TMJ
/ Bruxism
Bite and Occlusion
An area often overlooked during
a clinical examination is the patient's Occlusion or bite.
Therefore, I'd like to discuss some important factors
on the subject of Occlusion.
What is Occlusion or bite?
Occlusion is how your teeth come together when you close
your jaw. Your Occlusion is influenced by three primary
components: (1) teeth, (2) nerves and muscles, and (3)
bones. Another factor, which can affect the way your teeth
come together, is your posture.
Take note of the fact that when
you tilt your head back and bite, your teeth will hit
differently than when you tilt your head forward. The
same rule applies when you are lying down on your side.
Your lower jaw will shift to one side. We now need to
define ideal Occlusion or bite. I'm going to attempt to
explain this by describing some functional terms.
Centric Occlusion:
Centric Occlusion is the term used to define the habitual
position of closure. In other words, the position your
teeth are in when you repeatedly bite.
In an ideal centric Occlusion all
the teeth are in proper contact. The teeth are not in
cross bite, there is no under bite or over bite.
Canine Guidance:
Now let's try and explain how an individual with an ideal
bite functions. Starting at centric Occlusion and keeping
the teeth in contact as much as possible, we slide the
lower jaw to one side.
In an ideal Occlusion, when the
lower jaw is shifted to one side, the posterior teeth
should not touch.
What happens is that the lower
canine or eye tooth is riding up on the upper canine.
This is called Canine Guidance or canine protected Occlusion.
Canine protected Occlusion is an
important concept, especially for people who have excessive
wear on their teeth, erosion of their roots, gum recession,
and suffer from TMJ (temporomandibular dysfunction).
Nature's Biofeedback Mechanism:
There is a biofeedback mechanism that comes into play.
When the canines touch, nerves send a message back to
the brain which in turn sends a message to those large
muscles that close the jaw. That message says, "Hey
- ease up on the force", and the muscles relax.
When you take away that canine
protection, the muscles stay active. That's when you can
get clenching, grinding of the teeth, joint pain, fracturing
of teeth, excessive wear of the enamel on top of the tooth,
erosion of the root surface (abfractions), and gum recession.
If teeth are properly aligned all
the components that make up the occlusal system (teeth,
nerves, muscles, and bones) should function in harmony.
Here's an interesting note concerning
the forces that you can put on your teeth. Normal chewing
places about 68 lbs/sq inch of pressure on the back teeth.
If you intentionally clench your teeth you may increase
that force to about 150 lbs/sq inch. However, an individual
who clenches and grinds their teeth subconsciously at
night can place up 1200 lbs/sq inch of force. That sounds
like an industrial grinding machine!
Anterior Guidance:
In a normal bite the anterior (front) teeth guide the
posterior (back) teeth into position or centric Occlusion.
When the front teeth are placed together on their biting
edges the posterior teeth should not touch.
If the posterior teeth touch in
that position, the symptoms described above can occur.
There are some individuals whose front teeth do not touch
at all. They have what we call an anterior open bite or
have an overbite. This is due to bony (skeletal) discrepancy
between their upper and lower jaw bones. Sometimes this
can be corrected by a combination of orthodontics, surgery
to reposition the bones and/or crowns (caps).
Vertical Dimension:
Vertical Dimension is another factor to consider. If you
can picture a person without teeth, their face would be
collapsed. This means that they have a loss of vertical
dimension. You can have a decreased vertical dimension
by loss of teeth or by excessive wear of the posterior
teeth. Some individuals have a very steep overbite, which
can be helped by opening the vertical dimension. Often,
individuals with a decreased vertical dimension suffer
from TMJ. Vertical dimension can be increased by building
up the height of the posterior teeth.
Now let's list some of the signs
of possible occlusal/bite problems. If you think that
you have these signs, contact your dentist to evaluate
your Occlusion.
1. Heavy wear facets on the biting surface
of the teeth.
2. Receding gum tissue
3. Erosion/notching of the root surfaces
(abfractions)
4. Cracked/fractured teeth
5. Front teeth do not touch
6. Pain in the joint and muscles
7. Erosion of the biting surfaces of
the back teeth, loss of enamel
8. Clenching or grinding of the teeth
