TEETH- Is cleaning liquid enough?

i have 2 cats. Pillo- a flat faced himalayan & Uno- an american shorthair.
i bought a cleaning liquid for their teeth called "breath friend"
IS this enough for cleaning their teeth? -Pillo has a big gunk of yellow stuff on her side teeth (its not food)
do these cleaning liquids have expiry dates and what happens if i use it even if its expired?
Do you guys have any tips on cleaning their teeth?
its really difficult to clean pillo's teeth because of her flat face is hard to get a good grip on.
and uno is stressy and bites my fingers

PLeASE GIVE ADVICE!!!!
MANY THANKS

As to expiration dates, I'd contact the manufacturer. I'm not familiar with the product.

We only have one kitty that has a problem with plaque build up. She loves to be brushed, and always pushes her gums against the brush. So we started "brushing" the back of her lips/cheeks with a tooth brush. She LOVED it, and actually brushing her teeth became an easy task.

There are also "dental chews" that help clean the plaque off teeth. Have you tried these instead of brushing?

Also, if plaque build-up is a problem in your kitties, maybe it's best to go to the vet to get a dental. They can clean the teeth. We do this every year for Spooky (in addition to the brushing).

The yellow gunk is probably plaque, and you can actually "pick" it off with your fingernail if she'll let you. But that means there's more you can't see - so really a dental cleaning at a vet is the best thing to protect her teeth and gum health in the long run.

Laurie