Question

why does platelets in our blood form a patch when there's an injury in our mouth

Answer 1

If the platelets doesn't forms a layer on the wound ,then the blood present in our body comes out through that wound.Then we'll die ultimately.So,the platelets forms a layer on the wound and helps in blood coagulation. 

Answer 2

Because in our mouth Squamous epithelial cells will be present which form a patch