Biomech of Head Gear-Ortho / orthodontic courses by Indian dental academy

www.indiandentalacademy.com


INDIAN DENTAL ACADEMY

Leader in continuing dental educationwww.indiandentalacademy.com

“The crux of the variety of reports implying a direct or stimulating link between function and size is that tissue size is not an inheritable trait per se. Instead, the tissues and the organs which they comprise have a predetermined capacity to modify their sizes in response to the changing physiological conditions which impact these tissues and organs.”

Alphonse R.Burdi,

Professor of Anatomy, University of Michigan.


INTRODUCTION (Chaconas)

There are two types of forces used in orthodontics:

Orthodontic or tooth-moving forces, and orthopedic forces that affect the deeper craniofacial structures.

Orthodontic forces are those that are applied to the teeth by the wires of removable and fixed appliances. The force produced by adjustments to these wires ranges from 1 to 5 ounces, where as orthopedic forces are much greater.


DENTOFACIAL ORTHOPEDICS:(Pfeiffer&Grobety)

Treatment directed towards altering the relationship of the bony elements of the jaws and the pattern of activity of the oro-facial musculature.ORTHOPEDICS (Bioprogressive therapy; JCO 1978 Jan)

Orthopedics implies any manipulation that alters the skeletal system and associated motor organs. From the practical stand point, in the growing child, orthopedic alteration would be any manipulation which would change the normal growth of the dentofacial complex in either direction or amount.


The alteration of facial and skeletal configuration can be accomplished using 3 methods: (Graber, Rakosi, Petrovic)

1) Functional appliances: Are designed to change the patients pattern of function, alter the jaw relationships, and reprogram the neuro musculature, thus altering the functional matrix of the face.


2) Orthopedic appliances: Are designed to transfer force as directly as possible to the facial skeletal components.Forces generated may be much higher than those used for orthodontic tooth movement.

The appliances effectively influence sutural changes and bone growth. If used at an early age, functional appliances favorably alter the continuing facial growth pattern.


3) Orthognathic surgery: In which the orthodontist cooperates with an oral and maxillofacial surgeon and the treatment plan involves the surgical repositioning of the jaws and skeletal components of the face, is another option.

The use of functional and orthopedic appliances is highly growth dependent, and patients are best treated with these appliances at the earliest possible age.


EDWARD ANGLE and his followers believed that broad skeletal changes could be produced by orthodontic treatment. Any thing was possible, they believed, because malocclusions developed from “environmental factors”.

HISTORY OF ORTHOPEDICS:

(In 1920)


Early studies by BRODIE and others in the late 1940s and 1950s suggested that the skeletal pattern could not be altered significantly. The concepts of “the stability of pattern” was developed, reducing orthodontics primarily to dentoalveolar changes.

In 1936 a paper by OPPENHEIM revived the idea that headgear would serve as a valuable adjunct to treatment.

1940 the cephalometrics available, did not support the ANGLE’S concept.

After world war II, SILAS KLOEHN’S impressive results with headgear treatment of class II malocclusion became widely known.


GOULD has shown how changes in the inclination of the face bow affect the direction of the force and ultimately the direction of tooth movement. (AJO 1957)

GREENSPAN presented reference charts elaborating the different moments and forces produced with the various headgear designs.(AJO 1970)

In 1971 ARMSTRONG demonstrated the importance of the precise control of magnitude, direction, and duration of extra oral force to increase its efficiency and effectiveness in treating malocclusions in the late mixed dentition.(AJO1971)


CROSS BITE:

•Posterior cross bite bilateral or unilateral due to maxillary hypoplasia.

Transverse: (maxilla)

Clinical conditions requiring orthopedics:


CLASS-II MALOCCLUSIONS:

•Prognathic maxilla

•Retrognathism of mandible,•Combination type.

Antero-posterior:


CLAS-III MALOCCLUSIONS:

•Mandibular Prognathism

•Maxillary deficiency,

•Combination types.


•OPEN BITE

Skeletal open bite

•Vertical maxillary excess

.

Vertical:


DEEP BITE:

•Skeletal deep bite.

*Anterior forward rotation of the mandible

*Retroclination of maxillary base.


ORTHOPEDIC APPLIANCES FOR TRANSVERSE PROBLEMS

1. Palatal expansion in primary and early mixed dentition:

• W-arch

• Quad helix

• Fixed Jack screw

2. Palatal expansion in late mixed dentition:

• Palatal expanders- banded, bonded acrylic to teeth

• Hyrax

NiTi-palatal expanderwww.indiandentalacademy.com

Orthopedic Appliances to correct antero posterior variations:- Extra oral traction:Headgears-

•Cervical pull headgear.

•High pull headgear.

•Combination type.

•Protraction headgear.www.indiandentalacademy.com

Functional jaw orthopedics:

•Class-II functional aplliances

Removable functional appliances

Fixed functional appliances


Orthopedic treatment for vertical excess:

•High pull headgear to the molars.

•High pull headgear to a maxillary splint .

•Straight pull headgear.

•Functional appliance with bite blocks.

•High pull headgear to a functional appliance with bite blocks.


Maxillary deficiency:•The Delaire type facemask

•Maxillary protraction headgear

•Functional appliance for maxillary protraction

The Frankel III appliance


Mandibular excess:

•Class-III Functional appliances

•Chin cup treatment

Occipital pull chin cup

Vertical pull chin cup


Treatment for transverse skeletal expansion


Haas type expander

Hyrax expander

Minn-expander

NiTi palatal expanderwww.indiandentalacademy.com

The final expansion seen is usually a combination of skeletal and dental expansion.

Palatal expansion:

The CR of the palatal bones, lies above the line of application of force (which is at the cusps of the molar

teeth). Hence tendency for palatal shelves to rotate buccally in the transverse dimension.www.indiandentalacademy.com

1. Anteroposteriorly, the opening of the midpalatal suture is parallel; inferosuperiorly, the opening is triangular with the apex being in the nasal cavity.

2. The central incisors react as expected, considering that they are linked by elastic transseptal fibers. As the suture opens, the crowns converge while the roots diverge. When the crowns come into contact, the continued pull of the fibers causes the roots to converge toward their original axial inclinations. During this cycle, which usually takes about 4 months, the axial inclination of these teeth may vacillate as much as 50 degrees.

(AJO-DO 1970 Mar Andrew J Haas)


4. When the midpalatal suture opens, the maxilla always moves forward and downward. This is probably due to the disposition of the maxillocranial sutures. Sicher calls attention to the fact that these sutures are oriented in such a manner that growth would produce a downward and forward vector of maxillary movement.

3. The alveolar processes bend and move laterally with the maxillae, while the palatal processes swing inferiorly at their free margin. The effect is a dental arch expansion and an increase in intranasal capacity.


5. The change in maxillary posture invariably causes a downward and backward rotation of the mandible which decreases the effective length of the mandible and increases the vertical dimension of the lower face.

Since these hafting zone sutures are disengaged by the palatal expansion procedure, an effect similar to immediate growth is manifested in a downward and forward displacement of the maxilla.


ORTHOPEDIC TREATMENT IN ANTEROPOSTERIOR

DIMENSION:


Headgear:- Headgear is a common term for an appliance that is used for delivering a posteriorly directed extra oral force to the maxilla. It used in orthodontics to modify growth of maxilla, to distalize and protract maxillary teeth, or to reinforce anchorage.

When headgear is used for skeletal modifications,in growth modification, heavier forces are recommended. Such heavier forces bring about actions (compress) on the sutures of the maxilla, changing the magnitude and direction of their growth, and modifying the pattern of bone apposition at these sites, while the mandible grow normally (catch up with maxilla).


Headgear should usually be worn for at least 8 to 14 hr/day to achieve successful results. For orthopedic changes forces used are in the range of 250 to 500 g per side, and for dental movements they are in the range of 100 to 200 g per side.


The efficient use of the headgear requires a sound knowledge of basic biomechanics. Understanding how to control the direction and magnitude of the forces produced by various headgear designs is paramount in achieving desirable clinical results.

A headgear can deliver only a net single, simple force. A force is a vector quantity, having both a magnitude and a direction. It has a point of application. In addition, it has a line of action. An important principle in analyzing the force system for a headgear is the relationship to the center of resistance of maxilla or the first molar. A force passing through the center of resistance causes pure translation in the direction of the line of the force. Any other force produces translation and a rotation with a moment.

Biomechanics of Headgear


Center of resistance (CR)

Maxillary first molar

Entire maxilla

Entire maxillary teeth


If the LF is moved superiorly, the CRot moves coronally, and one gets a counterclockwise moment.

When the LF is applied through the CR, the object translates (all points of the object move the same distance along parallel lines).

Conversely, a more inferiorly positioned line of force will displace the CRot apically, creating a clockwise moment.


The magnitude of the moment produced by the headgear is calculated by multiplying the perpendicular distance (P) from the LF to the CR by the magnitude of the force. Thus, for a given force, the greater the distance from the CR that the force is applied, the greater will be the moment.

M=Fxd


The cervical headgear is applied in early treatment of C-II malocclusions to inhibit forward displacement of the maxilla or maxillary teeth, while the rest of the dentofacial structures continue their normal growth. This can cause a change in the intermaxillary relationship from C-II to C-I. Change in molar relation due not so much to the distal force, but to the clockwise moment that very effectively tips the molar crown distally.

Disadvantages: causes extrusion of upper

molars, but desirable in patients with short

lower facial heights.

Cervical headgear(Kloehn)


The effect of cervical headgear:

1. To erupt entire upper jaw,

2. To tend to move upper jaw,

3. To steepen the plane of occlusion (positive movement),

4. A first order moment tending to rotate each segment mesial out, distal in,

5. Because of the elastic properties of the inner bow, an expansile force to the upper jaw. www.indiandentalacademy.com

When the outer bow lies along the line of force (LFO), no moment occurs, and the force system will be reduced to a bodily moment in a posterior and extrusive direction.

If the outer bow is placed above this line, the moment produced by the force will be in a counter clockwise direction.

Bio mechanics of cervical headgear:


If the outer bow adjusted below this line, the moment created will be clockwise.

Shorter outer bow, there is tendency to steepen the occlusal plane.

Longer outer bow, there is tendency to flatten the occlusal plane. www.indiandentalacademy.com

PROTRACTION HEADGEAR:

1) Hickam chincup.

2) Delaire face mask.

Protraction headgear is used for skeletal and dental protraction of the maxilla in C-III malocclusions caused by a maxillary deficiency.


Biomechanics of protraction headgear: Protraction headgear exerts a mesial force on the maxilla below the center of resistance with an equal and opposite reciprocal force on the chin and forehead. The force on the chin may cause a change in the posture of the mandible that may effect its direction of growth. The counter clockwise moment on the maxilla and dentition caused by the line of force acting below the center of resistance leads to a tendency for extrusion of the maxillary posterior teeth with an associated opening of the bite.


Straight-pull headgear: This style headgear is a combination of the high-pull and cervical headgear, with the advantage of increased versatality.


Uses:• This is a choice in a C-II malocclusion with no vertical problems.

• To prevent anterior migration of maxillary teeth, or possibly translate them posteriorly.

Advantage:• It produces an essentially pure posterior translatory force. It is accomplished by placing the LFO through the CR, parallel to the occlusal plane.


Biomechanics of straight-pull headgear:Outer bow above LFO; will produce a posterior force, counter clockwise rotation, and most often an intrusive force.

If the LFO cants up anteriorly (attachment site of elastic is lower on headcap than at outer bow); an extrusive force will be produced.

If the outer bow is below LFO; the force produced will be posterior and superior and attachment will be in a clockwise direction. www.indiandentalacademy.com

ORTHOPEDIC TREATMENT FOR VERTICAL PROBLEMS


HIGH PULL HEADGEAR

This consists of a typical face bow (inner & outer bow) and a harness, which fits over the occiput of the head. It is commonly used in class-II correction in which controlling anterior open bite tendencies is part of problem. This style headgear always produces an intrusive and posterior direction of pull, due to the position of the headcap. www.indiandentalacademy.com

Biomechanics of high-pull headgear: If the outer bow is placed anterior to the LFO, either above or below the occlusal plane level, the moment produced will be in a clockwise direction. The magnitude of this moment will be proportional to the distance of the outer bow to the CR.

If a distal and intrusive movement with no moment is desired, the outer bow must be placed some where along the LFO. This force system would be beneficial in a log-face C-II patients with a high mandibular plane angle, where intrusion of maxillary molars would decrease facial height and improve the facial profile.


Short outer bow angulated high, this results in a force system at the unit’s CR with a moment that tends to flatten the occlusal plane and distal and intrusive force components.

The headgear forces line of action passes through the unit’s center of resistance with longer outer bow, no moment at CR & therefore no change in the cant of the occlusal plane, intrusive and distal components of the force are acting.

With longer outer bow, steepens plane of occlusion and a force with intrusive and distal components.such system might be

necessary for class-II open bite patients. www.indiandentalacademy.com

Vertical-pull headgear:

The main purpose of this headgear is to produce an intrusive direction of force to maxillary teeth, with posteriorly directed forces.

It is very useful when pure intrusion of buccal segments is required, as in the class-I open bite patient,


Bio mechanics of vertical pull headgear:•If the bow is hooked to the headcap so that the line of force is perpendicular to the occlusal plane and through the CR, pure intrusion may take place.

•If the outer bow placed anywhere in the anterior compartment,-counter clockwise moment;intrusive and posterior force.

•If the outer bow placed anywhere in the posterior section,-clockwise moment,vertical intrusive & horizontal forward forces


High pull headgear to a maxillary splint:

Used when a child with excessive vertical development of the entire maxillary arch and too much exposure of the maxillary incisors from beneath the lip.


Treatment for vertical mandibular excessChincup treatment: occipital pull chin cup; vertical pull chiun cup Occipital pull chin cup

Soft elastic appliance Interlandi-type appliance

Used in patients with short lower anterior facial height, pull of chin cup is below the condyle.


Vertical pull chin cup

Unitek design Summit design

It results in a decrease in the mandibular plane angle, & gonial angle; and increase in posterior facial height.


CONCLUSION Understanding how to control the direction and magnitude of the forces produced by various orthopedic appliances is paramount in achieving desirable clinical results. Decreasing the patients length of treatment and improving the treatment results would be the two benefits derived from applying well-planned force systems.



www.indiandentalacademy.comLeader in continuing dental education

Biomech of Head Gear-Ortho / orthodontic courses by Indian dental academy

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