Biomechnics in orthodontics /certified fixed orthodontic courses by Indian dental academy

BIOMECHANICS IN ORTHODONTICS

INDIAN DENTAL ACADEMY

Leader in continuing dental education
www.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.”


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.

HISTORY OF ORTHOPEDICS:

(In 1920)
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”.

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.
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.

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)

Clinical conditions requiring
orthopedics:
Transverse: (maxilla)
CROSS BITE:

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


Antero-posterior:
CLASS-II MALOCCLUSIONS:
•Prognathic maxilla
•Retrognathism of mandible,
•Combination type.


CLAS-III MALOCCLUSIONS:
•Mandibular Prognathism
•Maxillary deficiency,
•Combination types.


Vertical:
•OPEN BITE
Skeletal open bite
•Vertical maxillary excess
.


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 expander

Orthopedic Appliances to correct antero
posterior variations:-

Extra oral traction:
Headgears•Cervical pull headgear.
•High pull headgear.
•Combination type.
•Protraction headgear.

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 expander

Palatal expansion:
The final expansion seen is usually a combination of
skeletal and dental 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 inwww.indiandentalacademy.com dimension.
the transverse

(AJO-DO 1970 Mar Andrew J Haas)
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.

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.
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.

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.
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.

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.


Biomechanics of Headgear

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.

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


Cervical headgear(Kloehn)
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.

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.

Bio mechanics of cervical headgear:
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.

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.

PROTRACTION HEADGEAR:
Protraction headgear is used for skeletal and dental
protraction of the maxilla in C-III malocclusions caused by a
maxillary deficiency.
1) Hickam chincup.
2) Delaire face mask.


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.

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 classII 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.

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 logface 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.

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 excess

Chincup treatment: occipital pull chin cup; vertical pull
chiun cup
Occipital pull chin cup

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

Soft elastic appliance

Interlandi-type appliance


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

Unitek design www.indiandentalacademy.com
Summit design

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 wellplanned force systems.

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Biomechnics in orthodontics /certified fixed orthodontic courses by Indian dental academy

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