Objectives The aim of this investigation was to assess the association of magnetic resonance imaging (MRI)-diagnosed temporomandibular joint (TMJ) disorders [i.e., disc
displacement with reduction, disc displacement without reduction (DDNR), osseous changes (OC), joint effusion] on the same side as well as in the joints of the two sides of the
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Materials and methods A total of 199 patients undergoing bilateral MRI of the TMJs were included in the study.
A single variable correlation matrix was created to assess the within- and between-side correlation of single diagnoses.
Then, based on 12 possible combinations of diagnoses per each side, a contingency table was created to assess the chisquare values of the differences between the observed and expected frequencies of the different cross-combinations.
Multiple variable permutation test was performed to assess the null hypothesis that the diagnoses in the right and left joints are not related.
Results Within the signs of the same side, DDNR was positively correlated with OC. As for combination of diagnoses, the presence of a specific combination of signs on
one side implied the same combination of signs on the other side.
The global multivariate permutation test with Tippett combination was significant at p<0.001, showing that the null hypothesis of independence between diagnoses of the two sides was rejected.
Conclusions It can be suggested that disc displacement without reduction is associated with osseous changes of the same joint and that joints of the two sides are likely to be affected by the same combinations of MRI signs.
Clinical relevance This investigation supports the concept that the two temporomandibular joints work as a unit.