Guide Dr.. Chan Dr Chandralek dralekha ha B
By Dr.. Nilo Dr Nilofer fer
Prof & HOD Dept. Of Orthodontics Vydehi Vy dehi Institute Institute Of Dental Sciences Sciences
PG Student Dept. Of Orthodontics
Contents
Introduction Twin Block Block Principles Princi ples Development of Twin Block Stages Of Treatment Mode Of Action Appliance Appliance design Various V arious modifications Case selection Clinical management Effects of Twin Block References
Introduction Twin blocks are designed on aesthetic principles to free the patient of the restriction imposed by a one-piece appliance made to fit the teeth in both jaws without overly restricting normal movements of the tongue, lips and mandible.
Twin block appliances are simple bite blocks which achieve rapid functional correction of malocclusion by the transmission of favorable occlusal forces to occlusal inclined planes that cover the posterior teeth. The forces of occlusion are used as the functional mechanism to correct the malocclusion.
TWIN BLOCK PRINCIPLES The occlusal incline plane is the fundamental functional mechanism of the natural dentition. It plays an important role in determining the relationship of the teeth as they erupt into occlusion. A functional equilibrium is established under neurological control in response to repetitive tactile stimuli.
When mandible occludes in a distal relationship to the maxilla, occlusal forces have a distal component of force that is unfavorable to normal forward mandibular development. Inclined planes - represent a servo mechanism that locks the mandible in a distally occluding functional position.
Occlusal forces
Constant proprioceptive stimulus BONE Rate of growth Trabecular structure
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 occlusal inclined plane acts as a guiding mechanism causing the mandible to be displaced downward and forward with the appliance in the mouth The patient cannot occlude comfortably in the former distal position, and the mandible is encouraged to adopt a protrusive bite with the inclined planes engaged in occlusion.
The upper and lower bite – blocks interlock at a 70 degree angle. Full time wear takes advantage of all functional forces applied to the dentition including the forces of mastication. Muscle behaviour is immediately influenced through the placement of inclined planes. The muscles of mastication must adapt to the altered balance of occlusal forces by guiding the mandible into protrusive function. This guidance results in rapid soft tissue adaptation to achieve a new position in equilibrium in muscle behaviour. Rapid improvement in facial appearance occurs during the first few weeks and months of treatment
Development of Twin block The twin block appliance evolved in response to a clinical problem that presented when a young patient fell and completely luxated an upper central incisor……… Lip trap was causing root resorption and mortality Upper and lower acrylic plates with bite blocks were fabricated - advance mandible - reduce overjet and eliminate lip trap
Hence, the first twin block was fitted on 7th of September 1977. Although the root resorption was severe, this treatment worked and helped save the tooth.
Goal of the twin block appliance
To produce a technique that could maximize the growth response to functional mandibular protrusion by using an appliance system that is simple, comfortable and aesthetically acceptable to the patient
TWIN BLOCK STAGES
The Twin Block Technique has 2 stages :
1. Active phase : Posterior inclined planes adjust
the vertical dimension and correct the malocclusion by functional mandibular protrusion.
1.
Support phase : An anterior inclined plane is used to retain the corrected incisor relationship until the buccal segment occlusion is fully established. Occlusal cover is maintained over the posterior teeth to prevent eruption in treatment of anterior open bite. Orthopedic traction : Where necessary retractive forces may be applied by the addition of headgear tubes to upper first molars.
MODE OF ACTION Effects on the condyle: Rapid adaptive changes in the tissues surrounding the condyle when a full-time functional appliance is fitted. Intense cellular activity Proliferating connective tissue and capillary blood vessels Harvold (1983)
Effects on the muscles: Aggarwal et al AJO 1999 Electromyographic study on the adaptive changes during treatment. Bilateral electromyographic activity of the elevator muscles of the mandible i.e. anterior temporalis and masseter) was monitored over 6 months.
Results revealed a significant increase in postural and maximum clenching EMG activity, attributed to enhanced stretch (myotactic) 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 and not through passive tension.
The position of the mandible did not change significantly after fatiguing the protrusive muscles. It appeared that lateral pterygoid muscle was not responsible for new position of mandible after treatment with Twin Block. It is possible that TMJ adapted to displacement of mandible by condylar growth and surface modeling of the fossa.
1. 2.
3. 4. 5. 6.
Lund & Sandler (AJO 1998) compared 36 subjects (mean age 12.4 years) with 27 controls. The subjects showed favourable changes including : forward positioning of mandible increase in mandibular length (Ar-Pog – 2.4 mm more than controls) increase in SNB angle increase in lower anterior facial height overjet reduction by 7.5 mm buccal segment correction
Similar favourable changes reported by Caldwell & Cook (EJO 1999), Mills & McCulloch (AJO 2000) Toth (AJO 1999) Baccetti, Franchi & McNamara (2000 AJO)
Kevin O’Brien et al (AJO 2003) conducted a Multicenter trial in U.K. evaluating the effectiveness of early orthodontic treatment with the Twin-Block for Class II Div. 1 malocclusion.
They concluded that early treatment with the Twin-Block is effective in reducing overjet and severity of malocclusion. Most of this correction was due to dento-alveolar change.
Consist of – Upper and lower removable acrylic plates with bite blocks – Clasps to retain the appliances – Expansion screws.
Base plate Heat or cold cold cure cure acrylic Advantages Advantages - additional strength of heat cure - speed and and convenience convenience of cold cure Preformed bite blocks - manufactured in the correct size and shape for addition to cold cure acrylic
The lower block Covers Covers the occlusal surface of the t he lower premolars premolars or deciduous molars to occlude with the inclined plane on the upper block Extends to the distal marginal ridge of 2 nd premolar Flat occlusal bite bi te block - thinner thin ner buccolingual buccolingually ly in the lower lower canine region - allows freedom of tongue movement Angulation of blocks in relation to line of arch at right angles – advantage is that angulation maintained even after widening the archform along the line of alignment of teeth
Upper bite block Extends from the mesial surface of the upper second premolar posteriorly to first molar Only the lingual cusps of the upper posterior teeth need to be covered rather than the full occlusal surface – allows flexibility of clasp & ease of adjustment
Wire Components :
The clasps used in the standard twin block appliance are
Delta Clasp in the upper 1st molar Delta clasp in the th e lower lower 1st premolar Ball end interdental clasps in anterior region in both arches
Delta Clasp (0.7 to 6.75 mm SS wire)
The earliest twin blocks b locks had Adam’s Adam’s clasps Disadvantage Disadvantage - opens up slightly with repeated insertions and removal, which causes metal fatigue
Clark designed Delta clasp in 1985 Retentive loop was designed as closed triangula tr iangularr shaped loop and hence the name
Later the shape became circular for ease of bending (bird beak pliers No. 139)
Advantage Adva ntage The clasp does not open with repeated insertion in sertion and removal and therefore maintains better retention retention and requires less adjustment The apex of the t he triangle can be directed into mesial or distal interdental area, or The base of the triangle trian gle can be adapted adapted against the surface of the the tooth to form a line contact In deciduous dentition, C clasps are used for better retention
Labial Bow Used when severely proclined incisors need uprighting Should not be activated until correction of molar relationship has taken place otherwise the over jet may be reduced thus acting as a barrier, and limiting functional correction by mandiblular advancement
Expansion Screw Included in the upper appliance for compensatory expansion in the upper arch to accommodate the lower arch as the mandible translates forward Upper and lower midline screws may be used for unequal expansion Must act in horizontal plane not inclined downwards anteriorly
Activation Twice a week in growing children – one quarter turn of each screw at midweek and at the week end Less activation may be required for older children where tooth movements are slower
CONSTRUCTION Good set of impressions 2. Accurate construction bite 3. Models mounted on an articulator 1.
BITE REGISTRATION There are two types of bite gauges used to register bite for twin block: 1. 2.
George bite gauge Exactobite gauge
George bite gauge Has a sliding jig attached to a millimeter scale Designed to measure the protrusion path of the mandible determine accurately the amount of activation registered in the construction bite.
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
Exactobite or Projet 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 for construction of twin blocks 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.
Guidelines Horizontal consideration According to the Roccabado (1992), the position of maximal protrusion is not a physiological position and the range of physiological movement of the mandible is only 70% of the total protrusive path. This is also called freedom of movement.
Total protrusion path is calculated by measuring the overjet in most retruded position and then in the most maximal protrusion and finding the difference between the two. The initial activation should not exceed 70% of the protrusive path Average 5 – 10 mm on initial activation, depending upon the freedom of movement in protrusion function This degree of activation allows an overjet as large as 10 mm to be corrected
Midline consideration Centre lines should be coincident provided no dental asymmetry is present
Vertical consideration Two factors determine the amount of vertical clearance Thickness of the bite block Adequate vertical clearance must be available between the cusps of the upper and lower first premolars or deciduous molars to accommodate blocks of sufficient thickness (5 mm) to activate the appliance
Freeway Space Activation must open the bite beyond the freeway space to ensure that the patient can not drop the mandible into rest position and negate the proprioceptive functional response of the inclined planes
Intergingival height To establish the correct vertical dimension Measured from gingival margin of upper incisor to gingival margin of lower incisor when teeth are in occlusion Comfort zone for intergingival height for patients is generally found to be 17-19 mm Height of upper & lower incisors minus overbite
Horizontal Vs Vertical growth pattern Horizontal growth pattern - maintain edge to edge incisor relationship more easily (provided the overjet is not excessive) Vertical growth patterns – 1. May not tolerate the same degree of sagittal activation (weak musculature) 2. A smaller initial activation is necessary 3. Gradual mandibular advancement
Angulations of the inclined planes Earliest appliances articulated at 90° angle Difficult maintain a forward posture – blocks occluded on each other - posterior open bite Angle of inclination was changed from 90° to 45°.
The 45° inclined plane : Applies downward & forward components of force to the lower dentition which are equal to each other. So, After 8 years, the angulation was finally changed to the steeper angle of 70°. It was reasoned that this may encourage more forward mandibular growth.
Three phases
Active phase Support phase Retention phase
Active Phase Twin blocks are worn full time The objective is to correct arch relationships in the anterior-posterior vertical transverse dimensions Normally overjet and overbite are corrected within 6 months and the lower molars have erupted into occlusion into 9 months The average time is 6 – 9 months
Clinical management during active phase
Instructions to the patient 1st visit Ways to insert and remove the appliance Operation of screw – The screw is turned for the first time after the appliance has been worn for one week. Twice a week after one week. Once mid-week and again on the weekend Patient should be instructed to eat with the appliance Proper cleaning especially after eating
The clinician should check that the patient bites comfortably in a protrusive bite Overjet is measured for future reference The lingual acrylic of the appliance must be relieved The clasps are adjusted If a labial bow is present, it should be out of contact with the upper incisors
2nd visit : after 10 days Should be comfortable with the appliance If the patient is failing to posture forward consistently, reduce activation by trimming the inclined planes to achieve patient compliance
To correct deep bite Trimming of upper block occlusodistally by 1mm in case of deep overbite. No trimming should be done in case of reduced overbite or open bite.
3rd visit : after 4 weeks: Positive Progress must be noted Review of progress – reduction of OJ and correction of molar relationship. Adjustment of labial bow to keep out of contact (This is because we don’t want any retraction which would hamper mandibular growth Check up for screw activation & its effects Trimming of upper block as needed
4th visit : after 6 weeks Similar pattern of adjustment. REACTIVATION OF TWIN BLOCKS:
To increase the forward posture - by the addition of the cold cure acrylic to extend the anterior incline of the upper twin block
No acrylic added to distal of lower block Preformed blocks -reactivation of 2, 3 or 5mm increments maybe cold cured or light cured into place
Reactivation is needed when Protrusive path of mandible is restricted requiring gradual and progressive activation, as in a) Overjet is greater than 10mm b) In vertical growth pattern when patient cannot tolerate 10mm protrusion c) In adult treatment, when the muscles and ligaments are less responsive to a sudden large displacement of the mandible d) TMJ dysfunction
Support Phase The aim is to retain the corrected incisor relationship until buccal segment occlusion is fully established
An upper removable appliance with steep anterior inclined guide plane
The lower appliance is left out at this stage and the posterior bite blocks are removed to allow the posterior teeth to erupt into occlusion The upper and lower buccal teeth are usually in occlusion within 3 - 6 months. Full time wear necessary to allow time for internal bony remodeling - important phase, stability is excellent after twin block treatment which can be attributed partly to the supportive phase
Retention phase A normal period of retention follows treatment after occlusion is fully established During the retention period the appliance wear can be gradually reduced to night time wear Extends for 9 months usually
Average treatment time Active phase- 6-9 months Support phase- 3-6 months Retention phase- 9 months Average treatment time 18 months
Monitoring Condylar Position During Treatment
X-rays to evaluate position of condyle in the glenoid fossa
Before Rx with the teeth in contact Downward and forward position of the condyle when the appliance is inserted After the overjet has been reduced On completion of Rx
Incorporation of additional screws
Twin block Schwarz appliance
Twin block sagittal appliance
Incorporation of springs Springs can be fitted for individual teeth movement. They can be used to procline retroclined incisors in case of Class II div 2 malocclusion
Twin block Crozat appliance
Magnetic Twin Block To increase occlusal contact on the bite blocks Samarium cobalt and Neodynium boron magnets Attracting magnets Increased activation can be built Increase frequency and force of contact on the inclined planes, thus enhances the adaptive response
Repelling magnets Used with less activation built into the inclined plane Intended to apply additional stimulus to posture the mandible forward
Disadvantages —
Amount of activation not clear Reactivation would deactivate the magnet
Moss & Shaw 1990 reported a 50% increased rate of correction of overjet compared to a similar group of patients without the magnets
Twin block with Concorde face bow Indications
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 mandibular growth cannot assist the correction of a severe malocclusion
The Concorde face bow is a new means of applying intermaxillary and extraoral traction to restrict maxillary growth and at the same time to encourage mandibular growth in combination with functional mandibular protrusion
A conventional face bow is adapted by soldering a recurved labial hook to extend forward to rest outside the lips as an anchor point to combine intermaxillary and extraoral traction.
Intermaxillary traction was added to the appliance system to ensure that if the patient postured out of the appliance during the night the intermaxillary traction force would increase. This ensured that the appliance was effective 24 hrs per day.
Fixation of twin block Prior to fixation, teeth first fissure sealed and treated with topical fluoride : Two methods Zinc oxide or zinc phosphate cement Direct application of composites around clasps
Twin block Transpalatal arch
Twin block Hyrax appliance
Twin block lingual arch
Advantages of fixed Twin block
Patient cooperation not required
Works 24 hrs a day
No transitional phase between functional phase and the fixed phase so treatment time is reduced
Twin block with fixed appliance Simultaneous correction of arch relationship and alignment The presence of bite blocks prevents traumatic occlusion on the fixed attachments and avoid breakage as a result of excessive overbite An easy transition may then be made to a full fixed appliance phase to detail the occlusion and complete the treatment.
Criterias : Angles Class II division I malocclusion with good arch form Uncrowded or well aligned lower arch Upper arch that is aligned or can be aligned An overjet of 10 -12 mm and a deep overbite A full unit distal occlusion in the buccal segments Clinically good VTO Patient in active phase of growth
Treatment of deep overbite Trimming upper twin block occlusodistally to encourage eruption of the lower molars (separators can be placed) 1-2 mm clearance over the lower molars The inclined plane must remain intact, however to maintain the activation to propel the mandible down and forward
Vertical development slower than sagittal correction Should therefore be made as early as possible in treatment to allow vertical development to proceed concurrently with sagittal correction
Treatment Of Reduced Overbite Bite registration Activation should not be more than 70% of the total protrusive path Yellow Projet or exactobite to register a 4mm interincisal clearance with a 5mm clearance in premolar region Bite should be opened beyond the freeway space
Appliance design All posterior teeth must be in occlusal contact with the opposite bite blocks to prevent their overeruption In the lower appliance clasps placed on first molars to prevent their eruption Second molar eruption should be controlled by placing occlusal rests or extending the upper twin block distally
Orthopedic traction and Palatal spinner Application of intrusive orthopedic forces may be used to help control vertical growth
Intraoral elastic – first used by Dr Christine Mills Effective especially in vertical growers with weak musculature
Magnetic force - attracting or repelling force on the inclined plane.
Treatment Of Class II Div 2 Bite registration Incisors in an edge to edge occlusion
Appliance design
Sagittal screws Sagittal and transverse Three way screw
Springs
Triple Screw 20 – 80% ratio of posterior to anterior movement Designed to improve archform in anteroposterior and transverse dimensions simultaneously with improvement of vertical dimension due to twin block therapy
Treatment of class III Reverse Twin Blocks Have a reverse angulation of inclined planes to advance the maxilla using the lower arch as anchorage Important that the patients condyles are not displaced superiorly and or posteriorly in the glenoid fossae at full occlusion The force vector passes from the lower molar towards the gonial angle which is best able to absorb occlusal forces
Bite registration Not the same degree of activation because of less scope for distal displacement of the mandible Downward and backward forces absorbed at the gonial angle Teeth closed to position of maximum retrusion, leaving sufficient clearance between post teeth for bite blocks (2 mm interincisal clearance in fully retruded position)
Appliance design Three way expansion screw Distal movement of upper molars resisted by occlusion of lower bite blocks – net effect – forward driving force on upper arch
Lip pads Should be attached to the anterior segment of appliance
Reverse pull face mask Elastic force increased gradually 4-6 months of wear using heavy forces Can be used as a nighttime auxiliary
Treatment during mixed dentition Appliance modification Limited retention in deciduous teeth Methods to improve retention: Use of C clasp Bond composite on to the buccal surface of to create an undercut or Bond C clasp directly to deciduous molar
Synthetic crown contours, which are bonded onto the buccal surface to improve retention Grinding a concavity for a ball clasp Grinding retention grooves into buccal surface
Treatment Of Asymmetry
Effective in correction of facial and dental asymmetry.
Occlusal inclined plane ideal for unilateral activation
Appliance design Sagittal screws - more frequent turning of screw on the side that requires more distal movement Use of magnets
Treatment of TMJ Indicated in-early click when condyle is displaced distal to the disc Following objectives are attained
Immediate relief from pain Retraining of muscles to a healthy pattern & relief of muscle spasm Recapturing of disc by downward & forward posture of mandible Movement of teeth causing occlusal imbalance
Sagittal twin block – relieves compression on the joint Important to maintain posterior occlusal support at all times Full time commitment from patient
Comfort Patient wear twin blocks 24 hr per day and eat comfortably Aesthetics Twin blocks can be designed with no visible anterior wires without losing efficiency in correction of arch relationships. Function There is less interface with normal functions because the mandible can move freely in anterior and lateral excursion without being restricted by a bulky one piece appliance
Patient compliance Twin blocks maybe fixed to the teeth temporarily or permanently Removable twin blocks can be fixed in the mouth for the first week or 10 days of treatment Facial appearance The appearance is noticeably improved when twin blocks are fitted Improvements in the facial balance are seen progressively in the first three months of treatment.
Speech Patients can learn to speak normally with twin blocks. Does not distort speech by restricting movements of the tongue, lips or mandible
Clinical management Adjustment and activation is simple. The appliances are robust and not prone to breakage. Chairside time is reduced in achieving major orthopedic correction
Arch development Twin blocks allow independent control of upper and lower arch width Appliance design is easily modified for transverse and sagittal arch development
Mandibular repositioning Full time appliance wear consistently achieves rapid mandibular repositioning that remains stable out of retention
Vertical control Twin blocks achieve excellent control of the vertical dimension in treatment of deep over bite and anterior open bite Facial asymmetry Asymmetrical activation corrects facial and dental asymmetry in the growing child
Safety Twin blocks can be worn during sports activities with the exception of swimming and violent contact sports, when they may be removed for safety Efficiency Twin blocks achieve more rapid control of malocclusion compared to one piece functional appliances because they are worn full time
Age of treatment Arch relationships can be corrected from early childhood to adulthood However treatment is slower in adults but the response is less predictable
Integration with fixed appliances Simultaneous skeletal correction and alignment During the support phase an easy transition can be made to fixed appliances
Effects on hard tissue McNamara et al 1999 19 99 Studied the t he Rx effects produced by Twin Twin block and FR-II appliance appli ance compared compared with an untreated control group 1)Increase in mandibular length in Twin Block -3.0mm Frankel -1.9mm
2)Increase in lower anterior facial height was more in Twin block group 3)More extensive dentoalveolar adaptation adaptat ion was observed more m ore with the tooth borne Twin block block appliance
Effects on soft tissue
Rapid changes in craniofacial musculature due to altered muscle function. As appliance is worn full time, even during eating, rapid soft issue adaptation adapta tion occurs. Significant facial changes within 2-3 weeks.
Twin Block appliance increases the intermaxillary space - difficult diff icult to form an anterior oral seal by contact between the tongue and the lower lip patients adopt a natural lip seal without instruction. Good lip seal is a functional necessity to prevent food and liquid escaping from the mouth - so, no need for lip exercises.
Within a few days of fitting the appliances, the position of muscle balance is altered so that it becomes painful for the patient to retract the mandible. This has been described as the “Pterygoid Response” (McNamara) Formation of a tension zone distal to the condyle (Harvold)
Evaluation was done to see whether the protrusive muscles were responsible for mandibular repositioning after Twin Block therapy. It was found that fatiguing these muscles did not alter mandibular position in Twin block group after 6 months of treatment
In the pursuit of ideals in orthodontics, facial balance and harmony are of equal importance to dental and occlusal perfection We cannot afford to ignore the importance of orthopedic techniques in achieving these goals by growth guidance during the formative years of facial and dental development
Twin Block Functional Therapy - Applications in Dentofacial Orthopaedics.William J Clark
WJ Clark. The twin block technique. A functional orthopedic appliance system.AJODO1988;93(1):1-18 Illing et al. A prospective evaluation of Bass, Bionator and Twin block appliances. Part I-the hard tissues. EJO1998;20:501-516 Chintakanon et al. Effects of Twin block therapy on protrusive muscle functions.AJODO2000;118:392-6
