TWIN BLOCK

CONTENTS• INTRODUCTION• HISTORY• DESIGN OF TWIN BLOCK• RESPONSE TO TWIN BLOCK TREATMENT• SKELETAL CHANGES• DENTAL CHANGES

• STANDARD TWIN BLOCK• STAGES OF TREATMENT• INDICATIONS • CONTRAINDICATIONS• MODIFICATIONS• ADVANTAGES

Twin blocks are simple bite blocks with occlusal inclined

planes.

INTRODUCTIONcomprises 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.

HISTORY• The first Twin Block appliance

was fitted on 7th September 1977 by William Clark.

• Evolved in response to a clinical problem.

• Young patient who was son of a dental colleague fell and luxated theupper incisor

The twin block technique A functional orthopedic appliance systemWJ Clark - American Journal of Orthodontics and Dentofacial …, 1988

THE PATIENT WAS 8YRS AND 4 MONTHS

ENDODONTIC PINS WERE PLACED TO STABILIZE THE INCISOR, 4 MONTHS AFTER TREATMENT

DESIGN OF TWIN BLOCK Occlusal inclined plane

• The occlusal inclined plane is the fundamental functional mechanism of dentition.

• Cuspal inclined planes play an important part in determining the relationship of the teeth

• If the mandible occludes in a distal relationship to the maxilla (in class II) the occlusal forces acting on the mandible in normal function have a distal component of force that is unfavorable to normal forward mandibular development.

Twin-blocks constructed in a protrusive bite ,effectively modifies the occlusal inclined planes by means of bite-blocks

The bite blocks acts as a guiding mechanism causing the mandible to be displaced downward and forward.

The unfavorable cuspal contacts of a distal occlusion are replaced by favorable proprioceptive contacts on the inclined planes of twin-blocks to correct the malocclusion & to free the mandible from its locked distal functional position.

MANDIBLE UNLOCKED

RESPONSE TO TWIN BLOCK TREATMENT

When the mandible postures downward and forwards,there is

an area of immense cellular activity above and behind the

condyle referred as Tension Zone. This area is quickly

invaded by proliferating blood vessels and connective tissue.

The twin block technique A functional orthopedic appliance systemWJ Clark - American Journal of Orthodontics and Dentofacial …, 1988

A new pattern of muscle behaviour is quickly established whereby the patient finds it difficult and impossible to retract

the mandible to its former retruded position.

PTERYGOID RESPONSE

The muscles are the prime movers in growth, followed by bone remodelling as a secondary response. Hence muscle function must be altered over a sufficient period of time to allow adaptive bone remodelling changes to

occur, in order to reposition the condyle in the glenoid fossa.

McNamara JA. Neuromuscular and skeletal adaptations to altered function in orofacial region. AJO 1973)

SKELETAL CHANGES IN TWIN BLOCK THERAPY

Forward growth/repositioning of

the mandible is seen after twin block therapy.

Increase in SNB angle.

Little change in SNA angle indicating maxillary restraint, but was not detected because of

dentoalveolar remodeling disguising the skeletal effect.

Forward growth/repositioning of the mandible does result in a significant change in ANB, thus severity of

the class II skeletal pattern is reduced.

Increase in lower anterior facial height.

overjet reduction

retroclination of the upper incisors

proclination of the lower incisors.

Buccal segment correction occurred by distal movement of the upper molars

lower molar eruption in an anterior and superior direction.

Dental changes as a result of Twin Block therapy

STANDARD TWIN BLOCK• treatment of an uncrowded class II div 1 malocclusion with a good

arch form.

Clark’s Twin Block appliance consists of:• Base Plates • Bite block• Wire components: The Delta Clasp and Ball End Clasp• Other related components

• BASE PLATE

HEAT CURE

COLD CURE

additional strength and good accuracy

speed and easier manipulation.

BITE BLOCKThe inclined plane on lower bite block is angled from the mesial surface of the second

premolar or deciduous molar whichever present.

the lower bite block does not extend distally to the

marginal ridge on the lower second premolar.

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

The inclined planes are mostly angled at 70 degrees to the occlusal plane,although the angulation may be reduced to 45 degrees if the patient fails to posture

forwards consistantly

WIRE COMPONENTS

DELTA CLASP

designed by Clarke

retentive loops are shaped as a closed triangle or a circle

gives excellent retention on lower premolars

BALL END CLASP

are routinely placed mesial to lower canines

and in the upper premolar or deciduous

molar regions for interdental retention from adjacent teeth

BITE REGISTRATION

-mandible should be positioned protruded approximately 3mm distal to the most protrusive position that the patient can achieve ,while

vertically the bite is registered within the limit of the freeway space.

Woodside-1977

Woodside DG (1977) The activator. In: Graber TM, Neumann B, editors. Removable Orthodontic Appliances. Philadelphia: Saunders; pp. 269-336.

normal physiologic TMJ movement as 70% of the total joint displacement.

Roccabado

edge to edge incisor relation with 2mm interincisal clearance.

Overjet upto 10mm

The Exactobite or the project bite gauge is used to record a protrusive interocclusal record for the construction of the Twin Block.

The George bite gauge has a millimetre gauge to measure the protrusive path of the mandible and determine accurately the amount of activation registered in the construction bite.

• Activation should be within the masticatory muscle physiologic limit and ligament attachment limit.

• Total protrusive movement = overjet in centric occlusion – max protrusion possible

• Functional activation should not be more than 70% of above value

Sagittal activation –choosing the appropriate groove.

Vertical –blue colour gauge gives 3mm interincisal clearance

• Overjet greater than 10mm- initial activation of 7-8mm followed by further activation.

• Vertical dimension- should be 4 – 5mm(in the first premolar region).

SUMMARY OF BITE REGISTRATION

• Inter incisal clearance 2mm

• In first premolar region 5-6mm

• Molar region 1- 2mmDesign and management of Twin Blocks:reflections after30 years of clinical useWilliam Clark

STAGES OF TWIN BLOCK TREATMENT

Active phase

Support phase

Retention

ACTIVE PHASE

6-9 MONTHS

• the appliance is used to achieve correction of sagittal jaw position.

• After correction vertical discrepancy is corrected by selectively trimming the posterior bite blocks.

• achieve correction to class I occlusion and control of the vertical dimension by a three-point contact with the incisors and the molars.

• At this stage the overjet ,overbite and sagittal relationship is full corrected.

AIM

SUPPORT PHASE

4-6 MONTHS

AIM• to maintain the corrected incisor relationship until the buccal

relationship is fully interdigitated.

• To achieve this objective an upper removable appliance is fitted with an anterior inclined plane with a labial bow to engage the lower incisors and canines.

ANTERIOR INCLINED PLANE

RETENTIVE PHASE

9 MONTHS

• Treatment is followed by retention with upper anterior inclined plane appliance.

• Appliance wear is reduced to nighttime wear only when the occlusion is fully established.

FIXED APPLIANCE PHASE

Final detailing of the occlusion is completed using fixed appliance therapy

INDICATIONS

Class II div I malocclusion.

CONTRAINDICATIONS

Class II skeletal by maxillary prognathism

2. Vertically directed grower

3. Labial tipping of lower incisors

4. Crowding

MODIFICATIONS OF TWIN BLOCK

TRANSVER

SE DEVELOPMEN

T

SAGGITAL

DEVELOPMEN

T

SAGGITAL AND TRANSVER

SE DEVELOPMEN

T

TO CLOS

E ANTERIOR OPE

N BITE

Twin block for arch

development

TWIN BLOCK FOR TRANSVERSE DEVELOPMENT

TWIN BLOCK FOR SAGITTAL DEVELOPMENT

FOR BOTH TRANSVERSE AND SAGITTAL

In cases of laterally contracted maxillary arch; combined sagittal and tranverse expansion is required.This is brought about by• Three way sagittal appliance.• Triple screw sagittal appliance.

• This is mainly due to a combination of skeletal and soft tissue factors.• Bite registrationA 4mm interincisal clearance is achieved, resulting in approximately 5mm clearance between the premolars or the deciduous molars.

Sufficient block thickness is needed so as to open the bite beyond the freeway space – for intrusion of the teeth and at the same time makes it difficult for the patient to disengage the blocks.

TWIN BLOCK TO TREAT ANTERIOR OPEN BITE

• APPLIANCE DESIGN

The lower appliance extends distally to the molar region with clasps on the lower first molars and occlusal rests on the second molars to

prevent their eruption.

For the upper appliance Expansion screws for arch expansion A palatal spinner to control the tongue thrust A tongue guard A labial bow may be added to retract the upper incisors.

Pitfalls in the treatment of anterior open bite arise from careless management of the occlusal bite blocks.

Two common mistakes are to be avoided:

1. The over eruption of the second molars behind the appliance

2. Trimming of the upper bite block occlusally which allows the lower molars to erupt thereby propping the bite open and increasing the open bite

TREATMENT OF CLASS II, DIV I MALOCCLUSION

• Edge to edge bite with 2mm interincisal clearance.

• Center lines should coincide.• In vertical dimension 2mm interincisal

clearance is equivalent to clearance in first premolar region by 5-6mm and 3mm in the molar region

APPLIANCE DESIGN

Trimming -1-2 mm /visit

Molars erupt 6-9 months

Triangular wedge shaped area

Eruption of the pre molar

• Reduce the overjet and correct distal occlusion.

• Control overbite if the overbite is deep or an anterior open bite is present .

• Improve arch form by sagittal or transverse development.

• C- shaped clasps can be bonded to deciduous teeth for improved retention.

TREATMENT OF MIXED DENTITION

TREATMENT OF CLASS II DIV 2 MALOCCLUSION

• An edge to edge construction bite is registered to correct the distal occlusion in class Il division, 2 malocclusion.

• Management of Class Il div 2 malocclusion by advancing the mandible and proclining the upper incisors with sagittal screws.

• Eruption of lower molars corrects vertical dimensions

APPLIANCE DESIGN

For the treatment of Class II Div 2 malocclusions , sagittal arch development is necessary.

• Sagittal Twin Blocks are used Upper block is modified by addition of two sagittal screws set in the

palate for anteroposterior arch development.

• The sagittal design is suitable for both upper and lower arches to increase the arch length.

TREATMENT OF CLASS III MALOCCLUSION

• Reverse twin blocks are designed to encourage maxillary development.

• reverse occlusal inclined plane cut at a 70 degree angle drive the teeth forwards by the forces of occlusion

• restrict forward mandibular development.

• POSITION OF THE CONDYLES

• Modification-lip pads may be used to support the upper lip clear of the incisors.

• Teeth closed to the maximum retrusion, leaving sufficient clearance between posterior teeth for occlusal bite blocks .

• Achieved by recording bite with 2 mm interincisal clearance in fully retruded position.

Appliance design:- In many cases, the maxilla is contracted in relation to occluding in distal

relation to the mandible. The three —way expansion screw to combine transverse and sagittal

expansion. Opening the screw has reciprocal effect of driving upper molars distally

and advancing the incisors.

MAGNETIC TWIN BLOCK

Two rare earth magnets used Samarium Cobalt Neodynium Boron

ATTRACTING MAGNETS

REPELLING MAGNETS

ATTRACTING MAGNETS

Increased activation can be built into the initial construction bite for the appliance.

Attracting magnets pull the appliances together and encourages the patient to occlude actively and consistently in a forward position.

Attracting magnets may accelerate progress by increasing the frequency and force of contact on the inclined planes.

REPELLING MAGNETS

• apply additional stimulus to forward posture the jaw as the patient closes into occlusion.

• amount of activation is not clear

• reactivation of the inclined plane would deactivate the magnets.

DISADVANTAGE

TWIN BLOCK IN TMJ THERAPY

GOALS -relieve pain by distal displacement.-restrain muscles to healthy pattern.-recapture disc by advancing mandible.-move teeth causing occlusal balance.-increase the vertical dimension.

STAGES OF TREATMENT

SAGGITAL DEVELOPMENT

Functional repositioning

Pain relieved immediately

Muscles are restrained

Disc is recaptured

Vertical development

Trimming the upper blocks

Vertical traction

Twin block biofinisher

• TWIN BLOCK BIOFINISHERExtruding lower molars by vertical traction to stabilize the TMJ

It is important to recognize that if pain is not relieved by forward posture, and the disc does not appear to be recaptured, there may be internal derangement, or folding of the disc. which will not respond to Twin Block therapy.

• Myofunctional therapy after maximum and stepwise advancement with the Twin Block appliance showed a favourable effect in the temporomandibular joint region. Stepwise advancement showed greater vertical growth and more favourable anteriorly directed horizontal growth in the temporomandibular joint region on a short-term basis

Doshi et al, Effective temporomandibular joint growth changes after stepwise and maximum advancement with Twin Block appliance, Journal of the World Federation of Orthodontists 3 (2014) e9-e14

TREATMENT OF FACIAL ASYMMETRY

• Occlusal inclined planes- capable of unilateral activation.

• Use of magnets.

FIXED TWIN BLOCK

Increase control by the operatorLimited indications-• Growth status of the patient• Patient cooperation.• One phase treatment is planned.

1st •ARCH DEVELOPMENT

2nd •ORTHOPAEDIC TREATMENT BY FIXED/FUNCTIONAL TWIN BLOCK

3RD •ORTHODONTIC CORRECTION BY BONDED FIXED APPLIANCED

• Clinical Management & Maintenance

• Blocks are checked for comfortable occlusion.• Deep bite correction- twin block lingual component is fixed to permanent

molars.• Vertical elastics and lingual hooks placed after occlusal blocked removed.• Appointment should be after 3-4 weeks

FUNCTIONAL COMPONENTS

The Twin Block Transpalatal Arch

The Twin Block Lingual Arch

The Twin Block Hyrax Appliance

Occlusal inclined planes

TWIN BLOCK TRACTION TECHNIQUE• The cases in which ,

response to functional correction is poor, the addition of orthopaedic traction force may be considered.

Indications :

• In treatment of severe maxillary protrution.

• To control vertical growth pattern by addition of vertical traction to intrude upper posterior teeth.

• In adult treatment where mandibular growth cannot assist correction of severe malocclusion.

• The Concorde Facebow--Before the development of twin block ,author used

extraoral traction with removable appliance as means of anchorage.

-A method was developed to combine extraoral and intermaxillary traction .

Concorde facebow helped in restricting maxillary growth, at the same time encouraged mandibular growth in combination with the functional

appliance.

• The labial hook is positioned extraorally 1cm clear of the lips.

• Traction component are worn only at night.

• Directional control of orthopedic force-

• Dixon et al,Mandibular incisal edge demineralization and caries associated with Twin Block appliance design, Journal of Orilwitonfics, Vol. 32. 2005, 3 10

The use of a Southend clasp on the upper and lower incisors of a Twin-block appliance :• reduces retroclination of the upper incisors;• reduces proclination of the lower incisors;• applies control to the incisors which may enhance the skeletal correction.

Trenouth et al,A randomized clinical trial of two alternative designs of Twin-block Appliance, Journal of Orthodontics, Vol. 39, 2012. 17-24

DESIGNER TWIN BLOCK

ADVANTAGES OF TWIN BLOCK

Comfort of the patient

Aesthetics

Function

Patient compliance

Facial appearance

Speech

Clinical management

Arch development

Vertical control

Facial asymmetry

Age of treatment

Integration with fixed appliances

Treatment of TMJ dysfunctions

The effects of Twin Blocks: A prospective controlled study ( David Ian Lund 1998 AJO)

OBJECTIVE:This study was designed to investigate the maxillomandibular skeletal and dentoalveolar changes produced by the Twin Block appliance compared with those changes experienced by an untreated control group.

• The treatment group consisted of 36 subjects, mean age of 12.4 years

• The control group consisted of 27 subjects with a mean age of 12.1 years.

• These patients were observed for a mean time of 1.2 years

ANGULAR MEASUREMENTS

LINEAR MEASUREMENTS

Is mandibular growth increased?

• statistically significant increase in mandibular length measured from Articulare-Pogonion, with some forward movement of Pogonion, both of which are desirable outcomes of treatment.

• 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.

• Baumrind and Korn and Haynes found similar changes in Ar-Pog. . (1986 AO,AJO 1981)

• However, the Twin Block appliance produced a greater change over a shorter treatment period

Do Twin Blocks restrain maxillary forward growth?

• When forward growth of the maxilla was assessed little change in SNA was observed thus indicating little maxillary restraint.

• The results do not suggest any significant headgear effect associated with the Twin Block

• some degree of maxillary restraint might have occurred but was not detected because of dentoalveolar remodeling disguising the skeletal effects of the treatment.

Is there a beneficial sagittal change?

the forward growth of the mandible does result in a significant change in ANB thus the severity of the Class II skeletal pattern is reduced.

Does tooth tipping contribute greatly to correction?

There was a significant amount of tipping of the labial segment teeth in both arches.

• The maxillary incisors were retroclined,

• mandibular incisors were proclined as a result of treatment, which greatly contributed to correction of the overjet.

Does anteroposterior molar movement aid correction of the malocclusion?

• A restraining effect on the upper molars was demonstrated to the extent that there was slight distalization along with a statistically significant forward movement of the lower molars.

• This change in molar position aids the correction of the disto-occlusion

Do Twin Blocks control the vertical position of the teeth?

• There was a significantly increased eruption of the lower molars during treatment after judicious trimming of the bite blocks.

• This not only contributes to overbite reduction and closure of lateral open bites but also helps with Class II molar correction.

The following case report documents a 12-year-old boy with 11 mm overjet treated by a phase I growth modification therapy using twin block appliance with lip pads in a stepwise mandibular advancement protocol [4],[5],[6] followed by a phase II preadjusted Edgewise appliance therapy to settle the occlusion and correct the remaining dental discrepancy.

Management of severe Class II malocclusion with sequential modified twin block and fixed orthodontic appliances

Enhance forward growth of the mandible to improve facial profile and mandible/cranial base relationship.Reduce overjet and overbite.Achieve Class I incisor and buccal segment relationships.Eliminate lip trap and improve lip competency.Relieve crowding and align teeth.

Aims of treatment

Phase I: Growth modification therapy

• An acrylic twin block appliance with lip pads was given for full-time wear with an initial mandibular advancement of 6 mm and interocclusal clearance of 5 mm in the 1st premolar region.

After 6 months, the appliance was activated by advancing the mandible by 5 mm to achieve an edge to edge incisor relationship. The patient was instructed to turn the maxillary expansion screw once a week and was reviewed every 4 weeks. Bite blocks were trimmed to achieve proper vertical eruption of the posterior dentition to reduce the deep bite.

The twin block appliance was removed after 12 months of treatment. Normal overjet, overcorrected molar relationship, and lip competency were achieved by phase I orthopedic stage

Post functional appliance

photographs

Phase II: Fixed appliance

• Utility intrusion arch fabricated using 0.016” × 0.022” SS wire was placed in the maxillary arch for 3 months for incisor intrusion . The archwires were subsequently changed to 0.017” × 0.025” stainless steel wire for torque control.

• Class II elastics were worn full time to maintain the buccal relationships and overjet.

• Root paralleling was carefully adjusted, and cusp seating was carried out by vertical elastics at the end of treatment. The total treatment was completed in 25 months. Upper and lower Hawley's retainers were given immediately after the fixed orthodontic appliance was removed

Results :

• The post treatment facial profile of the patient demonstrated noticeable improvement with good facial esthetics, straight facial profile, and balanced competent lips.

• The intraoral occlusion revealed satisfactory result with characteristics of well-aligned dentition.

• Overjet and overbite were reduced to 3 mm and 2.5 mm, respectively. • Class I canine and molar relationship with good buccal interdigitation

were also achieved.

• The twin block appliance due to its acceptability, adaptability, versatility, efficiency, and ease of incremental advancement without changing the appliance has become one of the most widely used functional appliances in the correction of Class II malocclusion. It can eliminate etiologic factors such as sucking habits and lip trap, restore normal growth, and reduce the severity of skeletal abnormalities.

Effectiveness of treatment for Class II malocclusion with the Herbst or Twin-block appliances: A randomized, controlled trial

Kevin O’Brien

• The aim of this study was to evaluate the effectiveness of Herbst and Twin-block appliances for established Class II Division I malocclusion. The study was a multicenter, randomized clinical trial carried out in orthodontic departments in the UK. A total of 215 patients (aged 11-14 years) were randomized to receive treatment with either the Herbst or the Twin-block appliance.

• Treatment with the Herbst appliance resulted in a lower failure-to-complete rate for the functional appliance phase of treatment (12.9%) than did treatment with Twin-block (33.6%). There were no differences in treatment time between appliances, but significantly more appointments (3) were needed for repair of the Herbst appliance than for the Twin-block.

• There were no differences in skeletal and dental changes between the appliances;however, the final occlusal result and skeletal discrepancy were better for girls than for boys. Because of the high cooperation rates of patients using it, the Herbst appliance could be the appliance of choice for treating adolescents with Class II Division 1 malocclusion. The trade-off for use of the Herbst is more appointments for appliance repair. (Am J Orthod Dentofacial Orthop 2003;124:128-37)

DESIGN OF TWIN BLOCK

DESIGN OF HERBST APPLIANCE

Conclusions

• Phase I treatment is more rapid with the Herbst appliance, but overall duration of treatment is similar to that with the Twin-block • The Herbst appliance is prone to debonding an component breakage • There are no differences in the dental and skeletal effects of treatment

Treatment effects produced by the Twin-block appliance and the FR-2 appliance compared with an untreated Class II sample

Linda Ratner Toth, and James A. McNamara, Jr AJO 99

• cephalometric study compares the treatment effects produced in

• 40 patients treated with the Twin-block appliance

• 40 children treated with the FR-2 appliance

• 40 untreated Class II controls

significant increases in mandibular length were observed in both treated groups.

The Twin-block achieved an additional 3.0 mm of mandibular length, whereas the Fränkel 1.9 mm more than did the controls.

No restriction of midfacial growth in either appliance group relative to controls

A increase in lower anterior facial height in both treatment groups.

more dentoalveolar adaptation was observed in tooth-borne Twin-block appliance than with the tissue-borne FR-2.

The Twin-block and FR-2 samples both showed significant retroclination and extrusion (eruption) of the maxillary incisors.

The Twin-block patients exhibited distal movement of the upper molars; however, there was no extrusion.

Slight lower incisor proclination was noted greater in the Twin-block group compared with the other .

CONCLUSION

Facial harmony and balance are of equal importance to dental occlusion perfection. One cannot ignore the importance of orthopaedic techniques in achieving these goals by growth guidance during the formative years of facial and dental development.

The integration of orthodontic and orthopaedic techniques offer a new initiative in restoring facial balance.

REFERENCES• 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)• The twin block technique A functional orthopedic appliance system• WJ Clark - American Journal of Orthodontics and Dentofacial …, 1988• Design and management of Twin Blocks:reflections after30 years of clinical use William Clark• Doshi et al, Effective temporomandibular joint growth changes after stepwise and maximum

advancement with Twin Block appliance, Journal of the World Federation of Orthodontists 3 (2014) e9-e14

• Dixon et al,Mandibular incisal edge demineralization and caries associated with Twin Block appliance design, Journal of Orilwitonfics, Vol. 32. 2005, 3 10

•

• Trenouth et al,A randomized clinical trial of two alternative designs of Twin-block Appliance, Journal of Orthodontics, Vol. 39, 2012. 17-24

• The effects of Twin Blocks: A prospective controlled study ( David Ian Lund 1998 AJO)

• Management of severe Class II malocclusion with sequential modified twin block and fixed orthodontic appliances

• Effectiveness of treatment for Class II malocclusion with the Herbst or Twin-block appliances: A randomized, controlled trial

• Treatment effects produced by the Twin-block appliance and the FR-2 appliance compared with an untreated Class II sample

• Linda Ratner Toth, and James A. McNamara, Jr AJO 99