INBDE (Integrated National Board Dental Examination) Practice Exam

What is the movement of the TMJ when opening halfway?

1. Hinge rotation

2. Gliding movement

3. Lateral excursion

4. Circumduction

The correct answer is: Hinge rotation

When the temporomandibular joint (TMJ) opens halfway, it primarily undergoes a hinge rotation movement. This type of movement occurs in the initial phase of jaw opening, where the condyle rotates within the articular fossa of the temporomandibular joint. This movement allows for an initial opening arc of the mandible before other movements like translation or gliding occur. Gliding movement refers to the translation of the condyle along the articular eminence after the initial hinge rotation. Lateral excursion involves moving the mandible from side to side. Circumduction is a complex movement that combines rotation and translation but is not typically observed during the initial phase of jaw opening. Therefore, in this case, the correct answer is the hinge rotation movement, as it best describes the primary movement of the TMJ when opening halfway.