The influence of the renewal or the single application of the peroxide gel on the efficacy and tooth sensitivity outcomes of in-office bleaching-A systematic review and meta-analysis

Objective To answer the question: ``Does the peroxide gel application regimen (single application vs. renewal) influence the efficacy and the tooth sensitivity outcomes of in-office tooth bleaching?{''} Methods The search was done in Pubmed, Cochrane, LILACS, Scopus, Web of Science, and EMBASE in February 2021 (updated in July 2021). Randomized clinical trials (RCT) comparing the single application vs. the renewal protocols of HP were included. The meta-analyses were performed for the objective (Delta E-ab), subjective (Delta SGU) color changes, and absolute risk of tooth sensitivity (TS). Heterogeneity was evaluated using Q test (I-2). Cochrane Collaboration tool assessed the risk of bias (RoB). The GRADE evaluated the certainty of evidence. Results Five RCT studies remained. Two studies showed high RoB, and three presented some concerns. No significant differences were observed between the protocols in terms of the Delta E-ab, Delta SGU, and TS. Delta E-ab exhibited substantial heterogeneity (I-2 = 87%), while Delta SGU (I-2 = 60%) and the TS (I-2 = 62%) presented a moderate one. The certainty of evidence was considered low or very low, depending on the variable response and the evaluation time. Conclusion The application regimen (single vs. renewal of HP) did not impact color change or the absolute risk of TS. Clinical significance The renewal of bleaching gel during the in-office appointment may not be necessary. However, there is at least a low certainty of evidence. Because of this, further randomized clinical trials with appropriate methodology on this topic are encouraged. (AU)