Consider the following excerpt from the Neurologic Rehabilitation Institute at Brookhaven Hospital.
... high school football players wearing store-bought mouthguards were more than twice as likely to suffer mild traumatic brain injuries than those wearing properly fitted, custom mouthguards.
“Researchers and, most importantly, parents, are looking for ways to better protect children against concussions,” said lead author Jackson Winters, DDS, a pediatric dentist who also served as a high school and collegiate football official for 28 years. “Consumers may believe that today’s advanced helmet design provides sufficient protection, but our research indicates that, when compared to over-the-counter versions, a custom-made, properly fitted mouthguard also is essential to player safety.”
The study followed 412 players across six high school football teams. Three teams (220 players) were randomly assigned to wear custom-made mouthguards, while the remaining three teams (192 athletes) wore standard store-bought mouthguards of their own choice. All players used the same style of helmet during the study.
You can read the whole article from the Neurologic Rehabilitation Institute here.