I have retainers and there is a build up of this white gunk. I read online that you can use Sonicbrite to receive rid of this. I have tried my pharmacies/chemist, none of them appear to stock them. Does anyone know where can I find them, I live in Sydney, Australia by the way. I know I can go online and purchase them but they are too expensive (international Shipping). Thanks.
You could go to your dentist and ask whether they inventory it or if it's possible for them to receive it for you at a cheaper price.