I have a black lab that weighs in at about 120 lbs, he loves people and when you look at him he smiles. It is creepy and freaks out strangers, he wags his tail and bares his teeth at the same time, kind of a silence of the lambs thing.
Showing some tooth as part of the Happy Smile is not big deal. It's when the lips are retracted and the hair rises that it becomes a concern (like my part Chesapeake).
My Black Lab has big white teeth (that's all they can see, 'cause NO light is reflected by the dog) that scare folks (who obviously don't know Labs) when she smiles the Happy Dog Smile.
My last dog, a German Shepherd/Golden Retriever mix had what was called the 'Shepherd Smile.' When he 'smiled' it looked like he was snarling and ready to bite.
He'd wag his tail, come right up to you with that 'Shepherd Smile.'
I happened to love it when he did that. Folks who were just meeting him for the first time or service people who came to the house didn't have a clue and were terrified of him -- I liked it that way. :-)
One time some unsolicited salesman came to the door and was acting like a jerk. I whistled for "Jerry" to come running from where ever in the house he was. Sure enough, he came running with his 'Shepherd Smile' showing at which point I opened the front door and said "Get 'em!"
This jerk had no clue all Jerry wanted was to say hello and get a pet or two as he ran screaming down my driveway for his car. LOL!!!
I miss that dog. He died 7 years ago. Best dog I ever had, and I've had dogs all my life. Funny, every dog I've ever had has been great in their own way and they all have a special place in my heart. When I pray, I ask the Lord to send them to come get me "when my time comes." I miss 'em all.