Patients are being overcharged for NHS dental work by up to £109 million a year, the Tories said.
An analysis of data from primary care trusts (PCTs) across England suggests dentists could be recalling patients just weeks after their first treatment and then charging them twice.
In October, the Government said it believed dentists could be recalling healthy patients for check-ups and dividing courses of treatment unnecessarily.
Chief dental officer Barry Cockroft has been in talks with health chiefs about the issue.
The way payments are divided under the dental contract means dentists can claim twice as much by spreading treatments across different appointments or calling patients back for unnecessary check-ups.
Guidance from the National Institute for Health and Clinical Excellence (Nice) says no patient should be called back to their dentist for a check-up within three months.
The Government has also said patients only have to pay once for each course of treatment and, if they need further work within two months of completing that course, they do not have to pay anything extra.
The Conservatives questioned every PCT in England to find out how many patients were having to go back to their dentist within a three-month period for treatment and were paying more than once.
According to the Tories, this data shows that dentists are pushing patients just over the two-month limit of what can be counted as one course of treatment, charging patients twice and therefore earning more money.
If the advice from Nice had been followed, then up to 6.5 million slots could have been freed up for people who do not have an NHS dentist, the Conservatives said.