Hypothesis for the lack of a muscular antagonist to the lateral pterygoid

Abstract

Listen

Translate article

BackgroundDuring physiological function of the temporomandibular joint, we have to rely only on elastic structures (in particular the bilaminar zone) for repositioning of the articular disc. A real muscle, however, would be functionally more reasonable. In patients, a decrease of this elasticity is possibly one of the reasons for temporomandibular joint malfunctions, which affect between 16% and 36% of the population. MethodThis study assesses the morphogenesis of the murine (Mus musculus) temporomandibular joint with particular regard to the masticatory muscles, to throw light on this topic. To that end, a collection of 11 murine heads ranging from prenatal stages E13.25 to E20 was used and early postnatal stages P0 to P4, which were prepared as histological sections (thickness 8–10 µm) and stained conventionally in order to examine them with light microscopy. Next, the temporomandibular joint and selected surrounding structures, along with the masticatory muscles, were threedimensionally reconstructed using analySIS® software. Subsequently, specific morphometric analyses were performed. Results and ConclusionsThe evaluation of the results led to the following conclusions:1.The mechanical aspect of developmental processes has been brought more into focus again by recent research groups. Our morphometric study serves as a contribution towards testing the descriptions of mechanical forces explained by Blechschmidt, who maintained that muscles arise from mesenchymal tissue, which is stretched under the direct mechanical forces of the developing skull. The anterior region of the temporomandibular joint, where most of the masticatory muscles are situated, increases sixfold in size from stages E14.5 to P4, whereas the posterior region, where instead any muscle formation, the bilaminar zone was observed, only increases by twofold in size. This could be one of the reasons for the lack of an antagonist to the lateral pterygoid muscle.2.Some ambiguities in the knowledge of fundamental embryology regarding the masticatory muscles of the mouse, such as the regions of insertion and the number of bellies, were clarified.3.Taken together, this investigation provides a comprehensive view of the morphogenesis and morphology of the mouse temporomandibular joint and the selected neighboring structures, and it enables this model organism to be used for further studies.