Accually there is.
New study suggests mouthwash may quickly kill the coronavirus in human saliva
Commonly-used mouthwashes are able to kill the coronavirus within 30 seconds of exposure in laboratory conditions, a new study from scientists in the U.K. has found.www.cnbc.com
It's not peer reviewed yet though. This is a pre-print. It does seem that this is being looked into by some people
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And I guess that it would make sense to use mouthwash before doctor visits.