This systematic review aimed to describe and characterize internal tooth bleaching techniques, conventional (walking-bleach) and combined (inside–outside), referring to their efficacy. The research was conducted on the main databases: PubMed, Cochrane Library, EMBASE, and Web of Science. Only randomized controlled trials and cohort studies were considered, on humans of 18 years old or older. A Population, Intervention, Comparison, Outcome (PICO) question was designed to evaluate the scientific evidence. The quality of each randomized controlled trial and cohort study was evaluated using the Cochrane Handbook for Systematic Reviews of Interventions and the Methodological Index for Non-Randomized Studies (ROBINS-I), respectively. The walking-bleach and the combined techniques were both effective at the end of the treatment, obtaining similar aesthetic results. Regardless of the technique used, internal tooth bleaching is an effective procedure, with good aesthetic results, in the treatment of non-vital teeth. The cervical barrier is a standard of care in internal bleaching techniques and should be used. Considering the similarity in the esthetic results obtained in both techniques, the concentrations used for both, and since the biocompatibility of the bleaching agent is more important than its efficiency or speed in obtaining results, the combined technique should be considered the method of choice rather than the walking-bleach technique.
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