbond XT.  (n = 25) and group II, NRC/ Transbond XT according to the manufacturer's instructions. Shear bond strength was measured with a universal test machine with a crosshead speed of 1 mm/min for half of the specimens. The rest of specimens were aged for 6 moths and the shear bond strength was measured. Data were analyzed using analysis of variance (ANOVA), Tukey honestly significant difference.

Result: The shear bond strength to enamel treated with 10% lactic acid (122.1±6.8)  and 20% lactic acid (118.7±7.9) fo 0 seconds were significantly higher (p>0.05). The mean bond strength for phosphoric acid was intermediate (81.6±7.5). Shear bond strength was significantly reduced after aging for all groups ((p > 0.001).

Conclusion: Lactic acid etched the tooth enamel in a manner similar to that of phosphoric acid. Lactic acid could be used in place of phosphoric acid as enamel etchant and may present less risk of adverse reaction in vivo.