The number of north and north-east residents registered with a dentist is among the lowest in the country.
According to a new report, 72% of people in Grampian and 76% of people in Highland were on the books of a dentist in March 2015.
The government figures show the north of Scotland lags well behind the rest of the country, where an average of 84.4% of people are registered with an NHS dentist.
Jonathan Iloya, NHS Grampian consultant in dental public health, said the number of people signed-up to a practice had more than doubled since 2008, which he called a “significant achievement”.
And he suggested “historical challenges” meant many patients continued to be registered with a private practice, meaning they did not feature in the NHS figures.
NHS Highland agreed that a “historic level of private dental provision” was responsible for the lower numbers.
Dr Iloya said: “The latest provisional figures show that the proportion of the population registered with an NHS dentist as at March 2016 is 75.5%, which represents an additional 21658 new registrations in Grampian in a 12-month period.”
Programmes such as Childsmile were also improving registration among children, he said.
He added: “As an organisation we are completely committed to working with all stakeholders towards the continuous improvement of oral health in the north-east.”
A spokesman for NHS Highland said the situation was improving in the region, with increased registration in 2016.
He added: “The level of NHS registered patients in Highland attending their dentist is encouraging, and regular attendance at the dentist is one of the key ways in which patients can maintain and improve their oral health.
“Going forward NHS Highland is committed to addressing oral health inequalities through improving access for the most vulnerable patients via its public dental services while working with high street dentists to ensure that all communities within the area have access to NHS dental registration.”
