直丝弓矫治技术的临床应用课件.ppt

Etiologic Factors of Malocclusion Orthodontic Research office of Xi’an Jiaotong University Stomatology Hospital Min,Zou Congenital causes Acquired causes Mechanisms of individual malocclusion Hereditary causes Environmental causes 一、Hereditary Factors Hereditary Factors ：The characters has been fixed when the spermatid combined with the oocyte. Heredity：The transmission of traits encoded in GENES from parent to offspring.Say that similarity that between the parenthood. Gene is the basical unit of genetic material. Malocclusion feature is the polygene determine. Experiments with crossbreed dogs by Stock and Johnson At the beginning of 19th century，through crossbreeding pure-blood dogs with significant difference on coronal and occlusal relation-ship,the data from p3 shows that the cross breeding dogs appears obvious malocclusion. Conlusion： Hereditary factors play an important role in the development of malocclusion. Heritability of craniofacial feature Heritability of teeth arche feature ，and the later one is easier affected by the environment factors.Heritability has more effects on the bone proportion,and the teeth relation-ship is more likely influenced by the environment factors. Two pathway of hereditary factors induced malocclusion forming . The disproportion between the size of tooth and the size of jaw. The hereditary disproportion between maxillary and mandibular size or shape of maxillary and mandibular ,which would cause improper occlusal relationships. First Race evolution Transition of living environment：From creeping to upright-walking ,the size of jaw has degenerated . Race evolution Changes in dietary structure ：The function of mastication organ has degenerated gradually. Race evolution Lopsided degeneration of mastication organ:MuscleJawsTeeth Individual development Malocclusion has closely related to heredity,and is polygene decided . Evironmental factors induce various types of malocclusion with diverse manner or intensity thro