Cavities should be filled as soon as possible, through a treatment known as filling, and it is best not to delay. If a cavity could have been simply filled within a month, it might further become infected, causing inflammation of the dental nerve and leading to conditions such as pulpitis or apical periodontitis. Direct filling won't be possible; the tooth will need treatment before it can be filled. Cavities are a type of hard tissue decay caused by bacterial infection. If it's an adult's cavity, the progression is relatively slow and may only advance partially within a month, not reaching the dental nerve. However, in children, cavity progression is very rapid; if not promptly treated, severe dental nerve pain could occur within a month, necessitating further dental treatments.