You should get your dog into a routine of accepting brushing their teeth.
There are several ways to do this. You can use gauze wrapped around your finger with a dab of toothpaste on the gauze to gradually get your dog used to the feeling. Then with training, you can advance to a finger-tip toothbrush you put over your finger to brush your dog’s teeth. They also have toothbrushes made specifically for dogs. Always use toothpaste meant for dogs, never human toothpaste.
Routine dental care by your vet is also very important. Good dental care is crucial to the health of your dogs.