Hello individual have different shades of teeth. Some are more yellowish some have whiter teeth. In some cases teeth become yellowish due to fluorosis. Fluorosis occur due to high level of fluoride in water or diet which occurs at the time of development only. So we can do bleaching of teeth for naturally yellowish teeth which gives very good result Comparatively fluorosis teeth have less satisfactory results in bleaching More vigorous brushing of teeth make teeth more yellowish