Lin 1991.

Methods	FLUOROSIS STUDY Country of study: China Geographic location: Xinyuan (F); Langan and Jiayi (non‐F) Year of study: not stated Year of change in fluoridation status: NA Study design: cross‐sectional
Participants	Inclusion criteria: school children aged 7‐14 years Exclusion criteria: not stated Other sources of fluoride: not stated Social class: low socioeconomic status, mean annual income of about 200 yuan Ethnicity: not stated Residential history: not reported Other confounding factors: not stated
Interventions	All natural fluoridation Group 1: 0.88 ppm Group 2: 0.34 ppm
Outcomes	Dental fluorosis Age at assessment: 7‐14 years
Funding	Not stated
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Sampling	Low risk	Used rRandom stratified sampling
Confounding	High risk	Did not account for the use of fluoride from other sources
Blinding of outcome assessment (detection bias) All outcomes	High risk	Insufficient information
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	It is unclear whether data presented for all participants assessed for dental fluorosis
Selective reporting (reporting bias)	Low risk	Outcome of interest reported
Other bias	High risk	The examiners do not seem to have been calibrated