Meireles 2010.

Methods	Title: double‐blinded randomised clinical trial of 2 carbamide peroxide tooth bleaching agents: 2‐year follow‐up Trial design: double‐blinded, randomised clinical trial Location: not reported Language: English Number of centres: 1 Recruitment period: not reported Funding source: not reported
Participants	Participants: not reported Total number: 183 Inclusion criteria: 6 anterior maxillary teeth with a colour shade C1 or darker evaluated teeth should not have more than 1/6 of the buccal surface restored, and the restoration should not interfere with the spectrophotometer readings volunteers should have good oral health (no dental caries and periodontal disease) good general health (no disease that could interfere with the study results) volunteers should be at least 18 years old Exclusion criteria: volunteers under orthodontic treatment or with tetracycline stained teeth volunteers reporting past or present hypersensitivity or those having non‐vital anterior teeth volunteers that used tooth whiteners within the past 3 years smokers, pregnant or lactating women volunteers without schedule availability Number randomised: 92 Method of randomisation: randomisation table Method of allocation concealment: not reported Method of blinding: labels were removed Number evaluated: 91
Interventions	Total number of intervention groups: 2 Control: carbamide peroxide 10% in tray Experimental: carbamide peroxide 16% in tray Duration of treatment: 2 hours per day for 3 weeks
Outcomes	Improvement in tooth shade: ΔL, a*, b* values recorded Oral impact on daily performance (OIDP) 0 = no sensitivity; 1 = mild sensitivity; 2 = moderate sensitivity; 3 = considerable sensitivity and 4 = severe sensitivity The self‐reported general health was based on a Likert scale: excellent; very good; good; regular; bad (latter categorized in excellent/very good and good/regular)
Notes	Sample size calculation: mentioned Adverse effects: tooth sensitivity Health‐related quality of life: reported Key conclusions of the study authors: "The whitening effect evaluated by visual shade matching and digital spectrophotometer remained similar after 6 months of bleaching treatment using any of the carbamide peroxide concentrations tested. Additionally, the high consumption of staining beverage and food had no influence in the whitening effect longevity. Quality of life is complex and encompasses different domains. Although positive impact of the dental bleaching was detected, with patients showing more their teeth without embarrassment, difficult in dental hygiene and pain resulting from the treatment were also reported, and this can negatively impact daily performances. Dentists must consider these aspects when performing aesthetics procedures" This is a 2‐year follow‐up report of the previous study Correspondence required: no Contact: SS Meireles; soniasaeger@hotmail.com
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "A randomisation table to allocate the participants in each study...."
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "The product concentration label was removed, therefore, the examiners and participants were blinded to the agent"
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not mentioned
Incomplete outcome data (attrition bias) All outcomes	Low risk	1 dropout. Plausible effect size (difference in means) among missing outcomes not enough to have a clinically relevant impact on observed effect size
Selective reporting (reporting bias)	Low risk	All outcomes described were reported. Conclusions are in accordance with the results
Other bias	Low risk	None