Training your dog to wear a muzzle is an important first step as it gives him time to get used to it, meaning it's a less stressful experience. However, a muzzle is not intended to calm your dog as such, but to prevent him biting, barking and chewing, if aggression is the reason he’s wearing it. And roughly misusing a muzzle, or using a muzzle that is a poor fit, can actually lead to negative behavior.