Use of Miswak or Brushing Teeth during Fasting:
A miswak is a short stick which is taken from the branches of a particular tree, known as ‘araak’. When the outer skin is removed, it can be used as a toothbrush. Normally it is used without any toothpaste. It apparently has good cleansing effects on the teeth. The use of such a miswak is recommended during ablution and before prayer.
To use a miswak or a toothbrush while fasting is permissible. However, when one uses toothpaste, one puts one self unnecessarily in a position which could spoil one’s fast. When one rinses his mouth, one needs to do that thoroughly, not as one normally does in ablution. Therefore, there is really a danger of swallowing something involuntarily. That is enough to render his fasting invalid for the day. From another point of view, it is discouraged to use a miswak or toothbrush after midday on any fasting day. The Prophet mentions that the smell of the mouth of a person who is fasting is “better, in Allah’s sight, than the smell of musk.” When he uses a miswak or a toothbrush, he spoils that smell. This is the reason why it is discouraged. But it does not invalidate his fasting if he does not swallow anything of the water with which he rinses his mouth or washes out the toothpaste.