Gerlach 2002b.

Methods	Title: comparative response of whitening strips to a low peroxide and potassium nitrate bleaching gel Trial design: randomised, examiner‐blinded clinical trial. 2 arms Location: not reported Language: English Number of centres: 1 Recruitment period: not reported Funding source: Procter & Gamble
Participants	Participants: mean age of 37 years Total number: 34 Inclusion criteria: be willing to have their teeth whitened Exclusion criteria: patients who has undergone bleaching or restoration of the maxillary anterior dentition patients with ongoing tooth sensitivity Number randomised: 34 Method of randomisation: not reported Method of allocation concealment: not reported Method of blinding: not repeated Number evaluated: 32
Interventions	Total number of intervention groups: 2 5% carbamide peroxide bleaching gel + potassium nitrate in custom tray: once daily application 6% hydrogen peroxide bleaching strip: twice daily application Duration of treatment: 7 days
Outcomes	Improvement in tooth shade ΔL, a*, b* were recorded. Increase in ΔL and decrease in b* indicates whitening
Notes	Sample size calculation: not reported Adverse effects: tooth sensitivity and oral irritation Health‐related quality of life: not reported Key conclusions of the study authors: "Twice daily application of 6% hydrogen peroxide strip resulted in better whitening compared to 1 daily application of 5% carbamide peroxide. Sensitivity was less with 6% hydrogen peroxide" Contact: gerlach.rw@pg.com
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Study subjects were randomly assigned to 1 of 2 groups." However, method is not reported
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "randomised examiner‐blinded clinical study." However, method is not reported
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "randomised examiner‐blinded clinical study." However, method is not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "2 subjects missed the day 7 visit" Comment: missing outcome data balanced in numbers across intervention groups
Selective reporting (reporting bias)	Low risk	All outcomes described were reported. Conclusions are in accordance with the results
Other bias	Low risk	None