Starting at 3 to 4 months old and lasting until 7 to 9 months old, a Shih Tzu will be teething. When milk teeth fall out, this does very little other than perhaps cause a bit of odd puppy bad breath.
However, when 42 adult teeth are emerging in place of those 28 puppy teeth, this brings an incredible amount of itching on the gums and an intense desire to chew.
A puppy will indeed chew on just about anything, in a desperate attempt to quell his discomfort. If you have the right teething toys, he will not need to search long to find some relief.
*** Please note that offering ice cubes (plain or flavored with fruit
juice such as 100% real apple juice) is also a great method for helping with this. And if you find that crunching on ice helps your Shih Tzu puppy, do use both ice and toys.
The important design to look for with teething toys are durable toys but with give. It's best to have some with flavors (this keeps a puppy interested) and some that have have various textures.
A puppy needs to be able to work parts of the toy to areas that are itching at any one particular moment. Toys with tiny bumps are often great 'scratchers'. You will find that some marked as 'dental' toys work very well, since these have those tiny protrusions.