## 4 Discussion
The changes in the color of each tooth sample were documented by acquiring an image with a digital camera in the present study. The images were subsequently analyzed using Adobe(r) Photoshop CS2 to determine the changes in the color of the tooth. This analysis was unaffected by external colorimetric factors such as the illumination and the color of gingival surfaces. The ShadeEye NCC is a type of colorimeter that reads visible light using a filtered photodetector and calculates the information of chroma, value, and hue. It is expressed as L*a*b* colorimetric or XYZ colorimetric values [27]. However, since it is a device that measures a small area of the tooth, color errors may occur if the measuring tip is not always located in the same area. The VITA Easyshade is an effective method of observing color tone differences by directly comparing teeth with existing color samples, and it is the most commonly used method in clinical practice [28]. However, there are problems such as limitations in the color tone range, subjective factors when selecting a color tone, and inconsistency in selection due to ambient light sources, etc. In this study, three methods of measuring tooth color were used. The CIELAB color system was used to measure color change due to whitening in extracted teeth, and the color change in the cadavers was performed using ShadeEye NCC and VITA Easyshade, which are measurement methods mainly applied in clinical practice. Cadavers have been used to evaluate the suitability and efficacy of drugs in clinical research. A measurable change in the brightness of the teeth was determined using ShadeEye NCC and the VITA Easyshade method in the present study. In the evaluation using VITA Easyshade, it was confirmed that the brightness of the teeth increased by 5 levels. Cadaver teeth treated with DW and NCP using ShadeEye NCC showed an \(\Delta E\) value of 4.0. Considering that the change in tooth color can be seen with the naked eye when the \(\Delta E\) values is 3, the highest \(\Delta E\) value is 7.86, which can be considered a high value. Although the experimental NCP device could not treat the entire tooth with plasma evenly, it was found to have a high tooth bleaching effect. In future human clinical studies, NCP will be applied evenly to all teeth through improvements in equipment to ensure the same whitening effect. This result not only means that the quantity of \(\bullet\)OH produced by NCP decomposing water could be sufficient for teeth whitening; it also means that if NCP is applied to teeth whitening, water can be used instead of dangerous HP. [PERSON] et al. [15] conducted additional research on alternative materials and reported that tooth bleaching performed using chlorine dioxide is faster than tooth bleaching performed using HP. However, [PERSON] et al. [13] reported that the use of chlorite-based bleaching agents can lead to the erosion of minerals and the formation of cracks in the tooth structure. Several materials that can be used as alternatives to peroxides have been investigated; however, no effective alternatives with no harmful side effects have been identified. In contrast, several studies have demonstrated the efficacy and safety of the application of plasma with existing tooth-bleaching agents [13; 14; 24; 25; 26]. The present study demonstrated that treatment with NCP combined with DW can yield the desired tooth-bleaching effect without the inclusion of the adverse effects associated with HP treatment, underscoring an advancement in the field of dentistry. The amount of \(\bullet\)OH generated was investigated to support the bleaching mechanism, as NCP generates many active species, including OH, O, H, O\({}_{3}\), and NO. OH reacts with chromophores as macromolecular stains switch to small molecular stains. Several previous studies have reported results similar to those of the present study. [PERSON] et al. [24] and [PERSON] et al. [22] reported that \(\bullet\)OH was an important reactive species in tooth bleaching.