Matis 2006.

Methods	Title: extended bleaching of tetracycline‐stained teeth: a 5‐year study Trial design: split‐mouth, randomised controlled trial Location: Wuhan University School of Stomatology, China Language: English Number of centres: 1 Recruitment period: not reported Funding source: Ultradent
Participants	Participants: not reported Total number: 59 Inclusion criteria: 18 years of age willing to sign a consent form willing to return for periodic evaluations willing to refrain from tobacco use for first 9 months of study presence of 6 maxillary anterior teeth no more than 1/6 of the facial surface of above teeth covered with restoration presence of tetracycline staining Exclusion criteria: use of bleaching agents in past 3 years use of tobacco during previous 30 days Loë and Silness gingival score > 1 study teeth lighter than A3 history of disease that would interfere with study presence of gross pathology pregnant or lactating Number randomised: 59 Method of randomisation: not reported Method of allocation concealment: not reported Method of blinding: not reported Number evaluated: 44
Interventions	Total number of intervention groups: 3 10% carbamide peroxide 15% carbamide peroxide 20% carbamide peroxide Duration of treatment: 6 months
Outcomes	Improvement in tooth colour: colourimeter readings in CIELa*b* for Vitalescence Restorative Masters Shade Guide
Notes	Sample size calculation: not reported Adverse effects: tooth and gingival sensitivity Key conclusions of the study authors: "The maximum lightening that occurred within 6 months happened during the first month of bleaching. Values increased the most during the bleaching of tetracycline stained teeth. There were small changes in the green red or blue‐yellow spectrums of colour throughout the study. At 4.5 years post‐bleaching, all 3 concentrations of bleaching agents had retained more than 65% of their original colour change. Increased tooth sensitivity occurs with higher concentrations of CP gels" Correspondence required: no Contact: Dr Bruce A Matis; Bmatis@ijsd.njpui.edu
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "At baseline evaluation, subjects were randomly assigned to 1 of 6 groups." However, method is not mentioned
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "Subjects were not aware of the concentration of bleaching agent they were using." However, method is not mentioned
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	Of the 59 subjects who initially enrolled in the study, 44 completed the 5‐year evaluation. 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