Ziebolz 2007.

Methods	Title: efficacy and oral side effects of 2 highly concentrated tray‐based bleaching systems Trial design: randomised, 2‐armed, parallel clinical study Location: University of Göttingen, Germany Number of centres: 1 Recruitment period: not reported Funding source: study supported by Kettenbach, Germany
Participants	Participants: 20 to 48 years old Total number: 60 Inclusion criteria: restoration or caries free teeth Vita shade score of A2 or darker no crowns on upper cuspids or incisors Exclusion criteria: tooth hypersensitivities anterior restorations poor oral hygiene generalised gingival recession caries, heavy structural alteration of the tooth structure tetracycline or fluorosis staining Number randomised: 60 Method of randomisation: stratified, randomised distribution Method of allocation concealment: not reported Method of blinding: not reported Number evaluated: 56 (4 dropouts) ‐ three dropouts in VW due to therapy pain and one dropout in OP due to therapy pain.
Interventions	Total number of intervention groups: 2 7.5% hydrogen peroxide gel in tray (Visalys) 20% carbamide peroxide gel in tray (Opalescence) Duration of treatment: 12 days
Outcomes	Tooth colour change: L*, a*, b* values: increase in L* and decrease in b* indicated lightening of teeth Hypersensitivity: 0 to 10 (0 = no hypersensitivity, 10 = high hypersensitivity) Acceptability: comfortable, slightly disturbing, uncomfortable or very uncomfortable
Notes	Sample size calculation: not reported Adverse effects: sensitivity Health‐related quality of life: not reported Key conclusions of the study authors: "The bleaching systems demonstrated significant tooth colour improvement for Δb* and ΔL*. They did produce significantly different whitening response for Δb*, with Opalescence showing significant higher Δb*. After bleaching therapy, the intensity of tooth hypersensitivity was increased significantly compared to baseline, with no significant difference between both groups" Contact: Dr Dirk Ziebolz, dirk.ziebolz@zm‐goettingen.de
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "A stratified, randomised distribution of the subjects to the 2 treatment 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	Not mentioned
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not mentioned
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "3 subjects from the Visalys group and 1 from the Opalescence group withdrew during bleaching therapy..." 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