Let pets get used to being touched

Generally dogs are not used to having their teeth touched, especially adult dogs. For them, touching the mouth, nose or teeth is a potential threat, so if If you want to brush its teeth, you first need to disarm it.
Choose a time when your dog is relaxed, such as when he is lying down and resting. Start by stroking his mouth, and gradually transition to being able to lift his lips, and then to being able to touch his teeth. Every time you make an action, don't force it if the dog resists. If it accepts it at any time, immediately praise it, pet it, or reward it with small snacks to let it know that this action is not only harmless but also beneficial.

Let your dog get familiar with the feeling of a toothbrush and brushing

Whether you use a long-handled toothbrush or a finger toothbrush, let them get familiar with the process.
Apply a little bit of their favorite toothpaste on the toothbrush, and then let them smell, lick, or even bite naturally so that they can get used to the feeling of the bristles rubbing against their teeth.
Similar to touching the teeth, the process of getting familiar with the toothbrush and toothpaste also takes a while. Don't rush to start brushing when the dog is still resistant and fearful, otherwise it may resist brushing its teeth for the rest of its life.
Try gently brushing the front teeth with a toothbrush or finger cot, such as the large canine teeth, so that the dog can get used to the brushing action, and can be rewarded with snacks.

Let the dog become familiar with the taste of toothpaste

Be sure to choose toothpaste specially designed for dogs. Human toothpaste contains ingredients that cannot be digested and are even toxic to dogs, while dog toothpaste contains ingredients that are indigestible and even toxic to dogs. Toothpaste is not only edible, but a good toothpaste will taste like meat or milk. Dogs will love them like snacks and will naturally not resist brushing their teeth.
Put a little toothpaste on your index finger. Don’t rush to rub the dog’s teeth. Let him smell and lick it naturally. If he likes it, give him some more to make him feel that it is as delicious as a snack and is useless. Damn good things.