My 19 year old grandson had his wisdom teeth extracted on Monday. I have not seen him but his Mother says she noticed something at the side of his mouth that looked like dried blood.  He said he had already asked his dentist about it and she said it was a stretch mark.  I have never heard of this.
Hi, As per your complaint the appearance of Chat Doctor.  I would however need an image of the spot for better understanding of the cause of the spot and advise you accordingly. Upload images by asking a direct question by going to my profile. You can also consult an oral surgeon and get evaluated. Hope I have answered your query. Let me know if I can assist you further.