The Twin Block

January 4, 2018 | Author: Mohammed Hossam Elnaggar | Category: Orthodontics, Tooth, Mouth, Dentistry Branches, Dental Anatomy
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The Twin Block ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS Orthodontics is specifically concerned with correcting irregularities of the teeth, but the term orthodontics does not adequately describe the treatment of skeletal disharmony and the wider esthetic aims of a specialty as concerned with facial balance and harmony as it is with balanced functional occlusion. Dental malocclusion is frequently secondary to abnormal skeletal development. The approach in treating such mal-occlusions changes from an orthodontic one with the primary emphasis on dental correction to an orthopedic one with the goal of correcting the underlying skeletal abnormality. This difference in approach recognizes the existence of two schools of thought in evaluating the aims of orthodontic treatment. An essential distinction in terminology exists between orthodontics and dentofacial orthopedics. The term dentofacial orthopedics conveys to the patient that treatment can significantly alter and improve facial appearance in addition to correcting irregularity of the teeth.

The challenge of functional therapy is to maximize the Se nc ,c potemtal ot growth and guide the growing f™ce and T veloping denmion toward a pattern of optimal de« o'met In the dentition the force of occlusion of the teeth is the mo , natural functional mechanism tha, can be used to i n,Lence the structure ot the supporting bone. This natural process of bony remode ing forms the basis of functional correction with the twin block technique. The fundamental concepts of functional therapy have changed yen- little since the development of the monobloc bv Kobm (1902). Over the years, however, functional appliance design has been progressively modified for daytime and nieht-time wear. Recent improvements in the design of functional appliances have led to more consistent results in functional orthopedic treatment. A significant advance is the introduction of appliances

for full-time wear, including during eating. to maximize functional forces in the developing dentition.

THE TWIN BLOCK TECHNIQUE Twin blocks are simple bite-blocks that effectively modify the occlusal inclined plane; these devices use upper and lower bite-blocks that engage on occlusal inclined planes. Twin block appliances achieve rapid functional correction of malocclusion by transmitting favorable occlusal forces to the occlusal inclined planes covering the posterior teeth. The Occlusal Inclined Plane The occlusal inclined plane is the fundamental functional mechanism of the natural dentition. In normal development, cuspal inclined planes play important roles in determining the relationship of the teeth as they erupt into occlusion. Occlusal forces transmitted through the dentition provide constant proprioceptive stimuli to influence the growth rate and adaptation of the trabecular structure of the supporting bone. Fixed occlusal inclined planes have been used to alter the distribution of occlusal forces in animal experiments investigating the effects of functional mandibular displacement on mandibular growth and adaptive changes in the ternporo-mandibular joint (TMJ) The proprioceptive sensory feedback mechanism controls muscular activity and provides a functional stimulus or deterrent to the full expression of mandibular growth. If a distal occlusion develops, the occlusion of the teeth represents a servo mechanism that locks the mandible in a distally occluding functional position.

Twin blocks are simple bite-blocks with occlusal inclined planes.

Twin Blocks Twin blocks are designed for full-time wear; they correct the maxillomandibular relationship through functional mandibular displacement. Twin blocks achieve rapid functional correction of malocclusion by modifying the occlusal inclined plane, guiding the mandible forward into correct occlusion. The forces of occlusion are used to correct the malocclusion . Upper and lower bite-blocks interlock at a 70-degree angle; they are designed for full-time wear to take advantage of all functional forces applied to the dentition, including the forces of mastication. Wearing bite-blocks is similar in feel to wearing dentures and patient can eat comfortably with the appliance in place . with functional correction or occlusal relationships can be achieved in most cases without the addition of any orthopedic or traction forces.

Twin blocks modify the occlusal incline plane to guide the mandible forward into correct occlusion.

The twin block technique has two stages: 1. Active phase: Twin blocks use posterior incline plane to adjust the vertical dimens and correct the malocclusion by functional mandibular protrusion 2. Support phase: An anterior inclined plane is used to retain the corrected mcisor relationship until the buccal segment occlusion is fully established.

BITE REGISTRATION In Class II, division 1 malocclusion a protrusive bite is registered to reduce the overjet and distal occlusion by 5 to 10 mm on initial activation of twin blocks depending on the freedom of movement in protrusive function. This

degree of activation allows an overjet as large as 10 mm to be corrected without further activation of the twin blocks. In growing children with overjets as large as 10 mm, the bite may be activated edge to edge on the incisors with a 2-mm interincisal clearance if the patient can posture forward comfortably to maintain full occlusion on the appliances. In the vertical dimension, 2 mm of interincisal clearance is equal to approximately 5 or 6 mm of clearance in the first premolar region. This usually leaves 2 mm of clearance distally in the molar region and ensures that space is available for vertical development of posterior teeth to reduce the overbite. This method of activation allows an overjet as large as 10 mm to be corrected on the first activation without further activation of the twin blocks. Larger overjets invariably require partial correction, followed by reactivation after initial correction. The amounr of initial activation for an individual patient is related to the ease with which the patient postures forward into a protrusive bite; in choosing the amount of activation, the clinician should consider the effect of forward posture on the profile. If the patient postures forward easily, an edge-to-edgc occlusion is commonly activated. This occlusion is reproduced most easily by the patient and is equivalent to biting edge to edge on the incisors. In considering guidelines for activation of functional appliances, Roccabado (personal communication, 1992) observes that the position of maximal protrusion is not a physiologic position. He concludes from examination of the function of the rnandibular joint that the range of physiologic movement of the mandible is no more than 70% of the total protrusive path Patients who may have difficulty in maintaining an edge to-edge position m protrusion must be identified Freedom Of movement in forward posture ,s assessed by measuring the all protrusive path of the mandible. The overjet is measured in the fully retruded position and then in the position of maximal protrusion. The difference between these two measurements is the total protrusive path. Measuring the protrusive path helps identify patients who have a limited range of protrusive movement and would therefore be unable to maintain contact on the inclined planes if activation exceeds the physiologic range of movement. The George bite gauge is a convenient instrument to register a protrusive bite because it has a sliding jig attached to

a millimeter scale; it is designed to measure the protrusive path of the mandible and can be subsequently adjusted to record a protrusive bite of no more than 70% of the total protrusive path. Patients with horizontal growth patterns normally mantain an edge-to-edge incisor relationship more easily, provided the overjet is not excessive, whereas patients with vertical growth patterns may not tolerate the same degree of sagittal activation. A smaller initial activation is then necessary, and mandibular advancement must proceed more gradually by increments of activation. Even in patients with horizontal growth patterns, a physiologic limit to the amount of protrusion that can be tolerated in initial mandibular advancement is evident. Overjets greater than 10 mm require stepwise reactivation by the addition of cold-cure acrylic to the anterior incline of the upper twin block during the course of treatment. However, even fa treating patients with larger overjets, only one reactivation is normally required to correct most malocclusions. The amount of vertical activation also is important and is determined by two factors. First, adequate vertical clearance must be available between the cusps of the upper and lower first premolars or deciduous molars to accommodate blocks of sufficient thickness to activate the appliance. The blocks are normally 5 to 6 mm thick between the first premolars. Second, the vertical activation must open the bite beyond die freeway space to ensure that the patient cannot drop the mandible into rest position and negate the propnoceptive functional response of the inclined planes. For the same reason, opening the bite beyond the freeway space may be an im portant factor in ensuring that the appliance is active wher the patient is asleep. Bite Registration for Twin Blocks The bite is registered for twin blocks in the same protrusive position used for other functional appliances. tne exactobite bite registration device is recommended for accur* control in registering a protrusive bite .the gauge allows the clinician to choose variable amounts of total activation bv selecting the appropnate groove . the upper incisors in registering the protrusive bite the blue exactobite gauge registera a 2mm vertical clearance

of the upper and lower incisors. Activation aims to achieve reduction of overjet , correction of distal occlusion and midline correction .

Exactobite When registering the bite the clinician should give the patient a mirror . The patient should be shown the way to bte correctly into the Exactobite before the clinician applies wax ,o register the bite. The patient should be instructed to occlude with the mldlmes coincident, and the Exactobite should be positioned with the upper incisors occluding in the appropriate groove to reduce the overjet when the mandible closes into the mclsal guidance groove. A relatively firm wax is used to register the occlusion. This wax is dimensionally stable and allows the occlusion to be correctly registered on models in the laboratory.

The activation of functional appliances normally exceeds the adaptive potential of periodontal and dentoalveolar tissues in altering the existing equilibrium of forces acting within the craniofacial structures and stimulating adaptive skeletal change in response to altered muscle activity. If the amount of activation significantly exceeds the mandibular growth potential, dentoalveolar compensation may occur to allow the stomatognathic system to adapt to a position of functional occlusal balance. Essentially, the rate of activation is related to the anticipated rate of sagittal growth. As with any functional appliance, care must be taken not to procline the lower incisors. Procumbent lower incisors in the initial malocclusion may militate against choice of a functional appliance or require a decision on possible extraction and combined fixed and removable appliance therapy.

CONTROL OF THE VERTICAL DIMENSION Occlusal bite-blocks provide an occlusal table that can be adjusted differentially to control the vertical dimension. Deep or reduced overbite is usually related to disproportion in upper and lower facial height. This diagnosis is determined by clinical examination of the patient in full-face and profile views to assess facial balance. The findings of clinical examination should be confirmed by cephalometric analysis. Cephalometric radiographs should be taken with the patient positioned in natural head posture. Typically a patient with a brachyfacial growth pattern has a more horizontal growth pattern in the mandible, where deep overbite is associated with reduced lower facial height. A patient with a dolichofacial growth pattern on the other hand frequently has a reduced overbite related to a proportional increase in lower facial height. Management of overbite should take into account the facial proportions and improve facial balance by controlling the vertical dimension.

VERTICAL ACTIVATION TREATMENT OF DEEP OVERBITE Vertical control in treatment of deep overbite associated with a brachyfacial growth pattern aims to increase lower facial hight by correcting the incisors to an edge-to-edge relationship while adjusting the height of the upper biteblock in the molar region to encourage molar eruption. The goal is to increase the vertical dimension and improve the profile by increasing lower facial height. Deep overbite is reduced by overcorrecting to an edge-to-edge incisor relationship with an interincisal clearance of 2 mm in the protrusive bite. In recording the construction bite, the clinician normally leaves 5 mm of clearance in the first premolar region, which is equivalent to 2 mm of clearance distally in the molar region. Overbite reduction is achieved by trimming the occlusal cover on the upper twin block occlusodistally to encourage eruption of the lower molars. The inclined plane must remain intact, however, to maintain the activation to propel the mandible down and forward. The occlusion is cleared over the lower molars by 1 to 2 mm only. This clearance is sufficient to allow eruption of lower molars but not large enough to allow the tongue to pass between the teeth, which would prevent eruption. In all functional techniques, vertical development in the buccal segments is commonly slower than sagittal correction. Vertical correction should therefore be made as early as possible in treatment to allow vertical development to proceed concurrently with sagittal correction. The occlusal surface of the upper bite-block is progressively trimmed at each visit to maintain sufficient clearance over the lower molars to allow eruption. The clinician assesses clearance by passing an explorer between the teeth to ensure that the lower molars are not in contact with the upper block. Adequate interlocking wedges must be maintained to preserve the sagittal correction of arch relationships. The leading edge of the inclined plane of the upper bite-block is maintained intact throughout the rwin block phase of treatment to preserve the active mechanism for functional correction (Figure 13-5).

At the end of the active phase the incisors and molars should be in correct occlusion. At this stage an open bite is still present in the premolar region because of the presence of the bite-blocks. The final adjustment is to trim the lower block slightly to reduce the open bite in the premolar region. Eruption of lower molars occurs more quickly if separating elastics are placed in the interdental contacts with adjacent teeth at the start of treatment. Active eruption of lower molars may be encouraged by applying vertical elastics from the upper appliance to hooks on the lower molars. This is especially useful in older patients in whom eruption by natural forces tends to be slower. Vertical activation treatment of reduced overbite Patients with dolichofacial growth patterns have vertical growth patterns with increased lower facial height associated with reduced overbite and anterior open bite. This clinical situation requires careful management because the vertical growth pattern is often unfavorable for conventional functional correction.

All posterior teeth must be in occlusal contact with the opposing bite-blocks to prevent overeruption, which increases the anterior open bite and accentuates the vertical growth tendency If second molars erupt distal to the appliance, eruption should be controlled by placing occlusal rests or extending the upper twin block distally over the upper second molars to contact the lower second molars. Failure to observe this procedure complicates treatment considerably. Additional directional forces also may be used to help control vertical growth through the application of intrusive orthopedic forces to the upper posterior teeth.

Occlusal cover is maintained over the posterior teeth to prevent eruption in treatment of anterior open bite.

APPLIANCE DESIGN Standard Twin Blocks Standard Twin Blocks blocks are suitable for treatment of uncrowded class II, division 1 malocclusions with good archforms and overjets large enough to allow unrestricted forward translation of the mandible for full correction of distal occlusion (see Figure 13-12. A). Patients with Gass II, division 1 malocclusions typically have narrow upper arches, wirh the lower arches in distal occlusion. During treatment a midline screw is routinely included in the upper appliance for_com-pensatory expansion in the upper arch to accommodate the lower arch as the mandible translates forward. The standard design of rwin blocks dierefore has provision for midline jexpansion. The inclined planes are positioned mesial to the upper and lower first molars, uith the upper block covering the upper molars and second premolars or deciduous molars. The lower blocks should not extend fully to the distal of the ^second premolar or deciduous molar. Therefore the inclined plane is positioned slighdy forward of the lower first molar. Clearance is necessary to allow the lower molar to erupt to increase the vertical dimension in the treatment of excessive overbite. The upper appliance has delta clasps on the upperJirst molars; additional ball clasps may be placed inrerdemally, distal to rhe canines, or between the

premolars or deciduous molars. The lower appliance is a simple bice-block with delta clasps on the first premolars and ball clasps mesial to the canines .

Variations in Appliance Design Arch development. Twin blocks have the advantage of versatility of design in comparison with conventional one-piece functional appliances that apply an equal amount of expansion to both dental arches. Separate upper and lower twin block appliances allow independent control of arch development. Upper and lower midline screws may be used for unequal expansion in both arches. If the lower arch is expanded transversely, additional expansion is often required in the upper arch to compensate. The arches may be expanded at differential rates over time to achieve unequal expansion (Figure 13-14). Appliance design may be modified by the addition of screws, springs, and bows to move individual teeth. Arch development can proceed in both arches by a combination of transverse and sagittal components to meet the requirements of the individual patient. Provision for combined transverse and sagittal expansion may be made by adding a three-way screw or using a three-screw sagittal design with a midline screw in addition to the two sagittal screws in the palatal acrylic.

Twin Blocks in Mixed Dentition The primary indication for twin blocks in early mixed dentition is in Class II, division 1 malocclusion in which prominent upper incisors rest outside the lower lip and are vulner-able to fracture because they are not protected by the lips. Twin blocks can fulfill three objectives at this stage of development: 1. They can reduce overjet and correct distal occlusion. 2. They can control overbite if the overbite is deep or anterior open bite is present. 3. They can improve arch form by transverse or sagittal development. These objectives are achieved using a similar approach to treatment as is used in the permanent dentition, with modifications in appliance design to meet the requirements of the mixed-dentition stage of development. The deciduous molars and canines may not provide adequate undercuts for fixation, but this problem is easily overcome. In mixed dentition the appliance design is modified by using C-shaped clasps that may be directly bonded to deciduous teeth with composite to temporarily fix the appliances in the mouth for 10 days to initiate full-time appliance wear. After a few

days the clasps can be freed and the composite left in place to improve undercuts for fixation. In the initial stage the twin blocks may even be cemented or bonded directly to the teeth in addition to the application of composite to secure the clasps. This fixation enables the patient to adjust to wearing the appliance full time during the critical first few days. At this stage of development the procedure of temporary fixation of twin blocks to the teeth carries minimal risk, especially if first permanent molars are fissure sealed.

Stages of Treatment Twin-block treatment is described in two stages. Twin blocks are used in the active phase to correct the anteropostcrior relationship and establish the correct vertical dimension. Once this phase is completed, the twin-blocks are replaced with an upper hawley's type of appliance with an anterior inclined plane which is then used to support the corrected position as the posterior teeth settled fully into the occlusion. Stage I—Active Phase Twin-blocks achieve rapid functional correction ot mandibular position from a skeletal retruded Class II to Class I occlusion using occlusal inclined planes over the posterior teeth lo guide mandible into correct relationship with the maxilla. In all functional therapy, sagittal correction is achieved before vertical development of posterior teeth is complete.

The upper block is trimmed occlusodistally to leave the lower molars 1-2 mm clear of the occlusion to encourage lower molars to erupt and reduce the overbite. By maintaininga minimal clearance between the upper bite block and the lower molars, the tongue is prevented from spreading laterally between the teeth. This allows molars to erupt more quickly. At each subsequent visit, the upper bite block is reduced more under the control of the orthodontist. This led progressively to clear the occlusion with the lower to the development of "non-compliant appliances". The appliances in "noncompliance" treatment have a couple of features in common. molars to allow these teeth to erupt, until finally all the acrylic has been removed over the occlusal surfaces of the upper molars allowing the lower molars to erupt fully into occlusion. Throughout this trimming sequence, it is important not to reduce the leading edge of the inclined plane, so that adaptive functional occlusal support is given until a 3 point occlusal con tact is achieved with molars in occlusion. Average time 6-9 months to achieve full reduction of overbite to a normal incisor relationship and to correct the distal occlusion.

Stage 2: support phase-anterior inclined plane. The objective of the second stage of treatment ,s to retain the cor reeled incisor relationship until buccal segment occlusion is fuUy established. To achieve this objective, an upper removable appliance is fitted with an anterior inclined plane to engage the lower incisors and canines (Figure 1316). This appliance is worn full time initially to allow the buccal segment occlusion to settle; it is then used as a retainer. The lower twin block appliance is left out at this stage, and the removal of posterior bite-blocks allows the posterior teeth to erupt. Full-time appliance wear is necessary to allow time for internal bony remodeling to support the corrected occlusion as the buccal segments settle fully into optimal interdigitation. 281 The upper and tower buccal teeth are usually in occlusion within 4 to 6 months. Full-time appliance wear is continued during the support phase for another 3 to 6 months to allow functional reorientation of the trabecular system before any reduction of appliance wear occurs during the retention period (Harvold, 1973) (Figure 13-17).

The support phase may be considered as important as the active phase. Stability is excellent after twin block treatment; this can be attributed partly to the support phase, during which a functional retainer is used to stabilize the corrected incisor relationship while the buccal teeth settle fully into occlusion.

FITTING TWIN BLOCKS Instructions to the Patient Patient motivation is an important factor in removable appliance therapy, and a protocol should be established for patient instruction when appliances are fitted. An ideal way to introduce a patient to twin blocks is to demonstrate appliances on models to explain the action of the inclined planes in correcting the bite. Simply by biting the blocks together correctly. the patient encourages the lower jaw to adapt and grow to correct the malocclusion . The appliance system is simple and easily understood. even by young patients. When the appliances are placed in the mouth, a noticeable improvement m facial appearance occurs immediately. This i, an excellent motivating factor to encourage the patient to wear the appliance, especially if the clinician explains that this change will be permanent within a few months if the twin blpcks are worn full time. The patient is instructed on tin-ways to insert and remove the appliances and operate the screw. The screw is turned for the first time after the appliance has been worn for 1 week. Twin blocks achieve correction by the forces of occlusion, and therefore the patient must learn to eat with the appliances in place, removing them only for cleaning after every meal to avoid food stagnation under the appliances. Depending on the patient and the expected response, the appliances may heremoved for eating for the first few days until they have settled in comfortably, but they must then be worn during meals because the forces of occlusion are used to correct the malocclusion, and these forces are most active when the patient is eating.

CLINICAL MANAGEMENT Stage 1: Active Phase First visit—on fitting twin block appliances. The overjet is measured before treatment with the teeth in occlusion and the mandible fully retruded; this measurement is recorded for future reference. The lingua] flange of the appliance must be relieved slightly lingual to the lower incisors to avoid gingival irritation as the appliance is driven in by the occlusion during the first few days. The clasps are adjusted to hold the appliances securely in position without impinging on the gingival margin. If a labial bow is present, it should be out of contact with the upper incisors. The clinician should

check that the patient bites comfortably in a protrusive bite. Selected eases benefit by bonding appliances for the first 10 to 14 days. Second visit—after 10 days. The patient should be wearing the appliances comfortably and eating with them in position after 10 days. The initial discomfort of a new appliance should have resolved, and the patient should be biting comfortably in the protrusive bite. If the patient is failing to posture forward consistently, the clinician should consider reducing activation by trimming the inclined planes slightly. Patient compliance is important in removable appliance therapy, and encouragement should be offered for success in becoming accustomed to the appliance quickly; reassurance should be provided on any difficulties. The patient should turn the screw under supervision, and at this stage, only minimal adjustment is made to the appliance if necessary. Improved muscle balance becomes evident quickly in the face because the appliance is worn full time. This improvement should be noted for the patient and parents as an encouraging sign of early progress. Overbite correction in case of deep over bite Third visit after 4 weeks. At each visit, progress. viewed by measuring the overjet. At the same time the occlusion is checked for correction of the buccal segment relatioships. Positive progress should now be noted in facial muscle balance; this should be confirmed by a reduction in overjet, measured intraorally with the mandible fully retracted Minor adjustment is necessary only to keep the labial bow of contact with the upper incisors and ensure that the lower molars are not in contact with the upper block in cases of deep overbite. The clinician should check that the screw is opening correctly and adjust the clasps if necessary. Fourth visit—after 6 weeks. A similar pattern of adjustment and checking of occlusion and overjet should occur at' the 6 weeks. The clinician should trim the blocks in the recommended sequence to reduce deep overbitc. Subsequent adjustment visits normally occur at 6-week intervals, and a steady correction of distal occlusion and reduction of overjet should occur, with concurrent eruption of lower molars to reduce the overbite.

Progress in treatment. Twin block appliances arc simple, and treatment is normally uncomplicated. The upper arch must not be overexpanded into crossbite; it should he checked at each visit, and the clinician should stop the operation of the screw if necessary. An overjet as large as 10 mm can be corrected without reactivating the bite blocks it the rale and direction of mandibular growth arc favorable. Full correction of sagittal arch relationships can he achieved in as little as 2 to 6 months, thus producing a normal incisor relationship. At this stage the overjet is fully corrected, and the buccal segments are still out of occlusion because of the presence of the bite-blocks. In treatment of deep overbite, functional techniques consistently achieve sagittal correction of arch relationships before compensatory vertical development in the buccal segments is complete. Clark holds that clinical management is simplified by introducing a single large activation when the appliances are (11 ted provided the growth pattern is favorable for functional correction. On statistical analysis of the results of 76 consecutively treated patients, Clark (1994) found this regimen results in significant growth modification in comparison with untreated controls. Progressive mandibular advancement they be beneficial, however, in cases in which the growth pattern Management of overbite. As indicated previously deep overbite is reduced by overcorrecting the molars to edge to-edge relationship before reducing the height of the blocks. Vertical development of the lower molars"' aged from the beginning of the active phase of Treatmem by progressive trimming of the upper bite-block occlusodistally to allow the lower molars to erupt. At the end of the active phase the incisors and molars should be in correct occlusion At this stage an open bite is still present in the premolar region because of the presence of the bite-blocks. As a final adjustment at the end of the twin block stage the upper -surface of the lower block is trimmed to allow the open bite in the premolar region to reduce before progressing to the support phase. Adequate interlocking wedges must be preserved to maintain anteroposterior correction of arch relationships. This method of reducing overbite through controlled eruption of posterior teeth supported by occlusal bite-blocks results in favorable changes in facial balance by increasing lower facial height. If the overbite is reduced before treatment, overeruption of posterior teeth, which further reduces the overbite, should be prevented. AH erupted teeth

must then be in occlusal contact with the bite-blocks. If second molars erupt during the active phase, occlusal cover or occlusal rests must be extended to prevent overeruption of these teeth. In treatment of cases of reduced overbite or open bite, clasps are placed on the posterior teeth and the appliances are left clear of the anterior teeth to encourage eruption of the incisors. In addition, a vertical-pull headgear may be used to apply intrusive force to the upper molars to reduce the vertical component of growth. Repelling magnets may be incorporated in the posterior bite-blocks to enhance depression of these teeth. Stage II—Support Phase The aim of the support phase is to maintain the corrected incisor relationship until the buccal segment occlusion is fully interdigitated. To achieve this objective an upper removable appliance is fitted with an anterior inclined plane to engage the lower incisors and canine. The lower twin-block is left out at this stage and removal of the posterior bite blocks allow the posterior teeth to erupt. Full time appliance wear is necessary to allow time for internal bony remodeling to support the occlusion as the buccal segments settle into occlusion . RETENTION Treatment is followed by retention with the upper anterior inclined plane appliance. Appliance wear is reduced to night time wear only once the occlusion is fully established. A good buccal segment occlusion is the cornerstone of stability after correction of arch-to-arch relationship. The appliance affected advanced mandibular position will not be stable until the functional support of a full buccal segment occlusion is well established.

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