Clarkson 1992.

Methods	FLUOROSIS STUDY Country of study: Ireland Geographic location: Ireland Year of study: 1984 Year of change in fluoridation status: 1964 Study design: cross‐sectional
Participants	Inclusion criteria: children aged 8 and 15 years Exclusion criteria: none stated Other sources of fluoride: increase in use of fluoride‐containing toothpaste and infant formula made with fluoridated water Social class: not stated Ethnicity: not stated Residential history: not stated Other confounding factors: problems of consistent levels in the fluoridated supply during the 1960s and early 1970s
Interventions	Group 1: 'optimal' level ‐ ppm not stated (artificial fluoridation) Group 2: 'low' level ‐ ppm not stated (natural fluoridation)
Outcomes	Dental fluorosis (Deans Index); enamel defects (DDE) Age at assessment: 8 and 15 years
Funding	Not stated
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Sampling	Low risk	A stratified proportional random sampling procedure was used with size of school with fluoridation status and sex as stratifying factors
Confounding	High risk	Did not account for the use of other fluoride sources or SES
Blinding of outcome assessment (detection bias) All outcomes	High risk	Insufficient information
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	The number of participants recruited was not reported and there was a variation in the number of children examined for enamel defects and children interviewed on perception of defects. It is not clear whether data were presented for all recruited participants
Selective reporting (reporting bias)	High risk	Data not in suitable format for analysis
Other bias	Low risk	No other apparent bias