The apical end of a root canal filling should be 1 to 1.5 mm short of the radiographic apex to prevent overextension beyond the apical foramen, which can cause periapical irritation or damage to periapical tissues. This distance ensures effective cleaning and sealing of the apical portion while avoiding extrusion of filling material into periapical tissues, reducing postoperative complications and promoting better healing. Overfilling beyond the apex can lead to persistent inflammation and failure, while underfilling significantly short of the apex risks residual infection. Therefore, precise length control within this range is critical for successful endodontic treatment outcomes.
Reference: Pathways of the Pulp, Cohen & Hargreaves, 12th Edition.