The effects of mechanical forces on tissues and cells / rotary endodontics courses online

The effects of mechanical
forces on tissues and cells
www.indiandentalacademy.com

Conclusions from histological and
other studies
1. Various cell types are involved in tissue
remodeling during orthodontic treatment
2. Many cellular components participate in this
response
3. The plasma membrane is the site of initial
interaction between cells and mechanical
forces

Conclusion
One of the main effects of orthodontic
forces on paradental cells may be
alteration of the open-state of
mechanosensitive ion channels. Some of
the ions that enter cells under these
circumstances may promote and
modulate the cellular response to the
applied forces.

Cell adhesion
All cells adhere to their ECM. Adhesion is
required for survival. Exceptions are
blood and metastasizing tumor cells.
Adhesion molecules (integrins) are
connected to the ECM, as well as to the
cytoskeleton.

Cell adhesion
Therefore, cell adhesion molecules can be
regarded as important links in the
transduction of mechanical stresses from
the ECM to the cytoplasm and nucleus.
Consequently, cell adhesion molecules may
be playing a key role in orthodontic tooth
movement.

Cell adhesion and orthodontics
Adhesion molecules facilitate stretching of
PDL cells in tension sites, and rounding
of cells in compression sites. The latter
cells frequently become detached and
undergo apoptosis, while the former cells
detach and reattach, to regain their
original shape.

Actin filaments in a human plateletwww.indiandentalacademy.com

Actin filaments in a stretched human PDL
fibroblast

The cytoskeleton and orthodontics
Cytoskeletal elements in all paradental cell
types are the vehicle whereby mechanical
stresses are transmitted directly from the
strained ECM to the cell nucleus.
The cytoskeleton modulates all changes in
cellular shape and size.

In the nucleus, fast- and slow-response
genes are activated by the mechanical
force, initiating a reaction cascade,
culminating in functions such as
synthesis of signal molecules and ECM
components, proliferation,
differentiation, and motility.

Thus, the cytoskeleton is clearly a pivotal
link in the transduction of orthodontic
forces into strained paradental cells.
Moreover, it also assists in transporting
new cell products to the plasma
membrane for secretion.

What are early biochemical
signs of cell stimulation by
mechanical forces? (0-15 min)

How do mechanical forces activate
paradental cells?
To answer this question, we first must
define cell activation, then identify and
list important steps in this complex
process. We need to remember that in
our patients, cells responsive to
mechanical forces can also interact with
other factors of local or systemic origin.
These factors may modify the cells’
reaction to the applied forces.

Interleukin -1ß in cat gingivalwww.indiandentalacademy.com

Conclusions
At the plasma membrane level,
transduction of chemical and mechanical
signals into target cells involves
interactions in and between receptors.
These reactions may be affected by other
signal molecules derived from the
nervous and immune systems,
paracrines, and the patient’s diet and
drugs.

Effects of applied tension in the
ECM on attached cells
A demonstration with a schematic
model
By Donald Ingber et al, 1985
(The tensegrity model, 1995)

What lessons can the orthodontist
learn from studies about physical and
biochemical effects of mechanical
forces on cells, tissues, and whole
organisms?

The orthodontist should be familiar
with these studies, because mechanical
forces are the main therapeutic means
in orthodontics. Such knowledge can
define the biological principles and
limitations of tooth movement, in
general terms and for individual
patients.

Essentially, it is known that applied
mechanical forces strain the ECM and
cells attached to it, and that direct
transduction of this strain to the
nucleus is facilitated by the
cytoskeleton.

In the nucleus, genes are activated,
leading to a variety of responses, such
as proliferation, differentiation,
motility, and synthesis of cytokines,
growth factors, enzymes, and ECM
components. The plasma membrane
plays an important role in these
events, with its receptors and
mechanosensitive ion channels.

This basic knowledge implies that
clinical limitations may result not only
from factors such as age and force
magnitude, but also from cellular and
molecular variables. Increased
understanding and management of
these variables and their modes of
action should increase the proximity
between orthodontics and medicine.

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