Bismillahirohmaneerohim (In the name of Allah, the Most Merciful, the Most Compassionate)
The Siwak, as we know was used by the Prophet salallahualaihiwassalam in his lifetime. Abu Hurayra reported that the Messenger of Allah salallahualaihiwassalam, may Allah bless him and grant him peace, said, "If it was not for the fact that I might have been overburdening my community - or the people - I would have ordered them to use the siwak for every prayer."
Therefore from this, the use of the siwak is a strong suggestion for the community by the Prophet salallahualaihiwassalam. But it wasn't enforced to be as the toothbrush or to use the siwak for every prayer. The community have the option to use the siwak or to use the toothbrush. It is not stated in the Qur'an that a Muslim must use the siwak. But I have prefered to use the siwak anyway.
"Gold is to be paid for by gold, silver by silver, wheat by wheat, barley by barley, dates by dates, and salt by salt - like for like, equal for equal, payment being made on the spot. If the species differ, sell as you wish provided that payment is made on the spot" (Hadith Muslim)
Paper money used to be a debt of real wealth of gold and silver, and this would not be allowed because of the prohibition from one of the Prophet’s Hadith about any transactions in gold, silver, wheat, barley, rice and dates is to be done on the spot and hand to hand. If the paper money represents gold, therefore this transaction goes against the hadith as the gold is not being transferred from one person to another.
But paper money now do not base its value on gold or silver, so it doesn't contradict with the hadith and seems like it will be permissible to use it as money. There are some that states that money should have intrinsic value because of the Hadith that has been stated above. The rationale to that statement was, all of the six items have value and can be used as money. In my research, I've not encountered that wheat, barley or dates was used as money (please advise me if I'm wrong on this). These items are perishable (may be eaten, rotten and etc) so it is rarely used as money. So, is it necessary for money needs to have intrinsic value? Who puts the value towards gold? If gold does not interest anyone, wouldn't the value of gold go down/depreciate? So it depends on the demand of the community to put the value on gold. What is the difference with fiat money? Fiat money too also depends on the demand.
I've not worked in an Islamic bank and I don't think I am biased towards Islamic banking. Some have gone to say that Islamic banking is a great deception and stuff like that. Although I do see some Islamic banks are not conducted properly, I don't think that it is a "great deception". Islamic banks needs to be improved with the help of the community.
The argument of gold as the ULTIMATE ISLAMIC MONEY, is not really accurate. Big transactions using gold will require delay payments and as the Hadith on gold earlier states that "sell as you wish provided that payment is made on the spot". I see this as a problem in using gold. If this problem and other problems on gold are being solved then there is nothing wrong on the usage of gold. I do not oppose gold nor do I support fiat money. Both have problems and in my opinion both may be used as money as long as it is being used properly.