Patent ID: 8920169

Claim:
A mouth opening instrument, comprising: an upper member configured to be attached on an upper jaw side within a mouth of a patient; a lower member configured to be attached on a lower jaw side within the mouth of the patient; a connecting section mutually connecting end portions of both the upper member and the lower member and permitting relative movement of distal portions of the upper and lower members respectively toward and away from each other that respectively corresponds to an opening or a closing of the upper and lower members and to a closing action or an opening action of the patient's mouth; an input section configured to receive operating state signals indicating an operating state of a dental treatment device, the operating state signals including a designated operating state signal; a control section comprising a brake arranged with the connection section and upper and lower members, the brake passively generating a resistance to the opening or closing of the upper and lower members, and the control section being configured to receive the operating signals from the input section and to control an amount of the resistance to the opening or closing of the upper and lower members; and wherein the control section receives the designated operating state signal from the input device and sets the resistance of the brake to the closing of the upper and lower members to a resistance greater than a resistance for closing the upper and lower members when the designated operating state signal is not received.