Assalamualaikum, Lets be careful and not mock this sunnah of prophet (saw). It is our iman that when Allah (swt) created knowledge, Allah (swt) made it in 100 parts, and one part was for this whole creation, the animals, the human, the scientist, the muffasir, muhadith, 'ulama, doctors, engineers, everyone e.t.c and the 99 parts was for prophet (saw). So to say that medical reports disapprove of this sunnah of miswak, that is itself denying that we do not have iman that prophet (saw) had the most knowledge in this creation. And to question and ask or maybe change the way of this sunnah is itself a mock, and and to deny this fact. We have very less knowledge compared to prophet (saw), and we do not know how much wisdom is behind just one sunnah and how many benefits are their. Wether they are seen or unseen benefits, internal or external, worldly or the akhirah e.t.c So we must accept that this sunnah is the best of the actions that can be done.