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Removable Appliances Removable orthodontic appliances have two immediately apparent advantages: (1) they are fabricated in the laboratory rather than directly in the patient's mouth, reducing the dentist's chair time, and (2) they can be removed on socially sensitive occasions if wires on the facial part of the teeth would be visible, or can be made almost invisible if fabricated from clear plastic materials. In addition, removables allow some types of growth guidance treatment to be carried out more readily than is possible with fixed appliances. These advantages for both the patient and the dentist have ensured a continuing interest in removable appliances for both children and adults. There are also two significant disadvantages: (1) the response to treatment is heavily dependent on patient compliance, since the appliance can be effective only when the patient chooses to wear it, and (2) it is difficult to obtain the two-point contacts on teeth necessary to produce complex tooth movements. Because of these limitations, removable appliances in children are most useful for the first of two phases of treatment, with fixed appliances used in the second phase and contemporary comprehensive treatment for adolescents and adults almost always requires fixed, non-removable appliances. In the 1925 to 1965 era, American orthodontics was based almost exclusively on the use of fixed appliances while in Europe continued development of removable appliances and all treatment was done with removables. There were three major reasons for this trend: (1) Angle's dogmatic approach to occlusion, with its emphasis on precise positioning of each tooth, had less impact in Europe than in the United States; (2) social welfare systems developed much more rapidly in Europe, which tended to place the emphasis on limited orthodontic treatment for large numbers of people, and (3) precious metal for fixed appliances was less available in Europe, as a consequence of the social systems and because the use of precious metal in dentistry was banned in Nazi Germany. A major part of European removable appliance orthodontics of this period was functional appliances for guidance of growth. A functional appliance by definition is one that changes the posture of the mandible, holding it open or open and forward. Pressures created by stretch of the muscles and soft tissues are transmitted to the dental and skeletal structures, moving teeth and modifying growth. The monobloc developed by Robin in the early 1900s is generally considered the forerunner of all functional appliances, but the activator developed in Norway by Andresen in the 1920s was the first functional appliance to be widely accepted. Andresen's activator became the basis of the "Norwegian system" of treatment. Both the appliance system and its theoretic underpinnings were improved and extended elsewhere in Europe, particularly by the German school led by Haupl, who believed that the only stable tooth movement was produced by natural forces and that alterations in function produced by these appliances would give stable corrections of malocclusion. This philosophic approach was diametrically opposite to that espoused by Angle and his followers in the United States, who emphasized fixed appliances to precisely position the teeth. These opposing beliefs contributed to the great differences between European and American orthodontics at mid-20th century. In the European approach at that time, removable appliances often were differentiated into "activators," or functional appliances aimed at modifying growth, and "active plates" aimed at moving teeth. The two European orthodontists deserve special mention for their contributions to removable appliance techniques for moving teeth. Martin Schwartz in Vienna developed and publicized a variety of "split plate" appliances, which could produce most types of tooth movements. Philip Adams in Belfast modified the arrowhead clasp favored by Schwartz into the Adams crib, which became the basis for English removable appliances and is still the most effective clasp for orthodontic purposes. Functional appliances were introduced into American orthodontics in the 1960s, through the influence of orthodontic faculty members with a background in Europe (of whom Egil Harvold was prominent), and later from personal contact and fixed appliances spread to Europe at the same time. A major boost to functional appliance treatment in the United States came from the publication of animal experiment results in the 1970s showing that skeletal changes really could be produced by posturing the mandible to a new position and that true stimulation of mandibular growth could be achieved. (tension of the m. pterygoideus lateralis provoke gowth in condylar catilage) At this point, the dichotomy between European and American orthodontics has largely disappeared. European-style removable appliances, particularly for growth modification during first-stage mixed dentition treatment, have become widely used in the United States, while fixed appliances have largely replaced removables for comprehensive treatment in Europe. Modern removable appliance therapy consists largely of the use of (1) various types of functional appliances for growth guidance in adolescents and, less frequently, in children; (2) active plates for tooth movement in preadolescents; and (3) clear plastic aligners for tooth movement in adults. Functional Appliances These appliances have no force-generating springs or screws and depend only on soft tissue stretch and muscular activity to produce treatment effects. The original functional appliance design was a block of plastic covering the teeth of both arches and the palate. It was made to fit loosely, advance the mandible several millimeters for Class II correction, and open the bite 3-4 mm. By drilling the plastic body is possible to guide erupting teeth into the wanted position. In most cases (ClassII) is needed to impede eruption of upper posterior teeth while allowing eruption of lower posterior teeth. Lower incisors are capped to control forward displacement of the lower arch, to prevent them from erupting and control their tendency to tip facially. Usually, the lower molars are free to erupt, while the upper molars are prevented from erupting by the acrylic shelf between the teeth. Later, a lot of modifications named by their authors were described. There was a tendency for prolonged using of appliance (24 ours a day) and to incease the effectiveness of the apliances. To obtain this, there wereo ways: 1. to cut – down the acrylic body 2. to include the active components (screws, springs...) Bionator The bionator, originated by Balters and sometimes still bearing his name, is best described as a cut-down activator with an inter-occlusal shelf and incisor capping if desired. Palatal coverage is eliminated. As with the activator, lingual flanges stimulate forward posturing of the mandible and shelves or blocks between the teeth provide vertical control. Long labial bow stimulates the lip seal and distal parts of is eliminates the pressure of the cheeks. The palatal arch stimulates funtion of the tongue. There are 2 types, for Class II Div. 1 cases and for anterior open bite. The Klammt elastic open activator I tis the most loosely fitted functional appliance without occlusal bite blocks. The small plasic parts may or may not reproduce the oral teeth surfaces. The 2 labial bows and palatal arch play the same role as in bionator. It is indicated for Class II Div. 1 and deep bite cases with good formed dental arches without crowding. Bimler appliance The acrylic body is reduced to a minimum and is replaced by wire parts. It is very elasic so it was thought it is capable to transmit the functional impules to the dentition. Its construction is very complicated. Bimler described more types for Class II Div. 1, Class II Div. 2 and Class III malocclusions. Frankel function regulator The Frankel appliance (which Frankel called the function regulator) is the only tissueborne functional appliance. A small pad against the lingual mucosa beneath the lower incisors stimulates mandibular repositioning. Much of the appliance is located in the vestibule. It alters both mandibular posture and the contour of facial soft tissue. It serves as an arch expansion appliance in addition to its effects on jaw growth because the arches tend to expand when lip and cheek pressure is removed. What is more, traction produced by vesibular shields provoke periosteum to bone apposition on vestibular surface of the maxilla. Frankel described 4 types but today the appliance is used mostly for Class III corection. Twin block The twin block appliance can be used as either a removable or fixed (cemented) device, but usually is removable. Its maxillary and mandibular portions are configured so the interaction of the two parts controls how much the mandible is postured forward and how much the jaws are separated vertically The appliance has the advantage of allowing nearly a full range of mandibular movement, easy acclimation and reasonable speech, so that it can be worn most of the time. The greatest disadvantage is that displacement of incisors can occur freely. There are some modifications of activator and bionator designs that include expansion screws or springs to move teeth. The springs and screws added to a functional appliance produce tooth movement that often detracts from correction of the underlying jaw discrepancy. With any functional appliance, there is a tendency for the lower incisors to be moved facially and springs and screws magnify this undesirable side effect. For this reason, active components have little or no place in modern orthodontics, and now are used much less than previously. The funcional apliances can be used in combination with extraoral force. ( Lehman appliance, maxilator). The major advantage is possibility to control rotation of the cclusal plane which increases skeletal effect and helps to corect skeletal dicrepancy. Clinical acceptability of functional appliances As a general rule, simple and sturdy functional appliance designs are more effective than complex and fragile ones. Children and adolescents are not known for their gentle treatment of removable appliances; if something can be broken easily, it will be. The original activators, and the twin block appliance, have a significant advantage from this perspective. The bionator is less sturdy, and its relative fragility is the greatest weakness of the Frankel appliance. Vertical control always is a key element, and one of the advantages of functional appliances in general is the control of eruption they provide. Blocking the eruption of some teeth and allowing the eruption of others is the key to correcting deep bite or open bite problems. The activator and bionator designs are particularly easy to adjust so that some teeth can erupt while others are blocked. Finally, acceptability to the patient is critical. One important factor in acceptability is the extent of interference with speech, which can make full-time wear impossible. The original activators do interfere with speech and for all practical purposes cannot be worn to school. Removing the palatal plastic and making the appliance into a less bulky bionator helps significantly (while also making the appliance more fragile, of course). Twin block appliances produce even less interference with speech and can be compatible with full-time wear, and the Frankel appliance (after a period of adaptation) does not interfere with normal speech, so that children can wear it to school routinely. Indication of functional appliances 1. in cases where the main problem is the altered function ( habits like sucking, lip biting, tongue thrusting, mouth breading, insertion of the lower lip under the incisors....) 2. in cases where the dentoalveolar compensaton was lost (contact between he incisors is he impuls for A-P compensation, occlusal contact of the distal teeth for vertical compensation) 3. in adolescents (in maximum growth spurt) to stimulate the mandibular growth Removable Appliances for Tooth Movement Tooth movement with removable appliances in children almost always falls into one of two major categories: (1) arch expansion, in which groups of teeth are moved to expand the arch perimeter; (2) repositioning of individual teeth within the arch. Active plate cosist of: 1. baseplate 2. retentive components (clasps, labial bow) 3. active components (springs, screws) 1.The framework of an active plate is a baseplate that serves as a base in which screws or springs are embedded and to which clasps are attached. It followes the lingual surface of the teeth and alveolar process and extend as far as the first molars. The upper plate is reduced and in the midline ends at first premolars region. 2.Retention of an active appliance is critical to its success. The best springs are ineffective if the appliance becomes displaced. By far the most useful and versatile clasp for contemporary removable appliances is the Adams crib. This clasp is made of 0.7 mm wire.The retentive points of the clasp must fit well into the undercuts for good retention. When this clasp is used for children, it may be necessary for the points to slip slightly into the gingival crevice. This step is accomplished by trimming away stone interproximally on the laboratory cast, so that the clasp can fit far enough to engage undercuts below the height of contour. When a new removable appliance is received from the laboratory, or when a patient returns for adjustments, it is often necessary for the dentist to tighten the clasps by simply bending the clasp slightly gingivally from its point of attachment. It is also possible to bend the retentive points inward to obtain better contact in the undercut areas. As a general principle, the more active a removable appliance is to be and the greater the force applied during its use, the more clasping is required to hold it in place. There are another clasps used: Schwartzs, drop shaped, triangle shaped,... Labial bow may be only retentive component or may be activated for incisor movement. There are many variations in its shape depending on the desired teeth movement. It is usually made of 0,8 mm steel wire. 3.The active element is a jackscrew placed so that it holds the parts of the plate together. Opening the screw with a key then separates the sections of the plate. Position of the screw depend on desired teeth movement. It can move the single tooth or a teeth group. The screw offers the advantage that the amount of movement can be controlled, and the baseplate remains rigid despite being cut into parts. The disadvantage is that the force system is very different from the ideal one for moving teeth. Rather than providing a light but continuous force, activation of the screw produces a heavy force that decays rapidly, and rapid reactivation of the appliance has the potential of damaging the teeth. If the force levels become too high, the appliance is likely to be displaced. This is the most common problem with expansion plates: activating the screw too rapidly results in the appliance being progressively displaced away from the teeth rather than the arch being expanded as desired. In contrast to the heavy, rapidly decaying forces produced by a screw, nearly optimum light continuous forces can be produced by springs in a removable appliance. Like the edges of an active plate, however, these springs contact the tooth surface at only one point, and it is difficult to use them for anything but tipping tooth movements. The guideline for tooth movement with a spring from a removable appliance therefore is that this is acceptable for a few millimeters of tipping movement. Root control is needed for more than 3 to 4 mm of crown movement. In designing springs for tooth movement, two important principles must be kept in mind: (1) the design must ensure adequate springiness and range while retaining acceptable strength. This usually means using recurved or looped wires for additional length,and (2) the spring must be guided so that its action is exerted only in the appropriate direction. Because smaller wires are not strong enough, it is unwise to fabricate springs for removable appliances from steel wire smaller than 0.5 mm. Larger diameter wires usually are preferred. In general, it is better to use a larger wire for its (considerably) greater strength, and then gain springiness and range by increasing the length of the spring, than to use a smaller wire initially. . As treatment proceeds, three adjustments are necessary when an active removable appliance is being used appropriately: tightening of clasps when they become loose, activation of the spring or springs, and removal of material from the baseplate. Activation of the springs must be done carefully, and not more than approximately 1 mm at a time. The more the spring is activated, the more difficult it becomes to keep it in the proper position. Too much activation usually displaces either the spring or the whole appliance. Baseplate material must be removed from the path of a tooth that is to be moved. Failure to relieve the baseplate near a spring is a common error.