Dentists have been carrying out botox treatment despite not being properly qualified, cosmetic surgeons say.
Dentists are thought to charge between £150 and £200 for botox injections
The government announced a reform of cosmetic surgery regulation last month amid concerns over patient safety.
At the time beauticians and unqualified doctors were blamed for providing "rogue" services to satisfy the booming demand for the anti-wrinkle therapy.
But BBC News has been told scores of dentists offer the treatment as a sideline for between £150 and £200.
One plastic surgeon, who did not wish to be named, said he knew of a number of dentists who offered the therapy.
He said: "They do it on the side of their private and NHS dentistry work. It is a good way of earning a bit of extra money."
Adam Searle, president of the British Association of Aesthetic Plastic Surgeons, added: "Dentists are carrying out these treatments but are they properly qualified?
"I thought their expertise was in teeth, not cosmetic procedures."
In the UK, botox is a prescription medicine but is not licensed for cosmetic use.
Doctors who do give the injections for lifestyle reasons are personally responsible for any ill-effects although adverse affects, such as swelling or rashes, are rare.
As it remains unlicensed for cosmetic use, there are no exact figures for how many people use it.
However, it is estimated two-thirds of the 50,000 cosmetic procedures each year are non-surgical, such as botox and lip fillers.
About half of the work is carried out by fully-qualified cosmetic surgeons.
But an expert group set up by Sir Liam Donaldson reported beauticians and untrained doctors were also getting in on the act, sometimes at so-called botox parties where groups of people gather at hotels to have a drink and try out beauty treatment.
Dentists are divided over whether they should be offering such treatments.
The British Dental Association would not comment on whether it was right for their members to be involved in botox therapy and did not know how many were.
In a statement, the dentist trade union body said: "Dentists who undertake botox treatment should be properly trained and ensure that they have appropriate professional indemnity arrangements in place."
The Healthcare Commission, which will start regulating non-surgical cosmetic procedures from next spring - invasive surgery already falls under its remit, said people offering botox cosmetic services would need to have specialist training and qualifications.
A spokeswoman said: "Dentists, along with other people wanting to offer these procedures, will have to sign up to that if they want to continue."