Since tooth decay is an irreversible change, it can only be eliminated through treatment. If the decay is shallow, reaching only the superficial and middle layers of dentin, resin filling can be considered directly. However, if the decay is deeper, reaching the deep dentin layer or very close to the pulp chamber, firstly, pulpal treatment is needed to promote the formation of restorative dentin by using calcium hydroxide similar preparation to the bottom of the cavity to isolate the resin from stimulating the pulp, and then resin filling can be performed. It can minimize the irritation of resin to the pulp and protect the tooth.