Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 21 0 2024 08 13 1 7 EN Narges Panahandeh Dental Research Center, Research Institute for Dental Sciences, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran Shervin Sedighi Private Practice, Tehran, Iran Shervin Mohammadkhani Private Practice, Tehran, Iran Sogol Nejadkarimi Department of Operative Dentistry, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran Amir Ghasemi Dental Research Center, Research Institute for Dental Sciences, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2021 06 30 2022 08 05 Objectives: This study assessed the efficacy of different combinations of oxalic acid, 35% hydrogen peroxide, and 5.25% sodium hypochlorite (NaOCl) for bleaching of tooth discolorations caused by hemoglobin. Materials and Methods: In this in vitro study, 40 sound extracted human premolars were disinfected and decoronated. Their primary color parameters were measured (T1). The teeth were then centrifuged with human blood for 3 days, rinsed, polished, and their color parameters were measured again (T2). They were randomly divided into 4 groups (N=10) and treated as follows: Group A: in-office bleaching with Pola-Office Plus followed by 30 seconds of light-curing, group B: 0.24 M oxalic acid for 5 minutes followed by in-office bleaching, group C: 5.25% NaOCl for 5 minutes followed by in-office bleaching, and group D: 0.24 M oxalic acid (5 minutes) followed by 5.25% NaOCl (5 minutes) and subsequent application of in-office bleaching gel. The color parameters of the teeth were measured again (T3). Data were analyzed by one-way ANOVA and paired sample t-test (alpha=0.05). Results: T2-T3 ∆E in groups B and D was significantly higher than that in group A (P<0.05); the difference between groups B and D was not significant. The mean ∆E and ∆L in group C were not significantly different from those in group A (P>0.05). ∆L significantly and equally increased in groups B and D after bleaching. Conclusion: Application of oxalic acid followed by in-office bleaching gel is more effective than the bleaching gel alone for correction of tooth discolorations caused by hemoglobin. https://fid.tums.ac.ir/index.php/fid/article/view/4117 https://fid.tums.ac.ir/index.php/fid/article/download/4117/2062