When I first started the dog grooming business, I asked the local veterinarian if he had any advice.  He said that we should not cage dry the dogs because they can get overheated.  He had a dog who died that week from overheating at  the groomer's.  My employee told me her mother's died at the groomer's that way too.  Cage drying can be done safely, however for older dogs or dogs with short faces (like your shih-tsus and pugs) the heat can be intolerable.  That is why since day ONE we have hand dried each and every dog.  If your dog is very upset and unmanageable with the dryer,  we may put him in a wire, open cage with a dryer on a lower setting.

Hand drying is a slower way to groom a dog, and time is money.  However, I feel that your pet needs to be as safe and as comfortable as can be!