Permanent tooth decay refers to the decay occurring in newly erupted teeth. The most common case is the first permanent molar, also known as the six-year molar, which emerges quietly in the mouth at the age of six. Once this tooth emerges, it cannot be replaced for life. If this tooth decays, it is necessary to fill the tooth as soon as possible; otherwise, if the decay reaches the dental nerve, it could lead to pulpitis. Alternatively, for newly erupted teeth, sealants should be applied to the pits and fissures of the teeth to slow down the pace of decay. Permanent tooth decay requires us to intervene with treatment as early as possible; otherwise, it may cause pain or even tooth loss.