Sem 4 /certified fixed orthodontic courses by Indian dental academy


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Sem 4 /certified fixed orthodontic courses by Indian dental academy

  1. 1. CURRENT STATUS OF TWIN BLOCK INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2.                 Introduction Clarks Twin Block Modifications in TBA Retrospective studies on TBA Prospective studies on TBA Patient Compliance Various designs Clip on fixed appliance ( M. Read ) Cohort study proving efficiency Modified TB for treatment of Class II div 2 Modified TB for treatment of Class III Morphological study: Finite element scaling analysis Optical surface scanning for assessment of effect of ( TB ) on soft tissues Animal study Animal study Conclusion
  3. 3.   Introduction: A wide range of functional appliances is available for the correction of Class II skeletal and occlusal disharmonies (eg, Bionator,FR-2 of Frankel, fixed and removable Herbst appliances Among these, the Twin-block originally developed by William Clark has gained increasing popularity during the last decade. The appliance is indicated for the correction of Class II malocclusions characterized in part by mandibular skeletal retrusion. In the dentition the force of occlusion of teeth is the most natural functional mechanism that can be used to influence the structure of the supporting bone. This natural process of bony remodeling forms the basis of functional correction with the Twin Block technique.
  4. 4.      THE OCCLUSAL INCLINED PLANE The occlusal inclined plane is the fundamental functional mechanism of the natural dentition. Cuspal inclined planes play an important part in determining the relationship of the teeth as they erupt into occlusion. Occlusal forces transmitted through the dentition provide a constant proprioceptive stimulus to influence the rate of growth and the trabecular structure of the supporting bone TWIN BLOCKS Twin blocks are bite-blocks that effectively modify the occlusal inclined plane to induce favorably directed occlusal forces by causing a functional mandibular displacement. Upper and lower bite-blocks interlock at a 45° angle and are designed for full-time wear to take advantage of all functional forces applied to the dentition including the forces of mastication. TWIN BLOCK APPLIANCES Twin blocks may be either removable or fixed
  5. 5. APPLIANCE DESIGN REMOVABLE TWIN BLOCK    The upper appliance is retained by modified arrowhead clasps. Adding ball-ended clasps in the labial or buccal segments may increase retention. A midline expansion screw provides compensatory lateral expansion of the upper arch to accommodate a functional protrusion of the lower arch from its retruded position. Labial and lingual bows (as needed) are included to control upper incisor angulation. In the lower arch, retention is often obtained by l-mm interdental ball clasps in the lower incisor region combined with clasps in the buccal segments. The delta clasp was specifically designed to extend the area of contact of the clasp in the undercut and to improve retention with a closed triangle to increase resistance to fatigue. This combination of clasps gives excellent retention and is very effective in limiting proclination of lower incisors during the twin block stage.
  6. 6.    In mixed dentition treatment, clasps are placed on the lower incisors and on deciduous molars or first permanent molars. The lower appliance may be split anteriorly with the addition of a screw or helical spring to expand and develop the lower arch, if desired. The upper bite-blocks cover the lingual cusps of the upper posterior teeth, extending to the mesial ridge of the upper second premolar. This allows the clasp to be more flexible and improves retention of the appliance. Full occlusal cover is necessary in the lower premolar region to compensate for the discrepancy in arch width and to allow the inclined planes to interlock in occlusion. The lower bite-block extends to the distal marginal ridge of the lower second premolar
  7. 7. Clarks TB
  8. 8.     BITE REGISTRATION The amount of mandibular protrusion depends on the ease with which the patient can posture forward. As a general rule, the initial activation should reduce the overjet by 5 to 7 mm leaving 3 to 5 mm interocclusal clearance in the first premolar region. The interocclusal clearance is increased where there is increased overbite and the bite-blocks are designed to allow the free eruption of the lower molars to reduce theoverbite by increasing the lower facial height. Exactobite
  9. 9.   The Excatobite or Projet Bite Gauge is designed to record a protrusive bite for construction of Twin Blocks. The blue bite gauge registers 2mm vertical clearance between the incisal edge of the upper and lower incisors, which is an appropriate interincisal clearance for bite registration in most Class II division 1 malocclusion with increased overbite. The incisal portion of the bite guage has three incisal grooves on one side that are designed to be positioned on the incisal edge of the upper and a single groove on the opposing side that engages the incisal edge of the lower incisior. The appropriate groove in the bite guage for bite registration is selected depending on the ease with which the patient can posture the mandible forwards.
  10. 10.  The registration bite should allow for correction of midlines in cases in which they are displaced by functional occlusal interference or guidance into habitual occlusion.
  11. 11.    CLINICAL MANAGEMENT The technique is described in two stages, an active phase with twin blocks and a support phase with a guide plane after correction of arch relationships. STAGE 1— ACTIVE PHASE Twin blocks are removed for eating for the first 3 days until the initial discomfort from appliance wear has been resolved. Thereafter, the appliances are worn continuously. The upper midline screw is turned a one-quarter turn every week to 10 days until the arch width is adequate to accommodate the lower arch in its corrected position..
  12. 12. Clinical response in active phase    Within a few days of fitting the appliances, the position of muscle balance is altered so that it becomes painful for the patient to retract the mandible. This has been described as the "pterygoid response" (McNamara) or the formation of a "tension zone" distal to the condyle (Harvold). It is rare for such a response to be observed with functional appliances that are not worn full-time. The rapid clinical response confirms the summary of adaptive responses in functional protrusion experiments with fixed inclined planes by McNamara. The placement of appliances results in an immediate change in the neuromuscular proprioceptive response. Provided all phasic and tonic muscle activity is affected, the resulting muscular changes are very rapid, and can be measured in terms of minutes, hours and days. Structural alterations are more gradual and are measured in months, whereby the dentoskeletal structures adapt to restore a functional equilibrium to support the altered position of muscle balance.
  13. 13.   If the patient's rate of growth is slow or the direction of growth is vertical rather than horizontal, it is advisable to advance the mandible more gradually over a longer period of time to allow compensatory mandibular growth to occur. Full correction of sagittal arch relationships can be achieved in as little as 2 to 6 months, giving a normal incisor relationship with the buccal segments out of occlusion due to the presence of the bite-blocks. It is a consistent feature in functional techniques that sagittal correction of arch relationships is achieved before compensatory vertical development in the buccal segments is complete.
  14. 14.    Management of overbite Overcorrecting the incisors to an edge-toedge relationship before reducing the height of the bite-blocks reduces deep overbite. This method of reducing overbite by controlled eruption of posterior teeth supported by occlusal biteblocks results in favorable changes in facial balance by increasing lower facial height.
  15. 15.  Vertical development of the lower molars is encouraged from the beginning of the active phase of treatment by progressively trimming the upper bite-block occlusodistally to allow the lower molars to erupt. At the end of the active phase, the incisors and the 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 biteblocks. The lower block is trimmed over a period of 2 or 3 months to reduce the open bite in the premolar region. It is important to maintain adequate interlocking wedges to maintain anteroposterior correction of arch relationships  
  16. 16.    STAGE 2 - SUPPORT PHASE The aim of the second stage of treatment is to retain the corrected incisor relationship until the buccal segment occlusion is fully established, using an upper Hawleytype removable appliance with an inclined guide plane to retain the sagittal relationship. The upper and lower buccal teeth are usually in occlusion within 4 to 6 months and the support phase is continued for a further 3 to 6 months to allow functional reorientation of the trabecular system before the position is retained (Harvold).
  17. 17.      CLASS II BITE REGISTRATION: In class II division 1 malocclusion a protrusive bite is registered to reduce the overjet and the distal occlusion on average 5-1-mm on initial activation, depending on the freedom of movement in protrusive funtion.. The activation should not exceed 70% of the protrusive path. Larger overjets invariably require partial correction, followed by reactivation after the intial correction is complete. In the vertical dimension a 2mm interincisal clearance is equivalent to an approximately 5to6mm in the first premolar region. This is usually leaves 3mm clearance distally in the molar region, and ensures that space is available for vertical development of posterior teeth to reduce the overbite. It is very important to open the bite slightly beyond the clearance of the free-way space to encourage the patient to close the appliance rather than allow the mandible to drop out of contact into rest position, which is one of the disadvantages of making the blocks too thin.
  18. 18.    CLASS III BITE REGISTRATION: It is not possible to build-in the same degree of activation in the construction bite for functional correction of Class III malocclusion compared to Class II correction, because there is less scope for displacement of the mandible. The Blue exacobite is used to register a construction bite with the teeth closed to the position of maximum retrusion, leaving sufficient clearance between the posterior teeth for the occlusal bite blocks. This is normally achieved in the fully retruded postion.
  19. 19. APPLIANCE DESIGN:  The saggital design is used to advance the upper incisors to correct the lingual occlusion in treatment of Class III malocclusion.  In many cases, the maxilla is contracted laterally in addition to occluding in a distal relationship to the mandible. This is an indication for combined sagittal and transverse expansion using a threescrew sagittal appliance which includes a midline screw to complement the action of the saggital screws.
  20. 20.   An alternative design uses a three-way expansion screw to combine transverse and sagittal expansion. This is also effective in expanding a contracted maxilla and in correcting lingual occlusion if used in combination with reversed inclined planes. Lip pads may be added to support the upper lip clear of incisors to enhance forward movement of upper labial segment.
  21. 21. Reverse TB
  22. 22.    The reverse pull facial mask can be attached to the upper Twin Block to maximize the forward component of force on the maxilla. A sagittal appliance is used in the upper arch. The elastic force is increased gradually from the time the facial mask is fitted and as the patient adapts to the pressure. A starting pressure of 8oz using bilateral 3/8 in elastics is recommended for 1st 2 weeks. The force can be later increased to 14oz by using 1/2inch elastics. A maximum of 14 oz with 5/16 inch elastic can then be delivered
  23. 23.    CORRECTION OF ANTERIOR OPEN BITE Reduced over bite or anterior open bite is often related to unfavorable vertical growth. Throughout treatment, all posterior teeth must remain in contact with the opposing bite blocks to prevent over eruption. Intrusion of posterior teeth helps reduce anterior open bite and encourages a favorable mandibular rotation to close the mandibular plane angle. The second molar need to be avoided from over eruption by including occlusal rests even before these teeth erupt in order to control their eruption. These patients benefit from phased progressive activation to allow their weak muscles to adapt more gradually to mandibular advancement. Vertical Elastics or attracting magnets help to solve this problem.
  24. 24. BITE REGISTRATION FOR ANTERIOR OPEN BITE  Exactobite designed to register a 4mm interincisal clearance resulting in approximately 5mm clearance between the cusps of the first premolars or deciduous molars is used.  Blocks of thickness sufficient to open the bite beyond the freeway space to intrude the teeth, and to make it difficult for the patient to disengage the blocks are used.
  25. 25.    APPLIANCE DESIGN IN TREATING ANTERIOR OPEN BITE The lower appliance extends distally to the lower molar region with clasps on the lower first molars and occlusal rests on the second molars to prevent their eruption. It is not necessary to extend acrylic to contact the upper and lower anterior teeth so that they are free to erupt to reduce the anterior open bite. A palatal spinner can be added to the upper appliance to help control an anterior tongue thrust. The spinner is an acrylic bead that is free to rotate round a transpalatal wire positioned in the palate.
  26. 26.    Intra Oral Traction to Close Anterior Open Bite Intraoral elastics can be used to accelerate bite closure as an efficient alternative to high-pull extraoral traction. This method introduced by Dr. Christine Mills in Vancouver was used mainly to maintain occlusal contact on the appliances overnight. Running vertical elastic between upper and lower appliances or to brackets or bands with gingival hooks reinforces the intrusive effect of the bite blocks. The elastics are worn at night to maintain occlusal contact of all the posterior teeth on the bite blocks to intrude posterior teeth.
  27. 27.    Magnetic force in correction of Anterior Open bite Magnets are incorporated in the inclined planes on the posterior bite blocks to increase the intrusive focus. Dellinger in 1986 investigated the effect of repelling magnets and found that they increased the opposing forces in the occlusal bite blocks to intrude opposing teeth. Attracting magnets increased the frequency of occlusal contacts on the inclined planes. These accelerated both anteroposterior and vertical correction
  28. 28.    TREATMENT OF CLASS II DIV 2 MALOCCLUSION Retroclined upper incisors are responsible for holding the mandible in a distal position in Angle's Class II Div. 2 malocclusion. Twin blocks have the effect of unlocking the malocclusion by releasing the mandible from an entrapped position of distal occlusion and thereby encouraging a rapid transition to class I arch relationship. Releasing the mandible downwards, forwards, and encouraging the lower molars to erupt achieve correction of class II div 2 malocclusion. At the same time, the upper incisors are advanced to achieve a normal upperto-lower incisor relationship that is cleared far enough forwards to accommodate the advancing mandibular arch of closure.
  29. 29.    Bite Registration The construction bite in Class II div 2 malocclusion is registered with the incisors in edge-to-edge occlusion. When the overbite is excessive, the clearance between the posterior teeth is correspondingly increased. The occlusal bite blocks are made thicker in the premolar region, to allow the clearance of the upper and lower incisors. The amount of mandibular advancement is limited in class II Div. 2
  30. 30.     Appliance Design: The upper twin block incorporate two sagittal screws set in the palate for antero-posterior development. The screws expand the arch by advancing the upper incisors and at the same time, drive the upper buccal segments distally and buccally along the line of the arch. This sagittal design is suitable for lower expansion also. If the upper arch is constricted as well in such a case, the triple screw sagittal twin block is useful to improve the arch form in AP and transverse directions.
  31. 31. FIXED TWIN BLOCKS  Twin block appliances may be designed for direct fixation to the teeth by bonding. Preformed wedge attachments are being designed at present for direct fixation to molar bands to allow simpler application in fixed appliance technique. 
  32. 32.      Magnetic Twin Blocks The role of magnets in Twin block therapy is to accelerate correction of arch relationships. Two types of rare earth magnets (samarium cobalt & neodynium boron) are used. Attracting magnets: It pulls the appliances together and encourages the patients to occlude actively and consistently in forward position. It increases the frequency and force of contact on the inclined planes. It can be used in the patients having weak musculature. Repelling magnets : They deliver additional forward mandibular posture without reactivation of blocks. Magnets are recommended where speed of treatment is important.
  33. 33. FIXED TWIN BLOCKS The advantages of fixed appliances compared to removable appliances are, the increased control by the operator, which does not rely on the compliance of the patient. The functional components of fixed twin blocks are : 1. The twin block Transpalatal arch This consists of a transpalatal arch with occlusal inclined planes over the posterior teeth that can be cemented in place. Occlusal wire tags that are extension of the transpalatal wire secure the inclined planes. The entire assembly is secured on Wilson lingual tubes on upper molar bands by the standard Wilson plug-in attachment. 2. The twin block lingual arch The occlusal inclined plane component in the lower arch is combined with the Wilson 3D lingual arch and extends over the occlusal surfaces of the lower deciduous molars, or premolars, depending on stage of development.
  34. 34.       Fitting the appliance Correct arch forms of both the arches are achieved before fitting the appliance. After achieving this, the lingual arches are removed and impressions are taken over molar bands to construct the fixed twin block appliance. The occlusal components of Twin Blocks are designed to be removable from the lingual tubes on molar bands together with the Wilson lingual attachment. It can be fitted by assembling the twin block appliances and band as one piece & cementing it, or the molar bands are cemented 1st, followed by attaching the occlusal and lingual attachments. Light cured material is used for additional working time. Twin Block Hyrax appliance Transverse development can be combined simultaneously with mandibular advancement by adding twin blocks to a RPE appliance like hyrax screw. The lower appliance can be anchored on lower second deciduous molars and may incorporate a lower lingual arch
  35. 35. RETROSPECTIVE STUDIES     Mills and McCulloch McNamara and Baccetti ( Treatment timing ) Trenouth Parkin and sandler - Comparison of 2 modifications
  36. 36.    Mills & McCulloch : 1998 Ajo 28 treated patients with skeletal Class II malocclusions were compared cephalometrically to a control group of untreated individuals The mean age was 9 years 1 month. The mean observation period was 14 months Design :    It was a modification of Clarks Twin Block appliance An acrylic labial bow was added to the lower incisor area to improve retention. Elastic hooks were soldered onto the delta clasps of the upper and lower members of the appliance.
  37. 37.  These hooks allow vertical elastics to be worn at night to encourage the patient to keep the mandible closed forward into the appliance while sleeping, thus increasing the effective wearing time in a 24-hour period.
  38. 38.    Like Clarks design : 1. The maxillary appliances had a midline expansion screw that was used to correct the transverse relationships as the mandible came forward with growth. 2. Labial bows were not used on the maxillary appliances of any of the patients in this design keeping with the recommendations of Clark to minimize lingual movement of the upper incisors during treatment
  39. 39. Bite Registration: The initial wax construction bite was taken with the mandible protracted approximately 6 mm and opened vertically by about 5 mm. In the patients with slight asymmetries of the mandible, the construction bite was taken with the upper and lower midlines coincident in an effort to correct the asymmetry by encouraging differential growth of the mandible.
  40. 40.     EFFECTS A. Skeletal : 1. Effect on maxilla: The TB group experienced on average a slight inhibition of forward maxillary growth. In TB group SNA reduced by 0.9 ° as compared to +0.1° increase in control . 2. Effect on mandible: The mandibular unit length (measured from Co to Gn) increased by 6.5 mm in the Twin Block group in contrast to only a 2.3 mm increase in the control group. Ramus height increased 4.1 mm in TB group as compared to 1.2 mm in control. Mandibular body length (Go-Gn) increased by 3.0 mm in TB group which was almost twice as that of the control subjects.
  41. 41.  The mandibular growth accounts for the 1.9° increase in angle SNB in the treatment group as compared with almost no change in the control group. 3. Vertical changes:  Both anterior facial height and posterior facial height increased significantly in the Twin Block group during treatment (5.6 mm and 4.3 mm), respectively. So, In spite of the change in vertical facial height, there was no net increase in the angle of SN to mandibular plane in the treatment group.
  42. 42.
  43. 43.    B. Dentoalveolar: Dentoalveolar changes were evident in the treatment group. Maxillary teeth : An average up righting effect of 2.5° on the upper incisors was observed during Twin Block treatment, but almost no change occurred in the control subjects. Molars: Twin Block group experienced a distalization effect on the upper molars of 1.6 mm. Control group: Upper first molars came forward 1.5 mm in the control group relative to the vertical reference plane, and only about 0.3 mm was attributable to tooth movement.
  44. 44.     2. Mandibular teeth : The lower incisors were proclined thrice in the Twin Block group (5.2° compared with only 1.4 ) during treatment . The lower molars erupted on average almost four times as much (2.3 mm compared with 0.6 mm) in the Twin Block group as in the control group. The net dentoalveolar change for the lower molars is a mesial movement of 1.4 mm in the treatment group as compared with only 0.2 mm for the control group. When the distance from the lower molars to the vertical reference plane (through S perpendicular to PP) was measured, a total increase of 5.2mm (1.4 mm dental and 3.8 mm skeletal) was noted for the Twin Block group compared with only 1.9 mm for the control group.
  45. 45.      3. Overjet: The overjet was decreased in total 5.6 mm in the treatment group. Nearly two thirds of this decrease could be accounted for by the forward growth of the mandible 4. Molar relation In the Twin Block treatment group, molar overjet reduced by 6.2 mm as compared with a reduction of only 0.4 mm in the control group. Mandibular contribution = 3.8 mm skeletal + 1.4 mm dental = 5.2 mm Maxillary contribution = 1.6 mm dental - .6mm skeletal = 1mm net Thus in the treatment group, approximately 50% of the molar correction was accomplished by skeletal improvement in the lower jaw and 50% by dentoalveolar change in the upper and lower molars.
  46. 46.     Posttreatment changes after successful correction of Class II malocclusions with the Twin Block appliance Mills and Mcculloch (AJO 2000 July) study was done 3 years after the phase I Twin Block treatment. Do functional appliances place a "mortgage" on mandibular growth? In other words, if enhanced increments of mandibular growth are achieved during the active phase of treat-ment with a functional appliance, is this treatment effect negated by diminished increments of mandibular growth in the posttreatment phase? The mean post retention period (during which the patient had no Twin Block wear) was 14 months.
  47. 47. (Art-Go) increased less in the Twin Block group (2.5 mm) than in the controls (3.0 mm) These differences indicate a tendency for some "rebound" effect after treatment with the Twin Block appliance
  48. 48.
  49. 49. Maxillary Changes Posttreatment  There was a trend for slightly less forward maxillary growth in the Twin Block treatment group from T2- T3 than in the untreated controls.  The saddle angle opens slightly (0.9°)  The mandibular plane angle increases slightly (1.0°)  Greater increase in anterior facial height (1.2 mm) seen in the Twin Block group.
  50. 50.
  51. 51.    The posttreatment incisor overjet measurement increased in the Twin Block group (1.0 mm), whereas it tended to decrease slightly in the untreated controls (-0.1 mm). The molar relationship as measured in the sagittal plane showed a mean relapse of 1.2 mm in the Twin Block group as compared with almost no change (0.1 mm) in the control group . Although there was a trend toward slightly smaller mandibular growth increments in the treatment group than in the controls, most of the positive gain in mandibular size achieved during the active treatment phase were present 3 years posttreatment.
  52. 52.      Timing for TB treatment Baccetti & McNamara AJO 2000 AUG In their study evaluated skeletal and dentoalveolar modifications produced by Twin block appliance in 2 samples of subjects with class II disharmony treated at different stages of mandibular skeletal maturity, as determined by cervical vertebral maturation. It was a retrospective study and 35 out of 79 patients were evaluated after Twin block therapy.. The treated sample were divided according to skeletal maturity at the start of treatment by CV maturation. Mean age of ETG was 9 years at T1 ( stage 1 or 2 ). Mean age of LTG was 12 years 11 months. CVM stage was stage 3 to 5. Clarks TB appliance was used.
  53. 53. Optimum treatment timing for Twin-block therapy of Class II disharmony appears to be during or slightly after the onset of the pubertal peak in growth velocity.
  54. 54.       Major favorable effects induced by functional therapy in LTG in comparison with earlier phases are: LTG : Greater skeletal contribution to the correction of the molar relation(67 %) Skeletal contribution to overjet correction was 54 %. Larger and clinically significant increments in total mandibular length and in ramus height More posterior direction of condylar growth, a biological mechanism enhancing supplementary mandibular lengthening and reducing the amount of forward condylar displacement in favor of elective mandibular growth and reshaping
  55. 55. ETG LTG
  56. 56. Trenouth (AJO 2000 Jan) evaluated the TB appliance in the treatment of Class II div 1 malocclusion ON 30 patients. It was a retrospective study. Treatment effects: 1. The overjet was reduced during treatment by over 7 mm. The treatment effect was greater than 2ME. ( Method Error) 2. The angle ANB(- 2.6° showed a statistical significant reduction with a treatment effect greater than 2ME, which was mainly due to a statistically significant increase in angle SNB (+ 2°). There was a small but statistically significant reduction in angle SNA, but the treatment effect was less than 2ME.
  57. 57. 3.Linear changes : A.) No significant maxillary change (Ar-A, Co-A) B.) Clinically significant increase in mandibular length (Ar-B, Co-B, Ar-Po, Co-Po). 4. The upper incisor angulation was significantly reduced with the interincisal angle correspondingly increased, both treatment effects greater than 2ME. There was no significant change in the lower incisor angulation. 5. The MM angle remained virtually unchanged during treatment but decreased in the control group and the difference was statistically significant.
  58. 58. Parkin & Sandler (AJO 2001 June) in their retrospective study compared the skeletal and dental changes contributing to Class II correction with 2 modifications of the Twin-block appliance    The aim of this study was to enhance the skeletal effects of the Twin-block appliance in the hope that dentoalveolar effects would make less of a contribution to the correction of the malocclusion TB appliances that use a labial bow (TB1). TB appliances that incorporate high pull HG and torquing spurs on the maxillary central incisors (TB2).
  59. 59.      Dentoalveolar effects Despite the addition of torquing springs (TB2) to the maxillary central incisors, average of 6.9° retroclination was observed. In the mandibular arch of the TB2 group, there was 6.4° of proclination of the mandibular incisors, as compared to 8.2° in the TB1 group. Increased distal movement of the maxillary molars in the TB2 sample. Their vertical eruption appears to have been restricted when compared with the TB1 sampl Skeletal effects The TB2 group demonstrated restraint in the anteroposterior position of the maxilla. The SNA angle was significantly reduced in the TB2 sample, despite slight tipping of the maxillary plane in an anticlockwise direction.
  60. 60.    The ANB value was significantly more reduced in the TB2 sample, suggesting that this appliance was more effective in reducing the sagittal Class II discrepancy. The LFH / TAFH ratio increased in the TB1 sample and remained unchanged in the TB2 sample. This was the most significant difference between the 2 groups The results demonstrated that the addition of headgear to the appliance resulted in effective vertical and sagittal control of the maxillary complex and thus maximized the Class II skeletal correction in the TB2 sample. Use of the torquing springs resulted in less retroclination of the maxillary incisors in the TB2 sample when compared with the TB1 sample; however, this difference did not reach the level of statistical significance
  61. 61. Prospective studies Lund and Sandler  RCT of Twin block  Psychological effects of Twin Block therapy  Effects on Protrusive muscle function  MRI study to evaluate the effects on TMJ 
  62. 62.  Lund and Sandler(AJO1998) . The Lund and Sandler group also experienced slightly more labial proclination of the lower incisors (mean of 8.2°) as compared with the Mills study where there was a mean proclination of 5.2°. This difference may be related to the difference in the appliance design. In Mills study, an acrylic labial bow was used for retention purposes on the lower anterior teeth whereas the Lund and Sandler group had only ball clasps on the labial of the lower incisors
  63. 63.  Chintakanon et al (AJO Oct 2000) investigated Protrusive mandibular function, including maximum protrusive force and fatigue time, was investigated in 66 children displaying Class II Division 1 malocclusion. 32 children were treated with the Clark Twin-block appliance and the other 34 children served as untreated controls. Crosssectional data based on pretreatment records showed that maximum protrusive force ranged from 18.5 N to 160 N, with a mean of 80.3 ± 30.7 N. Maximum protrusive force was significantly higher in males than in females Maximum protrusive force in the group of children with disk displacement was not significantly different from that of the group without disk displacement.
  64. 64.     Maximum protrusive force increased significantly in untreated group because of growth. The measured change in the Twin-block-treated children was not significant. Fatiguing the protrusive muscles did not alter mandibular position in the Twin-block group after 6 months of treatment. This study does not support the lateral pterygoid hypothesis, as there was no evidence of an increase in mandibular protrusive function after treatment with the Twin-block functional appliance
  65. 65.     A prospective study of Twin-block appliance therapy assessed by magnetic resonance imaging Chintakanon, ( AJO 2000 Nov ) 40 children displaying Class II Division 1 malocclusion were involved in a prospective magnetic resonance image investigation to evaluate the effects of Twin-block functional appliances on the temporomandibular joints. None of these children had clinical signs or symptoms of temporomandibular disorders. 19 children were treated with a Clark Twin-block appliance for 6 months; the other 21 children received no treatment and served as controls
  66. 66.    Comparison between control and Clark Twinblock groups suggested that Reduction of the condylar axial angle represents a feature of untreated Class II growth patterns, whereas axial angle stability with Clark Twin-block therapy may suggest alteration of condylar growth direction. Condyles that were positioned at the crest of the articular eminence by the Clark Twin-block at the beginning of treatment had reseated back into the glenoid fossa after 6 months. However, 75% of the condyles were more anteriorly positioned in successfully treated Clark Twin-block cases.
  67. 67.     None of the subjects demonstrated dual bite or Sunday bite as a result of treatment with CTB. There was no clear evidence of remodeling of the glenoid fossa at the eminence as a result of Clark Twin-block treatment. The initial prevalence of asymtomatic disk displacements for the combined groups was 7.5% anterior, 5% medial, and 12.5% for lateral disk displacement. Clark Twin-block therapy had neither positive nor negative effects on disk position, and there was no convincing evidence that the disk was recaptured
  68. 68.     Kevin O’Brien, AJO (2003 sept) In this study a randomized Controlled trial was done that studied the effectiveness of early orthodontic treatment with the Twin-block ap-pliance. Phase I was treatment with a functional appliance, to correct the Class II skeletal discrepancy, when the child is 7 to 10 years old. This was followed by phase II treatment with fixed appliances. Appliance used was A modification of the Clarks Twin-block appliance. A passive maxillary labial bow was used to aid anterior retention and retrocline the maxillary incisors if they were proclined. In narrow maxillary arch compensatory lateral expansion of the arch was achieved with expansion screw.
  69. 69.       Skeletal versus dental change Early intervention with a Twin-block appliance successfully reduced dental overjet, molar discrepancies, and severity of malocclusion. This was achieved by a combination of dental and skeletal change. Skeletal changes : The amounts of overjet and molar change that were attributable to skeletal change were 27% and 41 %, respectively. Skeletal change was statistically significant; it amounted to only 1.9 mm, which might not be considered to be clinically significant or useful. The most important changes resulting from treatment were dentoalveolar.
  70. 70.    Twin-block showed small restraining effect on maxillary growth. This might have occurred because of the labial bow on the Twin-blocks. This design was adopted because all the operators used labial bows on their Twinblocks to increase retention and to control the maxillary incisors. As a result, the labial bow might have retroclined the maxillary incisors, and the position of A point might have been influenced.. Clark suggests that a labial bow should not be used because, by retroclining the maxillary incisors, the amount of potential skeletal change is reduced. In this study, Class II div 1 patients on average had proclined maxil-lary incisors, and, at the end of Twin-block treatment, the incisor angulation was normal and not over-retro-clined.
  71. 71.  Prospective study VS retrospective study  2 retrospective investigations ( Millls & MCulloch , Baccetti & Mcnamara ) that have evaluated the effect of early Twin-block treatment showed the amount of skeletal change that contributed to overjet correction as 50%, and this does not reflect our finding.  Most likely reason for higher skeletal changes is that retrospective investigations, because of the inherent selection bias, tend to overestimate the effects of treatment. In these studies maxillary labial bow was not used, whereas in RCT a passive maxillary labial bow was used to aid anterior retention and retrocline the maxillary incisors if they are proclined.   Based on the findings of the several randomized trials, we can conclude that early treatment with a functional appliance does not, on average, change the Class II skeletal pattern of a child to a clinically significant degree.
  72. 72.  Kevin O ‘Brien in his multicenter randomized controlled trial ( AJO Nov 2003 ) reported higher self-concepts and more positive childhood experiences than did the controls who received no orthodontic intervention. However, both groups, at baseline and at 15 months, had self-concept scores that exceeded population norms  Their findings of enhanced self-concept for treated patients do not support past findings. For example, in the study by Dann et al, (ANGLE 1995 ) the investigators did not seek to reduce the overjets, and labial bows were not placed on the bionator appliances. Dan reduced the overjet by a mean of 2 mm, it could be that the esthetic appearance of the children’s teeth was not changed enough to have an impact on self concept.
  73. 73.   In Kevin O’Brien’s multicenter RCT, if the incisors were proclined, an active labial bow was used which reduced the overjet, leading to a mean reduction in overjet for the treatment group of mm. This, of course, would result in an improvement to the the appearance of the dental malocclusion and could have influenced psychosocial responses in a more dramatic way. . With respect to negative social experiences, authors finding suggest that children who received the Twin-block intervention reported significantly fewer negative social experiences posttreatment. that could positively influence self-esteem including "feeling bet-ter about themselves" and "improvement in appear-ance
  74. 74.     Patient compliance In evaluating the effects of any treatment, patient compliance must be considered, and non cooper-ation rate of 16% was similar to that in other investigations A major problem with most forms of removable functional appliance therapy for treating Class II maloc-clusions is that much patient cooperation is required. However, although the morphological effects of fixed functional appliances have been investigated, only 1 study has evaluated their coopera-tion rates: A multicenter randomized controlled trial (AJO 2003 Aug) that compared the effectiveness of the Herbst and the Twin-block appliances. The authors concluded that both appliances had similar effects on the dentition and skeletal pattern, but the non completion rates were 12% with the Herbst and 33% with the Twin-block. Unfortunately, these authors also found that the trade-off for the greater completion rate with the Herbst was more visits to repair fractured appliance components or debonds.
  75. 75.  After this study, Michael Read decided that a problem with the Herbst appliance was that the link between the mandibular and maxillary dentitions was fixed. This might lead to high levels of stress in the components, resulting in fracture or debonds. They thought that a method of reducing this was to develop a fixed functional appliance in 2 separate parts. As a result, they decided to adapt the Twin-block appliance so that it could be fixed to the teeth.
  76. 76. Michael Read BJO 2001 march Clip on fixed appliance  Appliance design :  In this appliance acrylic blocks were attached to bands on the lower premolar and upper molar teeth. The blocks of acrylic rest on and cover the occlusal surface.  The way in which the appliance is constructed allows the, fixed appliance to be placed at the same time as the Class II relationship is being corrected so there is an overlapping of the phases. This ensures a seamless transition to the fixed phase and, there-fore, significantly reduces treatment rime.
  77. 77. First Visit     Separators are placed mesial and distal to the upper first molars, and mesial and distal to the lower first and second premolars. Second Visit Bands are selected for the upper first molars and the lower premolars. The acrylic blocks are attached to the bands by 3D lingual and buccal tube assemblies .These are welded to the lingual surface of the lower second premolar band and the palatal surface of the upper first molar band. Upper and lower impressions are taken over the bands in alginate impression material The construction bite is taken with the mandible advanced to the desired position
  78. 78.   The bands are removed from the mouth and seated accurately in the impressions. The impressions and construction bite are sent to the laboratory for the fabrication of the appliance. The blocks are constructed on the model in the laboratory. A tube is soldered to the lower wings of this first premolar bracket to accept the buccal retaining wire of the lower block and a lingual arch also is fitted.
  79. 79.   Third visit: The block is inserted into the buccal tube and rotated to seat into the lingual tubes. Bands are cemented in position and the blocks are located and checked for fit. There should be an even contact between the blocks on one side and blocks on both sides should also meet at the same time.
  80. 80.    Fourth Visit This visit should be scheduled for a week or 10 days after the appliance is fitted. The patient should be asked at any discomfort from the teeth or temporomandibular joint and any discomfort. The appliance cannot be removed by the patient, and the small gap between the blocks and the occlusal surface is filled with glass ionomer cement. The blocks are standard Twin-block design with steeply inclined planes interlocked at about 70° to the occlusal plane.
  81. 81.      Timing of the treatment: A major requisite of this appliance is the full eruption of the lower premolars to enable a well fitting bands placement. The most favorable time to treat patients with this appliance is during the peak of the pubertal growth. Advantages of the appliance: Patient co-operation is not required. It works for 24 hours a day. A full fixed appliance can be placed at the same time as the class II correction is being carried out. Treatment time is short because of full time wear
  82. 82.       There is no transitional phase between functional phase and the fixed phase. So the treatment time is reduced because of overlap of functional and fixed phase. It is less bulky than other functional appliances. Disadvantages: Breakage of appliance. Appliance construction needs a skilled technician Oral hygiene problem Repair: The repair is fairly straightforward; this frequently involved replacing loose blocks or bands. If a band had split, it was replaced.
  83. 83.      Clip -on fixed functional appliance Study proving efficiency M. Read & Kevin O'Brien (AJO 2004 April) evaluated the effec-tiveness of a modified version of this appliance in a prospective cohort. Kevin and Read in their study showed that the clip-on fixed functional appliance is an effective and rapid method of treating Class II malocclusion. It was well accepted by patients. However, if these data are compared with those from a randomized controlled trial of the effectiveness of Herbst and Twin-block appliances, it appears that the treatment times obtained with this appliance are slightly less. 
  84. 84.    When we compare the cephalometric measures, it also appears that this appliance produces somewhat similar changes to both the removable Twin-block and the Herbst appliance; these, of course, included normal mandibular growth. The only factor that influenced the final discrepancy was the pretreatment discrepancy. It appears that treatment contributes to reducing the discrepancy but does not totally eliminate it. Finally the results of treatment as recorded by the PAR index show that this treatment is highly effective. Patient Cooperation Most important clinically relevant finding was the treatment completion rate. This was substantially more than authors previous study in which they had non- completion rates of 13% and 33% for the Herbst and the Twin-block appliances, respectively. It therefore appears that this appliance is well tolerated, and its use seems to obtain high levels of cooperation.
  85. 85.    Importantly, the mean number of visits needed to repair the Herbst appliances in Kevin O’Brien’s previous study was 4.3; in this study, the mean number of additional visits was 2.3. Therefore, we can assume that the clip-on fixed functional appliance fractures less than the version of the Herbst appliance that they evaluated. Reasons for this: First, in the Herbst appliance, the pistons connect the maxillary and mandibular appliance, and this might lead to stresses on the appliance components, particularly in lateral excur-sions. Furthermore, orthodontic bands and standard wire components retain the appliance, and this might lead to increased flexibility of the appliance and more resistance to flexural forces. In addition, the acrylic blocks might distribute the vertical forces of occlusion to the occlusal surfaces of the teeth and minimize the possibility of breakage.
  86. 86.    This was a prospective cohort study, without a control. This study design was adopted to evaluate the feasibility of the appliance. This prospective cohort study showed that This modification of the Twin-block appliance is an effec-tive method of treating Class II malocclusion in terms of the morphological effects on the dental and skeletal tissues. The main theoretical advantages of this appliance over the removable Twin-block are that patient cooperation is enhanced and the appliance is active for 24 hours a day, there is no transition phase between the functional and fixed appliance phases, and it is less bulky. A randomly allocated prospective study with long- term evaluation is required to fully evaluate the efficacy of this appliance.
  87. 87. MODIFIED TWIN BLOCK IN TREATMENT OF CLASS II DIV 2 Bite registration The bite registration is taken with the buccal segment relationship in an over corrected position, this may result in an edge-to-edge incisor position or a slight reversed over-jet. However, by ensuring that there is 7-8 mm of separation in the buccal segments, there should be no incisal interference as the upper labial segment is proclined.
  88. 88.  The appliance design Appliances are modifications of the Clark Twin Block. The additional modifications for each are as follows: Addition of one anterior screw with torquing spurs to both upper central incisors
  89. 89.
  90. 90.   Double cantilever spring behind the upper labial segment followed by bonding of the upper labial segment with preadjusted Edgewise fixed appliances. Sectional fixed appliance can be placed from the outset and commence correction of axial inclination early in treatment. So the complete transition into fixed appliances is also enhanced as alignment has already occurred during functional phase.
  91. 91.   Class III Twin Blocks: Kidner & DiBiase evaluated a modified version of Clarks Twin Block (BJO Sept 2003 ) Fourteen subjects under 12 years ( mean age 11 years ) of age with a Class III malocclusion and reverse overjet were included in case series. Indications The indications for treatment with the reverse Twin Block are those cases in the mixed dentition with a reverse overjet associated with a mild sagittal skeletal discrepancy and an average or reduced anterior vertical dimension.
  92. 92.   Bite registration Bite registration was taken in maximum retrusion with about 2 mm inter-incisal clearance. Design A modified version of the Clark Class III Twin Block was constructed from heat-cured acrylic resin with inclined planes at 70 degrees directing occlusal force downwards and backwards.
  93. 93.   A midline palatal screw was incorporated for expansion of the upper arch where this was required. A lower labial bow and Adams clasps or ball-ended clasps on upper and lower first molars and premolars (0.7 mm diameter stainless steel wire) retained the appliance. If premolars were not present then Adams clasps were placed on deciduous molars or C clasps on deciduous canines.
  94. 94.     There were significant changes in the inclination of the incisors with the upper incisors being proclined the lower incisors retroclined. Angle SNB decreased and the anterior vertical dimension and maxillary mandibular planes angle increased. The appliance was effective at correcting reverse overjet during the mixed dentition as an alternative to the Frankel FR III appliance or an upper removable appliance alone. Changes occur rapidly with a mean treatment time of only 6.6 months, which compares favourably with the FR III appliance that was shown to have a mean treatment time of 3.1 years and achieved similar results. Changes were mainly dento-alveolar, due to proclination of the upper incisors and retroclination of the lower incisors. Skeletal change is limited to slight downward and backward rotation of the mandible, with an associated increase in anterior, vertical dimension.
  95. 95.     Herbst VS TB Kevin O'Brien et al (AJO 2003 Aug) reported the results of a randomized clinical trial that evaluated the effectiveness of orthodontic treatment with either a Herbst or a Twin-block functional appliance. One disadvantage of removable functional appliances is that extensive cooperation is needed, and discontinuation rates can vary between 9% and 15% with the Twin-block. One solution to noncompliance is to use fixed functional appliances, such as the Herbst appliance. Appliance used in this study Twin block: Clarks Twin Block was modified. Maxillary labial was incorporated in the design. Herbst appliance: Cast Cobalt Chromium design as described by Panchrez.
  96. 96.     Non Compliance: Twin Block group showed 33.6 %. Herbst Group showed 12.9 % didn’t complete the functional appliance phase of treatment. So non completion rate with TB was 2.4 times more than Herbst appliance. But, Herbst appliance was prone to damage resulting in debonding and fractured components. It could be suggested that the trade-off for the increased compliance rate is that the patient must return to the clinician for several appliance repairs during the functional phase of treatment
  97. 97.       Evaluation of the morphologic effects of the appli-ances shows that most of the changes were dental; the maxillary incisors were retracted and the mandibular incisors were proclined. In addition, the skeletal changes were less than those reported in retrospective investigations. Patient cooperation with the Herbst appliance was better than that with the Twin-block. Phase I treatment was more rapid with the Herbst appliance, but overall duration of treatment was similar to that with the Twin-block. The Herbst appliance is prone to debonding and component breakage. There are no differences in the dental and skeletal effects of treatment between the 2 appliances, but there was a marked sex effect: girls responded to treatment better than boys. There was more residual maloc-clusion for boys than for girls The Herbst appliance has some advantages over the Twin-block, mostly concerning increased compliance. Nevertheless, the trade off for these benefits is the additional cost of appliance construction and the extra visits for appliance repair
  98. 98. Morphological study    Finite element scaling analysis Optical surface scanning for assessment of effect of ( TB ) on soft tissues Animal study Animal study
  99. 99.      Localization of effect of TBA by Finite element scaling analysis- A morhometric study ( AJO 2001 April) GD Singh and Clark Previous studies, on Cephalogram only were unable to localize the effects of TBA on mandibular growth. In this study geometric morphometric techniques was used that have become available for the assessment of allometry (size-related shape change) in patients undergoing orthodontic therapies. Cephalometric studies demonstrate generic mandibular lengthening, but the actual sites of putative mandibular bone growth are not determinable Thirty mandibular landmarks were digitized from cephalographs of 46 children (prepubertal, =10 years old) and 53 adolescents (pubertal=13 years old) to determine mandibular morphological changes in patients with Class II Division 1 malocclusions treated with Twin-block appliances.
  100. 100.     Posttreatment changes prepubertal patients Prepubertal male configuration. Condylar neck shows 12% increase in local size. Apex of coronoid process and antegonal notch show 17% decrease in local size. Ramus and corpus show 10% increase in local size. Symphyseal region shows decrease in local size of 3%.
  101. 101.       B. Prepubertal female configuration. Condylar neck shows 3% increase in local size. Apex of coronoid process 4% increase in local size. Coronoid process and angle of mandible 5% decrease in local size. Ramus show increase in size more anteriorly, Symphyseal region indicates no change in local size. Pubertal male and female configurations are similar except that the pubertal male, show negative allometry in the ramus, gonial angle, or the symphysis.
  102. 102.     Mandibular length (articulare–gnathion) increased overall by 5 mm, from 110.8 mm to 116.2 mm, after treatment. The corpus length (gonion–gnathion) increased by3 mm, from 71.5 mm to 74.6 mm. The ramus height (articulare–gonion) increased by 3 mm, from 45.5 mm to 48.8 mm. Positive allometry was noted in the mandibular corpus, posterosuperior area of the ramus, the midregion of the corpus, and the dentoalveolar process, which are not related to muscle insertions.
  103. 103.  Areas exhibiting isometry and negative allometry may be related to muscle attachment. Specifically, negative allometry at the gonial angle and the antegonial notch relates to the attachments of the masseter muscle, whereas isometry extends over its area of insertion on the ascending ramus. Similarly, areas of negative allometry on the coronoid process relate to the insertion of the tendon of the temporalis muscle. The area of the mental protuberance and the symphysis exhibit a negative allometry that may be associated with the insertion of the mentalis muscle. In the pubertal male, however, no negative allometry is observed in the ramus, gonial angle, or the symphysis.
  104. 104.    Distal aspect of condylar neck consistently showed positive allometry at all stages examined in line with the LPM hypothesis. Localization of growth in the condylar neck with concomitant remodeling of the coronoid process may reflect the correction of mandibular form achieved with TBA. TBA therapy may involve developmental modulations at the condylar cartilage, remodeling of the ramus and corpus, and osteogenic deposition in dentoalveolar regions.
  105. 105. McDonagh, & J. P. Moss, ( EJO April 2001) evaluated the effect of different functional appliances on the soft tissues as assessed by cephalometry and optical surface scanning.  42 patients were randomly allocated to Bass, Twin Block (TB), and Twin Block + Headgear (TB +Hg) groups.  Lateral cephalograms and optical surface scans were recorded before and after the 10-month study period.
  106. 106.     Appliance used: Bass Appliance 2 &3 TB appliance. Clarks TBA was used. The first molars were also clasped in high angle cases to allow attachment of occlusal stops to prevent eruption of the second molars. Flyover tubes were included in the region of the second premolars to facilitate the attachment of highpull headgear. Optical surface technique: precision of this technique is better than 0.5mm
  107. 107.         Bass group : Chin point and sulcus inferioris was positioned forward by 3 – 5mm. The vertical dimension was increased by 5 – 7mm at Menton. TB group Chin point moved forward by 1 – 3mm. LAFH increased by 5 – 7 mm, which was larger than cephalometric value. TB + HG group (without incisal coverage) Retraction of upper lip 1 – 3mm occurred. LAFH increased by 7 – 9 mm. All three groups showed forward positioning of Sulcus Superioris compared with Labrale Superioris suggesting a straightening of the upper lip.
  108. 108.  The optical surface scanning and cephalometric results were consistent in the sagittal dimension. In the vertical dimension, however, the optical surface scans consistently recorded a greater increase compared with cephalometric values. However, the Bass appliance produced greater forward positioning of soft tissue pogonion as assessed by optical surface scanning.
  109. 109.     The Effect of Continuous Bite-Jumping in Adult Rats: A Morphological Study ( Angle 2004 Feb ) Rabie and Hagg The growth of condyle and glenoid fossa of growing rats could be enhanced by bite-jumping appliances. TMJ growth is regulated by factors endogenously expressed by cells in the condyles, as well as in glenoid fossa. Forward mandibular positioning led to a change in the biophysical environment of TMJ that led to the release of key regulatory factors that enhanced condylar growth. Because these factors were endogenously expressed by cells in the condyles and glenoid fossa in response to mechanical strain, a similar effect might occur in adult rats, regardless of their growth status. This was a morphological study, to ensure a continuous forward advancement in adult rats, the incline bite plane was inserted on the upper incisors; a lower crown with an anterior incline plane was also bonded to the lower incisors.
  110. 110. control   Experimental Changes observed were Changes in size and angle, the appearance of the condyle surface were also changed. In the control, the surface of the condyle looked more like a bone. On the contrary, the surface of the condyle on days 30 and 60 of the experimental groups showed translucence, especially in the posterior part, indicating formation of cartilage.
  111. 111.    The apposition of bone was differential and did not occur on the anterior surface of the condylar head but only on the posterior and superior surfaces, the size as well as the shape of the condylar head were affected, which was also supported by the reduction of the angle of the condylar process to the mandibular plane. Results demonstrated that condyles of the experimental group animals were elongated. The longitudinal growth of the condyle was thus due to increased bone apposition in the posterior part of the condyle and superior part of the condylar head. Bite-jumping appliances can improve proliferation of mesenchymal cells in the condylar cartilage in young rats. The same mechanism may also exist in adult species. When more mesenchymal cells transform into chondrocytes, there will be more bone formation in the condyle. Thus, mandibular advancement could also stimulate the adaptive growth of the condyle in adult rats.
  112. 112.   Because there was no increase in the length of the mandibular base, the remodeling of the condyle ultimately resulted in the increase in mandibular length .This finding supports the opinion that the length of mandible is not entirely predetermined by genetic factors. This study demonstrated that adaptive morphological changes could be achieved by 30day continuous mandibular advancement in adult rats. Because of the new bone apposition in the posterior condylar head, the angulation of the condylar process was significantly affected, as well as the length of mandible and condylar process.
  113. 113.   Based on the prospective RCT of TB appliance by Kevin O’Brian et al it may be concluded that functional appliances could result in statistically significant improvements for skeletal Class II patients. These results indicate that early traetment increases a child’s self – concept and reduces negative social experience. Gianelley (AJO 1995) advocates the use of full banding one-stage treatment with maxillary molar distalizing techniques used in the late mixed dentition stage. Hopefully, the severe skeletal Class II patients involved would qualify to be included in that 9% to 10% of patients whom He considers suitable candidates for functional appliance treatment. If not successfully corrected while actively growing, these patients ultimately may require orthognathic surgery to correct their mandibular deficiency or multiple years of fixed edgewise treatment to achieve a "camouflage" correction. In addition, they also have increased risk of incisor fracture due to lip incompetence.
  114. 114. Thank you For more details please visit