The Thames is 215 miles long and while there are portions that are 100% wrapped in civilisation I think there are areas in both the tidal and non-tidal sections that are totally wild.
Obviously experimental archaeologists have to try and ignore airplanes, plastic bag waste, and their own good health and shiny teeth but I think this kind of activity is amazing.
"Totally wild" is probably an exaggeration, considering there is virtually nowhere in southern England that could reasonably be considered totally wild.
The nearly entire length of the river is navigable, with the flow controlled by locks and weirs. This isn't to minimize their achievement, but they didn't have to contend with rapids, shallows or swamps like the river would have had back in the stone age.
People have practiced dental hygiene since forever:
> Since before recorded history, a variety of oral hygiene measures have been used for teeth cleaning. This has been verified by various excavations done throughout the world, in which chew sticks, tree twigs, bird feathers, animal bones and porcupine quills have been found. In historic times, different forms of tooth cleaning tools have been used. Indian medicine (Ayurveda) has used the neem tree, or daatun, and its products to create teeth cleaning twigs and similar products; a person chews one end of the neem twig until it somewhat resembles the bristles of a toothbrush, and then uses it to brush the teeth. In the Muslim world, the miswak, or siwak, made from a twig or root, has antiseptic properties and has been widely used since the Islamic Golden Age.
Obviously experimental archaeologists have to try and ignore airplanes, plastic bag waste, and their own good health and shiny teeth but I think this kind of activity is amazing.