Root canal , the pulp chamber, dental pulp, root end, apex, number of root canals per tooth depends on the number of the tooth roots ranging from one to four, five or more in some cases. Sometimes there are more than one root canal per root, variable internal anatomy. An unusual root canal shape, complex branching and multiple root canals are considered as the main causes of root canal treatment failures.,  a secondary root canal goes unnoticed by the dentist and is not cleaned and sealed, it will remain infected, causing the root canal therapy to fail. lateral parts fins, anastomoses and accessory canals, lateral component , vital or necrotic pulp, infectious elements . a single root contains two canals, mesial roots of lower molars. radiographs, cone beam computerized tomography , CBCT , rotary nickel titanium (NiTi) files ,  canals with flat-oval or tear-shaped cross sections, lingual recesses remain un-instrumented. canal is flat and use of hand instruments to try to overcome this problem, Tissue or biofilm remnants along such un-instrumented recesses may lead to failure due to both inadequate disinfection and the inability to properly obturate the root-canal space.