Dental students are normally taught about the necessity of an overview radiograph in the screening for and in the early detection of undiagnosed hard tissue changes of the maxilla and of the mandible (neoplasms, tumors or any strange lesions). Most dental students have also been told the questionable value of the panoramic radiograph because of the superimposition of the structures due to the construction of the X-ray machine with its two axes of rotation ( focus and film in opposite directions). On the other hand the panoramic radiograph is the only routinely used radiograph in the dental practice in which comparisons between the right and the left sides of the jaws can be made, as both side are projected in the same film without any change of head position.
However,comparisons of horizontal dimensions are not possible due to the superimposition of structures.Vertical dimensions can be compared as the focus of the X-ray machine is long and narrow. From this point of view the panoramic radiograph therefore shows its strength and its unquestionable clinical value in assisting the dentist in finding the correct vertical and frontal relations between the two jaws. In other words, in evaluating the occlusion from a functional point of view the panoramic radiograph is an aid of utmost importance.
Steps in determining the vertical condylar / ramus asymmetries:
1. Determine the most posterior point of the two condyles and the mandibular angels.
2. Draw a line through the two points of each mandibular side. This line we have named ” the ramus tangent “.
3. Draw new lines through the points perpendicular to ” the ramus tangent” and do so also between the most superior point of the condyle and “the ramus tangent “.
4.Measure the condylar heights ( CH )and measure the ramus heights( RH ).
At a vertical mandibular asymmetry you most often will find a difference in vertical height between the two condyles as the ramus portion of the mandible is a most stable part of the mandible and is less reacting on traumata etc during growth and development.
In evaluating the condylar asymmetry it was suggested ( Habets LLMH,Bezuur JN,Naeije M, Hansson TL. The Orthopantomogram,an aid in diagnosis of temporomandibular joint problems 2. The vertical symmetry. J Oral Rehabil 1988;15:465-471) to measure the condylar heights on ” the ramus tangent “. The condylar asymmetry,expressed in percentage is calculated accordingly, ( Right-Left/Right+Left)x100%. An asymmetry bigger then 3% is to be considered a true morphological asymmetry.
If you want to estimate the vertical difference in mm between the two condylar heights you absolutely need to adjust for the magnification of the machine used.
From many years of daily clinical experience it seems as if a condylar asymmetry might be a major reason for an asymmetrical stomatognathic system and its asymmetrical function. The ” shorter condyle ” side is most often found on the mediotrusive side at laterotrusive bruxing. When there is a lateral slide between the retruded contact position of the mandible ( RCP } or the centric relation ( CR ) and the intercuspal position ( ICP ) or the centric occlusion ( CO ) the slide seems to be most often directed towards the ” shorter condyle “side. It seems consequent that a condylar asymmetry most likely will result in an asymmetrical function, bruxism with orofacial pain of either mainly arthrogeneous origin or of mainly myogeneous origin.
To recognize a condylar asymmetry, when present, is therefore in my opinion of utmost importance for the registration of the mandibular position used in diagnostics and in the treatment ,topics to which I will return within shortly.
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