The HINGE AXIS concept!

How do we conceptualize the hinge axis and how does it function in practice?

The hinge axis of mandible rotation, also known as the mandibular hinge axis, is an anatomical reference point representing the axis around which the lower jaw or mandible can rotate during its movements. This axis is crucial in the field of dentistry and maxillofacial sciences for various diagnostic and treatment purposes, particularly in relation to the temporomandibular joint (TMJ) and occlusion studies.







The actual hinge axis can be determined through three methods:
1. Anatomic
2. Graphic/needle and paper/
3. Computerized/electronic (CADIAX)

The last method is considered the most precise.

THE RESULT OF INVESTIGATION OF THE COMPUTERIZED/electronic(CADIAX)/
The needle is pointing to the individual hinge axis of this patient. It is right at the external acoustic meatus.

RIGHT SIDE



LEFT SIDE

CONCLUSION:
The hinge axis of this patient is not within the condyle, and it is asymmetrical.



ONE MORE QUESTION!
How can we be certain that the hinge axis of the current patient was accurately recorded? In this video from condylography, you can observe the repetitive and clearly defined movement of the hinge axis. This movement was recorded by a computer following the condylography protocol.















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The problem of the HINGE axis concept!

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Let’s start with the concept of the HINGE AXIS. We have been taught that the hinge axis is located somewhere in the condyle. If the hinge axis is indeed located within the condyle, then human beings invented the articulator. The articulator replicates the movements and the position of the lower jaw relative to the skull! Working with the articulator is akin to working directly on the human being, given that it replicates the same hinge axis recorded from the patient. After the recording of the hinge axis, we visualize it as depicted in the picture. ONE PROBLEM! Recording the hinge axis on condylography precisely determines the hinge axis. Condylography is a computerized method for determining the hinge axis and tracking the movements of the jaws. After removing the sensors, we can accurately mark the exact location of the hinge axis. CONCLUSION FOR THE RIGHT JOIN: The hinge axis is located at the margin of the external ear duct. While we were taught that the anatomical hinge axis is ty
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THE HINGE AXIS CONCEPT

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TP1

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The diagram below shows the protrusion and open/close movement of the condylar hinge axis.  When both lines overlap, it indicates that the recording was done correctly.  The therapeutic position was recorded on the Gothic Arch. As you can see, the TP is not in front of the arrow, but somewhere in the middle. I performed the condylography measurement and found that the therapeutic position is at approximately 2.74 mm on the right side and 1.24 mm on the left side from the reference position (RP).  Please check the condylographic tracings.   The Gothic arch was designed on these tracings, and the therapeutic position was fixed based on these designs. The results of the condylar reposition are shown in the pictures below! Right side Before condylar reposition After condylar repositioning                                                                            Left side  Before condylar repositioning After condylar repositioning  
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