Dogs will start to lose their teeth when they are 2 to 4 months old. At this time, when all the deciduous teeth have grown in, they will start to lose their teeth. This will last until about 8 to 12 months, when all the teeth will be replaced. Some dogs may It will take until the dog is one year old to complete the replacement, which is normal. If the dog's teeth have not been completely replaced after the age of two, it is best to go to the hospital to have the teeth extracted.