正畸资料的生物机械原理.pptVIP

The biological basis of the orthodontic Therapy Fengshan Chen Tongji University Law 1In orthodontics, tooth moves through bone and brings the periodontal ligament with it. The basis of the Periodontal Ligament (PDL) Normal width 0.25 mm or 250 micrometers. Cells, fibers, ground substance. Cells of PDL Fibroblasts Osteoblasts, osteoclasts Cell rests of Malassez Mesenchymal stem cells They all proliferate at different stages of tooth movement. You must know what functions each has in tooth movement. Fibers of the PDL Collagen and oxytalan Some of them are stretched, torn and ruptured, whereas others are compressed and undergo aseptic necrosis Ground substance of the PDL Proteoglycans and other proteins Their contents and expression are altered upon tooth movement Water squeezed in and out during tooth movement Alveolar Bone Thin cortical bone and porous (lamina dura) Fluid pumped in and out of the PDL Trabecular bone underneath Must remodel before teeth can be moved Law 2Tooth cannot move unless bone apposition and resorption take place. Law 3There will be no tooth movement unless there is a force. The basis of Force The force must have the right characteristics such as the magnitude and duration ---- it must meet certain threshold. Force Types Light, continuous forces Never declines to zero. Interrupted forces Declines to zero Intermittent forces Declines to zero Force Magnitude (Level) In the range of 10 to 200 grams. Varies with the type of tooth movement. Light, continuous forces are currently considered to be most effective in inducing tooth movement. Heavy forces cause damages and fail to move the teeth. Force Duration Threshold --- 6 hrs per day. No tooth movement if forces are applied less than 6 hrs/d. From 6 to 24 hrs/d, the longer the force is applied, the more the teeth will move. Law 4Orthodontic tooth movement is not the only type of tooth movement. Types of Tooth Movement Eruption Active Passive Lateral drifts Physiological Due to loss of adjac