Yeah definitely not common. At least in American culture, it's strange for someone to carry a toothbrush for work/school most individuals brush their teeth only in the morning and night.
its actually pretty common in korean culture, my friends do this after lunch too and i was so shocked lol.
Oh my! I'm from Brazil and it's pretty common to brush teeth at least three times a day, so pretty much everyone carries a toothbrush with them. We brush at work and even at school. LOL
Sooooo, is it not common to brush your teeth after lunch at the office and keep the items there? I'm pretty shocked with this new information... LOL