There are many projects that can be done for whitening. Photon rejuvenation, picosecond and water needle whitening are all good, such as photon rejuvenation and picosecond, which have a quick effect, but they need to be done once in a while to consolidate and maintain stability. Like what I often do, Demarey Water Light is a gradual whitening, and it takes an injection every once in a while, but I didn't expect the effect to last so long and the price is more cost-effective. So in my opinion, mainstream whitening projects are effective, and the difficulty lies in whether they can persist.