Static Occlusion, Dynamic Occlusion and Guidance
Working side and non-working side.
Previous pages have looked at mandibular movements in the saggital (forward-back) plane.
We will now examine the effects of the mandible moving in lateral excursions.
Static occlusion is the study of contacts between the teeth when the jaw is not moving. The contacts are points (seen as dots when articulating paper is used).
For example, close your teeth in your intercuspal position (i.e. where they meet best). Is your bite heaviest on your back teeth? Is it evenly spread over all the back teeth? Is there hardly any weight on the front teeth? Many dentists would describe that as the “ideal”. If you are providing a crown or filling for a patient like this, you would try not to disturb such an occlusion by leaving the restoration high (or low).
Click the picture on the top right to see the ink marks made with a static occlusion (intercuspal position in this case - the patient was asked to "tap together on the back teeth").
Freedom In Centric
Bite on your back teeth. Can you slide a tiny way forwards before you bump into your anteriors? If so, you have "Freedom In Centric Occlusion" (also known as "Long Centric"). Remember - Centric Occlusion is another word for Intercuspal Position (ICP).
The picture to the right shows no freedom in centric - ICP causes marks to appear on the incisors. Compare it with the picture above, which has freedom in centric.
Dynamic occlusion is the study of the contacts that teeth make when the mandible is moving – contacts when the jaw moves sideways, forwards, backwards, or at an angle. The contacts are not points, they are lines.
If you get a patient to grind their teeth in every direction on piece of articulating paper, you will see the lines formed by dynamic occlusion
Although the jaw is moved by muscles, the contact lines depend on both the teeth positions and shapes (obviously), and the shape of the TMJ. These shapes GUIDE the occlusion.
You may have heard the phrases posterior guidance and anterior guidance used when the mandible moves about in protrusive and lateral excursions Can you say what the terms mean?
Can you define these terms?
Types of anterior guidance in lateral excursions.
Click the pictures to see typical ink marks associated with each type of guidance. Note the dots formed by intercuspal position (static), and the lines caused by a lateral excursion to the right.
If you slide you teeth to your right, and only your right canines contact during this lateral excursion, then you have canine guidance. This is reckoned to be a good thing, as canines are excellent at coping with lateral forces. If this happens, you are said to have a canine-protected occlusion. (The same idea applies to the left of course.)
Click to magnify
If however when you slide laterally a number of teeth on your working side are in contact at the same time, all sharing the load, this is called group function. This might happen if your canines have worn down over time, or are crooked.
This is reckoned to be second best. With group function, the heaviest loads should ideally be near the most anterior of these teeth, and lighter loads near the back.
Click to magnify
|Working side interference
When you move your jaw laterally, if the first contact is just on a single tooth near the back (on the working side), this is called a working side interference. For example, perhaps there is an upper molar which has tilted into an adjacent extraction space.
Click to magnify
|A non-working side interference is when any tooth on the opposite side makes the first contact.
Click to magnify
These interferences are providing anterior guidance, but as the name suggests, not in a way that dentists approve of ! They are considered the least desirable types of anterior guidance.
Educational aims of this juce
This page aims to introduce the lateral mandibular movements.
It explains and discusses:
• Static occlusion
• Freedom In Centric
• Dynamic occlusion
• Working side and non-working side
• Canine Guidance
• Group function
Pictures show the typical appearance of the dental arch with various types of guidance when articulating paper is used.
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