Oral antibiotics can help control infections that have spread beyond the tooth into surrounding tissues, but they usually cannot eliminate the source of infection inside the tooth.
When a tooth's pulp becomes dead or partially dead, the blood supply inside the tooth is compromised. Because oral antibiotics travel through the bloodstream, they may not reach the infected tissue inside the root canal system effectively.
Root canal treatment removes the infected or damaged pulp tissue, cleans the inside of the tooth, and seals the space to eliminate the source of infection. Antibiotics may sometimes be recommended as part of treatment, but they do not replace removing the source of infection within the tooth.