A device which is used by horse dentists to keep the horse's mouth open while performing dental examination or care. It comprises crescent-shaped bite-plates on which the incisors rest, and metal ratchets mounted on a halter, and is typically used to check on dental spurs which develop on cheek-teeth and cause mouth injuries to adult horses, to proceed to the floating of these spurs, to extract teeth and to perform any other kind of dental care.