When cats change their teeth, they will experience symptoms such as loss of appetite, red and swollen gums, bleeding, bad breath, and gum inflammation. Generally, kittens start to change their teeth when they are about four months old. At this time, the deciduous teeth will slowly fall out and permanent teeth will grow. When the cat is changing its teeth, it is best to feed the cat some liquid food that is easier to chew, and to supplement nutrients and calcium. At the same time, the cat's mouth should be cleaned every day to avoid gum inflammation or bad breath.