Old cement is difficult to remove if you don't have the right equipment. (Ultrasonic scaler, ultrasonic cleaner, or air abrasion.) Better to have it professionally done.
You have to remove the old cement with the help of ultrasonic tool.It is a special kind of dentist toll.I am also using this..
Sorry. I misunderstood your question.
To remove the old cement, I usually use an ultrasonic scaler (dental cleaning tool) to remove it.
I would recommend seeing a dentist to remove the old cement and getting it recemented there.
What does the instructions on the bottle say? I wasn't aware that you could purchase glass ionomer cement in a store. As a dentist, we normally would clean it was its setting and make sure we remove all of it prior to it hardening. If it is harden, then special dental tools are used to remove it such as an ultrasonic scaler or metal scaler to scrap it off.