What is the ruling on using a siwak during and after the prayer?

Using the siwak is a confirmed Sunnah (definition). The Prophet, peace and blessings be upon him, said: "Were it not that I would overburden my Ummah, I would have commanded them to use the siwak with every prayer." Its recommendation before prayer is because prayer is a state of drawing near to Allah, requiring perfection and cleanliness to demonstrate the honor of worship. Therefore, there is no impediment to using the siwak during the call to prayer (iqama), after it, or before commencing the prayer.