A veterinarian should be able to provide assistance. A food change associated with a dog's dermatitis is interesting since some dogs can develop food allergies. Again, a veterinarian should be able to help you with this issue. Dogs reach sexual maturity around 6 or 12 months of age. Smaller dogs get there earlier.
Puppies usually chew on things because they are teething.
As new, permanent teeth come in, they can irritate the gum tissue. Chewing on something helps loosen the baby teeth and allows the new teeth to come in. Some dogs continue to chew on things out of habit, and it can be a bad habit if they chew on the wrong things. They can splinter and cut their mouths, or puncture their stomach or intestine if swallowed. Dogs produce a large amount of saliva.