More than half of children in boroughs such as Tower Hamlets and Newham suffer from 'advanced, untreated dental decay' - the national average for England and Wales is 35 per cent.
Advanced decay can lead to mouth cancer later in life, yet many parents avoid taking their children to a dentist because of concerns over the cost of treatment.
'Our community dentists say many parents are not aware that children can register and be treated by a dentist for free, so we are launching a campaign to address the issue,' said communications manager Jennifer Anderson.
The authority is asking dentists across the region to promote their NHS credentials. It has also put posters on more than 100 buses and bus stops across north-east London.
The posters use images of healthy, smiling children next to teenagers with bad teeth to illustrate the effects of tooth decay.
Advisory leaflets and information cards are being distributed around dentists' surgeries and health centres. A helpline has been set up for parents who want to register with an NHS dentist.