Tissue response with new changes

Tissue reaction toTissue reaction to
dentofacial orthopedicdentofacial orthopedic
appliancesappliances
www.indiandentalacademy.com

Past 20 years have seen an increasing awareness
of the potential of Dentofacial Orthopedic
appliances as a valuable tool in armamentarium of
orthodontist.
They are important weapons in the arsenal and can
accomplish results which are not possible with
mechanical appliances.
Introduction

Dentofacial orthopedic appliances have
been designed
to affect neuro-muscular and functional
pattern
to impede or enhance growth vector or
growth magnitude
to achieve tooth movement

The goal of dentofacial orthopedic
appliances is to elicit a proprioceptive
response in the stretch receptors of the
orofacial muscles, ligaments and in
sutures, and as a secondary response, to
influence the pattern of bone growth
corresponding to support a new functional
environment for the developing dentofacial
complex

Historical Background
Julius Wolff 1892, presented the law of bone
transformation which illustrates form and function
relationship
Wolff stated, every change in form and function of
bone, or in there function alone, is followed by
certain definite changes in their internal
architecture and equally definitive secondary
alterations in their external conformation in
accordance with mathematical laws

Culmann 1866 developed a mathematical
“trajectorial theory” of bone architecture based on
the principle of stress directions in more
homogeneous materials
Rodan and Martin 1981, Komn et al 1988 and
Erickson 1988 - osteoclast differentiation may
require interaction with osteoblast or their
precursors
Historical
Background

Frost 1964, Parfitt 1979 defined pathways of
remodeling process by Quantum Theory
• Replacement of bone occurs in quantized packets
through the coordinated action of organized cellular
units.
• These units were called basic multicellular unit or
BMU.
Historical
Background

Basset 1964 –
Bent bone can be straightened if bone is removed
from the tensile side and added to the compression
side. This implies that remodeling is controlled by
the polarity of the tangential wall stress: tensile
stress favor osteoclastic activity while compression
stress favor osteoblastic activity.
Historical
Background

Frost 1964 - Flexural Neutralization Theory (FNT)
• Remodeling is not controlled by the polarity of
tangential wall stress (i.e. compression or tension)
but by the tendency of the applied load to alter the
relative curvature of the surface
• Increased surface convexity stimulate osteoclastic
activity and decreased surface convexity favored
osteoblastic activity
Historical
Background

Lanyon and Smith 1969, 1970 ………
• First method of quantification of bone adaptation to
mechanical loading.
• The principle orientations of trabeculae coincides
with the principle compressive and principle tensile
strain directions.
This was the first quantitative experimental
demonstration of “Wolff’s law”
Historical
Background

Principles of Dentofacial
Orthopedics
Growth, Modeling and Remodeling
Form and Function Relationship

Modeling and Remodeling
Principles of Dentofacial Orthopedics

Sigma
RemodelingRemodeling
A-R-F cycleA-R-F cycle

Form and Function relation
Melvin Moss in 1960’s suggested that function
of soft tissues surrounding the dentofacial
skeleton (i.e. Functional Matrix) determines the
form of the underlying Skeletal Units.
Many orthopedic appliances used in Functional
Jaw Orthopedics, alter the function of various
function matrices resulting in the alteration in
form of skeletal units

Factors Controlling Bone Modeling
Mechanical
– Disuse atrophy
– Bone Maintenance
– Physiological Hypertrophy
– Pathological overload

Endocrine
– Bone metabolic hormones
– PTH, Vitamin D, Calcitonin
– Growth Hormones
– IGF I, IGF II, Somatotropin
– Sex Steroids
– Testosterone, Estrogen
Paracrine and Autocrine
– Wide variety of local agents

Factors Controlling Bone Remodeling
• Metabolic
– PTH – increases activation frequency
– Estrogen – increases activation frequency
• Mechanical
– Peak load in microstrain<1000 uE, more
remodeling
– Peak load in microstrain>2000 uE, less
remodelling
– Where uE represents percent deformation X 10-4

Role of Calcium in bone
modeling and remodeling

Decreased Serum Ca++
Increased PTH
Increased Vitamin D
Bone
Immediate
Increased Ca++ diffusion from bone fluid
Short-Term
Increased Resorption and Decreased formation
Long-Term
Increased remodeling frequency
Increased Serum Ca++

Methods of studying Bone
physiology
Accurate assessment of the orthodontic or
orthopedic response to applied loads requires
time markers (bone labels) and physiologic
indices (deoxyribonucleic acid [DNA] labels,
histochemistry, and in situ hybridization) of bone
cell function.

1. Mineralized sections
2. Polarized light
3. Fluorescent labels
4. Microradiography
5. Autoradiography
6. Nuclear volume morphometry
7. Cell kinetics
8. Finite element modeling (FEM)
9. Microelectrodes
physiology

Mineralized sections
• Effective means of preserving structure and
function relationships accurately.
• Less processing distortion occurs.
• The inorganic mineral and organic matrix can be
studied simultaneously.
• Even without bone labels, micro radiographic
images of polished mineralized sections provide
substantial information about the strength,
maturation, and turnover rate of cortical bone.
physiology

Polarized light
• Detects the preferential
orientation of collagen
fibers in the bone matrix.
• Loading conditions at the
time of bone formation
dictates the orientation of
the collagen fibers to best
resist the loads to which
the bone is exposed.
physiology

• Permanently mark all sites
of bone mineralization at a
specific point of time.
• Histomorphometric
analysis of label incidence
and interlabel distance is
an effective method of
determining the
mechanisms of bone
growth and functional
adaptation
Fluorescent labels
physiology

They fluoresce at different wavelengths (colors), six
bone labels can be used:
(1) tetracycline (10 mg/kg, bright yellow);
(2) calcein green (5 mg/kg, bright green);
(3) xylenol orange (60 mg/kg, orange);
(4) alizarin complexone (20 mg/kg, red);
(5) demeclocyclin (10 mg/kg, gold); and
(6) oxytetracycline (10 mg/kg, greenish yellow)
physiology

Microradiography
• Assesses mineral
density patterns.
• Provides information
about the growth and
adaptation of the
skeletal sites most
affected by orthodontic
and facial orthopedic
treatment.
physiology

Autoradiography
• Specific radioactive labels for
proteins, carbohydrates, and
nucleic acids are injected at a
known interval before tissue
sampling is done.
3H-thymidine labeling of cells
synthesizing DNA (S phase
cells)
3H -proline labeling of newly
formed bone matrix.
physiology
O – original bone
P – PDL
N – New bone
→ - Radioactive labelswww.indiandentalacademy.com

Nuclear volume morphometry
• Used for assessing the mechanism of
osteogenesis in orthodontically activated PDL’s
• Measuring the size of the nucleus is a
cytomorphometric procedure for assessing the
stage of differentiation of osteoblast precursor
cells.
physiology

• Increase in nuclear size (A' to C) that occurs as
committed osteoprogenitor cells (A' cells)
differentiate to preosteoblasts (C cells) is the rate-
limiting step in osteoblast histogenesis.
• A localized mechanical stimulus (orthodontic force),
creates a reciprocal pulse of A - A’ and C - D
waves that generate huge numbers of osteoblasts.
Cell kinetics
physiology

• To assess stresses and strains within mechanically
loaded structures.
• The estimates of initial stress have been useful for
defining the mechanical conditions for initiating
orthodontically induced bone resorption and
formation.
Finite element modeling (FEM)
physiology

Microelectrodes
• Detect electrical potential changes associated with
mechanical loading.
• Used to measure changes in electrical potential in
the extracellular space of the PDL during the initial
response to orthodontic force.
• Widened areas of the PDL have a more negative
electrical potential, and compressed areas have a
more positive electrical potential.
physiology

Normal Histology of tissues in
Dentofacial Complex

Bone
• Dense outer sheet of compact bone
• Central medullary cavity (bone marrow).
Normal Histology
Osteon
Osteocytes
Haversian
Systems

Periosteum
• Outer layer
• Inner layer
• Endosteum………
This membrane consists of a
layer of loose connective
tissue, with osteogenic cells
that physically separates the
bone surface from the
marrow within
Normal Histology

Woven bone
• The first bone formed in
response to any trauma,
osteotomies and
orthodontic loading.
• It is compacted to form
composite bone,
remodeled to lamellar
bone, or rapidly resorbed
if prematurely loaded.
Normal Histology

Lamellar bone
• A strong, highly organized,
well-mineralized tissue,
makes up more than 99%
of the adult human
skeleton.
• The full strength of
lamellar bone is not
achieved until
approximately 1 year after
completion of active
treatment.
Normal Histology

Composite bone
• Composite bone is an osseous tissue formed by
the deposition of lamellar bone within a woven
bone lattice, a process called cancellous
compaction.
• Composite bone is an important intermediary
type of bone in the physiologic response to
orthodontic loading.
Normal Histology

Suture
Normal Histology

Five Layers of Suture (at birth)
(Pritchard et al 1956)
Normal Histology

Five Layer Vs Three Layer Concept of suture
During Suture formation, there are five layers i.e.
cellular and fibrous layer of both bones and
additional intervening loose mesenchymal layer
(Pritchard et al 1956)
Moss (1957) and Weinman and Sicher (1955)
– Three layered concept i.e two interconnecting
fibrous layer with a highly cellular middle zone
Normal Histology

Which Concept is Correct?
Normal Histology

Enlow 1968, Latham 1971, Kokich 1976
-Single fibrous membrane
-No evidence of any definitive layers
Normal Histology

Temporomandibular joint
Ginglymo-arthodial joint
Normal Histology

Condylar cartilage
• A fibrous connective tissue
layer, (surface articular zone)
• A highly cellular intermediate
layer (transitional or
proliferative zone)
• A cartilage layer with
irregularly arranged
chondrocytes, (hypertrophic
zone)
• A zone with endochondral
bone ossification (bone
formative zone).
Normal Histology
Articular disk
Articular zone
Proliferative
zone
Fibrocartila-
genous zone
Calcified
cartilage
Subarticular
bone

Articular disc
Normal Histology
• Anterior part
– Collagen fibers
arranged transversely
& in AP bundles
– Avascular
• Posterior part
– Loose textured, fibrous
C.T. richly supplied with
blood vessels and
nerve endingswww.indiandentalacademy.com

Changes in bone tissue can be in
the form of
Piezoelectric Concept
Periosteal Pull

Piezoelectricity
Piezoelectricity in bone is an
electric change produced by
the deformation of crystalline
structure such as
hydroxyapetite crystals,
collagen and fibrous proteins,
which is believed to stimulate
bone cells and thus bone
formation.

Periosteal pull
• The matrix producing and proliferating cells
in the cambium layer of periosteum are
subjected to mechanical stimuli
• The mesenchymal cells in periosteum
under tension acquire the character of
osteoblasts and it responds with bone
deposition.
• Whenever the pressure exceeds a certain
threshold, reducing the blood supply to
these cells, osteogenesis ceases.

Tissue Response

Response of PDL to Orthodontic Force
• Changes in PDL are
of Coordinated
modeling and
remodeling process
• Intermittent loads
( headgear – 12
hrs/day) result in
tooth movement
Tissue Response

Response in PDL improves with
Increased loading time
Increased Duration
Night time wear
Roberts and Fergusson, 1989 –
3 hour of continuous loading is necessary to
achieve maximum displacement of tooth within
PDL and trigger the cellular responses
necessary to resorb and form bone
PDL Response

Roberts et al, Morey 1979, 1985
suggested that maximum cell proliferation
in PDL occurs during resting hours i.e.
night time for humans.
PDL Response

Orthopedic effects

Effects of mandibular advancement:
• Anterior glenoid fossa relocation
• Condylar displacement in the glenoid fossa
• Proliferation of the posterior part of the fibrous
disc
• Maxillary and mandibular tooth movement
• Changes in maxillary position.

Two concepts of adaptation
1. Increased condylar growth
2. Remodeling of the glenoid fossa i.e. anterior
relocation of glenoid fossa

Glenoid fossa and Articular disc
response to mandibular advancement
The new bone formation appeared to be localized
in the primary attachment area of the posterior
fibrous tissue of the articular disc in the direction of
tension exerted by the stretched fibers of the
posterior part of the disc.

The posterior part of the articular disc, between the
postglenoid spine and the posterior part of the
condyle shows increase in thickness and active
cellular and connective tissue response associated
with numerous enlarged fibroblasts in active stage.
This response stabilize the anterior condylar
displacement
Glenoid fossa and Articular disc response

Changes from day 3- 14
E
X
P
E
R
I
M
E
N
T
A
L
C
O
N
T
R
O
L
3 days 3 days
7 days 7 days
14 days 14 days

Changes from day 14- 30
E
X
P
E
R
I
M
E
N
T
A
L
C
O
N
T
R
O
L
14 days 14 days
21 days 21days
30 days 30 days

Control group
1 Step advancement
Step-wise advancement

Mandibular protrusion resulted in the
osteoprogenitor cells being oriented in the
direction of the pull of the posterior fibers
of the disc and also resulted in a
considerable increase in bone formation
(wolfs law) in the glenoid fossa .

Condylar response
Expression of Sox 9
It is a high mobility group
type transcription factor that
controls the differentiation
of mesenchymal cells in
chondrocytes by directly
activating gene expression
for Type II Collagen

Hypertrophy and hyperplasia
of the prechondroblastic and
chondroblastic layers of the
condylar cartilage
Deposition of new bone also
occurred along the anterior
surface of the postglenoid
spine.
Condylar response

Forward mandibular positioning accelerates and
enhances chondrocyte differentiation and cartilage
matrix formation in the mandibular condyle by
accelerating and enhancing the expression of Sox 9
and type II collagen.
Natural growth 40 days Forward positioning 5 days
ExperimentalControl
Condylar response

Natural growth 42 days
Natural growth 95 days
Forward positioning 7 days
Forward positioning 44 days
ExperimentalControl
Condylar response

A mandibular retrusion by chin cup therapy in
the animal study revealed a reduced thickness
of the prechondroblastic zone and a decrease
in the number of dividing cells.
Chin cup treatment had a retarding effect on
mandibular growth.
Effects of Mandibular Retrusion

ExperimentalControl

Experimental
Control
3 days 7 days 14 dayswww.indiandentalacademy.com

Response in Sutures
Compression of Facial Sutures
Stretching (Tension) of Facial Sutures
What is the sutural response to the
forces? www.indiandentalacademy.com

Effects of continuous
Headgear force
Sutural Response

Vitallium splint
Attached to Extra oral source of anchorage
Coil springs provided a force 700 gm at an angle
400
to occlusal plane
Force applied for 2 months
Sutural Response
Elder and Tuenge
1974

Cephalometrically…..
• Maxillary dentition moved
posterosuperiorly
• 50% change due to tooth movement
• 50% due to changes in bone
• Distance between implants decreased
• Significant changes in Zygomatico-
maxillary and Zygomatico-temporal suture
Sutural Response

Histologically…
• Marked resorptive activity of the
compressed zygomaticomaxillary and
zygomaticotemporal sutures
• Endosteal and periosteal compensatory
deposition
• Normal deposition in control samples
ExperimentalControl
Sutural Response

Posteriorly directed extra oral force to
the maxilla not only inhibits sutural
growth, but produces a significant
posterior displacement of the maxilla
Sutural Response

Is this Change Permanent?
What happens to the growth at the
sutures and the position of the
maxilla when force is
discontinued?
Sutural Response

Stability of changes in the Zygomatico-
maxillary and Zygomatico-temporal suture.. ?
It is possible through the use of extra-oral
traction to temporarily modify or redirect the
pattern of sutural growth
The skeletal changes are more stable over
the long term than the dental changes
Sutural Response

Would the result be more stable if
the forces were applied
intermittently?
Sutural Response

Brousseau and Kubisch 1977
Sample – 7 monkeys prepared with implants
headholders, splints and headgears
Amount of skeletal change was greater in
animals with continuous force
Inter-implant distance in continuous force
showed 2.4 times more skeletal change and
about 2 times more dental changes than the
intermittent group
Continuous Vs Intermittent
Sutural Response

• In both the groups, nearly all the dental changes
relapsed
• Sutures simply began to show bone deposition
with downward and forward growth of maxilla
• The greater the retraction of maxilla achieved
during the treatment, the greater the net
retraction maintained in post-treatment phase
Sutural Response

Jackson et al 1979
Sample – 4 Macaca nemestrina
Significant remodeling of all circummaxillary
sutures occured
Interimplant distance showed 3 – 5 times
separation in the sutures
Sutural response to Protraction Forces
Sutural Response

Histologically
Substantial widening with deposition at the bony
margins and the long collagenous bundles
traversing the sutural space
ExperimentalControl
Sutural Response

Histologically
Retaining the increased sutural width allowed bone
to fill in at the sutural margins, narrowing the
sutural gap and providing more stable result.
ExperimentalControl
Sutural Response

What 21What 21stst
century will bring tocentury will bring to
Dentofacial Orthopedics ?Dentofacial Orthopedics ?www.indiandentalacademy.com

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