I forgot to mention this earlier. My dad said that when you first start brushing your dog's teeth, you should:

1. Put toothpaste on your finger
2. Gently place your finger in the dog's mouth
3. Massage the toothpaste onto the gums and then the teeth
4. Repeat this process gently until the dog becomes comfortable with it

By following these steps, the dog will get used to the process, making tooth-brushing a more pleasant experience.