Histological changes in dentofacial orthopaedics1 /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


 Introduction
 Normal histology of bone
 Normal histology of TMJ
 Normal histology of sutures
 Bone dynamics
 Different methods of studying bone dynamics
 Factors affecting remodeling
 Histological changes in dentofacial orthopaedics

 Conclusion

Past 20 years have seen an increasing awareness of
the potential of functional 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.


 Improvement in orthopedic capabilities is

attributed to –
 Increased understanding of the biologic

principals of dentofacial growth and
development
 Improved mechanical capability to effect

skeletal change
 Improvement in diagnostic techniques


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


 Osteoprogenitor cells :
 Stem cells of

mesenchymal origin.
 In adults these are
present over bone
surface ( on both
periosteal & endosteal
aspect).
 They can proliferate &
convert themselves into
osteoblast whenever
there is need for bone
formation.

 Osteoblast :

 Bone forming cells derived from

osteoprogenitor cells.
 They are found lining on growing
surface of the bone.
 Nucleus is ovoid & euchromatic.
 The cytoplasm is basophilic
because of the presence of rough
endoplasmic reticulum.
 Osteoblast is responsible for laying
down the organic matrix of bone
(glycosaminoglycanes, proteoglyca
ns) including collagen fibers.
 Also responsible for calcification of
matrix.

 Osteocyte :

 Cells of the mature bone.
 Lie in the lacunae of the

bone.
 Eosinophilic or light
basophilic cytoplasm.
 Function :
I. Maintain the integrity of
lacunae and canaliculi.
Thus keep the channels
open for diffusion of
nutrition.
II. Removal or deposition of
matrix and calcium
when required.

WB – Woven bone
LB – Lamellar bone
ER – Endoplasmic reticulum


 Osteoclast :
 Bone removing cells

essential for
maintaining proper
shape of the growing
bone.
 Large cells (20 to 100
µm).
 Numerous nuclei (upto
20 or more).


 Bone lining cells :
 These cells form a continuous epithelium like layer on

the bony surfaces where active bone deposition or
removal is not taking place.
 These cells are flattened.
 Present on periosteal as well as endosteal surface.


 Dense outer sheet of compact bone
 Central medullary cavity (bone marrow).

Haversian System
Haversian Canal
Osteocytes


 Periosteum:
 Outer layer.
 Covered the entire surface of the

bone.
 Endosteum:
 Inner layer
 This membrane consists of a layer

of loose connective tissue, with
osteogenic cells that physically
separates the bone surface from the
marrow within

 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.

 It’s a newly formed bone.
 The collagen fibers are present

in bundles that appears to run
randomly in different
directions , interlacing with
each other . That’s why it is
called woven bone.
 It is compacted to form
composite bone, remodeled to
lamellar bone, or rapidly
resorbed if prematurely
loaded.

 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.


 The condyle of mandible

is composed of cancellous
bone covered by a thin
layer of compact bone.
 The trabeculae is
grouped in such a way
that they radiate from the
neck of mandible & reach
the cortex at right angles.
Thus giving maximum
strength to the condyle.

 During the period of

growth a layer of
hyaline cartilage lies
underneath the fibrous
covering of the
condyle. This
cartilaginous grows by
apposition from the
deepest layer of the
covering connective
tissue . At the same
time deepest layer is
replaced by bone.

Fibrous covering
Reverse cell
zone
Secondary
cartilage

Bone
trabeculae

 Articular fibrous covering :
 The condyle as well as articular

trabeculae is covered by a
thick layer of fibrous tissue.
 The fibrous layer covering the
articular surface of temporal
bone is thin in articular fossa
& thickened rapidly in the
posterior slope of articular
trabeculae.
 It has two fibrous layer :
o Inner layer – fibers are
arranged in right angle to bony
surface.
o Outer layer - fibers are
arranged parallel to bony
surface.

Bone

Inner
fibrous
layer
Outer
fibrous
layer

Upper
joint
space

Articular
disc

 Articular disc :

In young individuals the articular disc is composed of
dense fibrous tissue. The interlacing fibers are straight
& tightly packed.


 Articular capsule :
 Consists of an outer fibrous layer.
 The articular capsule is lined by synovial membrane

consists of internal cells which are of three types:
o First : rich in RER & is called fibroblast like cell or B
cell.
o Second : rich in golgi complex contains little or no RER
called macrophage like cell or A cells.
o Third : this has a cellular morphology between A & B
cells.

Five Layer Vs Three Layer
Concept of suture
 Pritchard et al 1956
During Suture formation, there
are five layers i.e. cellular and
fibrous layer of both bones and
additional intervening loose
mesenchymal layer.
 Weinman & Sicher (1955) and

Moss (1957) – Three layered
concept i.e two interconnecting
fibrous layer with a highly
cellular middle zone

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


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 and Erickson
1988 - osteoclast
differentiation may require
interaction with osteoblast
or their precursors

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.


Basset 1965 –
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.


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


Lanyon and Smith 1969
 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”

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.
2.
3.
4.
5.

6.
7.
8.
9.

Mineralized sections
Polarized light
Fluorescent labels
Microradiography
Autoradiography
Nuclear volume morphometry
Cell kinetics
Finite element modeling (FEM)
Microelectrodes

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.

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.


Fluorescent labels
 Permanently mark all sites

of bone mineralization at a
specific point of time.
 Histomorphometric analysis
is an effective method of
determining the
mechanisms of bone growth
and functional adaptation


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)


Microradiography
 Assesses mineral

density patterns.
 Provides information

about the growth and
adaptation of the
skeletal sites most
affected by orthodontic
and facial orthopedic
treatment.

S : Remodeled secondary osteons


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.

O – original bone
P – PDL
N – New bone


→ - Radioactive labels

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.


Cell kinetics
 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.


Finite element modeling (FEM)
 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.


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.

Modeling and Remodeling
Form and Function Relationship


 Modeling :

In bone
modeling, independent
sites of resorption &
formation change the
form of bone (size or
shape or both).
 Remodeling :
In bone remodeling a
specific coupled
sequence of resorption &
formation occurs to
replace previously
existing bone

Mineralized
bone surface
Mineralization

Mat
ure
oste
oclas
t

Osteoid

Preosteo
blast


 Cutting & filling cones

The cutting /filling cone has a head of osteoclasts that cut through the bone
& a tail of osteoblasts that form a new secondary osteon.

Harmonal & Metabolic
influences

Lamellar bone

MES – Minimum Effective Strain

Woven
bone(repair)

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 Remodeling
 Metabolic
 Growth harmone :
 Acts directly on human osteoblast like cells.
 Important in determining in longitudinal bone growth &
bone remodeling.
 Stimulate the proliferation of cultured OB, some (not all)
studies says that GH regulate the differentiation of cultures
OB.
 IGF-I :
 Important in bone remodeling.
 It is embedded in the bone matrix & can act as a coupling
factor between bone formation & resorption.

 IL 6 :
 The multifunctional cytokine IL 6 is involved in bone

remodeling.
 The regulation of growth factor interleukin 6 (IL-6) may
be critical for the control of bone resorption during
menopause.
 IL-6 is needed for the production of osteoclasts.
 Effect of Oestrogen on GH :
 Decrease in oestrogen level after cessation of ovarian

function leads to postmenopausal osteoporosis.
 Estrogen – increases activation frequency

 Cortisol :
 Involve in bone remodeling.
 Complex effect on bone tissue & bone cells.
 Increase cortisol level

Collagen expression
Collagenase expression
Degradation of Type I collagen

Decrease bone formation
 PTH :
 Increases osteoblastic 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)
The mechanostat concept of Frost as defined
by Martin & Burr (1990)

The peak strain history determines whether
atrophy, maintenance, hypertrophy, fatigue failure occurs.

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 increased in thickness and active
cellular and connective tissue response associated
with numerous enlarged fibroblasts in active stage.
This response stabilize the anterior condylar
displacement


EXPERIMENTAL
•F in articular layer.
•M parallel to
articular surface.
•O are randomly
packed, and lacunae
are small, which
indicates old bone

F in articular
layer become
oriented toward
pull (arrow)

F and M
are all dragged
towards pull
(arrow). F are
obviously
flattened and
lengthened by
stretching
pull.

CONTROL

3rd
Day

7th

Day

14th
Day
F : Fibroblast , M : Mesenchymal cells, O : Osteocytes

F and M are
arranged in
orderly
fashion

F & M are
arranged
parallel to
articular
surface

Experimental
Pull-oriented
(arrow) and
stretched
fibroblasts
(F)

•Proliferation of F
and M
•O are packed
in large lacunae,
indicates bone
deposition.

F and M
remain
oriented in
direction of
pull

Control
14th
day

21th
day

30th
day


Fibroblasts
are round
and
randomly
packed

F&M
arranged
in line
with
articular
surface

Cells are still
packed
parallel to
articular
surface



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 .


Histologically :
 Marked resorptive activity of the compressed
zygomaticomaxillary and zygomaticotemporal sutures.
 Endosteal and periosteal compensatory deposition.
Control

Experimental

IRREGULAR PATH OF SUTURE
REGULAR PATH OF SUTURE

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


Histologically :
 Substantial widening with

deposition at the bony
margins and the long
collagenous bundles
traversing the sutural space
 Retaining the increased
sutural width allowed bone
to fill in at the sutural
margins, narrowing the
sutural gap and providing
more stable result.

Control

Experimental

Continuous Vs Intermittent
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 growth showed 2.4
times more skeletal change and about 2 times more dental
changes than the intermittent group


 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


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.


Effects of Mandibular Retrusion
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.


Control

Experimental

Control

Experimental

3 days

7 days


14 days

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 growth of the pattern is proportional. This means

that the disharmony is present from before birth ; it
becomes neither better nor worse. It cannot be changed by
treatment. The teeth and the alveolar process constitute
the only area of the face whose change may be expected or
induced.”
Brodie,1946

 The A-R-F remodeling cycle

The entire sequence from activation to formation phase is called SIGMA, &
requires about 4 months in humans.

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Histological changes in dentofacial orthopaedics1 /certified fixed orthodontic courses by Indian dental academy

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