OBJECTIVE: Tooth bleaching procedures on nonvital teeth have been performed for crown discoloration caused by regenerative endodontic therapy (RET). However, leakage of bleaching agents across the root canal can be detrimental. This study aimed to assess and compare the penetration levels of hydrogen peroxide (HP) from different bleaching agents across calcium silicate-based coronal barriers in immature permanent teeth. METHODS: Fifty extracted single-rooted human teeth were randomly divided into four groups (n = 10): Group I (HH)-35% hydrogen peroxide (HP)
Group II (SS)-a mixture of sodium perborate (SP) powder and saline
Group III (SH)-a mixture of SP powder and 30% HP liquid
Group IV (CP)-10% carbamide peroxide gel. The control group (Group V, CC) was treated with distilled water. The bleaching agent was replaced on the 4th day, and penetration analysis was performed on the 7th day using ferro thiocyanate (FTC) method and a UV-spectrophotometer at a wavelength of 480 nm. RESULTS: Compared with the control group, the SH group (SP mixed with HP) showed a significant difference, indicating substantial HP penetration across the root canal space (p value <
0.0001). Intergroup comparisons also revealed a significant difference between the SS and SH groups (p value <
0.0001), suggesting that the SS group had less penetration. CONCLUSION: Compared with other bleaching agents, SP mixed with saline/water resulted in the lowest HP penetration in the pulp canals of the RET-simulated tooth models. CLINICAL SIGNIFICANCE: This study is the first to investigate HP penetration from different bleaching agents in teeth that have undergone RET, identifying the safest bleaching agent for use in these cases. This study also provides a foundation for further research to develop precise guidelines for nonvital tooth bleaching protocols in RET-treated teeth.