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Correct axis of rotation at condylar asymmetry It is impossible for me not to repeat the importance in every clinical situation to recognize a temporomandibular joint condylar asymmetry, when present. In not doing so the treatment cannot be correctly predicted. The treatment will not be as successful as was expected . Unnecessary adjustments of oral devices or, even worse, adjustments of permanent dentistry will disappoint the patient as well as the dentist with also the risk that the treatment will never be fully accepted despite tremendous efforts from both parties involved.

In the clinical situation or in the dental laboratory the conventional axis of mandibular rotation should never penetrate the centers of the two temporomandibular joint condyles at a condylar asymmetry.One condyle, the ” higher one “must determine the axis of rotation. If not, the axis of rotation could not be parallel to the horizontal plane, used as the reference at general rehabilitation.

image-1                                                  Wrong axis of rotation at a condylar asymmetry.

Correct axis of rotation at condylar asymmetryCORRECT AXIS OF ROTATION AT A CONDYLAR ASYMMETRY.

It is my opinion that the definition and the application of the generally used retruded position of the mandible ( RPM ),based upon the assumption that the two temporomandibular joints are equal, therefore needs to be reconsidered and slightly adjusted Clinically I have always worked with the retruded position of the mandible as my reliable position of reference.However for the past 25 years I  have advocated that the retruded position of the mandible ( RPM ) is ( should be ,if not yet ) determined and guided by the normally developed and functioning temporomandibular joint condyle. When the right side is the higher side RPM is to be written RPM (R). When the left side is the higher side RPM is to be written RPM (L) and when the two condyles are of equal height RPM is to be written RPM (=).In addition, when the two condylar heights are measured in the panoramic ( over view ) x-ray and the magnification factor  of the machine is compensated in the calculation the RPM(R) or RPM(L) at an asymmetry can be written i.e. RPM(R)1,5mm or RPM(L) 0,5 into the clinical documents. In that way the almost true difference between the two condylar heights easily can be compensated for in the necessary index to be used in the phase of rehabilitation clinically or at the laboratory via the Maaxloc device (info@dentatus.se)

In general the higher condyle determines what side is to be the guiding side for RPM. However, there is one exception under rare circumstances.At a ramus asymmetry when the total vertical dimensional difference between the two mandibular sides is determined by a major difference in height of the two rami, the vertical dimensional difference determined by the condyles is overruled.Then the biggest total mandibular vertical height may direct even the “shorter condyle” to be the guide in the registration of the retruded position of the mandible and the center of the hinge axis rotation. In this context “disturbing” precontacts or interferences enter a completely new perspective. Unilateral tooth contacts on the “higher condyle” side may indicate the correct vertical dimension of the occlusion. The lack of tooth contacts on the “shorter condyle” side may indicate the occlusal dimension that needs to be increased.Only interferences or precontacts on the “shorter condyle” side will then remain as traditional interferences i.e.disturbing tooth contacts.