If tooth decay is not completely cleaned out before filling, bacteria can continue to develop and multiply within the tooth, leading to more severe decay and potentially causing diseases such as pulpitis or periapical periodontitis. It is recommended that patients with cavities should undergo treatment based on the severity of the decay. Mild cavities usually only cause minor changes in tooth color; this can be gently abraded and then treated with fluoride materials. If the cavity is more severe, the decayed material inside the cavity should be completely removed, and then light-cured resin material can be used for filling. Deeper cavities may also require a protective pulp base.