Biesbrock 2004.

Methods	Title: a chewing gum containing 7.5% sodium hexametaphosphate inhibits stain deposition compared with a placebo chewing gum Trial design: cross‐over randomised controlled trial Location: USA Language: English Number of centres: 1 Recruitment period: not reported Funding source: Procter & Gamble
Participants	Participants: 18 to 70 years old. Mean age: 39.1 years Total number: 20 Inclusion criteria: 16 natural teeth with minimum 7 anterior teeth Exclusion criteria: previous history of hypersensitivity to test products multiple restorations fixed prosthesis temporomandibular joint disfunction Number randomised: 19 Method of randomisation: not reported Method of allocation concealment: not reported Method of blinding: not reported Number evaluated: 18
Interventions	Total number of intervention groups: 2 (cross‐over) 7.5% sodium hexametaphosphate chewing gum Placebo Duration of treatment: 2 weeks with 78 hours washout time
Outcomes	Improvement in tooth shade: reduction in stain ΔL, a*, b* values were recorded. Increase in L and reduction in b indicated whitening
Notes	Sample size calculation: not reported Adverse effects: not reported Health‐related quality of life: not reported Key conclusions of the study authors: "Sodium hexametaphosphate delivered from a chewing gum prevents dental stain formation and facilitates stain removal, which leads to a perceptible whitening benefit" Correspondence required: no Contact: Dr Aron RB, Procter and Gamble Company, Healthcare Research Center, Manson, Ohio, USA
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Subjects were randomly assigned to one of two treatment groups." However, method was not reported
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "Randomised, double‐blinded cross‐over trial." However, method was not reported
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "Randomised, double‐blinded cross‐over trial." However, method was not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "1 woman abandoned 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 were reported. Conclusions are in accordance with the results
Other bias	Low risk	None