MRI and biochemical investigation of the temporomandibular joint of juvenile pigs after sagittal advancement of the mandibulae

Abstract

Summary Orthodontic treatment leads to changes of the temporomandibular joint (TMJ). The extent and manner of alterations are not yet clarified completely. The non-invasive diagnostic methods do not provide any precise data about the extent of alterations. The aim of the present investigation was to analyse the TMJ cartilage after orthodontic treatment with non-invasive and invasive methods. For the present investigation, twelve 10-week-old pigs including six control animals were used. Treatment was carried out with build-ups on the molars for sagittal advancement of the mandibulae. Magnetic resonance imaging (MRI) and determination of the Ca ++ and Mg ++ content were carried out 4 weeks after implantation of the build-ups. Tissue samples for ion determination were taken from the posterior area of the TMJ (condyle and fossa). During condylar growth a significant increase in cartilage volume and decrease of Ca ++ and Mg ++ content was observed. The newly formed tissue had a water content of 80–90%. On MR images of animals with build-ups this area was visible as a bright zone with increased signal intensity. The determined stress potential of the condylar cartilage was reduced as a result of less functional stress in the posterior area accompanied by water intake. The newly formed cartilage matrix contained significantly less Ca ++ and Mg ++ , and cannot be defined as permanently stable cartilage.