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ObjectiveTo evaluate the influence of light exposure time on the adhesive strength and the failure mode of orthodontic brackets bonded to human enamel.Methods100 metal brackets were bonded with Transbond XT to the enamel bucal surface of human premolars. The sample was randomly divided into 5 experimental groups (n=20) according to the light exposure time (2, 4, 6, 8 and 10s) and light cured with an LED-curing device (1600mW/cm2). The specimens were thermocycled (5–55°C, 500 cycles), stored in distilled water (37°C, 7 days) and tested in shear, using an Instron universal machine (1 KN, 1mm/min). Failure mode was classified according to the Adhesive Remnant Index (ARI) using a stereomicroscope (20× magnification). Shear bond strength (SBS) data were analyzed with one-way ANOVA, followed by Tukey post hoc tests. The failure mode data were submitted to Kruskal–Wallis nonparametric test, followed by Tukey post hoc tests to the ranks. A significance level of 5% was set for all data.ResultsThe mean SBS values were 5.5±1.93MPa (2s), 7.4±1.95MPa (4s), 8.6±1.72MPa (6s), 9.3±1.64MPa (8s) and 11.6±2.65MPa (10s). Failure mode was mainly classified as Score 2. Both the SBS (p