Database Security - Which Database to use?

Currently my .net Desktop app uses an access database which i know has little security.

I need to secure the data so am looking for suggestions on the type of database to use.

I've tried SQlite with encryption, however during runtime the database is decrypted so can be opened whilst the app is running or should the app crash the database is left decrypted.

Can anyone recommend which database to use that will offer a good security option (ideally an encrypted database which the app can read/write but doesnt decrypt the database in a seperate file)

Thanks