A new review of earlier research  confirms the main rationale for dentists recommending soft-bristle toothbrushes over harder-bristle ones: They’re less apt to damage your gums.
The researchers sifted through nearly 2000 studies to get to the 13 that met their criteria. Of those, 6 focused on bristle shape, 2 focused on stiffness, and 5 focused on both together.
Hard-bristle toothbrushes produced more gingival lesions than medium- and soft-bristle brushes. A slight gingival recession width increase was identified in the end-rounded group, compared with the tapered group.
Softness, of course, is one of the main reasons why we recommend the Nimbus toothbrush  for those who prefer a manual brush (and there are some good reasons  to opt for manual instead of power brushes). The Nimbus’ extra soft fibers are also extra long, so they’re more able to clean hard-to-reach spots along the gum line – as you might expect from a brush designed by a periodontist.
But ultimately, bristle softness is the thing – more so than bristle shape. As the authors noted,
Both tapered and end-rounded toothbrushes were considered to be safe, and there was no evidence to indicate one type of toothbrush over another.
Whatever the kind of toothbrush you choose, of course, the main thing is that you use it regularly and effectively. It won’t clean your teeth by itself, after all.
And even more effective than that? Floss before you brush. Other research  suggests that this results in better removal of biofilm (plaque).
Really and truly.
Image by Santeri Viinamäki , via Wikimedia Commons