Dozens of students are in financial limbo after being told their courses no longer qualify for a third level grant.
A letter sent to students by Student Universal Support Ireland (SUSI) stated that as the course "does not lead to a major award at level 7 of the National Framework of Qualifications (NFQ), you are ineligible for a grant".
SUSI told the Irish Independent that it has not yet taken a decision on whether it will ask the students to repay grant money issued between September and December.
It claimed that according to the latest student support regulations published last May, approved courses must be full-time, and lead to a major award on the NFQ.
It also stated that some level 7 diplomas were not considered major awards.
Sarah Moyles (19), who is in the second year of her two-year dental nursing diploma at TCD, said that of the 22 students in her class, 18 did not receive their monthly grant installment yesterday as expected.
Many students who entered the course this year have also been affected, together with a number of those enrolled in the university's diploma in dental hygiene.
Students studying the same course at University College Cork have also had their grants withdrawn.
Ms Moyles, who is originally from Cavan, received her grant in monthly installments of €660 a month, which she used to pay her monthly rent of €400, transport costs of €70 and food.
She said she studied for 40 hours a week, including some night lectures, and did not have the time to take up a part-time job.
Ms Moyles told the Irish Independent that she was now worried about how she would cover her rent, which she was already behind on paying.
"I have outstanding rent to pay. I've a very understanding landlord, he doesn't mind, but now I'm going to find it hard to pay for previous weeks," she said.
Her mother Brid, who spoke about the issue on 'The Joe Finnegan Show' on Northern Sound FM, fears her daughter and some of her classmates could now have to drop out and apply for social welfare.
Head of the School of Dental Science at TCD June Nunn said SUSI did not make any attempt to inform the university of its decision before suspending the grants.
She said that despite heavy cuts in funding to the dental industry, there was still a "huge demand" for graduates from the two programmes.
When contacted by the Irish Independent, a spokesperson for SUSI said that following an internal audit review of awarded grants, an issue had arisen in relation to the two diplomas.
They confirmed that the grants had been suspended pending an examination of the issue, and that they had issued the affected students with a notice of such.
SUSI has already made payments towards the student contribution fee of €2,500 for some people affected, but is now considering stopping this too.