Teeth are used for eating with and can also be used for protection. Some animals have teeth that are made to chew on animal flesh while other animals have teeth that are made for chewing on plants. Some creatures don't have teeth at all. Adult humans normally have 32 teeth. Humans have baby teeth that fall out as children grow, and are replaced by adult teeth.
Acid damages teeth, and since human teeth are very limited in their abilities to heal, this can cause permanent decay. A common problem for teeth is dental caries, which is the decay of teeth in specific areas, which is caused by acid produced by bacteria. Simple carbohydrates (sugars) feed this bacteria and as the sugar is digested by the bacteria, acid is produced. This in turn burns a crevice into the tooth, giving the bacterial colony a protected place to stay (and continue producing acid). Proper dental hygiene, including tooth brushing and flossing helps to remove the acidic bacterial plaque, and the sugars the bacteria feeds on.
While animals can have similar issues, most animals are not exposed to nearly as many simple carbohydrates to feed harmful bacteria, and many species have superior healing abilities to humans.