The distribution maps of landmarks. Red dots represent MB landmarks, Purple dots ML landmarks, Blue dots the DB or D landmarks and Green dots the DL landmarks. (A) Root canal orifices in 2-rooted 3-canals, (B) centre of the canal primary curve in 2-rooted 3-canals, (C) intersection point of occlusal surface in 2-rooted 3-canals, (D) root canal orifices in 2-rooted 4-canals, (E) centre of the canal primary curve in 2-rooted 4-canals, (F) intersection point of occlusal surface in 2-rooted 4-canals. (G) Root canal orifices in 3-rooted 4-canals, (H) centre of the canal primary curve in 3-rooted 4-canals, (I) intersection point of occlusal surface in 3-rooted 4-canals.