Recently, I noticed that espresso drinkers tend to have more teeth staining than other coffee drinkers. I was wondering why this happens? After a closer look at the coffee compositions, there is an answer to my question. The dense, reddish-brown foam on top of espresso, is composed of tiny carbon dioxide and water bubble as shown in the article from this link which created a tartar black colour-like staining on the teeth. (
If you are an espresso drinker, you may need regular professional scale and clean to prevent those staining from building up.

Coffee Chart