In a letter ruling, the Missouri Department of Revenue determined that sales of both "boil and bite" athletic mouth guards and laminate mouth guards used by dentists are taxable.
The state exempts sales of prosthetic and orthopedic devices. The state defines a prosthetic device as "a device that replaces all or part of the function of a permanently inoperative or malfunctioning internal body organ and is medically required." The state defines an orthopedic device as a specific device "directly used for the purpose of supporting a weak or deformed body member or restricting or eliminating motion in a diseased or injured part of the body."
Neither type of mouth guard falls within the definitions of orthopedic or prosthetic devices. As a result, sales of mouth guards are taxable as sales of tangible personal property.