According to Official Guinness Records,
The most people involved in a dental health check at multiple locations is 101,309 and was achieved by Saveetha University (India) at 77 locations across India, on 27 November 2014. The record attempt was part of The India Smiles Campaign which took place in 77 schools across 16 cities in India.
For a complete list of 2014 records, please visit 2014 Guinness Records in India.