I'm looking for a mouth prop with a handle. Any suggestions?

My aunt has dementia and sometimes clenches her teeth making it impossible to do her oral care, properly. There are black stains on her teeth that we believe are caused by medication. We've found that the black stains do come off but we need a mouth prop to be able to do it adequately. I want one that has a handle (preferably) so that we can hold onto it while doing care. Any suggestions will be greatly appreciated.