Aim: Evaluate pain after using rotary instrument with different cutting motion and different number of instruments in vital mandibular teeth.
Materials and Methods: Thirty-two patient with vital mandibular first molar was selected for this study. The root canal treatment was done in single visit. The patients were asked to follow general instructions and to sign a printed informed consent that explains the aim of the study and obligates the patient to fill a pain diary before the treatment, after 3 hours after finishing of the treatment, 24 hours, 48 hours, 7 days. Root canals were mechanically prepared using the different techniques (8 vital teeth in each group). Group 1: The ProTaper Next files. Group 2:  
A primary reciprocating WaveOne Gold file. Group 3: A small reciprocating WaveOne Gold was used in reciprocating motion followed by primary reciprocating wave one gold file. Group 4: One shape rotary file. Obturation was carried out using the manufacture recommended gutta percha by selection of a master cone corresponding to the size of the master apical file. All canals were obturated using an epoxy resin-based sealer.
Results: Pre-operatively; there was no statistically significant difference between the four groups. Immediately post-operative; wave One gold (Primary) group showed the statistically significantly highest mean pain score. After 3 hours; wave One gold (Small and Primary) group showed the statistically significantly highest mean pain score. After 24 hours. 48 hours as well as 7 days; all groups showed no pain.
Conclusion: Reciprocating files showed more pain than rotation files.