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Twin block /certified fixed orthodontic courses by Indian dental academy

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Twin block /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing Dental Education www.indiandentalacade
  2. 2. CONTENTS • Introduction to Twin block • Occlusal inclined plane • Development of twin block • Diagnosis and treatment planning • Construction bite of Functional appliance • Bite registration in Twin Block • Method of Bite Registration • Evolution of Appliance Design • Standard Twin Block • Indications & Contraindications • Advantages • Stages of Treatment • Treatment of class II division 1 malocclusion deep overbite • Studies On Twin Block • Conclusion • Bibliography www.indiandentalacade
  3. 3. INTRODUCTION TO TWIN BLOCKS • The goal in developing the Twin Block approach to treatment was to produce a technique that could maximise the growth response to functional mandibular protrusion by using an appliance system that is simple, comfortable and aesthetically acceptable to the patient. • Twin blocks are constructed to a protrusive bite that effectively modifies the occlusal inclined plane by means of acrylic inclined planes on occlusal bite blocks. • The purpose is to promote protrusive mandibular function for correction of the skeletal Class II malocclusion. www.indiandentalacade
  4. 4. • It is designed for full time wear • they achieve rapid functional correction of malocclusion by modifying the occlusal inclined plane, guiding the mandible forward into correct occlusion • it uses forces of occlusion & mastication to correct the malocclusion. • Upper & lower bite blocks interlock at a 700 angle when engaged in full closure. • Bite blocks are similar in feel to wearing dentures & patients can eat comfortably with the appliance in place. www.indiandentalacade
  5. 5. • Early stages of their evolution, TB were conceived as simple removable appliances with Interlocking occlusal bite blocks designed to posture the mandible forward to achieve functional correction of a class II division I malocclusion. • In the treatment of class II division 2 malocclusion, appliance design is modified by the addition of sagittal screws to advance the upper anterior teeth. • Twin blocks satisfy both the patient & the operator as one of the most “patient friendly” of all the functional appliances. www.indiandentalacade
  6. 6. OCCLUSAL INCLINED PLANE • It 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. • If mandible occludes in distal relationship to maxilla, the occlusal forces acting on mandibular teeth during function will have a distal component of force i.e. unfavourable to normal forward development of mandible. • It act as a guiding mechanism displacing the mandible downward & forward. • With the appliance in the mouth patient cannot occlude in the former relation. So it aims at intervening treatment at earlier stage of development www.indiandentalacade
  7. 7. DEVELOPMENT OF TWIN BLOCK • It is true that “necessity is the mother of invention”. • Twin block appliance was developed in 1977 as a two piece appliance resembling a Schwarz- double plate & split activator. • Twin Blocks was evolved in response to a clinical problem when a dental colleague son , fell down, & the upper right central incisor was avulsed. Within few hours of the trauma the tooth was reimplanted and a temporary splint was constructed to hold the tooth in position. • The occlusal relationship was class II division 1 with an overjet of 9 mm and the lower lip was trapped lingual to the upper incisors. • To prevent the lip from trapping in the overjet it was necessary to design an appliance that could be worn full time to posture the mandible forward. www.indiandentalacade
  8. 8. • After 6 mons. with stabilising splint, the tooth had partiaaly reattached but there was evidence of severe root resorption. • At that time, simple bite blocks were designed. • The appliance mechanism was designed to harness the forces of occlusion to correct the distal occlusion and also to reduce the over jet without applying direct pressure to the upper incisors. • The upper and lower bite blocks engaged mesial to the first permanent molars at 900 to the occlusal plane when the mandible postured forward. • This positioned the incisors edge-to-edge with 2 mm vertical separation to hold the incisors out of occlusion. www.indiandentalacade
  9. 9. • The patient had to make positive effort to posture his mandible forward to occlude the bile blocks in a protrusive bite. • The first Twin Block appliances were fitted on 7 September 1977, when the patient was aged 8 years 4 months. • T he bite blocks proved comfortable to wear and treatment progressed well as the distal occlusion corrected and the overjet reduced from 9 mm to 4mm in 9 months. www.indiandentalacade
  10. 10. Angulation of the Inclined Plane: • During evolution of the technique, the angulation of the inclined plane varied from 90 to 450 to the occlusal plane, before arriving at an angle of 70°. • 900 angle: patient had to make a conscious effort to occlude in a forward position. Difficult to maintain a forward posture and, therefore, would revert to retruding the mandible back to its old distal occlusion position • Occluding the bite blocks together on top of each other on their flat occlusal surfaces- posterior open bite • This was experienced in approximately 30% of the earliest Twin Block cases. • It was resolved by altering the angulation of the bite blocks to 45° to the occlusal plane in order to guide the mandible forwards www.indiandentalacade
  11. 11. • An angle of 450 to the occlusal plane :applies an equal downward and forward component of force to the lower dentition. • Encourages a corresponding downward & forward stimulus to growth. • After using a 450 angle on the blocks for 8 yrs., the angulation was finally changed to the steeper angle of 700 to the occlusal plane to apply a more horizontal component of force. • It was reasoned that this may encourage more forward mandibular growth. www.indiandentalacade
  12. 12. DIAGNOSIS & TREATMENT PLANNING • Clinical examination is a fundamental guideline for a proper case selection. Clinical diagnosis has the advantage of providing an accurate prediction of 3- dimensional change in facial contour. • If the facial profile improves when the mandible is advanced with the lips tightly closed, then functional mandibular advancement is the treatment of choice. • The change in facial appearance is a preview of the anticipated result of functional treatment www.indiandentalacade
  13. 13. • Photographs: • Profile and frontal photographs with the mandible in retrusive and advanced position, are used to assess the changes that can occur during treatment. • Study models: • Occlusal changes can be checked by sliding the lower model forward and observing the articulation of the mandibular dental arch with that of the upper model. • Radiographs: • OPG is vital to study the dentition and condition of alveolar bone and periodontium. • TMJ X-rays may also be required to assess the joint condition before treatment. • Hand wrist film may be taken to assess the developmental status of the patient. • Lateral cephalograms to support and confirm the clinical diagnosis. www.indiandentalacade
  14. 14. • ARCH LENGTH DISCREPANCY: defines the amount of crowding present in the dental arch by compairing the space available with the space required to accommodate all the teeth in the arch in correct alignment. • Richter scale : helpful in treatment planning to classify the degree of difficulty of the malocclusion as mild, moderate or severe. In arch length discrepancy: Mild crowding 1-3mm Moderate Crowding 4-5mm Severe crowding 6mm or more • This is a sliding scale expressing degree of difficulty for dental correction by non extraction therapy. • The higher the value, the more difficult it is to resolve crowding permanently without extractions. • The Richter scale can also be applied when the measure of convexity is used to determine the skeletal discrepancy  A skeletal convexity of 1-3mm is within the range of normal  4-5mm convexity is moderate class II skeletal discrepancy  6mm or more in severe class II  The higher the convexity the more likely that functional orthopaedics is indicated to improve the skeletal relationship www.indiandentalacade
  15. 15. CONSTRUCTION BITE OF FUNCTIONAL APPLIANCE • Determines the degree of activation built into the appliance, aiming to reposition the mandible to improve jaw relationship. • The degree of activation should stretch the muscles of mastication sufficiently to provide a positive proprioceptive response. • At the same time, activation must be within the physiologic range of activity of the muscles of mastication and the ligamentous attachments of the temporomandibular joint. www.indiandentalacade
  16. 16. • According to Woodside (1977) in construction of the activator as described by Andresen (1910): • “A bite registration used commonly throughout the world registers the mandible in a position protruded approximately 3.0mm distal to the most posterior position that the patient can achieve, while vertically the bite is registered within the limits of the patient’s freeway space” • In North America, a similar protrusive bite registration is made, except that the vertical activation is 4mm beyond rest position. • Roccabado quantifies normal physiological TMJ movement as 70% of total joint displacement. • Hence, the maximal forward positioning of the mandible should not exceed 70% of the total protrusive path of the patient. • Beyond this position, the medial capsular ligament begins to displace the disc by pulling the disc medially & distally off the condyle. www.indiandentalacade
  17. 17. BITE REGISTRATION IN TWIN BLOCK TECHNIQUE • overjet of up to 10 mm : single activation to an edge-to-edge incisor relationship with 2mm interincisal clearance • If the overjet > 10mm, initial advancement of 7 -8mm is done followed by reactivation later. • Some patients had difficulty in maintaining the forward posture and occluding correctly on the inclined planes. • These patients usually had a vertical growth pattern with weak musculature and were unable to maintain the forward mandibular posture consistently. • To overcome this problem the activation of the appliance was reduced slightly by trimming the inclined planes until the patient occluded comfortably and consistently in the forward position. www.indiandentalacade
  18. 18. • There are two types of bite gauges used to register bite for twin block: • George bite gauge • Exactobite gauge/ Project bite gauge (name differs in the USA & UK) www.indiandentalacade
  19. 19. • GEORGE BITE GAUGE: Has a sliding jig attached to a millimeter scale designed to measure the protrusion path of the mandible • To determine accurately the amount of activation registered in the construction bite. www.indiandentalacade
  20. 20. • Total protrusive movement is calculated by first measuring the overjet in centric occlusion & then in the position of maximum protrusion. • The protrusive path of the mandible is the difference between the two measurements. • Functional activation within normal physiological limits should not exceed 70% of the protrusive path. www.indiandentalacade
  21. 21. • EXACTOBITE OR PROJECT BITE GAUGE: • Incisal portion has three incisal grooves to be positioned on the incisal edge of the upper incisor. • A single groove on the opposing side that engages the incisal edge of the lower incisor. The appropriate groove is selected • Designed to record a protrusion bite www.indiandentalacade
  22. 22. • Registers 2 mm vertical clearance between the incisal edges of the upper and the lower incisors. • 5 or 6 mm of clearance in the first premolar region and 3 mm of clearance distally in the molar region • Ensures that space is available for vertical development of posterior teeth to reduce the overbite. www.indiandentalacade
  23. 23. • Vertical Activation: determined by 2 factors. • Firstly, adequate vertical clearance must be available between upper and lower teeth to accommodate blocks of sufficient thickness to activate the appliance. • Secondly, the vertical activation must open the bite beyond the freeway space to ensure that the patient cannot posture out of the appliance when the mandible is in rest position. • Class II division 1 deep bite : blocks are not less than 5mm thick in the first premolar or first deciduous molar region with 2mm of interincisal clearance. • In CIass II division 2 malocclusion: edge to edge bite without 2mm interincisal clearance • Anterior openbite: bite is registered with greater interincisal clearance. www.indiandentalacade
  24. 24. • At bite registration a judgement should be made according to the amount of vertical space between the cusp tips of first premolar or deciduous molars to achieve the correct degree of bite opening to accommodate blocks of at least 5mm thickness. www.indiandentalacade
  25. 25. • Single or Progressive activation: Petrovic et al (1981) found that stepwise activation is the best procedure to promote orthopaedic lengthening of the mandible on the basis of this Falke & Frankel (1989) reduced initial activation for mandibular advancement to 3mm. • Concept of progressive activation for functional correction to achieve the optimum growth response : investigated ( De Vincenzo & Winn 1989; Falke & Frankel, 1989) with differing result & require further investigation • Later on occlusal bite blocks was used to investigate the relative effects of progressive activation compared to a single large activation • Concluded that there is no difference in either orthodontic or orthopaedic variables between progressive 3 mm advancement and a single advancement averaging 5- 6mm. • Continous advancement by progressive 1mm activations shows a diminished but still significant response www.indiandentalacade
  26. 26. • .Progressive activation is found to be time consuming with no measurable improvement in the response. • large activation is more efficient than smaller progressive activations. • Carmichael, Banks & Chadwick : described a screw advancement mechanism for progressive activation of twin blocks. • Stepwise advancement may be beneficial in correction of large overjets, or in the treatment of vertical growth patterns, where smaller adjustments may improve patient tolerance www.indiandentalacade
  27. 27. METHOD OF BITE REGISTRATION: • The centric position is checked and the desired degree of activation decided. • The patient is then trained to bite in the desired position by giving him a mirror. • The wax is softened in a water bath and adapted. • The patient is instructed to bite into the desired position. • After the wax has hardened sufficiently, it is removed and chilled. • The models with the bite are articulated and the twin block is constructed. www.indiandentalacade
  28. 28. CONTROL OF THE VERTICAL DIMENSION • The mechanism of control of the vertical dimension differs in fixed and functional therapy. • fixed mechanics: the teeth remain in occlusion during the course of treatment, and the effect is limited to intrusion or extrusion of individual teeth to increase or decrease overbite and level the occlusal plane. • Functional appliances are designed to influence development in the anteroposterior and vertical dimensions simultaneously, control of the vertical dimension is achieved by covering the teeth in the opposing arches & controlling the intermaxillary space. • The management of the appliance differs according to whether the bite is to be opened or closed during treatment. www.indiandentalacade
  29. 29. • Opening the bite: • It is necessary first to check that the profile is improved when the patient postures the mandible downwards and forwards, • This confirms that the bite should be opened by encouraging the eruption of the posterior teeth to increase the vertical dimension of occlusion. • Achieved by placing an occlusal table between the teeth to encourage increased development of posterior facial height by growth of the vertical ramus. • At the same time the occlusion is freed between the posterior teeth to encourage selective eruption of posterior tooth to increase the vertical dimension of occlusion in the posterior quadrants. www.indiandentalacade
  30. 30. • Closing the bite: • Reduced overbite or anterior open bite is often related to a vertical facial growth pattern. • The lower facial height is already increased and the vertical dimension must not be encouraged to increase during treatment. • An acrylic occlusal table is designed into the appliance to maintain contact on the posterior teeth throughout treatment. • This results in a relative intrusion of the posterior teeth while the anterior teeth are free to erupt, thereby reducing the anterior open bite www.indiandentalacade
  31. 31. • In treatment of reduced overbite it is very important that the opposing acrylic occlusal bite block surfaces are not trimmed. • All posterior teeth must remain in contact with the blocks through out treatment to prevent eruption of posterior teeth • By separating the posterior teeth it is possible to adjust the dimensions of the intermaxillary space anteroposteriorly & vertically to correct skeletal discrepancies. • The mechanics can be reversed, applying the same principles for correction of class III malocclusion. www.indiandentalacade
  32. 32. Establishing vertical dimension: The Intergingival Height • Intergingival height-used to establish correct vertical dimension. • Measured from the gingival margin of upper incisor to the gingival margin of lower incisor when the teeth are in occlusion • Help as a restorative approach to rebuild the occlusion in treatment of patients with TMJ dysfunction • Comfort zone-17-19 mm for adult patients & 15-17mm for young patients-equivalent to the combined heights of the upper & lower incisors minus overbite • Measured by using a millimeter ruler or dividers with a vernier scale • This is used as a guide to establish the correct vertical dimension during treatment www.indiandentalacade
  33. 33. • EVOLUTION OF APPLIANCE. It is important to design appliances that are “patient friendly” to remove any obstacles to compliance & to motivate the patient to cooperate in treatment. • The earliest twin blocks were designed 1. Occlusal bite blocks 2. Midline screws to expand the upper arch. 3. Clasps on upper molar and premolar. 4. Clasps on lower premolars 5. Inter dental clasps on lower incisors. 6. Springs to move individual teeth and improve the arch form as required www.indiandentalacade
  34. 34. STANDARD TWIN BLOCK • Labial bow: • In its earlier stages all twin blocks incorporated a labial bow to retract the upper anteriors. • Labial bow engaged the upper incisor, it tended to overcorrect incisor angulations-- retracting upper incisors prematurely and limiting the scope of functional correction with mandibular advancement. www.indiandentalacade
  35. 35. • This led to the conclusion that a labial bow is not always required unless it is necessary to upright severely proclined incisors and even then it must not be activated until full functional correction is complete and a class I buccal segment relationship is achieved. • In twin block treatment, a good lip seal is achieved naturally without additional lip exercises. The lips act like a labial bow and lip pressure is effective in uprighting upper incisors making a labial bow superfluous. www.indiandentalacade
  36. 36. • Clasps: • Though the early design of twin blocks incorporated Adam's clasps (modified arrowhead clasps, 1970 ), Clark introduced the Delta Claps in 1985 to enhance appliance fixation. • It is similar in principle to the modified arrowhead clasp but includes new features to improve retention, minimize adjustment and reduce metal fatigue, thereby reducing breakage. • Adam's clasp : designed to fit individual teeth and incorporates interdental tags and mesial and distal retentive loops that are directed lingually into undercuts and joined by a buccal bridge. • The slope and position of the crown heads allows the clasp to open slightly with repeated insertion and removal, thus it requires routine adjustment at every visit to maintain retention. This increases the risk of metal fatigue and breakage. www.indiandentalacade
  37. 37. Delta clasp (constructed-:0.70-0.75 SS wire) • The Delta clasp retains the basic shape of the Adams clasps with its interdental tags, retentive loops, and buccal bridge. • However, the difference is in the retentive loops which are shaped as a closed triangle (from which the name delta clasp is derived) instead of the open V shaped loop of the Adams clasp. • Modifications has produced circular loops which are easier to construct www.indiandentalacade
  38. 38. • Permanent dentition: placed on upper first molars & on lower first premolars, may also be used on deciduous molars. • Clark has evaluated that the breakage rate of Delta clasp (1 %) was significantly less than that of Adam's Clasp (10%) www.indiandentalacade
  39. 39. • Ball ended clasps: Ball shaped interdental clasps may be placed for increased retention. • Routinely employed mesial to lower canines & in upper premolar or deciduous molar region to gain interdental retention from adjacent teeth. www.indiandentalacade
  40. 40. • The Delta clasp can be adjusted in 2 ways • ->By placing pliers on the wire as it emerges from the acrylic. A slight adjustment extends the retentive loop of the clasp into the gingival or interdental undercut. • ->By grasping the arrowhead from the buccal aspect and twisting the retentive loop inwards towards the tooth to adjust into the mesial and distal undercut. www.indiandentalacade
  41. 41. • Base Plate • The base plate and occlusal bite blocks: made from heat cure or cold cure acrylic. • Advantage of heat cure acrylic is additional strength and precision (as blocks are first made in wax) • Cold cure acrylic: advantage of speed and convenience but strength is less. • Preformed bite blocks made of good quality heat cure acrylic are being manufactured for incorporation into cold cure appliances to combine convenience with strength and accuracy. www.indiandentalacade
  42. 42. • POSITION OF THE INCLINED PLANE: • Determined by the lower block. • It is important that the inclined plane is clear of mesial surface contact with the lower molar, which must be free to erupt unobstructed in order to reduce the overbite. • The inclined plane on the lower bite block is angled from the mesial surface of the second premolar or deciduous molar at 700 to the occlusal plane. • Lower block should extend distally to the buccal cusp of the lower second premolar or deciduous molar, stopping short of the distal marginal ridge , this allows the leading edge of the inclined plane on the upper appliance to be positioned mesial to the lower first molar so as not to obstruct eruption. www.indiandentalacade
  43. 43. • Buccolingually: lower block covers the occlusal surfaces of the lower premolars or deciduous molars to occlude with the inclined plane on the upper twin block. • Flat occlusal bite block passes forwards over the first premolar to become thinner buccolingually in the lower canine region. • The upper inclined plane is angled from the distal surface of the upper second premolar to the mesial surface of the lower first molar. www.indiandentalacade
  44. 44. • The flat occlusal portion then passes distally over the remaining upper posterior teeth , reducing in thickness as it extends distally. • Only the lingual cusps of the upper posterior teeth should be cover rather than full occlusal surface as it makes the clasps more flexible & allows adjustment of the clasps. www.indiandentalacade
  45. 45. INDICATIONS & CONTRAINDICATIONS • Indications : • Indicated for treatment of uncrowded permanent dentition with Class II division 1 malocclusion. • It is designed to correct Class II skeletal relationship, to correct molar relationship & to correct overjet. • Patient should be in growing age for favourable skeletal change achievement. o Treatment of Class II division 1 in mixed dentition period o Treatment of Class II division 1 with anterior open bite o Treatment of Class II division 1 with deep overbite o Treatment of Class II division 2 malocclusion o Treatment of Class III malocclusion www.indiandentalacade
  46. 46. • Contraindication: • Cases with vertical growth pattern • Crowding that may require extraction • When VTO is not positive www.indiandentalacade
  47. 47. By: STUTI MOHAN (contd . . .. . . . ) www.indiandentalacade
  48. 48. ADVANTAGES • Comfort • Aesthetics • Function • Patient compliance • Facial appearance • Speech • Clinical management • Arch development • Vertical control • Facial asymmetry • Safety • Efficiency • Treatment of temporomandibular joint dysfunction www.indiandentalacade
  49. 49. TWIN BLOCK TECHNIQUE-STAGES OF TREATMENT • Twin block Functional therapy is divided into three stages: 1.Active Phase 2.Support Phase 3.Retention Phase www.indiandentalacade
  50. 50. • ACTIVE PHASE: • correction of anteroposterior relationship & establishment of the correct vertical dimension. • Achieve rapid functional correction of mandibular position from a skeletally retruded class II to class I occlusion using occlusal inclined planes over the posterior teeth to guide the mandible into correct relationship with the maxilla. • In all functional therapy sagittal correction is achieved before vertical development of the posterior teeth is complete. • The vertical dimension is controlled by adjustment of the occlusal bite blocks. • At the end of active phase the aim is to achieve correction to Class I occlusion & control of vertical dimension by a three- point occlusal contact with the incisors & molars in occlusion. www.indiandentalacade
  51. 51. • Appliance fitting: it is first necessary to check that the patient bites comfortably in a protrusive bite with the inclined planes occluding correctly. To avoid irritation, it is important to relieve the lower appliance slightly over the gingivae lingual to the lower incisors. • Initial adjustment after 10 days: • The patient should now be wearing the appliances comfortably & eating with them in position. The initial discomfort of a new appliance should be resolved. • The patient should now be turning the upper midline screw one quarter turn per week • Deep overbite: the upper bite block should be trimmed clear of the lower molars leaving a clearance of 1-2mm to allow these to erupt. www.indiandentalacade
  52. 52. • If patient is failing to posture forwards consistently to occlude correctly on the inclined planes then this shows that appliance is activated beyond the patient’s tolerance level so the angulation of the inclined plane reduced to 450 • Adjustment visit – after 4 weeks: • The first monthly visit positive progress should already be evident with respect to better facial balance. • Progress can also be confirmed by noting the amount of reduction in overjet, as measured intraorally with the mandible fully retracted , this also helps in monitoring the progress. • Check that the screw is operating correctly, & adjust the clasp if necessary to improve retention , if the appliance include labial bow , adjust it so as to out of contact with the upper incisors. • In the treatment of deep overbite ensure that the lower molars are not in contact with the upper block. The upper block is trimmed occlusodistally to clear the occlusion. www.indiandentalacade
  53. 53. • Routine adjustment- time interval 6 weeks • A similar pattern of adjustment continues with steady correction of distal occlusion & reduction of overjet. • The upper arch width is checked at each visit, until the sufficient expansion to accommodate the lower arch in its corrected position . • Trimming of the upper block continues until all the occlusal cover is removed from the upper molars to allow the lower molars to erupt completely into occlusion • The overjet, overbite & distal occlusion should be fully corrected by the end of the twin block phase. www.indiandentalacade
  54. 54. • SUPPORT PHASE: • maintain the corrected incisor relationship until the buccal segment occlusion is fully interdigitated for this an upper removable appliance with an anterior inclined plane • Vertical control is essential during the support phase after reduction of overbite. • For this :a flat occlusal stop of acrylic extends forwards from the inclined plane to engage the lower incisors. • This maintains the intergingival height as the posterior teeth erupt into occlusion. • The upper & lower buccal teeth should normally settle into occlusion within 2-6 months, depending on the depth of the overbite www.indiandentalacade
  55. 55. • RETENTION PHASE: • Treatment is followed by retention with the upper anterior inclined plane appliance. • Appliance wear is reduced to night time only when the occlusion is fully established. • A good buccal segment occlusion is important for stability after correction of arch –to- arch relationship. www.indiandentalacade
  56. 56. TIME TABLE OF TREATMENT-AVERAGE TREATMENT TIME • Active phase: average time 6-9 months to achieve full reduction of overjet to a normal incisor relationship & to correct the distal occlusion. • Support phase: 3-6 months for molars to erupt into occlusion and for premolars to erupt after trimming the blocks. • Retention phase: 9 months, reducing appliance wear when the position is stabilised. • An average estimate of treatment time is 18 months, including retention. www.indiandentalacade
  57. 57. MANAGEMENT OF DEEP OVERBITE: • The upper bite block is trimmed occluso distally to allow the lower molar to erupt and reduce the deep bite with increase in lower facial height. • occlusion is cleared over the lower molars progressively at each visit by 1 to 2 mm only, to facilitate eruption. • At each subsequent visit for appliance adjustment the occlusion is cleared by sequentially trimming the upper block occluso distally to allow further eruption of lower molars. • The lower molars will erupt into occlusion normally within 6-9 months www.indiandentalacade
  58. 58. • End of the active phase: incisors and molars are in correct occlusion and deep bite corrected. • However the presence of bite blocks leads to openbite in the premolar region. The lower block is then trimmed slightly to allow the premolars to erupt with the appliance. • 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. www.indiandentalacade
  59. 59. • FUNCTIONAL REGULATION OF CONDYLAR CARTILAGE GROWTH RATE • A fundamental study of the relationship between form & function WAS carried out in animal experiments at the University of Michigan, and the results were summarised by McNamara (1980). • The studies evaluated changes in muscle function and related changes in bone growth in the rhesus monkey by a comparison of experimental and control animals as monitored by EMG, cephalometric & histological studies • Concluded: the findings were based on the use of fixed occlusal inclined planes that were designed to cause a forward postural displacement of the mandible in all active and passive muscle activity. • The pattern of muscle behaviour during the experimental period showed a cyclical change in response to functional mandibular propulsion www.indiandentalacade
  60. 60. • Initial placement of the appliance produced an increase in the overall activity of the muscles of mastication as the animal sought to find a new occlusal position. • A distinct change in muscle activity occurred within 1 - 7 days, characterised by a decrease in the activity of the posetior head of temporalis, an increase in activity OF MASSETER MUSCLE and increase in function of the superior head of the lateral pterygoid muscle • After 3 weeks , muscle activity was reached at a higher level of activity than the pre treatment record • This level of activity persisted for 4 weeks before a further decline in muscle activity over a period of 4 weeks to the level recorded before treatment. www.indiandentalacade
  61. 61. • The cycle of changes was completed in a 3 month period • These changes are consistent with an equilibrium of muscle activity before treatment which is disturbed by placement of the appliance. • T he level of muscle activity increases accordingly until, after a period of adjustment, a new equilibrium is reached at a higher level activity. • Further adaptations within the muscles over a period of time results in a reduction of muscle activity when a new equillibrium is again established at the same level that existed before tratment. www.indiandentalacade
  62. 62. • Muscle Respose to Twin Block appliance – An EMG study • India- Aggarwal et al -1999:Research on a group of patients Treated with Twin blocks • • Provides important information on the adaptive changes during treatment. • Bi lateral EMG activity of elevator muscles Of the mandible (i.e. anterior temporalis and masseter) was monitored longitudinally to determine changes in postural, swallowing and maximum voluntary clenching activity during an observation period of 6 months . • The muscle activity was measured at the start of treatment, within 1 month 0f Twin block insertion, at the end of 1 months and at the end of 6 months. www.indiandentalacade
  63. 63. • Results: significant increase in postural and maximum clenching EMG activity in masseter and in anterior Temporalis activity during the 6 month period of treatment • The increased activity can be attributed to an enhanced stretch (myotatic) reflex of the elevator muscles, contributing to isometric contractions. • The main corrective force for Twin Block treatment appears to be provided through increased active tension in the stretched muscles www.indiandentalacade
  64. 64. • The increased EMG activity during posture and maximum voluntary clenching supports active reflex contractions to play a dominant role in the neuromuscular changes with Twin Block treatment. • The results of this study reaffirm the importance of full-time wear for functional appliances to exert their maximum therapeutic effect by way of neuromuscular adaptation. • This study supports that repeated contact between the inclined planes during posture & clenching leads to uninterrupted stretch on the muscles spindle & repeated stimulation of stretch receptors www.indiandentalacade
  65. 65. • THE APPLIANCE : • A modification of the Twin Block appliance described by Clark was used. • Adams clasps:maxillary and mandibular first premolars • First molars and ball clasps to the lower labial segment to maximize retention. • A labial bow was also used that was soldered to the Adams clasp on the maxillary premolars. • The jaw registration was taken with approximately 7 to 8 mm protrusion and the blocks 6 to 7 mm apart in the buccal segments. • The steep inclined planes interlocked at about 70° to the occlusal plane. • Compensatory lateral expansion of the upper arch was achieved by means of an upper midline expansion screw that was turned once a week. • Reactivation of the blocks was carried out when necessary after 4 or 5 months therapy. www.indiandentalacade
  66. 66. The twin block functional appliance used. (a) anterior, (b) lateral, (c) upper occlusal, and (d) lower occlusal views. www.indiandentalacade
  67. 67. • After completion of functional appliance treatment , changes were evaluated by means of cephalometric analysis. • Result :Skeletal changes as a result of Twin Block therapy: • 1. A mean forward growth/repositioning of the mandible of 2.4 mm, measured at Ar-Pog, with some forward movement of Pogonion demonstrated after Twin Block therapy. But it was not possible to determine whether the increase in Ar-Pog was due to an increase in mandibular length or a repositioning of the mandible • 2. The most noticeable skeletal change was an increase in the angle SNB. • 3. There was an increase in lower anterior facial height. www.indiandentalacade
  68. 68. • Dental changes as a result of Twin Block therapy • 1. The mean overjet reduction of 7.5 mm involved a net 10.8° retroclination of the upper incisors and 7.9° proclination of the lower incisors. • 2. Buccal segment correction occurred by distal movement of the upper molars and lower molar eruption in an anterior and superior direction. • Conclusion :This study demonstrates that the Twin Block appliance is a very effective and efficient tool with which overjets can be reduced www.indiandentalacade
  69. 69. CONCLUSION • In the pursuit of ideals in Orthodontics, facial balance and harmony are of equal importance to ideal and occlusal perfection. The role of functional jaw orthopedic techniques is widely acknowledge in achieving these goals by growth guidance during the formative years of facial and dental development. • Twin blocks are extremely patient and operator friendly functional appliances. They have the gift of versatility of design, which allows their use in a variety of clinical situations to effectively correct different types of malocclusions. www.indiandentalacade
  70. 70. BIBLIOGRAPHY • William J Clark: Twin block functional therapy, applications in dentofacial Orthopaedic Mosby Company 2nd edition. • T.M. Graber ; Thomas Rakosi ;Alexander .G. Petrovic ;Dentofacial orthopedic with functional appliance;2nd edition, mosby, 1997; pgs. 268- 298 • William . J. Clark. Twin block technique. AmJ Orthod 1988 January;1-18 www.indiandentalacade