## 2 Materials and Methods
### Search Strategy  
A literature search was carried out using the following databases: PubMed, Medline via Ovid, Science Direct, the Cochrane database of systematic reviews via Ovid, and Scopus. This search used MeSH terms and keywords in different combinations, as described in the following paragraph. In addition, a manual search of the bibliographies of all full-text articles and related reviews selected from the electronic search was conducted. Finally, a manual search of Google Scholar using the same combinations was also performed.  
The search used the following MeSH terms: \"tooth bleaching\", \"tooth bleaching agents\", \"orthodontic appliance, removable\", and \"treatment outcome\", along with keyword searches. The search also used the following keywords: \"Dental bleaching\", \"tooth whitening\", \"tooth discoloration\", \"hydrogen peroxide\", \"carbamide peroxide\", \"clear aligners\", \"clear aligner appliance\"**, \"clear dental brace\", \"Invisalign\", \"treatment effectiveness\", \"clinical efficacy\", \"patient-relevant outcome\", \"orthodontic treatment\", \" orthodontic tooth movement\", and \"dental procedure\". The following searches and search terms were applied: (\"dental bleaching\" OR \"tooth bleaching\" OR \"tooth discoloration\") AND (\"orthodontic appliance removable\" OR \"clear dental brace\" OR \"clear aligner\"), (\"tooth bleaching\") AND (\"clear aligner appliance\" OR \"Invisalign\"), (\"dental bleaching\") AND (\"orthodontic appliance removable\" OR \"clear aligner appliance\") AND (\"clinical efficacy\"), (\"tooth bleaching agents\" OR \"carbamide peroxide\") AND (\"Invisalign\" OR \"clear aligner appliance\" OR \"orthodontic appliance removable\"), (\"tooth bleaching\" OR \"dental bleaching\" OR \"tooth whitening\" OR \"tooth bleaching\") AND (\"orthodontic appliance\" OR \"clear aligner appliance\" OR \"clear aligner appliance\" OR \"clear aligner appliance\" OR \"clear aligner appliance\" OR \"clear aligner\") OR \"clear dental brace\" OR \"Invisalign\") AND (\"treatment outcome\" OR \"clinical efficacy\" OR \"clinical effectiveness\") AND (\"orthodontic treatment\" OR \"dental procedure\"), (\"tooth bleaching\" OR \"tooth bleaching agents\" OR \"carbamide peroxide\"), (\"dental bleaching\" OR \"dental procedure\"), (\"  
OR \"hydrogen peroxide\") AND (\"orthodontic appliance removable\" OR \"clear aligners\" OR \"clear aligner appliance*\" OR \"clear dental brace\" OR \"Invaslagin\") AND (\"treatment outcome\" OR \"clinical efficacy\" OR \"treatment effectiveness\"), (\"tooth discoloration\" OR \"dental bleaching agents\" OR \"tooth whitening\") AND (\"orthodontic appliance removable\" OR \"clear dental brace\") AND (\"treatment outcome\" OR \"patient-relevant outcome\"). Where * includes singular and plural forms of the keyword.  
A specific question was formulated based on population, intervention, control, and outcome (PICO) criteria. According to these criteria, the population was patients treated with clear aligners, the intervention was tooth bleaching using clear aligners, the control was dental bleaching using conventional bleaching trays, and the outcome was the efficacy of tooth bleaching. The focused question of this systematic review was: \"Is dental bleaching during orthodontic treatment with clear aligners as effective as dental bleaching using conventional bleaching trays?\"