stones in salivary glands

I have had for years stones in my salivary glands.. From time to time I pass them from under the tongue and they
are small white and soft like cooked rice but the size of small peas. My question is: Does anyone know how and
why they form? Also, how can I flush them from the glands. It seems like they pass in the Fall of the year, I haven't
had any for many months pass now. Any help or advice would be appreciated. Thanks, Anne Tweet