Nunn 1992.

Methods	FLUOROSIS STUDY Country of study: England Geographic location: Hartlepool, Newcastle and Middlesborough Year of study: 1989 Year of change in fluoridation status: NA Study design: cross‐sectional study
Participants	Inclusion criteria: lifetime residents of study areas; children in selected schools aged 15‐16 years Exclusion criteria: children with fractured incisor teeth, orthodontic bracket or surface otherwise obscured Other sources of fluoride: not stated Social class: occupation of head of household recorded; participants of low and high SES were recruited when possible Ethnicity: ethnicity recorded but no expansion on variable Residential history: lifetime residents Other confounding factors: not stated
Interventions	Group 1: 1‐1.3 ppm Group 2: 1 ppm Group 3: 0.2 ppm
Outcomes	Enamel defect Age at assessment: 12 years
Funding	Financial assistance from the British Council
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Sampling	Unclear risk	There was insufficient detail reported to determine how selection took place
Confounding	High risk	Did not account for the use of fluoride from other sources. Balance of SES between groups was unclear
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Photographs of the maxillary central incisors of participants were cut out from the print and identified with a code which would prevent identification by the examiners
Incomplete outcome data (attrition bias) All outcomes	High risk	In England, data for 68% of examined participants were reported due to camera failure in a school of SES
Selective reporting (reporting bias)	Low risk	Expected outcome appeared to be present
Other bias	Low risk	No other apparent bias