Twin block
- 2. CONTENTS Introduction History Philosophy behind twin block therapy Angulation of inclined planes Diagnosis and treatment planning Indications and contraindications Bite registration Appliance design and construction Stages of treatment 2
- 3. Treatment of class II div I malocclusion deep overbite Treatment in mixed dentition Combination therapy Twin block traction technique Treatment of anterior open bite and vertical growth patterns Treatment of class II division 2 malocclusion Treatment of class III malocclusion 3
- 4. Treatment of facial asymmetry Magnetic twin blocks Adult treatment TMJ pain and dysfunction syndrome Flat earth concept of facial growth Growth response to twin block treatment 4
- 5. INTRODUCTION comprises of separate upper and lower units which are not joined together. simple bite blocks designed to be worn 24 hours a day achieve rapid functional correction of malocclusions by transmitting favourable occlusal forces to occlusal inclined planes that cover all posterior teeth. 5
- 6. HISTORY William J Clark was a Scottish orthodontist Introduced twin block in the year 1977 First twin block was given to a patient when aged 8 years 4 months Overjet reduced from 9mm to 4mm in 9 months 6
- 7. PHILOSOPHY BEHIND TWIN BLOCK THERAPY Considerable forces are applied through the muscles of mastication to the teeth and the underlying bony structures to influence both the internal and external structure of the basal bone. 7
- 8. It is this natural mechanism of bone remodelling by occlusal force vectors that forms the basis of functional correction by the Twin Block technique Schwarz A.M (1932) tissue changes incidential to orthodontics,Australian .J.orthod 8
- 9. ANGULATION OF INCLINED PLANES Earliest twin blocks were constructed with inclined planes articulated at 90 degrees Later altered to 45 degrees Finally changed to 70 degrees which is widely used now 9
- 10. DIAGNOSIS AND TREATMENT PLANNING Clinical Guidelines Photographs Study models Radiographs 10
- 11. DIFFERENTIAL DIAGNOSIS extraction or non extraction therapy Angle believed in accommodating all 32 teeth Tweed (1966) gained acceptance for premolar extraction therapy Begg(1965)was a strong advocate of routine extraction of premolars,and indeed in some cases advised the extraction of all first molars in addition to first premolars Begg PR (1965) Begg orthodontic therapy and technique. WB Saunders company, philadelphia 11
- 12. Ricketts et al(1979) supported non extraction line of treatment Ricketts recommends positioning the tip of lower incisor at +1 to +3mm relative to the A-Pog line for the best aesthetic result. Ricketts, R M. et al (1979) bio progressive therapy..Am J orthod 12
- 13. Arch length discrepancy Richter scale is helpful in treatment planning to classify the degree of difficulty of malocclusion as mild moderate or severe in arch length discrepancy. Mild crowding is in range 1-3mm Moderate crowding is classified as 4-5mm Severe crowding is 6mm or more 13
- 14. INDICATIONS Treatment of uncrowded permanent dentition with class II div 1 Designed to correct class II skeletal relationship, to correct molar relationship & to correct overjet Patient should be in growing age for favourable skeletal change Treatment of class II div 1 in mixed dentition period Treatment of class II div 1 with anterior open bite Treatment of class II div 1 with deep overbite Treatment of class II div 2 malocclusion Treatment of class III malocclusion 14
- 15. CONTRAINDICATIONS Factors that are unfavourable for correction by twin blocks include cases with vertical growth and crowding that may require extractions Examination of profile : If profile doesn’t improve when mandible is advanced that is a clear contraindication for functional mandibular advancement 15
- 16. BITE REGISTRATION Upto 10 mm overjet : edge to edge incisor relationship Overjet greater than 10mm: initial advancement of 7mm or 8mm followed by reactivation of the appliance after occlusion had corrected to initial bite registration 16
- 17. George bite gauge It has a millimetre gauge to measure protrusive path of mandible Total protrusive movement is calculated by first measuring the overjet in centric occlusion and then in position of maximum protrusion Bite forks comes in two sizes :2mm & 5mm 17
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- 19. Vertical activation An important principle is that the blocks should be thick enough to open the bite slightly beyond freeway space On average bite blocks are not less than 5mm thick in the first premolar or first deciduous molar region In treatment of anterior open bite it is necessary to register bite with a greater interincisal clearance 19
- 20. SINGLE or PROGRESSIVE ACTIVATION 20 Petrovic et al (1981): stepwise activation is better procedure to promote orthopaedic lengthening of mandible Falke & Frankel (1989): reduced initial activation to 3mm De Vincenzo &winn (1989):differing results and reuire further investigations
- 21. Later on occlusal bite blocks where used to investigate the relative effects of progressive activation compared to a single large activation Concluded that there is no difference in either orthodontic orthopaedic variables between progressive 3mm advancement and a single advancement averaging 5-6mm Continuous advancement by 1mm activations show a diminished but still significant response Petrovic et al (1981)the final length of mandible? Is it genetically determined:craniofacial biology,university of michigan 21
- 22. Control of vertical dimension Mechanism of control of vertical dimension differs in fixed and functional therapy Fixed mechanics: teeth remain in occlusion during course of treatment and the effect is limited to intrusion or extrusion of individual teeth to increase or decrease overbite and level of occlusal plane Functional appliances: influence development in antero posterior and vertical dimensions simultaneously, control of vertical dimension is achieved by covering teeth in opposing arches & controlling the intermaxillary space 22
- 23. Opening the bite In deep overbite cases check if profile improves when mandible is postured downwards and forwards This confirms that bite should be opened by encouraging eruption of posterior teeth to increase vertical dimension of occlusion 23
- 24. Occlusal tables or blocks placed between teeth encourage ramus to grow vertically thus increase posterior facial height. At the same time occlusion is freed between posterior teeth to encourage selective eruption of posterior teeth to increase vertical dimension of occlusion in posterior region 24
- 25. Closing the bite Reduced overbite or anterior open bite is often related to vertical facial growth pattern An acrylic block is designed to maintain the contact on posterior teeth throughout treatment. This result in relative intrusion of posterior teeth while the anterior teeth are free to erupt thereby reducing anterior open bite 25
- 26. APPLIANCE DESIGN AND CONSTRUCTION Earliest twin blocks where designed with Occlusal bite blocks Midline screws to expand upper arch Clasps on upper molar and premolar Clasps on lower premolars Inter dental clasps on lower incisors Springs to move individual teeth and improve the arch form as required 26
- 27. Standard twin blocks Labial bow Delta clasps Ball end clasps baseplate 27
- 28. Labial bow It tends to over correct incisor angulation Used to upright severely proclined incisors Earlier activation will act as a brake to limit functional correction by mandibular advancement 28
- 29. Delta clasp Improves retention Reduce metal fatigue Minimal need for adjustment 29
- 30. Ball end clasp routinely placed mesial to lower canines and in the upper premolar or deciduous molar regions for interdental retention from adjacent teeth Easy to fabricate Single gingival interference Less gingival irritation Indicated for additional retention 30
- 31. Base plate 31 Appliance can be made of heat cure acrylic or cold cure acrylic Cold cure acrylic: convenient and speed are advantages but compromises strength and accuracy Heat cure acrylic: additional strength and accuracy
- 32. Occlusal inclined plane- lower The inclined plane on lower bite block is angled from mesial surface of second premolar or deciduous molar at 70 degrees to occlusal plane Buccolingually it covers occlusal surface of lower premolars or deciduous molars to occlude with inclined plane on upper twin block Bite blocks are thinner buccolingually in lower canine region 32
- 33. Occlusal inclined planes- upper Angled from mesial surface of upper second premolar to mesial surface of upper first molar The flat occlusal portion then passes distally over the remaining upper posterior teeth in a wedge shape, reducing thickness as it extends distally 33
- 34. Position of inclined plane Angle stressed the importance of the first permanent molars and described the development of key ridge in the first molar region in response to functional forces applied to the molars. Clark tested the response by moving the inclined planes mesial to the first premolar region . this reduced both the efficiency of the appliance and the response to mandibular advancement. 34
- 35. STAGES OF TREATMENT Twin block treatment is described in two stages 35 Active phase Support phase
- 36. Stage 1: Active phase During the active phase, twin blocks are worn full time. The objective is to correct to the arch relationship in the sagittal, vertical and transverse dimensions. 36
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- 38. Sequence of trimming of blocks In treatment of deep overbite, bite blocks are trimmed selectively to encourage eruption of lower posterior teeth to increase vertical dimension and level the occlusal plane 38
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- 40. In anterior open bite and vertical growth patterns, posterior bite block remains un reduced and intact throughout treatment It results in intrusive effect of posterior teeth while anteriors are free to erupt,which helps to increase the overbite and bring the anterior teeth into occlusion 40
- 41. At the end of the active phase, there should be a three point contact in the incisor and molar region and the sagittal relationship should be in a slightly overcorrected position. Aim is to achieve correction to class 1 occlusion with overjet and overbite fully corrected 41
- 42. Stage 2: Support phase The objective of the support phase is to retain the corrected incisor relationship until the buccal segment occlusion is fully established. The appliance of choice is an upper removable appliance with anterior inclined plane 42
- 43. Lower twin block appliance is left out at this stage and removal of posterior bite blocks allows posterior teeth to erupt The upper and lower buccal teeth usually settle into occlusion within 4 to 6 months. Full time wear is continued for another 3 to 6 months to allow time for internal bony remodelling to support the corrected occlusion. 43
- 44. Retention Treatment is followed by retention with upper anterior inclined plane appliance. Appliance wear is reduced to night time only when occlusion is fully established. Good buccal segment occlusion is important to maintain the correction of arch to arch relationships 44
- 45. Timetable of treatment Average treatment time Active phase: avg. time 6-9 months to achieve full reduction of overjet to a normal incisor relationship and to correct the distal occlusion Support phase: 3-6 months for molar to erupt into occlusion and for premolars to erupt after trimming of blocks. Retention: 9 months, reducing appliance wear when the position is stabilised. An avg. estimate of treatment time is 18 months, including retention 45
- 46. Treatment of class II div I malocclusion deep overbite BITE REGISTRATION 2mm vertical clearance between incisal edges of upper and lower incisors Protrusive bite registered to reduce overjet and distal occlusion on avg. by 5- 10mm on initial activation depending on the freedom of movement in protrusive function. 46
- 47. Appliance design TWIN BLOCKS TO OPEN THE BITE Inclined planes must be clear of the lower molars so that they can erupt without obstruction Instructions should be given for proper insertion and removal of appliance 47
- 48. Full time appliance wear: temporary fixation of twin blocks Unique advantage of twin block Guarantees full time wear of appliance at the start of treatment The teeth should be fissure sealed and applied topical fluoride as a preventive measure prior to fixation 48
- 49. Two alternative methods of fixation of twin blocks The appliance may be fixed to the teeth by spreading zinc phosphate or zinc oxide on tooth bearing areas and seating the appliance in place adhering to the teeth. Twin blocks may also be bonded directly on to teeth by applying composite around clasps. this is useful in mixed dentition when ball end clasps may be bonded directly to deciduous molars to improve fixation 49
- 50. Soft tissue response As a result of altered muscle balance, significant changes in facial appearance are seen within 2 or 3 weeks of starting treatment with twin blocks As appliance is worn full time, even during eating, rapid soft tissue adaptation occurs to assist the primary functions of mastication and swallowing that necessitate an effective anterior oral seal 50
- 51. Reactivation of twin blocks Reactivation of the twin block can be done as a simple chair side procedure by the addition of cold cure acrylic to extend the anterior incline of the upper twin block mesially as the clinician inserts the appliance to record a new protrusive bite before the acrylic is fully set. No acrylic should be added to the distal incline of the lower twin block. Specially in deep bite cases as extending the occlusal acrylic of the lower block distally will prevent eruption of lower 1st molar. 51
- 52. 52 Indication for progressive reactivation of twin blocks If overjet is greater than 10 mm In vertical growth pattern In adult treatment In treatment of TMJ dysfunction In any case where full correction of arch relationships is not achieved after the initial activation, an additional activation is necessary.
- 53. Treatment in mixed dentition The principles of treatment are unchanged in mixed dentition, although the response to treatment may prove to be slower depending on patients rate of growth Mcnamara JA Burden,W L(1993) orthodontic and orthopaedic treatment in mixed dentition 53
- 54. Appliance design Similar design to permanent dentition Delta clasps are used on lower first or second deciduous molars Alternatively C clasp may be used for retention on deciduous molars Bonding composite on buccal surface of these teeth to get additional undercut. Grinding retention grooves Using synthetic crown contours 54
- 55. Occluso-guide appliance It’s a pre formed mini positioner appliance It is designed to fit upper and lower teeth and to act as a functional retainer by engaging the teeth in edge to edge relationship in a slightly open position with an inter incisal distance of 3mm Comes in different sizes Worn 1-2 hours per day and patient is instructed to actively bite into the appliance 55
- 56. Combination therapy Combination therapy describes the combined use of functional and fixed techniques in the management of malocclusion Optimum timing of treatment is either in late mixed dentition or early permanent dentition. In some cases twin blocks may be adapted for simultaneous use with fixed appliances 56
- 57. Twin block technique corrects skeletal discrepancies first, both in the anteroposterior and vertical dimension followed by alignment of the teeth The first phase phase ( skeletal correction ) may occur in mixed dentition and the second phase( dental correction ) may follow when almost all permanent teeth has erupted. 57
- 58. Twin block traction technique When the response to functional correction is poor, the addition of orthopaedic traction force may be considered. This method was limited to treatment of severe malocclusion, where growth is unfavourable for conventional fixed or functional therapy 58
- 59. Indications In treatment of severe maxillary protrusion To control a vertical growth pattern by the addition of vertical traction to intrude the upper posterior teeth In adult treatment where mandible growth cannot assist the correction of severe malocclusion 59
- 60. The concorde facebow Cousins & Clark in 1965 Concorde facebow apply intermaxillary and extra oral traction to restrict maxillary growth and to encourage mandibular growth in combination with functional mandibular protrusion Intermaxillary traction added to ensure effectiveness of appliance 60
- 61. Treatment of anterior open bite and vertical growth patterns Aetiology of the problem should be diagnosed Prognosis for correction of anterior open bite depends on the degree of skeletal and soft tissue imbalance Direction of facial growth also affects prognosis 61
- 62. Intra oral traction to close anterior openbite Intra oral elastics can be used to accelerate bite closure as an efficient alternative to high pull extra oral traction Introduced by Dr. Christine Mills in Vancouver The vertical elastics between upper and lower appliances reinforces the intrusive effect of the bite blocks 62
- 63. TREATMENT OF CLASS II DIV 2 Retroclined upper incisors are responsible for holding the mandible in distal position in angles class II div 2 malocclusion Correction is done by advancing mandible forward and downward and encouraging lower molars to erupt Upper incisors are advanced 63
- 64. Construction bite is registered with incisors in edge to edge occlusion Vertical development is the primary factor in correction of class II div 2 malocclusion with minimum advancement of mandible 64
- 65. Twin block sagittal appliance Witzig and spahl in 1987 used it for anteroposterior development of arch form Design of upper twin block is modified by addition of two sagittal screws set in palate for anteroposterior development It can be used in lower arch too to increase arch length 65
- 66. Combined transverse and sagittal development Three way screw 66 Triple screw sagittal appliance
- 67. Topics to be covered in next session Treatment of class III malocclusion Management of crowding Treatment of facial asymmetry Magnetic twin blocks Adult treatment TMJ pain and dysfunction syndrome Flat earth concept of facial growth Growth response to twin block treatment 67
- 68. Thankyou 68
- 70. TOPICS COVERED IN PREVIOUS SESSION Introduction History Philosophy behind twin block therapy Angulation of inclined planes Diagnosis and treatment planning Indications and contraindications Bite registration Appliance design and construction Stages of treatment 70
- 71. TOPICS COVERED IN PREVIOUS SESSION Treatment of class II div I malocclusion deep overbite Treatment in mixed dentition Combination therapy Twin block traction technique Treatment of anterior open bite and vertical growth patterns Treatment of class II division 2 malocclusion 71
- 72. TOPICS COVERED IN THIS SESSION Treatment of class III malocclusion Management of crowding Treatment of facial asymmetry Magnetic twin blocks Adult treatment TMJ pain and dysfunction syndrome Flat earth concept of facial growth Growth response to twin block treatment 72
- 73. Treatment of class III malocclusion: Reverse twin blocks The position of bite blocks are reversed compared to twin blocks for class II treatment Designed to encourage maxillary development by action of reverse occlusal inclined planes cut at 70 degrees 73
- 74. Occlusal forces exerted on mandible is directed downwards and backwards by the reverse inclined planes. 74
- 75. Case selection Early treatment is often indicated Simplest clinical guideline is ability to achieve edge to edge upper and lower incisors Prognosis is reduced when degree of skeletal discrepancy is more An initial RME is indicated in severe cases in younger patients Mc Namara 1993 75
- 76. Bite registration Construction bite recorded with 2mm inter incisal clearance with fully retruded position In brachyfacial class III additional vertical activation applied to further open the bite by giving 4mm inter incisal clearance 76
- 77. Lip pads To enhance the forward movement of upper labial segment It supports upper lip clear of the incisors 77
- 78. Reverse pull facial mask Adds additional component of orthopaedic force to advance maxilla by elastic traction In addition three-way expansion is incorporated. Elastic force is increased gradually Delaire et al 1972, Petit 1982 78
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- 80. Management of crowding Interceptive treatment for arch development initiated as early as possible Compatibility is checked by sliding lower model forward 80
- 81. In permanent dentition fixed appliance treatment may precede twin block treatment to correct an irregular arch form In less crowded cases fixed appliances may be intergrated with twinblocks 81
- 82. Treatment of facial asymmetry Sagital twin blocks give better control for correction of dental or facial asymmetry 82
- 83. Magnetic twin blocks Magnets in twin block accelerate correction of arch relationship Magnets often used are samarium cobalt and neodynium boron 83
- 84. Attracting magnets : pulls the appliances together and encourages the patient to occlude actively and consistently in a forward position Accelerated correction of distal occlusion Can be used in correction of facial asymmetry 84
- 85. Repelling magnets : The repelling magnetic force is intended to apply additional stimulus to forward posture as the patient closes into occlusion Used in twin blocks with less magnetic activation built into occlusal inclined planes 85
- 86. magnetic twin blocks cannot be reactivated by addition of acrylic to the inclined planes as this deactivates the magnets. Screws may be needed on the bite blocks for progressive activation of magnetic twin blocks. 86
- 87. Adult treatment Twin blocks can be used in treatment of adults if the skeletal discrepancy is not severe. In severe skeletal discrepancies, twin blocks are contraindicated and orthognathic surgery is the treatment of choice in adult patients. 87
- 88. TMJ pain and dysfunction syndrome No dental condition is more distressing for a patient than chronic tmj pain An excellent functional occlusion is the cornerstone of treatment for temporomandibular dysfunction. Ramfjord & ash (1983), Krough-Poulsen & Olsson (1968), Beyron (1954), Graf (1975) 88
- 89. Relief of pain- fundamentals of treatment Balanced occlusal support to relieve muscle spasm in initial stage of treatment Removal of cuspal interferences causing mandibular displacement on closure Good vertical support for the joints to function freely without compression of articular disc Freedom of movement with cuspal guidance and incisal guidance when mandible moves from centric occlusion Tripoding of occlusal contacts in final balanced occlusion 89
- 90. The reciprocal click A clicking joint is indicative of displacement of the articular disc off the head of the condyle . the timing of click on opening is significant in the prognosis for resolution: 1. early opening click up to 22 mm opening are usually easy to resolve 2. mid opening click 22-35mm of opening are moderate to resolve 3. late opening clicks over 35mm of opening are difficult to resolve. 90
- 91. Temporomandibular joint therapy The goals of therapy are: Relieve the pain caused by distal displacement of the condyle Retrain the muscles to a healthy pattern Recapture the disc when possible by advancing the displaced condyle Move the teeth that are causing occlusal imbalance and mandibular misguidance Increase the vertical dimension to reduce deep overbite 91
- 92. Twin blocks in temporomandibular joint therapy Twin blocks achieve the following objectives 1. Pain is relieved within 4 days of fitting twin blocks. 2. Facial balance is improved and muscle spasm relieved. 3. The disk is recaptured by posturing the mandible downward and forward to advance the condyles. 4. Rather than acting as a passive splint, twin blocks can move teeth that are causing occlusal imbalance. 5. The upper block may be trimmed selectively over the lower first molar only, using molar bands with vertical elastics to accelerate eruption. 92
- 93. Flat earth concept of facial growth Understanding the concept of volumetric growth of the face is as important as realising that earth is round and not flat Limitations of cephalometric analysis are mainly due to the conversion of a 3D structure to a 2D image 93
- 94. For example; given the three dimensional shape of mandible and its semi elliptical morphology, measurement from condyle to condyle is the meaningful representation of mandibular periphery than the midline projection of mandibular length from Condylion to pogonion 94
- 95. Measurement of peripheral length of mandible on dry skull using flexible ruler indicates that peripheral length on each side is 20% greater than the projected cephalometric linear distance from pogonion to Condylion. 95
- 96. The mathematical formula for the expansion of an object relating to percentage change is expressed as: 96 Any linear values multiplied by three to convert to volumetric values 1% of increase in radius of sphere increases the volume by 3% Head is more closely related to a sphere or an ellipsoid than the projected two dimensional cephalometric image
- 97. A cephalometric radiograph is used to interpolate the three dimensional changes in specific areas of craniofacial complex A slice of sphere is an appropriate model to illustrate this mathematical principle The volume of slice of sphere= angle/360o x 4/3#r3 The same principle can be applied to interpret volumetric changes in the middle third and lower third of the face 97
- 98. Response to twin block treatment Harvold demonstrated in animal experiments that when the mandible is advanced, a "tension zone" is created above and behind the condyle. This is an area of intense cellular activity quickly invaded by proliferating connective tissue and blood capillaries From animal studies, it may be deduced that retraction of the condyle results in compression of connective tissue and blood vessels and the resulting ischaemia is the principal cause of pain. This change in muscle activity is described by McNamara as the "pterygoid response" 98
- 99. Conclusion In the pursuit of ideals in Orthodontics, facial balance and harmony are of equal importance to ideal and perfect occlusion. 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. 99
- 100. References Twin block functional therapy-William j clark Tan et al,A preliminary report of a new design of cast metal fixed twin-block appliance, Journal of Onhodottíics, Vol. 34. 2007, 213-219 Woodside DG (1977) The activator. In: Graber TM, Neumann B, editors. Removable Orthodontic Appliances. Philadelphia: Saunders; pp. 269-336. McNamara JA. Neuromuscular and skeletal adaptations to altered function in orofacial region. AJO 1973) Dixon et al,Mandibular incisal edge demineralization and caries associated with Twin Block appliance design, Journal of Orilwitonfics, Vol. 32. 2005, 3 10 100
- 101. ACKNOWLEDGEMENT DR. RAJKUMAR. S.ALLE DR. SHWETHA.G.S DR. SHASHI KUMAR.H.C DR. SUMA.T DR. LOKESH.N.K DR. KIRAN.H DR. SIDHARTH ARYA DR. DHARMESH.H.S DR.BHARATI DR.FAISAL ARSHAD 101
- 102. Thankyou 102