Article Complex canal system Missed anatomy Second mandibular premolar Two roots Uncommon anatomies adult anatomical variation buccal mucosa case report clinical article clinical examination dental prophylaxis dental restoration edetic acid human hypochlorite sodium kerr pulp canal sealer male mandibular second premolar percussion restorative dentistry retreatment root canal filling material root canal obturation thermafil 25 tongue tooth radiography tooth root canal zinc oxide eugenol