RCT During Fasting
According to what you described, fasting is affected only when something passes from the mouth through the throat into the stomach, that is, when it is swallowed. If the local anesthesia, treatment, or medicine is applied only inside the mouth and you avoid swallowing it, then the fast remains valid. Also, using toothpaste is permissible (halal) during fasting, as long as you avoid swallowing it. However, if during the procedure medicine, blood, or water is accidentally swallowed, the fast could be affected. Generally, small unintentional amounts are overlooked by scholars, and the fast remains valid. Therefore, if you are careful not to swallow anything while undergoing the treatment, your fast is likely to remain intact.