Mohan 2008.

Methods	Title: clinical study to evaluate the efficacy of a novel tray‐based tooth whitening system Trial design: parallel, examiner‐blinded, stratified, randomised controlled trial Location: Department of Fixed and Removable Prosthodontics, Leeds Dental Institute, UK Language: English Number of centres: 1 Recruitment period: not reported Funding source: not reported
Participants	Participants: 18 to 70 years old Total number: 50 Inclusion criteria: available for the 2‐week duration minimum of 20 uncrowned teeth with at least 6 upper front teeth without crowns or large restorations a minimum baseline shade of A3 on 1 or more of the upper front teeth Exclusion criteria: orthodontics bands, partial removable dentures advanced periodontal disease, tumours of the soft or hard tissues 5 or more carious lesions requiring immediate restorative treatment allergy history, participation in another clinical study within 1 month prior to the study, recent whitening or bleaching of teeth pregnant women medical conditions which would compromise the subject's safety Number randomised: 50 Method of randomisation: not reported Method of allocation concealment: not reported Method of blinding: not reported Number evaluated: 49. 1 dropout from control group
Interventions	Total number of intervention groups: 2 Experimental: tray‐based 6% hydrogen peroxide Control: no treatment Duration of treatment: 14 days
Outcomes	Change in tooth shade Oral irritation Vita shade guide arranged based on lightness (B1 lightest and C4 darkest). 1 is lightest ‐ 16 is darkest b*: decreased b* indicates reduced yellowness; ΔL: increased ΔL is increased brightness
Notes	Sample size calculation: not reported Adverse effects: not reported Health‐related quality of life: not reported Key conclusions of the study authors: "Significant tooth whitening was evident after 3 days treatment with the tray‐based whitening system and colour improved with continued usage over 14 days. It also supports our previous study results that the WIO index is appropriate for assessing changes in tooth whiteness" Contact: Dr Naveen Mohan, Dental Health Unit, 3A Skelton House, Lloyd Street North, Manchester Science Park, Manchester, England M15 6SH, UK; iain.pretty@manchester.ac.uk (IA Pretty)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Balancing the 2 groups on the basis of baseline tooth colour, subjects were randomly assigned to either a tray‐based bleaching system or a non‐treatment control group." However, the method of randomisation is not mentioned
Allocation concealment (selection bias)	Unclear risk	Quote: "A parallel, examiner‐blinded, stratified 2‐group clinical study." No other details provided
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "A parallel, examiner‐blinded, stratified 2‐group clinical study." No other details provided
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "A parallel, examiner‐blinded, stratified 2‐group clinical study." No other details provided
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "1 dropout due to ill health was withdrawn from the study" Comment: 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 are reported. The conclusion is in accordance with results
Other bias	Low risk	None