 So, the ability of independent tooth movement is unique to humans and mammals in general. The tooth movement is possible because of the presence of pyridontal ligament which enables tooth movement. So, earlier the pyridontal ligament was not there, so there used to be ankylosis of the tooth. That is, the tooth used to be fused to the bone, there used to be no movement. And with evolution, the pyridontal ligament appeared and through the various biological activities of the pyridontal ligament and through the bone remodeling, tooth movement was possible. Orthodontic treatment, on the other hand, is made possible by the fact that teeth can be moved through the alveolar bone by applying appropriate forces. Orthodontic treatment is possible due to the fact that whenever a prolonged force is applied on the tooth, bone remodeling occurs around the tooth resulting in its movement. So, just to know the basic, these are the tooth supporting tissues. This is the gingiva, this is the cementum which you see around the root and between the root and the alveolar bone you can see the pyridontal ligament and this is the alveolar bone. So, what is pyridontal ligament? It is a specialized connective tissue which surrounds the root of a tooth, occupying the space between the root and the alveolar bone of the tooth socket. It consists of cells, ground substance, fibers, nerves and blood vessels. What are the cells present in the pyridontal ligament? There are osteoblasts, fibroblasts, cementoblasts, osteoclasts, cementoclasts and other cells like mast cells and macrophages. So, these osteoblasts and osteoclasts are very important because this is what constitutes bone remodeling. Osteoblasts are bone-forming cells and osteoclasts are bone-resorbing cells. Physiologic tooth movement. So, there are two types of movement, physiologic tooth movement and orthodontic tooth movement. Physiologic tooth movements are natural tooth movements whereas orthodontic tooth movements are when we apply force to move the teeth. So, what is physiologic tooth movement? Naturally occurring tooth movements that take place during and after tooth eruption is physiologic tooth movement. So, physiologic tooth movements includes tooth eruption, the basic eruption of tooth, migration or drift of teeth and changes in tooth position during mastication. What is tooth corruption? It is the axial movement of the tooth from its developmental position in the jaw to its final position in the oral cavity. There are three phases of tooth movement. One is pre-ruptive tooth movement, next is eruptive tooth movement, and next is post- eruptive tooth movement. It is pre-ruptive tooth movement, eruptive tooth movement and post- eruptive tooth movement. Pre-ruptive tooth movement is when the deciduous tooth is already erupted and the permanent tooth is trying to move from the developmental position to its axial position, that is, before the complete eruption. Eruptive tooth movement is when the permanent tooth tries to resolve the roots of the deciduous teeth and is trying to come out into its occlusion position. So, this is happening inside the bone, the first tooth which is this is when it is completely come out of the bone, that is extra-ocious and then it actually rips and comes into final occlusion. Post- eruptive tooth movement is if there is any occlusion where or in the proximal where or in order to compensate for any growth of the jaws when the teeth moves that is post- eruptive tooth movement. Now, what are the theories of tooth eruption? Don't confuse this with the theories of tooth movement. Theories of tooth movement is when we apply force, this is theories of tooth eruption, how the tooth erupts. So, first is the blood pressure theory, it is also called as hydrostatic pressure theory. According to this theory, the tissue around the developing root and this highly vascular. So, the pressure exerted by this highly vascular tissue between the developing tooth and its bony surroundings, it creates a mechanical force which causes the axial movement of the teeth. However, this theory was contraindicated by studies which proved that hypertensive drugs and changes in the pulse rate and blood pressure do not affect the tooth eruption. Next is the root growth theory. According to this theory, the bical growth of roots results in an axially directed force that brings about the eruption of teeth. This is not accepted because the teeth move a greater distance during eruption than the root length and the onset of root growth and eruption do not coincide. And the teeth that are malformed and lack roots also erupt. Next is the ham-cligament theory. This was stated by Ciccer. So, according to him, there is a band of fibrous tissue that exists below the root apex. It spans from one side of the alveolar bone to the other and it is seen below the root apex. So, this acts as a band and the developing root, it forces itself against this band of tissue which in turn applies an uplusely directed force on the tooth. Next is the periodontal ligament traction theory. This theory states that the periodontal ligament has fibroblasts that contain contractile tissue and the contraction of these periodontal fibres, especially the oblique fibres, results in the axial movement of the tooth. The other one is the intrapulpal pressure theory. Some form of pressure gradient is enabling eruption of the tooth like the vascular pressure from the pulp cavity. This again seems doubtful because if a pulpal pressure of 9mm of mercury is sufficient to bring about tooth eruption, alveolar bone growth theory, alveolar bone deposition results in teeth eruption. Role of dental follicle. This theory is the latest and is considered acceptable because the dental follicle is a connective tissue sac surrounding the developing enamel organ. This is what gives rise to the periodontal ligament. Experiments done have proved that if the tooth germs are removed and the follicle is left intact, the eruptive pathway still forms. If the developing tooth is inoculated out and the silica tooth replica is placed in its place within the follicle, the object erupts. This conclusively proves the importance of the dental follicle and its derivative, the periodontal ligament. Now what is migration or drift of teeth? Migration refers to the minor changes in the tooth position observed after the eruption of the tooth. Teeth shows a lifelong ability to drift through the alveolar bone, a process called physiologic tooth migration. Usually as a result of occlusion and proximal wear of the teeth to maintain the in the proximal and occlusive contact. Tooth movement during mastication. During mastication, teeth and periodontal structures are subjected to intermittent heavy forces that is up to 1 to 50 kilograms based on the type of foot being masticated. The tooth moves slightly within its socket and returns to its original position as the load is removed. When a tooth is subjected to heavy forces, the tissue fluid is present in the periodontal space being incompressible prevents major displacement of the tooth within its socket. Histology of tooth movement. This is what happens when we apply force to move the teeth. Histological changes seen during tooth movement vary according to the amount and duration of force applied and can be studied under two endings. Changes following application of mild force and changes following application of extreme force. Changes following application of mild force. Changes on the pressure side. The periodontal ligament in the direction of the tooth movement it gets compressed to almost one third of its original thickness. Then there is a marked increase in the vascularity of the periodontal membrane due to increase in the capillary blood pressure. This leads to the immobilization of fibroblast and osteoplast and because osteoplast are produced bone resorption happens. And that is how tooth moves to the pressure side. So when the forces are applied within the physiological limits the resorption is seen in the alveolar plate immediately adjacent to the ligament. This kind of resorption is called frontal resorption. Changes on the tension side. The area of the tooth opposite to the directional force is called the tension side. When you apply orthodontic force the periodontal ligament gets stretched. There is raised vascularity. There is mobilization of fibroblast and osteoplast. The bone forming cells and there is bone deposition. Now what are secondary remodeling changes? Whenever a force is applied to move teeth the bone immediately adjacent shows osteoclastic and osteoblastic activity on the pressure and tension side respectively. That is there is osteoclastic activity on the pressure side and osteoblastic activity on the tension side. In addition, bony changes also take place elsewhere to maintain the width or thickness of the alveolar bone. These changes are called as secondary remodeling changes. So when there is resorption happening immediately here then on the opposite side of the alveolar bone there is bone deposition. This is due in order to maintain the width or thickness of this alveolar bone. Now what happens when you apply extreme forces? Whenever extreme forces are applied to the teeth it results in crushing or total compression of the periodontal ligament. On the pressure side the root closely approximates the lamina dura compresses the periodontal ligament and leads to the occlusion of the blood vessels. The ligament is deprived of its nutrition supply leading to regressive changes called as hyalilization. For this hyalilization it is a form of tissue degeneration characterized by formation of a clear isonophilic homogeneous substance. In this case the bone resorption occurs in the adjacent marrow spaces and in alveolar plate below behind and above the hyalilization this kind of resorption is called undermining or rearward resorption. Now what happens on the tension side? The periodontal ligaments gets overstretched. There is tearing of the blood vessels and ischemia. There is increased osteoblastic activity and there is loose tooth in the socket with pain and hypremia. So in this diagram you can see this is the tooth. The orthodontic force is applied on this side so the tooth has to move to this slingually and this is the pressure side and this is the tension side. So normally what you see the pink is the pulp, the yellow is the dentine, the gray is the cementum and this horizontal line is the periodontal ligament and this is the bone. So this is how normally it looks but when there are histological changes that is when forces are applied when you apply mild forces you can see on the pressure side the periodontal ligament is compressed to only one third of its actual thickness. There will be an increased vascularity osteoclast will be released and there is bone resorption whereas on the tension side you can see that the periodontal ligament is stretched compared to its normal. There is an increased vascularity again here osteoblast are released so there is bone deposition the plus sign you can see. Now what happens when you apply extreme forces here you can see that the periodontal ligament is totally compressed there is occlusion of the blood vessels there will be no nutrition available here so there are regressive changes and there is hyalinization. So you can see that there is too much of resorption happening on the pressure side. Similarly on the tension side the periodontal ligaments are overstretched there is tearing of the blood vessels and there is increased osteoclastic activity and there is too much of resorption. So both side resorption happens and the tooth will be loose because there is not much bone growth supported. Now what is optimum orthodontic force? Optimum orthodontic force is one which moves the teeth most rapidly in the desired direction but it should cause least possible damage to the tissue and it should be within the patient which should cause only minimum patient discomfort. Now open hem and schwa stated that it is equivalent to the capillary pulse pressure which is 20 to 26 gram per square centimeter of throat surface area. Optimum orthodontic force should be 20 to 150 gram per tooth and optimum orthopedic force should be more than 300 grams of force. Now based on the different types of tooth movement different orthodontic forces and optimum forces are there that is for tipping rotation and extortion it is 35 to 60 grams of force for intrusion it is a minimum that is 10 to 20 grams of force for root uprighting it is 50 to 100 grams of force and for bodily movement this is the maximum that is 70 to 120 grams of force. Now what are the different phases of tooth movement when you apply force? This is categorized by Burstow he categorized his it into initial phase lag phase and post lag phase. So in the initial phase that is immediately after you apply force within a week in the first week that is there is very rapid tooth movement and then it immediately stops there will be up to 0.4 to 0.9 millimeter of tooth movement in the first week. Next is the lag phase there is little or no tooth movement occurring in this phase this is because of the formation of hyaluronic tissue in the pedontal ligament and only after this hyaluronic tissue is resolved further tooth movement can happen. So how does this hyaluronic tissue resolve? They resolve by the action of osteoclast and the macrophagocytic and enzymatic action of cells. So this lag phase will extend up to two to three weeks. So after initial phase after a week hyaluronic tissue is formed and in the lag phase the hyaluronic tissue is resolved and this extends from two to three weeks only after the hyaluronic tissue is removed further tooth movement happens. So that is the post lag phase that is tooth movement progresses rapidly as the hyaluronic zone is removed and the bone undergoes resorption. So this is a diagram which shows tooth movement to the different phases. So initial phase you can see there is rapid movement then there is a lag phase where the hyaluronic tissue is formed and there is a little or no tooth movement occurring and after the hyaluronic tissue is removed there will be a post lag phase whether the tooth movement further occurs. Theories of tooth movement pressure tension theory by Schwartz. Whenever a tooth is subjected to an orthodontic force it results in area of pressure and tension. The area of the pyridontium in the direction of tooth movement is under pressure while the area of pyridontium opposite the tooth movement is under tension. According to him areas of pressure show bone resorption while areas of tension show bone deposition. This is what we discussed earlier. The fluid dynamic theory also called as blood flow theory by Bien. He states that the pyridontal space consists of a fluid system made up of industrial fluid, cellular elements, blood vessels and ground substance. Tooth movement occurs as a result of alterations in fluid dynamics in the pyridontal ligament. The contents of the pyridontal ligament thus creates a unique hydrodynamic condition resembling a hydraulic mechanism and shock absorber. When the force is removed the fluid is replenished by diffusion from the capillary walls and recirculation of industrial fluids. When a force of greater magnitude and duration is applied such as during orthodontic tooth movement the interstitial fluid in the pyridontal space gets squeezed out and moves towards the apex and cervical margins and results in the decreased tooth movement. This is called the squeeze feeling effect. Bone bending and piezoelectric theory so Farar noted the deformation or bending of the interstitial alveolar bones when a force is applied. For this piezoelectricity it is a phenomenon observed in many crystalline materials in which a deformation of the crystal structure produces a flow of electric current as a result of displacement of the electrons from one part of the crystalline lattice to the other. A small electric current is generated when bone is mechanically deformed. The possible sources of electric current are collagen, hydroxyapatite, collagen hydroxyapatite interface and muco polysaccharides. So what happens when a force is applied the alveolar bone bends and there is deformation of the crystalline structure that is the alveolar bone. There will be generation of electric signals because the electrons are moving from one crystalline lattice to the other. There will be a change in bone metabolism, cellular differentiation and then there is tooth movement. Piezoelectric signals has two unusual characteristics that is one is a quick decay rate that is when a force is applied a piezoelectric signal is produced. Here you can see when the force is applied a piezoelectric signal is produced. This electric charges quickly dies off to zero that is declining to zero and even though it dies away to zero the force is maintained. When the force is released the electron flow in the opposite direction as seen here. So when there is application of force on the tool the adjacent alveolar bone bends. Here you can see when a force is applied here the alveolar bone bends like this and there is area of concavity and area of convexity. So area of concavity here it is negative charge don't confuse it with resorption this is negative charge and in the areas of negative charge there is bone deposition whereas area of convexity this is positive charge and non-bone deposition here there is bone resorption. So in short this is the biochemical reaction that happens when in orthodontic tooth movement. So this is a summary of the biochemical reaction. So when you apply orthodontic force there is first initially there is biophysical reactions happening that is there is bone deformation compression of periodontal ligament and there is tissue injury. This leads to the production of first messengers. First messengers are extracellular signaling molecules like hormones that is parathormone or prostablandins or neurotransmitters. This in turn results in the production of secondary messengers like cyclic KMP, cyclic GMP, calcium etc. This leads to an increase in cells of resorption and deposition that is bone remodeling and that is how orthodontic tooth movement happens. Now coming to the next stage what is acceleration of tooth movement. So reducing the time duration of orthodontic treatment could reduce the potential risk associated with the treatment such as root resorption, white spot lesions and periodontal problems and nowadays patients they are after us to reduce the treatment time and they need the treatment to be completed quickly. So what all can we do for that? So what are the approaches to accelerate orthodontic treatment? That is biological approach or the use of drugs, physical approach and surgical approach. So biological approach that is a transfer so we can inject certain materials or orally give certain materials substances which can increase the tooth movement. So by rankle is the receptor activator of nuclear factor Kappa B like it. So transfer of wrangling gene to the periodontal tissue has been found to induce prolonged gene expression for the enhancement of osteoclastogenesis, injection of exogenous prostaglandin over an extended period of time for the acceleration of tooth movement in animals. 125 dihydroxycholic alzepherol is a normal is a hormonal form of vitamin D and it plays an important role in calcium homostasis and calcitonin and parathyroid hormone. Experiments where vitamin D metabolite have been injected into the periodontal ligament was found to accelerate tooth movement and systemic administration of parathormon has found to increase tooth movement. Next is physical approach. So based on the concept of bone bending and bioelectric effects and they are noninvasive compared to surgical approaches. So one is low-level laser therapy also known as cold laser and it does not increase tissue temperature by more than one degree celsius. Osteoblastic and osteoplastic activities increase and collagen production is stimulated can reduce orthodontic treatment time by 30%. And there is an appliance called as axilla dent this causes resonance vibration. So the vibrations stimulate cell differentiation and maturation resulting in faster bone remodeling and more rapid tooth movement. It can increase the rate of tooth movement by 15% consists of an activator which delivers vibration and a mouthpiece that contacts the teeth. Next is ultrasound the use of flow intensity pulsed ultrasound or lipos to the alveolar process during orthodontic treatment promotes alveolar bone remodeling. Next is a surgical approaches. So it works by stimulating cells adjacent to the teeth or by reducing the resistance presented by the supporting bone and mechanically shifting the teeth. These procedures are invasive and may carry a risk. These approaches include intercepted alveolar surgery, osteotomy, corticotomy and psossession technique. What are the effects of drugs on induced tooth movement? So there are non-steroidal and inflammatory drugs like aspirin, biclofenac, ibuprofen, indometasin which reduces the bone resorption. This thereby leads to the reduced reduction in the tooth movement. Corticosteroids on the other hand is proved to increase bone resorption and thereby increases tooth movement. This phosphonates reduces bone resorption and reduces the tooth movement whereas acetaminophen the result of the usage of it the result is not yet proven and it proves that there is no influence. So we can safely administer acetaminophen to patients. Thank you.