Humans always wish to improve their quality of life. Particularly, the interest in appearances is increasing with the development in society and increase in income. In this respect, bleaching aesthetically increases self-satisfaction and is chosen as a method to ensure good impression on others. Therefore, it is expected that the demand for bleaching will increase in the future and will also cause a change in the bleaching methods.
We assessed the efficacy and safety of bleaching in the control and experimental groups using bleaching patches containing 3.0% hydrogen peroxide that were applied for 30 min once daily for 10 days.
△L* value was 2.50 ± 1.29 (p < 0.001) at 5 days after the attachment of the patches, indicating a significant color variation compared with that reported in previous studies [3, 13, 14]; this color variation was lower than that reported by Jung et al. . Considering the similarity in the experimental conditions between the studies, it is considered that the bleaching is affected by how tightly the patches are attached.
△a* value was −0.06 ± 1.25 at 7 days after the attachment of the patch (p < 0.05), which was similar to the results of previous studies [13, 15, 16]. Alternatively, although the color change was lower than those reported by Wen et al.  and Meireles et al.  (p < 0.05), it is believed that the result of this study is also significant, considering that there were differences in the bleaching ingredients and concentrations.
△b* value was 2.09 ± 1.80 at 10 days after the attachment, with significant color change verified (p < 0.05); however, this color variation was lower than those reported by previous studies [13, 16-18].
△E* value was 2.56 ± 1.28 on day 5 with a visibly identifiable level of change (p < 0.05), 3.31 ± 1.63 on day 7, and 4.75 ± 1.85 (p < 0.001) on day 10, showing a higher level of color change over time. This was at a similar level as that reported in some studies [19, 20] but lower than that reported in a majority of others [15, 21-25]. According to these results, it could be verified that the efficacy of bleaching is affected by the duration of application and the concentration. Based on these facts, it was verified that if bleaching is performed for 30 min once daily for >7 days using 3.0% hydrogen peroxide, the bleaching effect can be obtained at a visibly identifiable level.
The final color variation in this study was 4.75 ± 1.85, which was similar to that reported by Robert & Xiaojie . Sulieman et al.  reported that to obtain a bleaching effect using various concentrations of hydrogen peroxide, repeatedly applying low-concentration of hydrogen peroxide several times is more effective, and in case of high concentration, prompt color changes can occur; however, the concentration, time, duration of exposure, and safety might be more advantageous for color changes and its maintenance. In addition, application of high concentration hydrogen peroxide does not result in a significant difference in color changes .
Regarding the safety of bleaching patches, symptoms of tooth sensitivity occurred in two individuals (15.4%), gingival irritation in two (15.4%), and discomfort caused by attachment of patches in nine (69.2%), and such results did not affect dropouts. This corresponds to a study wherein most subjects complained of tooth sensitivity and discomfort, but it was at a minor level and did not act as a contributing factor toward discontinuing the trial [25, 26]. Moreover, the result was much lower than that reported by Bizhang et al. . Accordingly, it can be said that the bleaching condition in this study ensured safety because it did not result in tooth sensitivity or gingival irritation in the subjects.
The patches used in this study could be more tightly attached on the surface of teeth using the primer and were easily detachable without tools. Conversely, a previous study  reported that there was inconvenience in removing some remaining patches using a toothbrush; however, apart from this study, there is no study mentioning user convenience of using a tray or gel. Therefore, the patches used in the study were easy to attach and detach.
There are a few limitations of this study. First, the duration of applying the bleaching patches was limited to 30 min; therefore, the bleaching effect with extended duration of application was not compared. Second, how the active ingredients of the primer affect the bleaching effect was not measured because its control group was not selected. Therefore, further studies are suggested to determine the efficacy of bleaching patches with the increase in time by including a control group of 60 min.