If the apical infection alone rarely infects the adjacent teeth, if the apical infection is left untreated for a long time, the apical infection spreads to the surrounding tissues and causes osteomyelitis of the jawbone, from which point of view the apical infection can infect the adjacent teeth, as it causes inflammation of the entire corresponding area of the jawbone, causing loosening of the corresponding adjacent and all the teeth in the jawbone and overflow of pus from the infection in the jawbone. Apical inflammation can sometimes progress further and form periapical granulomas or periapical cysts, which may likewise develop and form cysts in multiple tooth sites, a condition that also means that the apical infection has invaded the adjacent teeth. Therefore, a simple periapical infection will not clinically infect the adjacent teeth, but the progression of periapical infection may invade the adjacent teeth.