If found early enough, decay can be reversible (i.e. it goes away itself) without treatment. This is only the case when the decay is small and still within the enamel (the outside shell of the tooth). Preventive measures alone including use of fluoride may help reverse the decay, i.e. allow the tooth to 're-mineralize'. Decay that has spread through into dentine (the softer inner part of the tooth) will need treatment. This will involve a dental filling. The earlier the cavity is treated, the smaller and easier any filling will be. There are a variety of materials that are used for tooth decay treatment. The different materials, their advantages, how fillings are placed and much more is covered in our fillings for teeth section. When a tooth is extensively decayed a filling may not be enough to fix the tooth. It may need an inlay, an inlay or crown to restore it.
If decay continues unchecked, it will reach the nerve of the tooth. As decay gets near the nerve this is usually when you might feel pain. When the nerve (pulp) of the tooth is damaged by decay, the tooth will root canal treatment, before the tooth is filled or crowned.
If decay progresses unchecked, the tooth may eventually rot away to the root and the tooth will need extracted