Aim: The aim of this study was to compare the intensity of postoperative pain following root canal preparation using two different single-file systems: reciprocating and rotary. Materials and methods: The study enrolled 60 healthy patients aged 18-50 years with symptomatic irreversible pulpitis in a single molar. Patients were randomly assigned to one of three groups: OneShape rotary files, Reciproc files, or traditional stainless steel K-files (control). The study aimed to compare pain outcomes between the different instrumentation techniques, with results providing insight into the impact of single-file systems versus conventional K-files on postoperative discomfort. Data analysis was done using SSPS software. Results: The control group included 12 males and 8 females with a mean age of 37.9 ± 6.4 years, while the Reciproc group had 9 males and 11 females with a mean age of 36.2 ± 3.5 years, and the OneShape group comprised 10 males and 10 females with a mean age of 31.4 ± 4.5 years. In terms of treated teeth, the control group had 9 maxillary and 11 mandibular molars, the Reciproc group had 13 maxillary and 7 mandibular molars, and the OneShape group had 8 maxillary and 12 mandibular molars. Conclusion: The intensity of postoperative pain was not affected by the instrumentation kinematics, whether single-file reciprocating or single-file rotary.