Itchy Ears in Cats

My cats seem to be scratchng their ears throughout the day with their back feet.  Some times I will see a rear foot inside the ear.   How can I tell if the itchy ears is dirty ears or mites?   Is it safe to put ear mite insecticide into a cats inner ear.   ?     I put Advantage on my cats every month for fleas.   My cats are indoor and outdoors cats.
I do not let my cats outdoors when it is dark out.  Only in the day light.  

[AnnieBrooke]

It is generally safe to put ear mite medicine into a cat's ear as long as it is formulated for cats.  You have to let it soak in, which the kitties don't like much, and it helps to rub the base of their ears from the outside to encourage it to move deep into the ear canal.  You also have to do it for many days, as I recall.  Call your vet for a product to use and advice on how to do it.

[Princessdaniella]

It is safe to use the medicine for Your cat as long as it is specifically designed for cats like Annie mentioned.
Revolution is primarily a treatment for fleas in cats and dogs but it is approved for ear mites in both. It is best to apply it and than rub your cats ear to help the medicine work its way into the ear canal that way if the cats shakes its head the medicine is still going in
Best of luck