It sounds like petechiae, or very tiny pinprick bruises (most of the time they are not painful at all) caused by broken blood vessels right under the skin. I have gotten them from coughing to hard, sneezing a lot, hard vomitting etc. If I remember correctly, I had them after I had recent surgery where I needed anesthesia. I am guessing that it is from either the mask being applied or the anesthesia, or the pressure from the dental work. They will fade away in a few days to a week.