Firs thing we must keep always in mind that Muslims must be always clean all over their bodies including the mouth which is the entrance to their bodies, Alhamdulillaah, we all understand the importance of oral hygiene. Science in the twentieth century has shown us the link between poor oral hygiene and certain diseases such as stroke, heart disease, pre-term babies, as well as general ill-health of a person.
However, while shuffling between electric/sonic toothbrushes, water picks and expensive dental treatments, we forgot that while the rest of mankind just recently discovered the toothbrush about a 100 years ago, one unlettered Prophet (Peace Be Upon Him) living in the middle of a desert 1400 years ago, already showed us the significance of brushing the teeth and keeping the mouth clean, the teeth of Prophet Muhammad (Peace Be Upon Him) were beautiful, perfect and pearly white at a time when the concept of oral healthcare was totally obscure and nobody beyond the age of 30 had  any teeth left!
He (Peace Be Upon Him) used the Siwaak or tooth stick to clean his teeth, the siwaak is a root of the araak tree found in and around Makkah city. He (Peace Be Upon Him) loved to use it and highly encouraged us to do the same.
Ibn Masood said: I used to gather siwaak sticks from the araak tree for the Messenger of Allaah (Peace Be Upon Him). (Narrated by Ahmad).
Now, I am not telling you to throw out your toothbrushes in the garbage. The Siwaak is an act of worship and a Sunnah for which you will be rewarded, so use it in addition to your toothbrushes, and gain the pleasure of Allaah, Most High.

 BENEFITS OF SIWAAK:

1) Siwaak is an act of worship and pleases Allaah
Prophet Muhammad (Peace Be Upon Him) said, Siwaak cleanses the mouth and pleases the Lord. (narrated by Albukhaari)

2) The Prophet (pbuh) highly encouraged it:
The Prophet (Peace Be Upon Him) said: Were it not for the fact that I did not want to make things too hard for my followers, I would have commanded them to use the Siwaak at every time of prayer.‌ (Bukhaari)

3) Medical benefits
While some educated Muslims consider the Siwaak barbaric and  uncivilized and look down upon those who use it, scientific studies have proven beyond doubt, that the Siwaak not only brushes the teeth and keeps them white, but also has antibacterial properties, fights gingivitis, eliminates bad breath, strengthens the gums, prevents plaque, helps in digestion, and contributes to the general health of the individual. (Islamic medicine by Dr. Mohammad Nezar al Dagr)

This is yet another proof of the truthfulness of the prophethood of Muhammad (Peace Be Upon Him).

TIMES WHEN SIWAAK IS RECOMMENDED
Siwaak is recommended at all times of night and day, but there are certain specific situations where use of the siwaak is even more strongly encouraged.

1) When making wudoo and at times of prayer.
The Prophet (Peace Be Upon Him) said: Were it not for the fact that I did not want to make things too hard for my followers, I would have commanded them to use the siwaak at every time of prayer. According to another report he said: at every time of making wudoo

2)When entering one's home :
When he (Peace Be Upon Him) entered his house, the first thing he would do was to use the Siwaak. (narrated by Muslim).

3) When getting up from sleep.

Hudhayfah (RA) said that when the Prophet Muhammad (Peace Be Upon Him) gets up during the night, he would clean his mouth thoroughly with the siwaak. (narrated by Bukhari,Muslim)

4) When the mouth emits odor:
Such as after eating food with a strong odor, like onions or garlic or because of not eating or drinking for a long time, etc.

5) When going to the masjid:

Using siwaak when going to mosque, it is very important because the angels are present in the mosque, and one is going to meet with other worshippers there, so his/her mouth will smell clean and fresh.

6)When reading Qurân and mentioning the Allaah:

7)When joining good gatherings

Important points about the Siwaak

1. The roots or twigs of the araak tree are the best to use and the root is better than the twigs, or any kind of sticks that are cleansing may be used, that includes toothbrushes and toothpastes

2. It is forbidden to use harmful or poisonous sticks or things that are not taahir (pure).

3. There is nothing wrong with using siwaak flavored with mint, lemon, etc.

4. The Siwaak should not be too dry, it may hurt the gums

5. The siwaak should be washed after use.
   Aaishah RA said: when ever Prophet Muhammad (Peace Be Upon Him) uses siwaak, he would give it to me to wash it. I would use it first, then wash it and give it back to him. (narrated by Abu Dawood)

Using siwaak when fasting
The scholars agree that there is nothing wrong with using siwaak during the day when one is fasting. However, one should avoid swallowing any bits of the siwaak.
Some people use the hadeeth The odor that comes from the mouth of the fasting person is better in the sight of Allaah than the scent of musk (Bukhaari) as evidence to not use the Siwaak. But, this is not applicable since this mouth odor is caused by the stomach being empty, not from the mouth itself and will not be dispelled by using the Siwaak.

 REVIVE THE SUNNAH
This beautiful Sunnah has been lost in the plethora of toothbrushes and modern technologies, and we have put our Siwaaks aside. We need to revive this great Sunnah. Not only will it earn us a beautiful smile, and a healthy mouth and body, but it will also earn us rewards and the pleasure of All-mighty Allaah.