Nathoo 2003.

Methods	Title: comparative clinical investigation of tooth whitening efficacy of 2 whitening gels Trial design: randomised, double‐blinded, parallel‐group trial Location: Oral Health Clinical Services, Piscataway, New Jersey, USA Language: English Number of centres: 1 Recruitment period: not reported Funding source: Colgate Palmolive
Participants	Participants: 18 to 70 years old. Mean age 28.5 years Total number: 59 Inclusion criteria: 18 to 70 years of age all maxillary anterior present with no restoration no allergy to any of the ingredients of bleaching agent Vita shade of A3 or darker Exclusion criteria: undergoing orthodontic treatment anterior tooth with prosthesis or veneers, crowns tumour of hard or soft tissues pregnant/lactating females oral prophylaxis in month or use of any whitening products any illness Number randomised: 59 Method of randomisation: not mentioned Method of allocation concealment: not mentioned Method of blinding: not mentioned Number evaluated: 59
Interventions	Total number of intervention groups: 2 Gel I: 25% carbamide peroxide Gel II: 8.7% hydrogen peroxide Duration of treatment: 3 weeks
Outcomes	Improvement in tooth shade The shade guide was arranged with 16‐shade tabs in order from B1 (1) to C4 (16)
Notes	Sample size calculation: not reported Adverse effects: none reported Health‐related quality of life: not reported Key conclusions of the study authors: "The authors concluded that all subjects exhibited statically significant tooth shade lightening. There was no significant difference in the between both gels for one time night usage for 2/3 weeks application. No adverse reaction was noted" Correspondence required: no Contact: Dr William DeVizio, William_devizio@colpal.com
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "double‐blinded, randomised, controlled, parallel‐group clinical trial." However, method of randomisation is not reported
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "double‐blinded, randomised, controlled, parallel‐group clinical trial." However, method of blinding is not reported
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "double‐blinded, randomised, controlled, parallel‐group clinical trial." However, method of blinding is not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "All the participants completed the study"
Selective reporting (reporting bias)	Low risk	All outcomes described were reported. Conclusions are in accordance with the results
Other bias	Low risk	None