Objective. To determine the effect of lactic acid at various concentrations on the shear bond strength of orthodontic brackets bonded with the resin adhesive system before and after water storage. Materials and Methods. Hundred extracted human premolars were divided into 5 treatment groups and etched for 30 seconds with one of the following agents: lactic acid solution with (A) 10%, (B) 20%, (C) 30%, and (D) 50%; group E, 37% phosphoric acid (control). Metal brackets were bonded using a Transbond XT. Bonding effectiveness was assessed by shear bond strength after 24 hours and 6 months of water storage at 37°C. The data were analyzed with 2-way analysis of variance and Tukey’s Honestly Significant Difference (HSD) test ( ). Results. Lactic acid concentration and water storage resulted in significant differences for brackets bond strength ( ). 20% lactic acid had significantly higher mean bond strength values (SD) for all conditions: 24 hours [12.2 (.7) MPa] and 6 months [10.1 (.6) MPa] of water storage. 37% phosphoric acid had intermediate bond strength values for all conditions: 24 hours [8.2 (.6) MPa] and 6 months [6.2 (.6) MPa] of water storage. Also, there were differences in bond strength between storage time, with a reduction in values from 24 hours and 6 months for all experimental groups ( ). Conclusion. Lactic acid could be used in place of phosphoric acid as an enamel etchant for bonding of orthodontic brackets. 1. Introduction The efficacy of various agents as an enamel etchants during bonding of orthodontic brackets has been studied [1–11]. Nevertheless, phosphoric acid has remained the principal enamel etchant since it was first introduced by Buonocore [12] in 1955 and used by Newman [13] in 1965. Phosphoric acid concentration between 30% and 40% results in the most retentive etching pattern [14, 15]. Acid etching of enamel is recommended with many dentinal bonding systems to improve the delivery of orthodontic treatment [1]. Claims of comparable bond strengths to enamel and dentin with conventional methods of bonding have meant that these adhesives are also suitable for orthodontic bonding [15–19]. The development of an adhesive bond requires establishing intimate contact between the liquid adhesive and the solid adherent, minimizing the stress concentration at the interface and reducing the influence of environmental factors on the interface integrity [20–22]. Therefore, the materials which are used today to adhere to the hard tooth structure must resist the surrounding influences in the oral cavity, including temperature changes [23].
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