Wisdom Tooth

"Gintoki rubs at the tip of the tooth with his thumb, disappointed to not feel it move under his finger. It would have been so much easier to deal with. He could have taken it out roughly, or seen a doctor, maybe, if the kids had learned about it and insisted Gintoki see someone.

Instead, it doesn't bulge, and Gintoki feels the shape of the tooth still half concealed under the gum. It's a wisdom tooth, Gintoki knows."

Or, Gintoki has a toothache.