Mandatory? No. There are many cats who have never had their teeth brushed or other dental care and they live a full healthy life with no dental issues. Then there are just as many cats who are prone to gingivitis, resorptive lesions, stomatis, and other issues unless they have regular dental care. Teeth, regardless of species, get sticky plaque and bacteria build up just from eating and drinking. Regular toothbrushing removes the plaque and bacteria and stuck food particles to keep the teeth and gums healthy.
This is the first time I hear that cat teeth needs to be brushed. Is it really mandatory. I can't quite imagine how my kitten would allow me inside her mouth. I can't even make her open it (when she took pills).
Ideally a cat's teeth should be brushed daily. With cats being cats, toothbrushing once a week would still be helpful. Use ony pet toothpaste and a small cat toothbrushor finger brush or even a piece of gauze wrapped around a finger. There are other forms of dental care you can give such as dental treats, additives to the water, liquids to squirt onto the teeth, etc. The only dental treats I recommend are the CET ones. The additives that go into the bowl of water are useless since a cat is not going to drink enough water from the bowl for the additive to have any effect on the teeth. Dental dry foods should be avoided since they are full of awful ingredients, super high in carbs, and most cats just swallow the pieces whole after a crunch or two.
Some people give their cats raw poultry gizzards and hearts and poultry necks for dental health. This is similar to what the domestic cat's wild ancestors do. Not all cats will touch raw meat or bones.
Before you start home dental care, have the vet check the cat's teeth for any signs of dental issues that needs immediate treatment.
Here's a video of how to brush a cat's teeth: http://partnersah.vet.cornell.edu/pet-owners/cat-teeth It will take a lot of patience (and treats) to get a cat to accept toothbrushing. It's easiest to start toothburhings on kittens. Older cats may put up a fight. My previous cat was 8 years old when I started brushing his teeth. I didn't think he'd let me but he just opened his mouth and let me rub the poultry flavored toothpaste on this teeth. It got to a point where he would actually sit under the cabinet where I kept his toothpaste and beg