ONHAs were pretreated with 25 μM estrogen for 2 h or 18 h followed by treatment with tBHP. Twenty-four hours later viability was determined using Trypan Blue. In tBHP treated compared to cells there was a significant reduction in cell viability cells that were mock treated (***, p=0.0002). ONHAs pretreated with estrogen for 2 h (*, p=0.0236) or 18 h (**, p=0.0053) prior to tBHP treatment had a significant increase in viable cells compared to tBHP treated cells. When compared to mock treated ONHAs, pretreatment with estrogen for 2 h still showed significantly reduced cell viability (**, p=0.0052), while pretreatment with estrogen for 18 h had no significant difference in viable cells compared to mock treated (ns, p=0.0982). Estrogen pretreatment for 18 h was significantly more protective than pretreatment for 2 h (*, p=0.0221). Experiments were performed in triplicate (n=3) and values were depicted as mean +/− SEM and analyzed using ANOVA (p=0.0002). For statistical comparison, the Bonferroni post-hoc test and Student t-test were used. Statistical significance was set at p ≤ 0.05.