Growth control 2

GROWTH CONTROL
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THEORIES OF GROWTH CONTROL
GENETIC & EPI GENETIC
Always at the forefront of any growth control
discussion is the old and perplexing question of
the real extent of “genetic” control.
The role of genetic preprogramming has long been
presumed by many to have a fundamental and
perhaps overriding influence in establishing basic
facial pattern and the features upon which internal
and external “environment” then begins to play.

 Recent researches have not been able to accept
the idea that simply stated, genes are the
exclusive determinants for all growth parameters
including regional amounts, velocities and minute
details of regional configerations.
 For eg, an osteoclast, a prechondroblast or a
contractile fibroblast each does its cellular
function when activated and it then ceases when
signals deactivate it.
 Its own internal genes are not the actual “starter
and stopper”.

 Thus, the intercellular condition activate an
intracellular process.
 A key factor is the recognition that the epigenetic
regulation can determine, to a substantial extent,
the behavioral growth activities of “genic” tissue
types.
 This means that these developmental “genic”
tissues do not actually govern their own
functions, rather, the role in growth is controlled
by epigenetic influence from other tissue groups
and their functional, structural, and
developmental input signals.
 In this hypothesis “Environment is not just
permissive & supportive but also regulative”.

BIOMECHANICAL FORCES
A powerful line of reasoning has historically
focused on the play of physical forces acting
on a bone to regulate its development ,
morphologic configuration, histological
structure and physical structure.
Wolff’s law of bone transformation,
introduced in late 1800’s quickly became a
leading and most useful working concept,and
is still quite valid.

 According to Wolff’s law a bone grows and
develops in such a manner that the composite of
physiologic forces exerted on it are accomodated
by the bone’s developmental process, thereby
adapting structure to the complex of functions.
 A major flaw in Wolff’s law has been lack of
distiction between physical forces acting on a
bone ( i.e. its hard part) and forces acting on the
osteogenic connective tissues ( periosteum,
growth cartilages, sutures, etc.) that actually
produce and remodel the bone.

SUTURES, CONDYLES AND
SYNCHONDROSES
 It was presumed that the growth, form and
dimension of a bone are governed by intrinsic
genetic programming residing within that bone’s
own bone – producing cells of the periosteum,
sutures and bone related cartilages.
 While influences such as harmones, and muscle
actions could augment these gene – dominent
growth determinants, bones such as mandible or
maxilla, and all of their morphologic features,
were held to be largely self – generated products.

 The displacements of bones as they enlarge
were also attributed to the expansive forces
residing within their osteogenic sutures and
cartilages and a “ thrust” by the new bone
tissues they produce.
 The idea expanded to include the concept
of growth “centers” that were presumed to
provide inclusive growth regulation for
each of the whole bones they serve.

 Today, most researchers discount the
notion of such “master growth centers”
replacing it with the concept of regional
“sites” of growth, each of which is
localized area having its own regional
circumstances and conditions and which
operates under its own regional process of
growth control.

THE NASAL SEPTUM
 It became understood that “centers” such as the facial
sutures, cannot actually drive the nasomaxillary complex
into downward and forward displacement. This is because
the suture is a traction – adapted (not a “pushing” and
pressure – adapted) type of tissues.
 James Scott, reasoned that the cartilaginous nasal septum
has features and occupies a strategic position that might
answer the question of what “motor” causes the midface
to displace anteriorly and inferiorly as it grows in size.
 Because cartilage is more pressure – tolerant tissue than
the vascular – sensitive sutures, it presumably has the
developmental capacity to expansively push the whole
nasomaxillary complex downward and forward. With this
thought, Scott’s famous nasal septum theory was born.

THE FUNCTIONAL MATRIX
 According to Moss, the head is a composite
structure , operationally consisting of a number of
relatively independent functions, olefaction,
respiration, vision, digestion, speech, audition,
equilibration and neural integration. Each
function is carried out by group of soft tissues,
which are supported and protected by skeletal
elements.
 Taken together, the soft tissues and skeletal
elements related to a single function are termed as
functional cranial component.

 The totality of all skeletal elements
associated with single function is termed as
skeletal unit.
 The totality of soft tissues associated with
single function is termed as functional
matrix.
 It may be further demonstrated that the
origin, growth and maintenance of the
skeletal unit depend almost exclusively
upon its related functional matrix.

The form (size and shape ) of any given skeletal
unit is related entirely to the form of its functional
matrix.
Two basic types of such matrixs are –
Periosteal
Capsular
Periosteal matrices act upon skeletal units in a
direct fashion by the process of osseous deposition
and resorption or of cartilaginous or fibrous tissue
multiplication. Their net effect is to alter the form
of their respective skeletal units.

 Capsular matrices act upon functional
cranial component as a whole in a
secondary and indirect manner. They do so
by altering the volume of the capsules
within which the functional cranial
components are embedded. The effect of
such growth changes is to cause a passive
translation of these cranial components in
space.

 Moss emphatically states that “bones have no
genes” although he admits that the origin of bone
form is primarily due to genetic factors upto a
certain point. After this unknown point, all
further morphologic changes are influenced by
environmental factors, eg: the maxilla origin,
determined by intrinsic genetic factor, but
thereafter all morphologic changes are influenced
by extrinsic or environmental factor which are
vision, olefaction, respiration, speech, digestion
and deglutation.

 Moss observed that any defect of the
functional matrix will result in a defect in
the skeletal unit associated with it and
that a defect in one cranial component
does not necessarily result in defects in
the other components nor is the growth
and development of one skeletal unit
necessarily related to the growth of
others.

 Functional matrix concept deals primarily
with the ultimate source of osteogenetic
regulation. Any genetic predetermination
of a bone morphologic characteristics by
self contained chromosomal design is
largely bypassed.
 The role of genes in cellular orgenelle
functioning (e.g. production of specific
tissue proteins – enzymes etc.) in response
to extracellular messangers that activate a
given cell, physiologic part in the grand
scheme.

 Stimuli emanating from the growth and actions of
any and every source within growing head and
body ( the functional matrix)directly or indirectly
function to turn on or turn off cellular organelle
activity in the bone producing cells. This yields
growing, changing, custom – fitted bone having
regional dimensions and configurations that
accommodate the changing developmental
conditions and biomechanical circumstances in
each localized region of each separate bone and
the aggregate of all bones in an interrelated
system. Each bone is precisely adopted to these
multiple developmental conditions because it is
composite of the conditions that regulate a bone’s
configuration, size fitting and timing involved.

CONTROL MESSENGERS
 Growth is carried out by specific , restricted
regional fields, each of which has differing
growth activity in amounts , directions, velocities,
and timing.
 The diverse cell populations within each of these
fields respond to activating intracellular or
extracellular signals.
 “First messengers” are extracellular activators for
which specific cell-surface receptors are
selectively sensitive. They include
biomechanical, bioelectric,hormonal, enzymatic,
oxygen,carbon dioxide etc., factors.

 A reception signal then fires a cascade of
“second messengers” within a given cell
that results in function of that cell and its
organelles, such as fiber production,
proteoglycan production, calcification,acid
or alkaline phosphatase secretion, and rate
and duration of mitotic cell divisions.
Adenyl cyclase and cAMP are second
messengers leading to cytoplasmic and
nuclear DNA – RNA transfers.

 In the immediate environment enclosing an
osteoblast or osteoclast, a first – messenger hormone
or enzyme, a bioelectric potential change, or a
pressure / tension factor acting on the cell’s outer
sensory membrane receptors can activate a second
messenger (membrane-bound adenyl cyclase), which
in turn accelerates the transformation of ATP to
cAMP within the cytoplasm, which then activates
the synthesis of other specific enzymes relating
specifically to bone deposition or resorption. Ionic
calcium is mobilized from mitochondrion storage,
and inner and outer membrane permeability is
altered that selectively controls the flux of other ions
in the synthesis and discharge of the products
secreted by the cell.

BIOELECTRIC SIGNALS
 The idea in brief , is that distortions of the
collagen crystals in bone, caused by minute
deformations of the bone matrix due to
mechanical strains, generate bioelectric
charges in the immediate area of
deformation (i.e. the piezo effect). These
altered electric potentials appear to relate ,
either directly or indirectly, to the
triggering of osteroblastic and osteoclastic
responses.

 There are two separate target categories for
the mechanical actions of muscles, and also
the effect of muscle and soft tissue growth
enlargements, gravity, and all other such
physical sources.
 One target is the cellular component of the
osteogenic connective tissues that cover a
bone. The outer surfaces of these cells are
loaded with receptors that are sensitive to
the direct effects of first messenger agents
and forces.

 The second basic target category is the calcified
part of the bone itself, the matrix, in contrast to
the covering connective tissues just mentioned.
 Mechanical forces produced both by growth and
by function acting on the calcified matrix cause
minute distortions that generate positive and
negative polarities.
 A minute concavity under active distortion is
known to emanate a negative(-) bioelectric
charge, and convexity generates a positive(+)
charge.

 Negative(-) charges then transmit to the
osteogenic cells within the connective tissue on
the concave side, firing osteoblast into a
depository activity.
 A positive(+) charge on the convex side activates
an osteoclastic resposne.
 The result is coordinated regional remodelling,
inside and outside surfaces alike, that shapes the
bone and enlarges its overall size.
 When mechanical equilibrium is achieved
between the bone and composite of growth and
functional forces playing on it, the polarities are
neutralized and remodeling activities are turned
off.

 While the piezo electric effect has been
found to be a good model for long-bone
remodeling, recent studies suggest that
other factors may be involved in tooth
movement and alveolar bone remodeling.
(Tuncay et al., 1990,1994)

NEUROTROPIC FACTOR
 It involves the network of nerves (all kinds,
motor as well as sensory) as links for feedback
interrelationships among all the soft tissues and
bone.
 The nerves are believed to provide pathways for
stimuli that presumably can trigger certain bone
and soft tissue remodeling responses.
 It is not believed, however, that this process is
carried out by actual nervous impulses. Rather it
appears to function by transport of neurosecretory
material along nerve tracts or by an exoplasmic
streaming within the neuron.

 In this way, feed back information is passed, eg;
from the connective tissue stroma of muscle to
the osteogenic periosteum of the bone associated
with that muscle.
 The “functional matrix” thereby operates to
govern the bone’s development.
 It is an interesting but yet incomplete hypothesis
in need of more study.

 A skeletal orthodontic problem may be defined as
one resulting not from malpositioned teeth on well
proportional jaws, but from a disproportion in the
size or position of the jaw themselves.
 Skeletal problem can occur in all 3 planes of space :
Anteroposterior plane – skeletal class II & classIII
Vertical – skeletal open bite or deep bite
Transeverse – skeletal crossbites
GROWTH MODIFICATION

 Only 3 approaches to the correction of
skeletal malocclusion are possible
1. Modification of growth
2. Camouflage of skeletal discrepancy
3. Surgical correction
The key decision in treatment planning is
selection of appropriate form of treatment.

Growth Modification
 Whenever a jaw discrepancy exists , the ideal solution is
to correct it by modifying growth, so that the skeletal
problem literally disappears as the child grows.
 There are 3 theoretic possibilities for growth
modification.
1. An absolute increase or decrease in the size of jaws.
2. Change in the spacial relation without increasing or
decreasing the size of skeletal structures. i.e. a change in
jaw orientation.
3. Acceleration of desirable growth.

Although last two of these theoretic possibilities
can be shown to occur but absolute inhibition of
growth & true growth stimulation leading to
absolute increase in jaw size is considerably
doubtful.
( Robertson 1983 , Weislander 1979 )
Most of the changes that occur during growth
modification can be explained by redirection of
growth and changes in its timing.

Timing of growth modification
 If the growth has to be modified, the
patient has to be growing.
 Growth modification must be done before
the adolescent growth spurt ends.

Principles in growth modification
 Maxilla grows by :
Apposition of new bone at posterior and superior
sutures,
In response to being pushed forward by
lengthening cranial base,
And pulled downward and forward by the growth
of adjacent soft tissues
 Tension at the sutures as maxilla is displaced
from its supporting structures appears to be the
stimulus for new bone formation.

 Similarly, the mandible is pulled downward
and forward by soft tissues in which it is
embedded. In response, the condylar process
grows upward and backward to maintain
temperomandibular articulation.

 If this is so, it seems entirely reasonable that
pressures resisting the downward and forward
movement of either of the jaw should
decrease the amount of growth, while adding
to the forces that pull them downward &
forward should increase their growth.

 Growth modification either through a
functional appliance or extraoral force is
aimed at maxillary sutures and / or
mandibular condyles.
 Therapy must be based on specific patients
problems
Mandibular
deficiency
Maxillary
Excess
Maxillary
deficiency
Mandibular
excess

Treatment of mandibular deficiency
 Functional appliance stimulate & enhance
mandibular growth and are obvious choice for
treatment.
 In functional appliance treatment, additional
growth is supposed to occur in response to the
movement of mandibular condyle out of the jaws,
mediated by reduced pressure on condylar tissues
or by altered muscle tension on the condyle.

 An acceleration of mandibular growth often
occurs but a long term increase in size is difficult
to demonstrate.
 An effect on maxilla, although small, is almost
always observed along with mandibular effects.
 When the mandible is held forward, the
elasticity of soft tissues produces a reactive force
against maxilla, and restrained of maxillary
growth often occurs.

 Functional appliances, especially the tooth
borne once, often place a distal force against
the upper incisors that tends to tip them
lingually.
 Most functional appliances exert a protrusive
effect on mandibular dentition because the
appliance contact the lower teeth and some of
the reaction from forward posturing of
mandible is transmitted to them.

 The combination of maxillary dental retraction &
mandibular dental protrusion that all functional
appliances create is similar to the effect of interarch
elastic ("class II elastic effect")
 The ideal patient for functional appliance should
have –
1. Normal or slightly excessive maxillary
development
2. Normal vertical height ( not long face )
3. Slightly protrusive maxillary incisor teeth
4. Normally positioned or retrusive but not protrusive
lower incisors.

 Mandibular dental protrusion usually
contraindicate functional appliance treatment.
 Functional appliance also can influence
eruption of posterior and anterior teeth. If
upper posterior are prohibited from erupting
and moving forward while lower posterior
teeth are erupting up & forward, the resulting
rotation of occlusal plane and forward
movement of dentition will contribute to
correction of class II dental relationship.

 The other possible treatment of mandibular
deficiency is to restrain growth of maxilla
with extraoral force and let the mandible
continuing to grow more or less normally,
catch up.
 Functional appliances are usually preferred
for mixed dentition treatment of mandibular
deficiency.

Treatment of vertical deficiency
(Short face )
 Skeletal vertical deficiency occurs almost always
in conjunction with an anterior deep bite , some
degree of mandibular deficiency and often with a
classII div.2 malocclusion.
 The reduced face height is often accompanied by
everted and prominent lips ( That would be
appropriate if face height were normal ).

 Growth is expressed in an anterior direction with a
tendency towards upward and forward rotation of the
mandible.
 The challenge in correcting this problems is to
increase the eruption of posterior teeth & influence
the mandible to rotate downward without decreasing
chin prominence too much.
 One way of correcting the problem is with cervical
headgear , taking advantage of the extrusive
tendency of the extraoral force directed below the
center of resistance of the teeth and maxilla.

 The other way is to use a functional appliance
( with or without mandibular advancement,
depending on the anteroposterior jaw
relationships ) that allows free eruption of the
posterior teeth.
 Cervical headgear produces more eruption of
the upper molars, while eruption can be
manipulated with a functional appliance so
that either the upper or lower molars erupts
more.

 Class II correction is easier if the lower
molars erupts more than the upper, which
means that – all other factors being equal –
the functional appliance would be preferred.
 The fixed functional appliances (herbst) are
not good choices in the mixed dentition
treatment of short face problems as it has
propensity to intrude the upper molars.

Treatment of maxillary excess
 Excessive growth of the maxilla in children with
class II malocclusion often has a vertical as well
as an antero-posterior component ( i.e. there is
too much downward as well as forward growth )
 Both the components can contribute to skeletal
class II malocclusion , because if the maxilla
moves downward, the mandible rotates
downwards & backwards. Thus the mandibular
growth is prevented from being expressed
anteriorly.

 The goal of treatment is the restrict growth of
the maxilla while the mandible grows into a
more prominent and normal relationship with
it.
 Application of Extraoral force is the obvious
approach but functional appliance treatment
also can be helpful, particularly in the
treatment of excessive vertical growth.

Effects of headgear to maxilla
 Extraoral force against maxilla decrease the
forward and / or downward growth by changing
the pattern of apposition of bone at sutures.
 Class II correction is obtained as the mandible
grows forward normally while the similar
forward growth of maxilla is restrained.
(mandibular growth is a necessary part of
treatment response )

 Extraoral force is almost always applied to
first molars via a facebow with a head cap or
a neckstrap for anchorage.
 To be effective , headgear should be worn 10
– 12 hrs per day, everyday , with emphasis on
wearing it from early evening ( right after
dinner ) until the next morning.
 The current recommendation is a force of 12
to 16 ounces (350 – 450 gms) per side.

 To correct a class II malocclusion, the
mandible needs to grow forward relative to
maxilla. For this reason it is important to
control the vertical position of maxilla &
maxillary posterior teeth.
 Downward movement of either the jaw or
teeth tends to projects the mandibular growth
more vertically, which nullifies most of the
forward mandibular growth that reduces class
II relationship.

Selection of headgear type
 3 major decisions to be made while selection
of headgear
1. Headgear anchorage location ?
2. How the headgear is to be attached to the
dentition ?
3. Whether bodily movement or tipping of the
teeth or maxilla is desired ?

 The length & position of outer headgear bow and the
form of anchorage ( i.e. headcap, neckstrap or
combination) determine the vector of force & its
relationship to the center of resistance of tooth.
These factors determine the molar movement.
 Thus straight pull or high pull headgear is preferred
over cervical headgear, to reduce elongation of
maxillary molars & better control the inclination of
mandibular plane.
 Functional appliance types that minimize tooth
movement are preffered to obtain maxillary skeletal
effects & minimize compensatory tooth movement.

Vertical Excess
 Excessive face height (e.g., with a skeletal open
bite or long face syndrome ) generally have a
normal upper face and elongation of maxillary
and mandibular posterior teeth, which accounts
for the steep mandibular plane and large
discrepancy between posterior and anterior face
height.
 The ideal treatment for these patients would be to
control all subsequent vertical growth so that the
mandible would rotate in an upward and forward
direction.

Hierarchy of effectiveness in
long - face class II treatment
HP headgear to functional with bite blocks
Bite blocks on functional appliance
High – pull headgear to maxillary splint
High – pull headgear to molars

Maxillary deficiency
 Skeletal maxillary constriction, which is
distinguished by a narrow palatal vault, usually
produces a posterior crossbite, and posterior
crossbite due to a narrow maxilla is an indication
for treatment at the time it is discovered.
 It can be corrected by opening the midpalatal
suture, which widens the roof of the mouth and
floor of the nose at any time prior to the end of
the adolescent growth spurt.

 Several methods of arch expansion are possible, but
to obtain skeletal effects, it is necessary to place
force directly across the suture.
 In preadolescent children, 3 methods can be used
for palatal expansion :
A split removable plate with a jackscrew or heavy
midline spring.
A lingual arch, often of the quad – helix design.
A fixed palatal expander with a jackscrew that is
either banded or bonded.

The palatal expander can be activated for either
rapid (0.5 mm or more per day), semirapid
(0.25mm/day), or slow (1mm/week) expansion.
 PALATAL EXPANSION IN PRIMARY
AND EARLY MIXED DENTITION.
 PALATAL EXPANSION IN THE LATE
MIXED DENTITION.

Anteroposterior and vertical
maxillary deficiency
 Both anteroposterior and vertical maxillary
deficiency can contribute to class III
malocclusion. If the maxilla is small or positioned
posteriorly, the effect is direct.
 If it does not grow vertically, the mandible rotates
upward and forward, producing an appearance of
mandibular prognathism that may be due more to
the position of the mandible than its size.

 For the children with a–p and vertical maxillary
deficiency , the preferred treatment is to move the
maxilla into a more anterior and inferior position,
which also increases its size, as bone is added at the
posterior and superior sutures.
 As with transverse expansion, it is easier and more
effective to move the maxilla forward at younger
ages.
 When force is applied to the teeth for transmission to
the sutures, tooth movement in addition to skeletal
change is ineviatable.

 Generally, it is better to defer maxillary protraction until the
permanent first molars have erupted and can be incorporated
into the anchorage unit.
 Face mask obtains anchorage from the forehead and chin,
used to exert a forward force on the maxilla via elastics that
attach to a maxillary appliance.
 To resist tooth movement as much as possible, the maxillary
teeth should be splinted together as a single unit.The
appliance must have hooks for attachment to the face mask
that are located in the canine–primary molar area above the
occlusal plane. This place the force vector is nearer the center
of resistance of the maxilla and limits maxillary rotation.

 Approximately 12 ounces of force per side is applied
for 14 hrs per day.
 Most children with maxillary deficiency are deficient
vertically as well as anteroposteriorly,thus, slight
dawnward direction of elastic traction between
intraoral attachment & the facemask frame is
desirable.
 Moving the maxilla down as well as forward,rotates
the mandible dawnward and backward,which
contributes to correction of a skeletal class lll
relationship.
 Downward pull would be contraindicated , however,
if lower face height were already large.

 Although the goal of facemask therapy is
forward displacement of the maxilla, both
downward–backward rotation of the
mandible, backward displacement of the
mandibular teeth, and forward displacement
of the maxillary teeth typically occur in
response to this type of treatment.

Functional appliances for maxillary
protraction.
 Frankel’s FR-III appliance, stretch the periosteum in a way
that stimulates forward growth of the maxilla.
 The available data , however, indicate little true forward
movement of the upper jaw. Instead, most of the
improvements is from dental changes. ( AJO 1994 )
 The appliances, allows the maxillary molars to erupt and
move mesially while holding the lower molars in place
vertically and anteroposteriorly, tips the maxillary anterior
teeth facially and retracts the mandibular anterior teeth. This
tooth movement helps in the development of a normal
overbite and overjet but has little effect on the skeletal
malocclusion.
 In short, functional appliance treatment, even with the use of
upper lip pads, has little or no effect on maxillary retrusion

Mandibular Excess
 Children who have class III malocclusion because
of excessive growth of the mandible are
extremely difficult to treat.
 The treatment of choice would appear to be a
restraining device (e.g. chin cup / chin cap ) to
inhibit the growth of the mandible, at least
preventing it from projecting forward as much as
otherwise would have occurred.
 Functional appliances also have been advocated
for mandibular excess patients.

 Inhibiting mandibular growth has
proven to be almost impossible , so with
both types of appliances, the major
effect is downward and backward
rotation of the mandible, which
decreases anteroposterior projection of
the chin by making the face longer.

Extraoral force to the mandible
CHIN CUP TREATMENT
• Chin cup therapy accomplish a change in
direction of mandibular growth, rotating the chin
down and back.
• In addition, lingual tipping of the lower incisors
occurs as a result of the pressure of the appliance
on the lower lip and dentition.
• This type of treatment is appropriate with normal
or reduced lower anterior face height but is
contraindicated for a child who has excessive
lower face height.

 A hard chin cup can be custom fitted from
plastic, using an impression of the chin, a
commercial metal or plastic cup can be used if
it fits well enough ; or a soft cup can be made
from a football helmet chin strap.
 A force of 16 - 24 ounces per side is directed
through the head of the condyle or a
somewhat lighter force below the condyle.

Class III Functional Appliances
 Class III functional appliances for excessive mandibular
growth make no pretense of restraining mandibular
growth.
 They are designed to rotate the mandible down and back
and to guide the eruption of the teeth so that the upper
posterior teeth erupt down and forward while eruption of
lower teeth is restrained.
 These appliances also tip the mandibular incisors
lingually and the maxillary incisors facially, introducing
an element of dental camouflage for the skeletal
discrepancy.

 Modifying true mandibular prognathism is a
difficult task regardless of the chosen method.
 For a child with severe prognathism, no
treatment until orthognathic surgery can be
done at the end of the growth period may be
the best treatment.

Growth control 2

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