Ruan 2005.

Methods	FLUOROSIS STUDY Country of study: China Geographic location: urban ‐ Bao Ji and Jing Bian Year of study: 2002 Year of change in fluoridation status: NA Study design: cross‐sectional
Participants	Inclusion criteria: not stated Exclusion criteria: absent or unavailable; non‐permanent residents Other sources of fluoride: no fluoride supply was provided by dental service and no fluoride supplement program was implemented in any of the communities Ethnicity: not stated Social class: the selected schools served rural communities where socioeconomic standards were comparable Residential history: permanent residents Other confounding factors: not stated
Interventions	All natural fluoridation Group 1: 0.4ppm Group 2: 1.0 ppm Group 3: 1.8 ppm Group 4: 3.5 ppm Group 5: 5.6 ppm
Outcomes	Dental fluorosis (TF Index); caries data also evaluated within the study but excluded from review due to study design Age at assessment: 12 and 13 years
Funding	The study was supported by the Norwegian State Educational Loan Fund
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Sampling	Unclear risk	13 schools were contacted and all children were invited to participate. The sampling frame for schools was not specified
Confounding	High risk	Even though fluoride supplement and fluoride supply by dental service were taken into account, the use of fluoride toothpaste (a common source) was not mentioned. It is not clear why it was not acknowledged or investigated
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The fluoride concentration of the local drinking‐water supplies was unknown to the examiner at the time of the clinical examinations, which took place with the students seated on ordinary chairs outside the school building
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data presented for all participants
Selective reporting (reporting bias)	High risk	Partial reporting of outcome ‐ only reported prevalence of fluorosis with TF score ≥ 3 (fluorosis of aesthetic concern)
Other bias	Low risk	No other apparent bias