A puppy finishes teething at approximately seven months of age, when his baby teeth are replaced by 42 permanent teeth. The teething process starts at around three weeks with the appearance of deciduous teeth, also known as milk teeth.
Teething causes discomfort, so excessive chewing is normal during this time. A puppy may chew anything he can get into his mouth, such as shoes, clothes and children's toys. Most experts recommend redirecting a puppy's attention with chew toys and reinforcing good behavior with praise and treats. This method of positive reinforcement is much more effective at correcting bad behaviors than scolding or yelling.