The miswak is a traditional Middle-Eastern toothbrush (so to speak) make from a twig of a particular branch, that is claimed to be especially effective. The dental efficacy has been studied, but frankly isn't very interesting - it is, essentially, just another form of abrasion for removing debris and plaque.
What is more interesting is that Islamic culture claims a myriad of other benefits, beyond dental. This is due to a sunnah on the subject, with the consequence that this is believed by a lot of Muslims.
I'll ignore the religious aspects (i.e. apparently Allah greatly magnifies his rewards for people using the miswak), as I believe such is beyond this site's remit; however, any Google search for "miswak benefits" will reveal the other claims, including:
Many of these seem quite extraordinary claims (for a toothbrush), but also feel like they should be pretty easy to investigate. While extraordinary, some are also not entirely beyond plausibility - for example, the headache/willow/salicylic-acid/aspirin connection.
So: has any research even been done into the non-dental, non-religious aspects of these claims? Or more simply: does the miswak help with digestion, eyesight, headache, memory or illness?