According to Donna Warren Morris, lead author of the study, it is tough to distinguish between a solid-head and a hollow-head toothbrush.
"The packaging on most power toothbrushes won't distinguish between a hollow-head and a solid-head design," Morris said. "The best way to identify a solid-head design is through the connection to the body of the power toothbrush. Naturally, there will be some space to connect the 2 parts but a significant portion will be solid, up to the bristles or brush head."
The researchers found that there was 3000x more bacterial growth on the hollow-head toothbrushes. During the research, the toothbrushes were exposed to 5 categories of oral microorganisms: anaerobes and facultative microorganisms, yeast and mold, oral streptococci and oral enterococci anaerobes, Porphyromonas gingivalis and Fusobacterium species.
"Toothbrushes can transmit microorganisms that cause disease and infections. A solid-head design allows for less growth of bacteria and bristles should be soft and made of nylon," Morris said. "It is also important to disinfect and to let your toothbrush dry between uses. Some power toothbrushes now include an ultraviolet system or you can soak the head in mouthwash for 20 minutes."