M.S.
You just get what you can. I still have to hold my 22 month old daughter down sometimes to get her teeth brushed.
Just let them do a little chewing on the toothbrush and then try to get a few brushes in especially at night.
Good luck
(Oh and my 3 year old still remembers when Santa told her last Christmas that she needs to brush her teeth every day morning and night. I could have kissed Santa for that because when she fights me on it I say what did Santa tell you and she brushes her teeth)