An army of dentists is being redeployed to join the front-line fight against Covid-19 after non-urgent dentistry was suspended amid the virus pandemic.
The Chief Dental Office for England said they would be asked to help at hospitals being built to boost critical care and other parts of the NHS.
And this year's contracts were being redrawn so dentists refusing to be redeployed would lose their NHS pay.
But the British Dental Association said it should be on a voluntary basis only.
And it called for protections for any staff at higher risk.
Mick Armstrong, who chairs the BDA, added: "The profession stands ready and willing to support the national effort to fight this pandemic with any workable emergency plan."
The letter, from Chief Dental Officer Sara Hurley, said the NHS contracts were being renegotiated to:
maintain cash flow
provide emergency dental services during the outbreak
free up staff to fight the virus
The new contracts would "actively enable staff time that is no longer required for routine dental activity to be diverted to support service areas with additional activity pressures due to Covid-19", it said.
"As part of the funding support, the NHS expects that dental practices will fully support the redeployment of professionals and staff working in dental services to support the wider NHS.
"In particular, we ask staff contact details are made available immediately and for practices to actively support any national or local calls for help.
"This will include helping to staff the new Nightingale Hospital that is being established in London and other similar facilities that may be established over the coming weeks."
There are also concerns about the many dental staff that have been laid off in recent weeks, as more and more practices have had to close their doors.
Many of the 12,000 dental practices in the UK contain a mix of NHS and private care - but if they continue to receive NHS funding, they will not be eligible for assistance under the chancellor's scheme for small businesses.
Mr Armstrong said: "By asking practices to choose between the NHS and other government support, it is inevitable many will fall through the gap.
"We urgently need government to offer flexibility over the issue."