Orthopaedic appliances

IntroductionIn orthodontic practice ,forces employed are basically of two types

-Orthodontic force (that moves the teeth efficiently ):applied using wires and other active components of fixed and removable or fixed appliancesForce produced by this appliances are light and range from 50-100 grams

-Orthopaedic force (effect the deeper cranio-facial structures):The orthopedic forces on the other hand are heavy forces of over 400 grams that bring about a change in the skeletal tissue

-Forces applied to the teeth have the potential to radiate outwards and affect the nearby skeletal structures.

-For such skeletal changes to occur, the forces employed should be over 400 grams.

-Thus the orthopedic appliances utilize the teeth as handles to transmit the forces to the adjacent skeletal structures.

-In order to produce skeletal changes, consideration should be given to the AMOUNT OF FORCE APPLIED and the DURATION OF FORCE.

BASIS FOR ORTHOPAEDIC APPLIANCES

AMOUNT OF FORCE

Heavy forces of over 400 grams totally compress the periodontal ligament on the pressure side and cause hyalinization that prevents the tooth movement.These heavy forces are conducted to the skeletal structures to produce an orthopedic effect.

DURATION OF FORCE

Intermittent forces ranges from 12-14 hours a day are believed to bring about minimum tooth movement but maximum skeletal change

The commonly used orthopedic appliances are A . HEAD GEAR

B . FACE MASK C . CHIN CUP

HEAD GEAR

Head gears

HEAD GEARMost commonly used extra oral orthopedic applianceUsed during the growth period to intercept or correct certain skeletal malocclusions as well as to distalize the maxillary dentition or maxilla itself.Also form one of the important adjuncts to control or gain anchorage.They derive anchorage from the cervical or the cranial regions.The major 3 components 1. Face bow2. The force element3. The head cap or cervical strap

FACE BOWTwo types of face bow1. Inner and outer bow type2. J hook type

Inner-outer bow typeThe face bow is a metallic component that helps in transmitting the extraoral forces on to the posterior teeth. The face bow consist of :A . Outer bow B . Inner bow C . Junction

Outer bow is made up of 1.5mm stiff round wire and is contoured to fit around the face the outer bow can be short, medium or long Short –outer bow is lesser in length than inner bow Medium – outer bow length equal to inner bow Long – outer bow is longer than inner bow The distal end of the outer bow is curved to form a hook that gives attachment to the force element .

Inner bow is made up of 1.25mm round stainless steel wire and contoured around the dental arch and molars .The inner bow is inserted in to the buccal tubes fixed on the maxillary first molars. Stops are placed on the inner bow from sliding too far through the tubes

The junction is the rigid joint of inner and outer bow it can be a. Simple soldered b. Wrapped soldered or c. Welded joint It is placed at the midline of the bows in case of symmetric forces required it can be shifted from midline when asymmetric forces are needed

Inner bow attached to the tube on first molar

junction

The ‘J’ hook type of face bow It consist of two 0.072 inch curved wire whose ends form hooks that are contoured to fit over a small soldered stop on the maxillary arch wire their normal site of attachment on the arch wire is between the lateral incisor and canine .the j hook type of face bow is therefore used along with maxillary fixed appliance having a continuous arch wire they are used for retraction of maxillary anteriors and have limited orthopaedic indications

The force elementIt is that part of the assembly which provides the force to bring about desired effect .this may comprise of Springs, elastics and other stretchable materials. The force element connects the face bow to the head cap or neck strap

The head cap or cervical strap The appliance takes anchorage from the rigid bones of the skull or from the back of the neck by means of a Head cap or a neck strap or a combination of the to the selection of this depends upon the individual patients needs

Principles in the use of headgears Headgear have the ability to move the dentition and the maxilla in all the three planes of space .

Factors to be considered when planning the use of headgears include A . Centre of resistance of the dentition :The inner bow of the face bow is generally attached to the maxillary first Permanent molars through buccal tubes on these teeth .Thus the force acting on the molars tends to displace them. A decision should be made whether bodily movement or tipping movement of the teeth is required .

B . Centre of resistance of maxilla The centre of resistance of maxilla as whole should also be considered when planning for headgears .It is believed to exist at the posteriosuperior aspect of zygomaticomaxillary suture . Under clinical Conditions the centre of resistance of the dental arch , as a whole should be considered this is located between the roots of the premolars

Forces passing through the centre of resistance of maxilla produce translation of the maxilla in a distal direction . While forces passing above or below this point causes rotation of the maxilla

The center of resistance for a molar is usually at the mid-root region. -Force applied at center of resistance causes bodily movement -Force applied below center of resistance causes distal crown tipping -Force applied above center of resistance cause distal root tipping

C . The point of origin of force Headgears derive anchorage from the occipital region of the cranium or the cervical region(back of the neck) . Occipital headgears produce a superior and distal force on the teeth and the maxilla , while cervical headgears inferior and distal force. Based on this criteria type of anchorage(point of origin) is to be selected

D . Point of attachment of forceThe point of attachment refers to the hook present on the distal end of the outer bow to which the force element is attached . It is possible to alter the direction of force to maxilla and the maxillary dentition by altering the point of attachment .

This can be done by varying -the length of the outer bow or

-by varying the angle between the inner and outer bow

Types of headgears Based on the site of anchorage headgears can be :1 . Cervical headgears

2 . Occipital headgears

3 . Combination headgears

4 . Vertical pull headgears

5 . Asymmetrical headgear

Cervical headgears These headgears obtain anchorage from nape of the neck . Cervical headgears causes extrusion of the maxillary molars leading to an increase in the lower facial height .They also move the maxillary dentition and the maxilla in a distal direction .These headgears are generally indicated in low mandibular angle cases , as in increase in lower facial height would be beneficial in such patients

considerationRelation of line of force to the centre of resistance is to be considered as if line of force is passing below the centre of resistance we can expect a clockwise rotation of maxilla

Cervical pull headgear

Occipital headgears These headgears derive anchorage from the back of the head . This type of headgear produces a distal and superiorly directed force on the maxillary teeth and the maxilla . These high pull Headgears produce a more vertically directed force and there for is used in individuals in whom an increase in vertical dimension is to be avoided . They decrease the vertical development of maxilla and there for indicated in long face class 2 patients and in patients with open bite tendencies

Combination headgears In this type of headgear ,occipital and cervical anchorage is combined . When the forces exerted by both are equal , a distal and slightly upward force is exerted on the maxillary dentition and the maxilla . By varying the proportions of the total force derived from the head cap and the neck strap the resultant force direction can be altered

Occipital headgear

Combination headgear

Vertical pull headgearThey are headgears that derive anchorage from the parietal region of the cranium and there for Produce a vertically directed force on maxilla and the maxillary dentition these headgears can be used to produce intrusive forces on the anterior region of the maxilla and there by producing a Counter-clockwise movement of maxilla . This is beneficial in the treatment of vertical maxillary excess and gummy smiles . Intrusive forces on the posterior aspect of maxilla can be of benefit in anterior open bite patients as it intrude the maxillary molars and therefore produces a clockwise movement of maxilla

Asymmetrical headgears They are used when differential anchorage is required on both sides of the maxillary arch. For Example a patient with class 2 molar relation on one side and a class 1 molar relation on the other side can be given an asymmetric headgear . The different force values are produced by Altering the length ofouter bow on each side and by variation of the angle between the outer And inner bows

Uses of headgears

A . Orthopaedic effect : Forces applied onto the maxilla can be used to restrict its downward and forward Growth . The distal force in such a case should be applied through the centre of resistance of the maxilla . The suggested range of force is 350-450 gms on each side for a minimum of 12-14 hrs /days are required Orthopeadic effects from extraoral forces are best tapped in pre adolescent years

B . Anchorage augmentation : Extra oral forces are used to reinforce anchorage when those Obtained from intraoral sources are insufficient . The headgear should be worn for approximately 10 hours/day for this purpose and force values of 300 gms /side are usually sufficient . In the maxilla anchorage reinforcement is achieved by restricting the mesial movement of molars

C . Distalization of molars : distal movement of upper molar may be required for correction of molar relation or to gain space for correction of crowding or retraction of anteriors this can achieved by using it for 14 hrs/ days . Unilateral distalization of molars is achieved using asymmetric headgear of cervical or combination type (larger force on the side of longer bow )D . Molar rotation : in order to derotate a molar the molar has to be banded with the buccal tube placed distally and then subsequently repositioned . Correction is achieved by adjustment of the inner bow so that it produces a rotational force on the molar . As soon as the correction is achieved ,the Face bow should be readjusted to apply a direct distal force

E . Space maintenance : a most effective method of maintaining arch length is by the use of extraoral forces the mesial movement of molar is prevented and the face bow does not interfere with erupting teeth . In this situation daily wear of approx. 8 hrs is sufficient

Face mask

IntroductionHeadgears are generally used for the purpose of reinforcement of anchorage or for maxillary Distalization . However, when an anterior protractory force is required , a protraction headgear is used . Facial mask therapy has gained popularity. The principal of pulling force on the maxillary structures with reciprocal pushing force on the forehead or mandible through facial anchorage is simple and mechanically sound enough to be used as a therapeutic procedure for treatment of prognathic syndromes, maxillary retrusions , clefts and mandibular prognathism

Hickham (1972) claims he was the first to use reverse headgear. However this modality was made popular by Delaire around the same time . A reverse pull headgear basically consists of a rigid extraoral framework , which takesAnchorage from chin or forehead or both for the anterior traction of the maxilla using extraoral Elastics that generate large amount of force up to 1 kg or more

Indications1 . In a growing patient having a prognathic mandible and a retrusive maxilla . It aids in pulling the Maxillary structures forward and pushing mandibular structures backward

2 . It can be used for bending the condylar neck for stimulating temporo-mandibular joint adaptation to posterior displacement of chin

3 . It can also be used for selective rearrangement of the palatal shelves in cleft patients

4 . It can be used in correction of postsurgical relapse osteotomies(or uncontrolled postsurgical Adaptations )

5 . It can also be used to treat certain accessory problems associated with nose morphology such as lateral deviations.

Sites of anchorage Anchorage for the purpose of maxillary retraction can be obtained fromA . Forehead B . Chin C . Or both chin and forehead

Anchorage from chin :This type of protraction head gear is commonly used in Britain ,chin cup with posts are employed . As the anchorage is obtained solely from the chin ,the force is transmitted to the condylar cartilage and thereby has a disadvantage of altering the growth of the mandible

Anchorage from chin & forehead

Anchorage from forehead (skull)

Anchorage from skull :Certain form of reverse pull head gears obtain anchorage only from forehead .The disadvantage include patient discomfort while sleeping , cost and time required in fabrication and fixing

Anchorage from chin & forehead : This face mask makes use of anchorage from both chin and forehead .Anchorage is spread over a larger area . Thus no excessive force is exerted onto the growth cartilage . However the disadvantage with this appliance are difficulty in speech and compromise in esthetics and Comfort due to size

Biomechanical considerations

Amount of force : The amount of force required to bring about skeletal changes is about 1 pound(or 450gms) per side

Direction of force : Most authors recommend a 15-20 degree downward pull to the occlusal plane to produce a pure forward translatory motion of the maxilla . If the line of force is parallel to the Occlusal plane, a forward translation as well as an upward rotation take place .

Duration of force : The time taken to achieve desired result is proportional to the amount of force utilized . Low forces (250 gm /side) take 13 months to produce desired results. However ,very high Force values like 1600-3000gms reduced treatment time to 4 -21 days

Frequency of use : Most authors recommend 12-14 hours of wear a day

Parts of a reverse pull headgear The reverse pull headgear consists of the following parts :

Chin cup: Most protraction headgears obtain anchorage from chin as well as the forehead . The chin cup is used to take anchorage from the chin area . It is usually connected to the rest of the face mask assembly by means of metal rods . The chin cup can the ready-made or can be fabricated from an impression from the patient’s genial region .

Forehead cap : The forehead support or cap or strap is used to derive anchorage from the forehead

Forehead cap

Chin cup

Metal frame

Elastics : Elastic force is used to apply a forward traction on the upper arch . Vertical posts of chin cup are used to attach the elastics on to the molars or hooks soldered on the arch wire . This sort of traction is purely for tooth movement

Intraoral appliance : The most common type of protraction device is a multibanded appliance with ridge Wire. Traction hooks are placed either in the molar or premolar region McNamara advocates a banded R.M.E. along with the protraction device that more or less resembles the banded Herbst appliance

Metal frame : The main component of a face mask assembly is the metal frame . It connects the various components such as the chin cup and the fore head cap . It also has provision to receive elastics from the intraoral appliance . The design of the metal frame differs based on the type of face mask

Metal frame

Elastics

Intraoral appliance

Types of reverse pull head gears

Protraction headgears by Hickham: developed in the early 60’s, this appliance uses the chin and top of the head for anchorage . The force distribution is as follows – 15% head ,85%chin . It consists of two short arms in front of the mouth to engage maxillary protraction elastics .It also has a chin cup from which originate two long arms . The two long arms run parallel to the lower border of the mandible and go vertically up from the angle of mandible and end behind the ears . An elastic strap is attached to the end of the long arms to encircle the headthe advantage of the appliance include relatively better esthetics and comfort than others with the option of unilateral force applicability . By adding a rubber cushion under one arm , Force to that side can be altered

Two short armsChin cup

Long arm

The elastic strap

Parts of hickem’s chincup

Face mask of Delaire :this was popularized by Delaire in the 60’s and also uses the chin and Forehead for support . The appliance is made up of a rigid wire framework which is squarish and kept away from the face . It has a forehead cap and a chin cup with a wire running in front of the mouth used for elastic attachment Tubinger model: this is a modified type of delaire face mask . It consist of a chin cup from which originates two rods that runs in the midline and is shaped to avoid the interference of the nose . The superior ends of the two rods house a forehead cap from which elastics encircle the head .In addition, a crossbar extends in front of the mouth which can be used to engage the elastics .The forehead cap and crossbar can be adjusted by sliding along the rod framework to suit the individual patient.

Forehead cap

framework

Wire running in front of mouth

Chin cup

Delaire face mask Tubinger model

Petit type of face mask : this is also a modified type of Delaire face mask. It consist of a chin Cup and a forehead cap with a single rod running in the midline from forehead cap to chin cup . A cross bar at the level of the mouth is used to engage elastics . The advantage of this model is that the forehead cap ,chin cup and the cross bar can be adjusted to suit the patient

Chin cup

IntroductionThe chin cup or thin cap as it is sometimes referred to is an extraoral orthopaedic device that covers The chin and is connected to a headgear . It is used to restrict the forward and downward growth of the mandible . The chin cup – face bow assembly consist of a chin cup that covers the chin , a head cap and an adjustable elastic strap that connects the chin cup with the head cap

Types of chin cups Chin cups are of two types . They are the occipital pull chin cup and the vertical pull chin cup

Occipital pull chin cup: This type of chin cup derives anchorage from the occipital region of the head . This is the most commonly used type of chin cup . It is used in class 3 malocclusions associated with mild to moderate mandibular prognathism .they are very successful in patients who can bring their incisors close to a edge-to-edge position at centric relation . They are also indicated in patients with slightly protrusive lower incisors as they invariably produce lingual tipping of the lower incisors

Vertical pull chin cup : this type of chin cup derives anchorage from the parietal region of the head . It is indicated In patients with steep mandibular plane angle and excessive anterior facial height . These Patients usually exhibit an anterior open bite

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Occipital pull chin cup

Vertical pull chin cup

Fabrication of chin cupChin cups are either fabricated individually for the patient or pre-fabricated commercially available chin cups can be used . The fabrication of chin cup requires an impression to be taken of the chin area. The cast is poured and the chin cup fabricated using self-cure acrylic resins

Force magnitude and duration of wearAt the time of appliance delivery a force of 150-300 grams per side is used . Over the next two months the force is gradually increased to 450-700grams per side . The patient is asked to wear the appliance for 12-14 hours a day to achieve the desired results

ReferenceOrthodontics the art and science – S.I. Bhalajhi

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