Masticatory Strains on Osseous and Ligamentous Components of the Temporomandibular Joint in Miniature Pigs

Aims: An animal study of functional biomechanics was undertaken to understand normal loading of the temporomandibular joint (TMJ) and to provide insight into the pathogenesis of TMJ disorders. Methods: Bone strain and ligamentous deformation were measured during mastication in 26 10-month-old minipigs. Half the subjects had undergone a surgical disruption of the left lateral capsular and disc attachments to the condyle 5 to 6 weeks previously. Rosette strain gauges were bonded to the left lateral surfaces of the squamosal bone near the TMJ, the condylar neck, and the mandibular corpus below the molar region. Differential variable reluctance transducers (DVRTs) were placed bilaterally in the lateral capsular tissue of the joints. Bone strains, ligamentous deformations, and the electromyographic activities of the masseters and lateral pterygoids were recorded during natural mastication. Results: In all animals on both working and balancing sides, mastication caused bone strains that were dominated by tension in the squamosal bone site and by compression in the other sites. Measurements from the DVRT revealed elongation of the lateral capsular tissue in the last phase of the power stroke and shortening in the initial phase of opening, which was almost simultaneous with the development of bone strain. Strain in the capsule ranged from 3 to 25%, with the strain of the balancing side exceeding that of the working side. The surgical disruption did not alter chewing side preference or bone strain, but a tendency toward more extensive ligamentous deformation on the intact side was observed. Furthermore, the ratio of masseter to lateral pterygoid activity was smaller on the disrupted side and larger on the intact side, in comparison to control pigs. Conclusion: Both osseous and ligamentous components of the TMJ are strained during mastication, and the latter are more deformed on the balancing side. Disruption of the lateral attachment had little effect on strain in the osseous components but appeared to increase strain in the capsule and to modify the balance of masticatory muscle activity.