Can I brush after root canal treatment?

Yes, you should brush as usual even while root canal treatment is under way, because the area around the tooth needs to be clean to heal without inflammation. The tooth being treated is sealed with a temporary filling and structurally weakened, though, so 1) brush that area gently with a soft brush, 2) pull floss out sideways rather than upward so the temporary filling is not dislodged, and 3) clean the rest of your teeth as thoroughly as usual. However, if the temporary filling comes out or severe pain develops, come in even before your scheduled appointment.