I can read my dog more by her actions than her face, although when she is happy and content, she squints. I have known a few squinters and it is a very engaging thing. She will also flatten her ears completely against her head while she squints. With ears the size of hers, that is not an easy thing to do. I have known dogs who “smile” or show their teeth in a happy fashion.
I once had a cairn terrier, Agnus was her name, anyhow she was a great smiler and in case you don’t know, even smaller terriers have excellent dentition and huge canines, so it was impressive to see and frightening if you didn’t know her. She was also adept at opening doors. I lived in a house where the bathroom door was very difficult to latch. I had a non doggy friend visit, used the toilet and seemed to be gone an extremely long period of time. I thought perhaps I better check to see she was okay, I approached the toilet, noticed the door was ajar and yelled in “Are you okay?” Turns out Agnus had opened the door and gone in to visit. Plopped herself right down in front of my friend as she sat on the throne and smiled her biggest smile. My friend was afraid to move, eheheheh I love dogs!
So yes, I think they do have facial expressions but to a very limited degree.