Objective: To evaluate the effect of preemptive analgesia of paracetamol and dipyrone in vital teeth professionally whitened in office. Material and methods: This was a pilot study of a blinded, paired sample, randomized clinical trial. Twenty volunteers requiring dental whitening, received, after the randomization, one of the formulations under study, one hour before the procedure: paracetamol 500 mg or dipyrone 500 mg as preemptive medications. Data collection was conducted by using two instruments: a record of research evaluation and visual analog scale (VAS), in which the patient was asked to score a value to the pain experienced before, during, 1 hour and 6 hours after the whitening procedure. Results: Most participants were female (75 %), of the age group between 18 and 27 years (75%). During the measurement of pain at pre-and trans-operative periods, VAS showed no statistically significant differences. At the post-operative period, immediately after, one and 6 hours after, clinically and statistically significant differences were observed, thus evidencing the superiority of treatment with Dipyrone 500 mg over the treatment with paracetamol 500 mg (p = 0.042, p = 0.003 and 0.0017, respectively). Conclusion: Dipyrone 500 mg exhibited higher effectiveness than Paracetamol 500 mg in the study population, as a technique of preemptive analgesia in tooth whitening procedure.