23. Biomechanics of mandibular movements – vertical and horizontal movements.
Explains how the mandible rotates and translates during opening and closing, with the rotation-to-translation sequence and the condyle-disc compartments. It then covers forward and sideways movement: the condylar and incisal paths, the Bennett angle and the Bennett movement. It also describes gothic arch tracing with its gothic angle, and a table of posterior and anterior factors that control the movement and whether each can be changed.
Topic 23 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 5 sections, about 368 words (3 min of reading), with 13 flashcards.
In this note
Introduction
Vertical movement: opening and closing
Horizontal movement: forward and sideways
Recording the horizontal border movements
What controls the movement
Introduction
The mandible moves in three dimensions, but any movement can be broken into two simple parts:
Rotation: every point turns around an axis.
Translation: every point moves the same way at the same time.
It is easiest to describe them as projections onto the three planes (sagittal, horizontal and frontal), each with its own axis of rotation.
Vertical movement: opening and closing
From the intercuspal position to the rest position the condyles mostly rotate around the terminal hinge axis.
Pure rotation lasts for about the first 12 mm of incisor opening. Then the TMJ ligaments and muscles force the condyles to translate: the lateral pterygoid pulls the condyle-disc assembly forward down the back slope of the eminence.
At maximum opening the movement is pure translation.
Closing reverses the sequence; the shape of the teeth decides the last part of the path.
The rotation happens between condyle and disc (lower compartment); the translation between disc and eminence (upper compartment).
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