A lot of people had horrible teeth so they hid them. They did speak and smile differently. When a person is missing teeth, or the ones they have have visible black abscesses, or, their teeth are stained dark brown from tobacco and strong coffee, or, they have bad breath from an infection in their gums or a rotten tooth, they get self-conscious and keep their mouths closed as much as possible.
Dental hygiene was a very different business the year the Dial came to town. There weren't any spin brushes. There wasn't fluoride in the water. Novacaine had just been invented!