Dental coupling member, mouthpiece, and orthodontic tool

A dental coupling member, comprising:

• a first elongated body including, in a first-orientation end region of the first elongated body, a first coupling part to be coupled with a first attaching part of a first dental appliance and including, formed in a second-orientation end region of the first elongated body, a screwing part;
• an outer tube including, in a second-orientation end region of the outer tube, a second coupling part to be coupled with a second attaching part of a second dental appliance, and being open at an end on a first-orientation end region side;
• a third elongated body which includes a screwed part formed in a first-orientation end region of the third elongated body and is inserted into the outer tube in a second-orientation end region of the outer tube, the screwed part being for screwing with the screwing part;
• and
• a protrusion projecting from an inner peripheral surface of the outer tube and facing an end surface of the third elongated body on the second-orientation end region side.