Anchorage in Orhodontics

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ANCHORAGE

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In simple terms anchorage in orthodontics is defined as resistance to unwanted tooth movement. Angle stated that there were many means for obtaining anchorage, including the tooth themselves and sources external to the teeth . He classified anchorage as simple , stationary, reciprocal, inter maxillary and occipital. INTRODUCTION

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Given Angle’s insistence on expansion of arches rather than extraction to deal with crowding problems, it is ironic that his edgewise appliance finally provided the control for root position necessary for successful extraction treatment. One of Angle’s last student, Charles Tweed , adapted the edgewise appliance for extraction treatment. Tweed placed tip back bends in the lower arch to vary the amount of distoaxial inclination of the lower posterior teeth. The amount of distal tip varied depending on the severity of malocclusion.

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When anchorage preparation as advocated by Tweed was used with standard edgewise appliance the tip, torque and offset bends had to be placed in each edgewise arch. The bends were then duplicated or increased in the successive arches as the case progressed. Reed Holdaway in 1952 described pre-angulation of the edgewise appliance in mandibular buccal segments as a method of setting up posterior anchorage units into tipped back or anchorage prepared positions.

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Graber: defines anchorage as the nature and degree of resistance to displacement offered by an anatomical unit when used for purpose of effecting tooth movement. Bennett and McLaughlin: emphasized the need to consider anchorage in all the three planes of space i.e., horizontal, vertical and lateral (transverse). White & Gardiner: it is the site of delivery from which a force is exerted. DEFINITION

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Horizontally anchorage control means limiting the mesial movement of the posterior segment while encouraging the distal movement of anterior segment. Vertically , anchorage control involves the limitation of vertical skeletal and dental development in the posterior segment and limitation or vertical eruption of, or even intrusion of anterior segments. In transverse plane It comprises of the maintenance of expansion procedures, primarily in upper arch, and the avoidance of tipping or extrusion of posterior teeth during expansion.

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Sources of Anchorage: extra-oral (ii) intra-oral Extra-oral anchorage is the anchorage in which one of the anchorage unit is situated outside the oral cavity . Extra-oral anchorage can be further classified as : Cervical Cranial Occipital parietal Facial eg. Delaire Facemask Intra-oral anchorage : It is the anchorage in which the resistance units are all situated within the oral cavity e.g., teeth, palate, muscular forces, inclined planes of teeth.

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Classification of anchorage: Acc to Moyers (i)Dep. On manner of force application: Simple Stationary Reciprocal (ii)Dep. On jaws involved: Intermaxillary Intramaxillary

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(iii) Dep. on site of anchorage: Intra oral Extra oral Muscular (iv) Dep. on no. of anchor units: Single / primary Compound Multiple/ reinforced

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Natural anchorage It comes from any resistance afforded within the arch according to the application of forces between any given teeth or group of teeth. Simple Anchorage : Dental anchorage in which the manner and application of force tends to displace or change axial inclination of the tooth or teeth that form the anchorage unit in the plane of space in which the force is being applied. In other words resistance of anchorage unit to tipping is utilized to move another tooth or teeth. Compound Anchorage : Here anchorage is provided by more than one tooth with greater support is used to move teeth with lesser support.

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Reciprocal / Multiple anchorage : It involves pitting of two teeth or two groups of teeth of equal anchorage value against each other to produce reciprocal tooth movement. Eg: closing of diastemas: two central incisors are pitted against each other.

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Stationary Anchorage : Dental anchorage in which the manner and application of force tend to displace the anchorage unit bodily in the plane of space in which the force is being applied is termed stationary anchorage (Graber).

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2. Reinforced Anchorage : It involves reinforcing the anchorage or resistance area either by adding more resistance units or by the use of various adjuncts. A simple way of reinforcing anchorage is to band the second molars. Various other ways include, the use of T.P.A., Nance holding arch, lower lingual arch. Tissue anchorage such as obtained by lip bumper can be efficiently used to distalize molars .

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This is obtained by various means namely: Extra oral force to augment anchorage Upper anterior inclined plane & SWED APPLIANCE Trans palatal arch

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3. Prepared Anchorage Prepared anchorage pre sets the teeth into disto-axial inclination, greatly increasing their resistance to displacement. This method is very effective for controlling anchorage, especially when anchorage is critical. 4. Active root thrust : This concept was put forward by Dr. Calvin Case in 1908 . It involves building bodily resistance into the anchor area through the use of extensions fixed to the bands of the molar teeth.

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Cortical anchorage : The cortical bone is more resistant to resorption than the medullary bone. The cortical anchorage concept makes use of this. Rickett’s advocated torquing the roots of buccal teeth outwards against the cortical plate as a way to inhibit their mesial movement. Torquing movements are limited by facial and lingual cortical plates. If a root is persistently forced against the cortical plate, tooth movement is greatly slowed, root resorption is likely and eventual penetration of cortical bone may sometimes occur.

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Graber has classified anchorage as intramaxillary anchorage and intermaxillary anchorage. Intramaxillary anchorage is the anchorage is which the resistance units are all situated with in the same jaw. If appliances are placed only in maxillary or mandibular arch they are considered, intra maxillary resistance units. Intermaxillary anchorage is anchorage in which the units situated in one jaw are used to effect tooth movement in the other jaw. Also called BAKER’S anchorage.

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SELECTION OF ANCHORAGE: Since anchorage must be selected to make proper use of the space created by extraction, a more rational approach of classifying anchorage would be the one which guides the operator to make use of the available space. Accordingly anchorage in mandibular arch can be put into three classes: DEPENDING ON ANCHOR LOSS EXPECTED: minimum, moderate and maximum anchorage.

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Minimum anchorage mechanics involved reciprocal forces between posterior teeth and anterior teeth with no effort to maintain a moment on the anchor area. Minimum anchorage mechanics are selected when the mandibular posterior teeth may be permitted to migrate mesially into half or more of the extraction site.

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Moderate anchorage mechanics involve placing an active root thrust or movement on the anchor teeth, causing bodily resistance in this area. Moderate anchorage mechanics are selected when the mandibular posterior teeth may be permitted to move forward into one fourth to one half of the extraction site.

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Maximum anchorage mechanics involve reinforcing the anchor teeth with all means available and reducing the workload required of the anchor area by developing forces outside the mandibular arch for as much of the desired tooth movement possible. Maxillary anchorage mechanics are selected when the mandibular posterior teeth may be permitted to move forward into no more than one fourth of the extraction site.

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We have a wide array of appliances available to gain and preserve anchorage in all the three dimensions of space. These adjuncts available are broadly classified into: extraoral and intra-oral appliances APPLIANCES USED:

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The extra oral appliances : Various Headgear assemblies,or retractors as some author prefers to call them, essentially constitute this group. Moyers adds the face mask to this group. The intra oral adjuncts can be grouped according to the plane of space in which they act. The transpalatal arch acts in all the three dimensions. Whereas lace backs, Nance/lingual holding arches, lip bumper act in anteroposterior direction. Head gear and face mask give adequate control in vertical plane . Where as T.P.A. and quad helix help to preserve the expansion in transverse plane.

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HEAD – GEAR Head gears are classified according to the point of origin of force: Cervical – Anchorage obtained from nape of the neck Occipital / Straight pull – anchorage obtained from back of the head. The line of traction is parallel to occlusal plane. Parietal / High pull – Anchorage obtained from upper part of the head and always above the center of resistance of tooth. Combi pull – The line of traction is between high pull and straight pull. Another variable in the headgear is the outer bow of the facebow: The outer bow can be long, medium or short.

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FORCE AND DURATION OF WEAR : Most of the authors agree that the amount of force applied to maxilla by the headgear should be between 400 – 800 gm (Graber, King, Blucher, Moore, Rickets, Wieslander, Sodensky, Ringberg, Borton, Pfieffer and Groberty ). Light continuous forces seem to produce more dental changes than skeletal . Whereas heavy force and intermittent wear is found to produce more skeletal change. According to Marcotte force values of 200 gms per side in mixed dentition and 500 gms per side in permanent dentition for 18-20 hrs / day suggested . Graber advocates force application of more than 400 gms for 10-12 hrs / day.

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FACE MASK: It is an extra oral anchorage source. It derives anchorage from facial bones. Sites of anchorage: From skull From chin From skull & chin Force applied: approx. 1 pound (450 gms) per side.

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TRANSPALATAL ARCH Transpalatal arch is a secondary method of anchorage support in upper posterior segment. It is made by 0.045” or 0.051” stainless steel round wire when it is soldered to the molar bands with loop placed in the middle of palate so that wire is placed 2 mm from the roof of palate. If the TPA is placed 6-8 mm down from palate it can induce molar intrusion due to tongue pressure. It can be used to expand maxillary molar width as well as stabilize against occipital pull head gear. After cross bite correction, it will maintain molar position against undesirable side effects of utility arches used in the maxillary arch.

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NANCE AND LINGUAL HOLDING ARCHES The Nance holding arch extends from maxillary molars to anterior portions of the palatal vault . It is a fixed appliance . An acrylic button, but half inch or less in diameter, is attached to the palate. This button must create light seal with the palate to prevent the creation of food trap. It is important to position the acrylic button against the vertical component of the palatal vault . The stabilizing lingual arch for the lower lie behind and below the lower incisors, so that it doesn't interfere with their retraction. The lower lingual arch is conveniently inserted from distal than from the mesial of molar tube.

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LIP BUMPER Lip bumper has been used for molar anchorage, prevention of poor lip habits and creation of increased space for mandibular arch.The appliance has stainless steel wire of 0.045” that spans the facial surface of mandibular arch without contacting teeth and is inserted into tubes attached to the mandibular molars. Anteriorly the wire is covered with plastic tubing or a shield made of acrylic that holds the lower lip away from the mandibular incisors. Forces from mentalis muscle are transmitted to mandibular molars, enabling them to move to an upright and distal position.

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BAKER’S ANCHORAGE: It is a type of intermaxillary anchorage. Class II traction applied between the lower molars and upper anteriors as well as Class III traction applied between upper molars and lower anteriors are referred to as BAKER’S ANCHORAGE.

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ANCHORAGE PLANNING: It is of utmost importance in the success of orthodontic treatment. Therefore it is very much essential to carefully assess the anchorage demands of the individual case and select the most appropriate treatment plan. It depends on the following factors: NUMBER OF TEETH TO BE MOVED: TYPE OF TEETH BEING MOVED TYPE OF TOOTH MOVEMENT DURATION OF THE TREATMENT

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CONCLUSION As orthodontic treatment continues to change and improve, innovative techniques may find acceptance in certain types of cases. Magnetic forces or electric stimulation may possibly show the path to an improved mechanotherapy. But by and large, the basic concept of arch wires placed in brackets to move teeth will remain the most efficient method. Fundamental principles of anchorage laid down by Tweed have remained unchanged and will continue to remain so. The list of adjuncts available may increase. The objective in selection of treatment mechanics is to have a bag a tricks’ that is large enough to treat most of the conditions, but not so large as to be unmanageable to incorporate into one’s practice routine.

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Good Luck

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THANK YOU