Morphology of the Masticatory Muscles and the Mandible in a 3D Image of Patients with Dentofacial Deformities. Summary of the Doctoral Thesis

Abstract

In the maxillofacial area the masticatory muscles take part in the creation of the biomechanical environment, and this, according to Moss’ function matrix theory and Wolff’s classic law of bone formation, may influence the skeletal components, their growth and development, as well as the final anatomical morphological manifestation in the dentofacial structures. The novelty of this research is based on researches of literature sources and they indicate that until now there have been no researches that would include simultaneous comparison of the morphological peculiarities of masticatory muscles and mandibles (as a craniofacial structure) in relation to the vertical and the sagittal plane in patients with dentofacial deformities. Also there have been no researches that place separately obtained magnetic resonance imaging and cone beam computed tomography data into a single 3D picture. The objective of this promotion work was to research the spatial parameters of the masticatory muscles and the anatomical parameters of mandible in a cone beam computed tomography image and their mutual relation in the sagittal and vertical planes in patients with dentofacial deformities. This research included 78 individuals who had dentofacial deformities before orthognathic surgery and normative individuals. The research groups where created according to the criteria found in the cone beam computed tomography lateral cephalometric image, and this approach facilitated the division of all the included patients into two research directions, according to the determined parameters in the sagittal plane (I, II and III skeletal class) and in the vertical plane (the groups of horizontal, neutral and vertical growth). The cross-sectional area and volume of musculus masseter and musculus pterygoideus medialis were analysed in an magnetic resonance image, while the linear anatomical parameters of the mandible (ramus height, body length, total length, interangular distance) were analysed in a cone beam computed tomography image. The spatial parameters of masticatory muscles and the parameters of the mandibular skeletal structures were separately compared against skeletal classes I, II, III and against the craniofacial growth type groups, and the correlations were analysed both within the whole group, and by using advanced analysis within skeletal classes I, II, III, and within the neutral, horizontal and vertical growth type groups. The results indicated that in the sagittal plane the volume parameter of musculus pterygoideus medialis significantly differs among classes I, II, III, and there is a significant and strong negative correlation between the parameters of the severity degree of the skeletal class and the parameters of musculus pterygoideus medialis. Furthermore, it was found that among the craniofacial growth type groups the volume and the cross-sectional parameters of musculus masseter differ significantly. However, the significant negative and strong correlation among the MP-SN indicators and all the parameters of the muscles researched confirms that the more vertical is the face morphology (i.e. the craniofacial growth type), the smaller in size and therefore weaker are the relevant masticatory muscles. In the neutral craniofacial growth type group and skeletal class I group, which are normative reference groups, the correlations between the muscle structures and mandibular structures were more significant and more pronounced – indicating higher probability of the importance of form-function relation for harmonious structure development, contrary to the situation regarding the dentofacial deformity groups. In general it can be concluded that musculus masseter is more sensitive to variations and more significantly influences the craniofacial vertical dimension, whereas musculus pterygoideus medialis – the sagittal dimension, but the volume as the spatial muscle size indicator is more important than the cross-sectional parameter in the craniofacial area. It would be advisable to specialists of orthodontics to bear in mind the significant nuances, differences, and associations that have been identified in this research among and within various dentofacial deformities, and which can be perceived as one of the basic understanding aspects in the physiological and anatomical level. The findings of the research in the future may serve as a basis for development of objective treatment evaluation system and open up new additional non-invasive treatment possibilities within myofunctional and orthognathic therapy.