Unit 1 - Active Removable Appliances PDF

Unit 1 ACTIVE REMOVABLE APPLIANCES Orthodontics II Dra. Elena Muñoz García Bachelor of Dentistry INDEX 1. INTRODUCTION 2. ACTIVE REMOVABLE APPLIANCES COMPONENTS a. PASSIVE b. ACTIVE c. FUNCTIONAL 3. CLINICAL USE  1. INTRODUCTION Removable appliances are devices...

Unit 1 ACTIVE REMOVABLE APPLIANCES Orthodontics II Dra. Elena Muñoz García Bachelor of Dentistry INDEX 1. INTRODUCTION 2. ACTIVE REMOVABLE APPLIANCES COMPONENTS a. PASSIVE b. ACTIVE c. FUNCTIONAL 3. CLINICAL USE  1. INTRODUCTION Removable appliances are devices which can be removed at some situations or during the moment of maintaining the correct buccal hygiene. They are fabricated in the laboratory (and adjusted extraorally rather than directly in the patient’s mouth) reducing the dentist’s chair time during this treatment phase. Removable appliances can be (depending on the effects): A. Passive (Hawley appliance): it doesn’t produce forces to induce dental movement, it just maintains the final dental position after an orthodontic treatment. After finishing an orthodontic treatment, a passive appliance will be needed to keep the results achieved. B. Active: Removable appliances that, if they are held on teeth and supported on alveolar mucosa, they can produce dental movement thanks to springs or screws. On this unit, we will talk about active removable appliances. Their main components are: - Resin plate or connecting plate. - Dental retention elements or stabilizing components - Active elements. - Passive elements.  2. ACTIVE PLATES COMPONENTS A) PASSIVE COMPONENTS - Principal resin plate. - Retention elements, hooks or retainers/stabilizing components: Adams’ clasp, circumferential clasp, ball clasp, arrow clasp… - B) ACTIVE COMPONENTS Springs - Free end: protrusion, mesio distal (anterior torquing springs) - Continuous: o Buccal arch o Progenie arch Screws C) FUNCTIONAL COMPONENTS - Bite blocks - Grids - Lateral acrylic extension - Lingual shield and oral screen 3. PASSIVE COMPONENTS 3.1. RESIN PLATE Principal resin plate: it is usually made of acrylic. It goes contacting teeth at the limit with the gum occupying the palate (on the upper arch) and the alveolar mucosa (on the lower arch). The main functions are: A. As anchorage and plate retention Active elements, to move teeth, usually have removable plates that are going to provoke reactive forces. This resin plate is capable to avoid reactive forces and distribute them on the plate surface. Moreover, when they contact with teeth and alveolar mucosa it allows to stabilize avoiding lateral and anteroposterior balance of the plate. The resin plate must be extended to the distal part of the last erupted molar (to increase the anchorage). The resin plate must be thin, but enough to avoid fractures (2 mm). There must be enough space to allow the tongue movement and phonation. The lower inferior plates thickness must be bigger than the upper. If not, it should have metallic reinforcement to avoid fractures. If the alveolar bone inclination/shape is noticeable, it can provoke damage on the gum (if that happens, the resin must be eliminated from the plate to avoid the excessive contact and ulcerous damage). B. Maintain the active and passive elements It is a link between all the plate elements. The elements’ inactive part, generally metallic, are embedded in the resin, that allows the free active part to be activated by the dentist (and this can produce dental movements). C. As active element itself The acrylic plate can act as an active element when it is divided into two parts and some of these parts is moved by an active element (a screw) against teeth (where it is supported) moving those teeth which receive the pressure. A common example is to divide in two parts the plate (in the middle part) creating to symmetrical parts. With the screw in the centre, it can be applied forces against lateral or anterior teeth when the screw is activated. The plate can also be divided into asymmetrical parts, obtaining differential anchorage. That means that the part which is supporting the bigger number of teeth is acting as anchorage and the zone with the smaller number of teeth will be the ones to be moved. In this way, it can be applied an asymmetrical expansion (dental) of just some lateral teeth or some anterior teeth depending on the screw direction.  3.2. RETENTION ELEMENTS, HOOKS OR RETAINERS/STABILIZING COMPONENTS If we want a correct effect of the appliance, it must be properly adapted to mouth. With the stabilizing components, the plate is fixed to some teeth (which are not going to be moved) at the limit between the tooth and the alveolar mucosa. For that reason, the retentive zones are: - Tooth limit with the alveolar mucosa. - Interproximal areas. There are many kinds of stabilizing components, made of stainless steel with different thickness (generally between 0,7 and 1 mm). A) Arrow end clasp (Schwartz). B) Adams’ clasp It is the most used because it is simple and effective. It has two arrows that are located at the retentive part of the tooth (joined by a middle bridge). Both ends use the mesial and distal concavities of the buccal side of premolars and molars (permanent or temporary). This kind of clasp is just used with premolars and molars. They come activated from laboratory but sometimes we need to activate them much more because they lose retention. The main inconvenients are that we need the contact point, and it also avoids dental eruption. C) Interdental rounded clasp This clasp is also really used. It is a clasp with a free end that has a ball on the edge. It is adjusted to the interdental space at the gingival papilla level. Those hooks are used for premolars and temporary molars in combination with an Adams’ clasps on the first permanent molars. D) Triangular clasp It is like the other one, but instead of having a ball at the end it has a triangular shape (the wire is bended around itself). This shape is adapted to the retentive part of the tooth. E) Circumferential clasp It is a free end hook, one of its parts goes inside the resin plate and it goes out through the interproximal surface. It goes around the buccal side of it and its free end is adapted to the retentive part of the tooth at the opposite side that it came out. F) Duyzing clasp It is made with two wires intertwined above the contact points until the centre of the buccal side. Then they are bended to gingival to be much more retentive.  4. ACTIVE ELEMENTS 4.1. SPRINGS A) Free end springs They are the real active elements of the plate (they produce movement when they are activated) and they are made with different designs and thickness depending on the movement that we want to obtain. To create these springs, it must be used an important amount of wire to give into the system more intensity and of course, more elasticity. For that reason, bends are created on the wire, springs, or loops. This confection will give more elasticity into the system due to the length increasement of the wire. The springs can be individual (just one tooth) or they can act into a group of teeth. It must be considered that if we activate a spring (and a force is applied to the tooth crown) the movement obtained will be and uncontrolled or tip movement (it will depend on the crown part where the force is applied). So, when the force point is near to the alveolar mucosa (it means, when it is near to the resistance centre of the tooth), the uncontrolled movement will be controlled, and it will be much more like a mass or bodily movement (however this pure mass movement can’t be obtained with active plates springs). Small dental rotations can also be corrected with these springs, especially on incisors (flat teeth) being the spring near to the alveolar mucosa. If a pure rotation is wanted, a pair of forces must be created, for that reason a force must be applied at the buccal part but on the opposite side of the tooth. If we want to create movement with the spring, it must be activated out of the mouth on the movement sense that wanted to provoke. To activate the spring: do it softly, between 1-2 mm per activation. If it is activated more than that, the plate is not going to fit the mouth and it won’t adapt properly (there will be intense reaction forces and the retention elements won’t be capable of standing that intense force). The spring must be activated step by step as the movement is being achieved. For example, on the protrusion springs, which main objective is to push teeth to the buccal side. They are usually made for one tooth, but sometimes it can be made a little longer to push two teeth. The two main conditions to act as a protrusion spring are: - To have enough space on the arch to move the tooth into the zone that we want to move. - If the tooth or teeth that we want to move to the buccal part are in crossbite position, it will be needed something to provoke disocclusion (bite blocks) to allow tooth to move into the correct part without interfering with the lower arch. Other example of free end springs is the mesiodistal movement springs. They move mesio distally the teeth. They can move every tooth, however it is just used on upper incisors and depending on how they are located, the movement will be mesial or distal (the helix will guide the movement). B) Continuous springs Both ends of the spring are embedded on the acrylic plate. The two kinds of continuous springs are: the buccal arch and the progeny arch. - Buccal arch: it goes out from the acrylic plate through an interdental space, generally distal to the canine and it goes to buccal. It holds the buccal side of the anterior teeth and then it goes again through the opposite interdental space. After coming out from the acrylic, at the canine level there is a gingival bend or loop (this bend can provoke the anterior or posterior movement if it is opened or closed). It can be done for the upper or for the lower teeth. The buccal arch can have two functions: it can be passive and acts as retention (retain teeth or increase the plate retention) if it is contacting teeth, but if it is separated from teeth (1 mm) it will be a protrusive limit for the teeth if the plate is being activated from springs. On the other hand, if the loop is being closed, as they contact with the anterior teeth, it provokes an active movement and a lingual movement of the incisors. So it can act as a passive or active element. - Progeny arch: it is a variety of the buccal arch; it changes the stiffness, and the loop is longer. It is much more flexible. It goes down to the lower third of the lower incisors’ crowns. If the bends are closed, the arch will descent more than 1/3. This kind of appliance can be used to correct anterior crossbites when the origin of this problem is dental. It also can be used as retention after treating an anterior crossbite. 3.2. SCREWS They are made of two metallic parts separated by a helix. When the helix is activated, both parts are separated, or they meet each other depending on the screw direction. Generally, it is pretended to be separated. There are many screws designs, it changes its size, the helix and the amount of activation needed. The most frequent are: - Expansion screw at the upper arch. - Expansion screw at the lower arch. - Individual screw to move one or two teeth.  - Special screws to do complex movements as the triple Bertoni screw. It has three parts and when it is activated, it moves laterally and anteriorly the parts, provoking lateral and anterior movement. Generally, a full turn of the screw produces 1 mm of movement. Each screw has 4 holes and usually just one can be seen. The activation is achieved when a key is introduced into this hole (each activation, means 0,25 mm), and it is turn on the arrow sense that is usually draw on the screw until other hole appears again. This can be done by the patient at home, for that reason we order their parents to do an activation, which it really means ¼ of activation (0,25 mm). The screws are not only for pushing teeth or separating parts of the resin plate, but it can also be used on the opposite sense. The mechanism will be locating the screw already opened on the plate and do the contrary movement. The plate can also be divided into two parts symmetrically but with a V hinge at the distal part of the opened side and putting the screw at the anterior side. This will provoke the arch expansion just on the anterior side, with a fan pattern. 4. FUNCTIONAL ELEMENTS Some removable plates elements can act as functional appliances where its active element will be the patient’s function. 4.1. BITE BLOCKS When it is needed, the acrylic part can be extended covering the occlusal part of some teeth (anterior or posterior) depending on the objective. This is known as bite blocks. Those bite blocks act increasing the vertical dimension and opening the bite, avoiding the teeth eruption of the covered teeth, and allowing the eruption of those teeth that are not covered. When using this kind of appliance on the frontal teeth, there will be posterior disocclusion and this will favor lateral posterior teeth eruption (it will improve deep overbite). On the other hand, if the bite block is located at the posterior side, anterior teeth will be free and with disocclusion and this will provoke the increasement of the overbite (useful in open bite problems). 4.2. GRIDS Stainless steel wire grids which main objective is to modify the tongue position. They can be for the upper or the lower arch. The upper ones are used when there is an anterior open bite due to the tongue position (between both arches) and it avoids the correct incisors’ overbite. The lower ones are used when the tongue is in a lower position, and it can provoke an excessive growth of the mandible. 4.3. LATERAL ACRYLIC EXTENSION The resin plate can be extended also to the lingual part of the opposite arch. This wing will continue until the lingual side of the lower molars to increase the anchorage. For example, if we want to obtain asymmetrical expansion of the upper maxilla, the wing must go to the lingual side of the lower molars at the side that we don’t want to expand. This element can also be used in case of functional mandible deviation to obtain or stabilize the mandible position after an expansion. The dental impressions must be registered into centric relationship. When the patients wear the appliance, the extension provoke the mandible reposition. For example, if the patient has a mandible functional deviation into the left, the upper appliance will have a wing which goes until the lingual side of the lower molars at the right lower arch. This will avoid the mandible movement into the left side. 4.4. LINGUAL/LABIAL SHIELD AND ORAL SCREENS Other element that can be used with those removable appliances is the lingual or labial shield located at the lower part, buccal to the lower incisors. It will avoid the lower lip interposition among the upper incisors. At the same time, it can favor the buccal movement of the lower incisors because it breaks the balance between the tongue and the lower lip. This same explanation, can be used to the rest of the oral muscles, using also acrylic shields at the lateral zones (lingual or buccal) changing the muscle balance if it is needed. CLINICAL USE OF REMOVABLE PLATES Indications Dental expansion, but not in basal expansion. Anterior crossbite correction. Habit correction. Small dentary movements (tip) and sometimes, incisor and canines’ rotations, coronal distal movement of canines and molars. Class I malocclusions with enough space to align and without severe posterior rotations. Anterior teeth rotations due to dental protrusion without increased overbite. Moderate anteroposterior malocclusions, susceptible of being corrected with intermaxillary force. As support to maxillary extraoral force. Combined with fixed appliances. As retention. Contraindications Severe anteroposterior malocclusions. Severe crowding (which need from extractions and mass movement can’t be achieved). Diastemas in anterior teeth without dental protrusion. Severe rotations specially in the posterior side. Advantages Less dental chair time. Bigger time between appointments. They allow better hygiene because being removable makes easier to take them out when eating. They do less damage. Easy to repair.  They can be used when fixed appliances can’t be used (big dental loss, enamel hypoplasia or malformations). More aesthetical than fixed appliances, most of their elements are located at the lingual side. Disadvantages The response to treatment is heavily dependent on patients’ compliance, it is only effective when the patient wears it. They affect to the patient phonation due to the palate acrylic. Longer treatment. Limited movements to produce complex tooth movement. Difficult to manage when extractions are needed.