Background. Occlusal splints are nowadays commonly used in dentistry to treat symptoms of myoarthropathies of the masticatory system, but also to treat simple occlusal parafunctions. Still, the exact mechanism by which the treatment works is unknown. The aim of this study was to find out the answers to following questions: 1. is there an immediate change of the minimum condyle-fossa distance and accompanying disc thickness by inserting a Michigan splint and 2. is it possible to displace the main loading area on the disc by inserting a Michigan splint?
Methods. For each subject and each temporomandibular joint (TMJ), four magnetic resonance imaging (MRI) recordings were taken in the following situations: maximum intercuspation without/with Michigan splint, maximum protrusion without/with Michigan splint (splint 3 mm). The image stacks were reconstructed to three-dimensional virtual models using the Amira™ software. Several measurements were taken on these models and subsequently compared within and across the subjects.
Results. No significant change in the global minimum condyle-fossa distance could be achieved by inserting a Michigan splint. However, in most TMJs (18 out of 20) a shift of the main loading area (the area with the smallest joint space) could be observed. This effect could cause an unloading of the otherwise most loaded zone. The intensities of MR images within the discs did not differ significantly intraindividually, thus indicating that all discs were segmented in the same way and were comparable. Most subjects (8 of 10) reached a more anterior condylar position during protrusion with inserted splint compared to the situation without splint.
Conclusion. With this method, no increase of the overall minimum TMJ space due to the sole insertion of a Michigan splint could be demonstrated, however a shift of the main loading area could be shown.