Good news for those that didn’t know: It is permissible to brush your teeth using tooth paste while fasting. Car must be taken not to swallow the toothpaste. The hukm is as for miswak. Some oppose this opinion by saying you have splashes to the mouth whilst brushing, there is taste, there is absorption through the muscosal membranes, etc.
These people should note and understand that some types of miswak are full of sap which cause splashes also, taste itself does not break a fast (even water has a taste reconigned in fiq), absorption through membranes does not break fast. Fast is only broken if the paste passes the throat (oesophagus) and therefore enters the stomach.
The masla for miswak is used as qiyaas upon brushing.
In a nutshell, brushing of teeth using toothpaste is allowed as long as the paste is not swallowed. Where an individual feels they cannot avoid swallowing, it is better they do not brush! [Positioned held by Mufti Azam Ahle Sunnah Mufti Rafiq al Hasni]
By Shaykh Abu Yusha Yasin of The Suyuti Institute