1. Anatomy of the root canals of the teeth of the permanent dentition, part 1;Hess,1925
2. Root canal morphology of the human mandibular first molar;Skidmore;Oral Surg,1971
3. Molar 4th canals: frequent cause of endodontic failure;Vande Voorde;Ill Dent J,1975
4. Root canal anatomy of the mandibular first molar;Vertucci;J NJ Dent Assoc,1974
5. Endodontic therapy of an unusual maxillary permanent first molar;Stabholz;J Endod,1983