Materials and Methods: In this randomized crossover clinical trial, 40 children with ages ranged from 5 years to 8 years whose mandibular primary first molars were eligible for pulpotomy, were selected and divided randomly into two groups. The right and left mandibular first molars of group A were anesthetized with infiltration and I. A nerve block techniques in the first and second sessions respectively. The left and right mandibular first molars of group B were anesthetized with I.A nerve block and infiltration techniques in the first and second sessions respectively. The severity of pain were measured and recorded according to sound-eye-motor scale by a certain person. Data was analyzed using Wilcoxon Signed Rank and Mann-Whitney U tests (P < 0.05). 

  Results: The severity of pain was lower in infiltration technique versus I.A nerve block. There were no significant differences between the severities of pain on pulpal exposure of two techniques. 

  Conclusion: It seems that infiltration technique is more favorable to anesthetize the mandibular primary first molar compared to I.A nerve block.