Some brothers told me not to use miswaak after Zuhar up to Ifthar. But, some brothers told that it is permissible to use.
Can I use a miswaak while fasting?
Yes, you can use miswaak while fasting.
Amir Ibn Rabia narrates: “I saw Hz. Muhammad (PBUH) using a miswak while fasting more times than I can count.” -Sahih Bukhari Volume 003, Book 031, Hadith Number 154.
It is not makrooh when a fasting person uses a miswak or a toothbrush dampened with water according to scholars.
Imam Nawawi RA, who was one of the greatest Shafi'e jurist, stated that it is permissible to use the miswak during the afternoon as well as whilst fasting. - Fathul Qarib al-Mujeeb by Sheikh Ahmad bin Husain, page 5.