The science: One of the many benefits of using a silicone toothbrush is its ability to gently but thoroughly clean the gums. What happens if you don't clean your gums regularly? The sticky biofilm, also known as plaque, will begin to accumulate in your mouth. When plaque isn't removed from your teeth, it hardens into tartar under the gumline. This leads to inflammation of the gum area surrounding a tooth's base (known as the gingiva). Inflamed gums swell, bleed, and can lead to periodontal disease.
Here is a study comparing plaque removal by a rubber-tipped (silicone) toothbrush with a nylon-tipped toothbrush. International Journal of Clinical Preventive Dentistry (IJCPD)