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This term originates from Latin and means “closure.”
Central occlusion is a state of evenly distributed tension of the jaw muscles, while ensuring simultaneous contact of all surfaces of the elements of the dentition.
The need to determine central occlusion is to correctly manufacture a partial or removable denture.
Central occlusion and central jaw relation
The concepts of centric occlusion and centric relation are often generalized, but their meanings are completely different.
Occlusion is the closing of teeth. No matter how the patient closes his mouth, if at least two teeth touch, this is occlusion. There are thousands of occlusion options, but it is impossible to see or determine them all. For a dentist, 4 types of occlusion are important:
- Front
- Rear
- Lateral (left and right)
- and Central
This is occlusion - uniform closure of the teeth.
Central occlusion is the maximum intertubercular closure of the teeth. That is, when as many teeth as possible for this person come into contact with each other. (Personally, I have 24).
If the patient has no teeth, then there is no central (or any) occlusion. But there is a central relation.
Ratio is the position of one object in relation to another. When we talk about jaw relationship, we are talking about how the mandible relates to the skull.
The centric relation is the most posterior position of the mandible when the head of the joint is correctly located in the glenoid fossa. (Extreme anterosuperior and midsagittal position). There may be no occlusion in the centric relation.
In the centric relation, the joint occupies the most superior-posterior position
Unlike all types of occlusion, the centric relation does not change throughout life. If there were no diseases or injuries to the joint. Therefore, if it is impossible to determine the central occlusion (the patient has no teeth), the doctor recreates it, focusing on the central relationship of the jaws.
To continue the story, two more definitions are missing.
Main features
Experts have determined the following indicators of central occlusion:
- Muscular. Synchronous, normal contraction of the muscles responsible for the functioning of the lower jaw bone.
- Articular. The surfaces of the articular heads of the lower jaw are located directly at the bases of the slopes of the articular tubercles, in the depths of the articular fossa.
- Dental:
- full surface contact;
- opposite rows are brought together so that each unit is in contact with the same and the next element;
- the direction of the upper frontal incisors and the similar direction of the lower ones lie in a single sagittal plane;
- the overlap of the elements of the upper row of fragments of the lower one in the front part is 30% of the length;
- the anterior units contact in such a way that the edges of the lower fragments abut the palatine tubercles of the upper ones;
- the upper molar comes into contact with the lower one so that two-thirds of its area is combined with the first, and the rest with the second;
If we consider the transverse direction of the rows, then their buccal tubercles overlap, while the tubercles on the palate are oriented longitudinally, in the fissure between the buccal and lingual of the lower row.
Signs of correct row contact
Are common:
- the rows converge in a single vertical plane;
- incisors and molars of both rows have a pair of antagonists;
- there is contact between units of the same name;
- the lower incisors do not have antagonists in the central part;
- the upper eighths have no antagonists.
Applies to anterior units only:
- if we conditionally divide the patient’s face into two symmetrical parts, then the line of symmetry should pass between the front elements of both rows;
- the upper row of fragments overlaps the lower one in the anterior zone to a height of 30% of the total crown size;
- the cutting edges of the lower units are in contact with the tubercles of the inner part of the upper ones.
Applies only to lateral ones:
- the buccal distal cusp of the upper row is based in the space between the 6th and 7th molars of the lower row;
- the lateral elements of the upper row close with the lower ones in such a way that they fall strictly into the intertubercular grooves.
Let's find out together how dental impressions are made and what modern material is used.
Read here about the purpose of filing the front teeth.
At this address https://orto-info.ru/ortodonticheskoe-lechenie/podgotovitelnyiy-period/separatsiya-zubov.html we will talk about the consequences of teeth separation.
Resting height and bite height
Bite height is the distance between the upper and lower jaws in the position of central occlusion
Bite height - the distance between the upper and lower jaws in the position of central occlusion
Physiological rest height is the distance between the upper and lower jaw when all jaw muscles are relaxed. Normally, it is usually 2-3 mm greater than the height of the bite.
Normally, it is 2-3 mm greater than the height of the bite
The bite can be high or low. Overbite due to improperly manufactured prosthesis. Roughly speaking, when artificial teeth are higher than their own. The doctor sees that the bite height is 1 mm less than the resting height, or equal to it, or greater than it
The lower third of the face is significantly larger than the middle third
Underestimated - with pathological abrasion of teeth. But there is also the option of incorrectly manufacturing the prosthesis. The doctor sees that the height of the bite is greater than the resting height. And this difference is more than 3 mm. In order not to underestimate or overestimate the bite, the doctor measures the height of the lower part of the face.
In the photo on the left, the lower third of the face is smaller than the middle third
Now you know everything you need, and we can return to the doctor.
2) He received wax bases with bite ridges from the technician. Now he carefully examines them, assessing their quality:
- The boundaries of the bases correspond to those drawn on the model.
- The bases do not balance. That is, they fit tightly to the plaster model throughout.
- The wax rollers are made with high quality. They do not exfoliate and are of standard size (in the area of the anterior teeth: height 1.8 - 2.0 cm, width 0.4 - 0.6 cm; in the area of chewing teeth: height 0.8-1.2 cm, width 0. 8 – 1.0 cm).
3) The doctor removes the bases from the model and disinfects them with alcohol. And he cools them for 2-3 minutes in cold water.
4) The doctor places the upper wax base on the jaw and checks the quality of the base in the mouth: does it hold, does the boundaries correspond, is there any balancing.
5) Next, the dentist forms the vestibular surface of the wax roller. He trims or extends it so that the patient's lip looks normal. That is, it did not stick out and did not sink.
6) After this, it forms the height of the roller in the anterior section. Here everything depends on the width of the red border of the patient’s lips. If the lip is medium, then the upper incisors (and in our case the ridge) stick out from under it by 1-2 mm. If the lip is thin, the doctor makes the roller stick out 2 mm. If it is too thick, the roller ends up to 2 mm under the lip.
The length of the incisor protruding from under the lip is about 2 mm
7) The doctor proceeds to forming the prosthetic plane. This is a rather difficult stage. We will dwell on it in more detail.
Errors allowed
Creating a prosthetic structure in conditions of malocclusion is a most complex orthopedic procedure, the quality of which depends 100% on the qualifications of the specialist and a responsible approach to work.
Violations in determining the position of central occlusion can lead to the following problems:
The bite is too high
- The folds of the face are smoothed, the relief of the nasolabial zone is poorly defined;
- the patient's face looks surprised;
- the patient feels tension when closing the mouth, while closing the lips;
- the patient feels that during communication the teeth are knocking against each other.
Low bite
- The folds of the face are strongly pronounced, especially in the chin area;
- the lower third of the face visually becomes smaller;
- the patient becomes like an elderly person;
- the corners of the mouth are lowered;
- lips sink;
- uncontrolled salivation.
Permanent anterior occlusion
- There is a noticeable gap between the front incisors;
- the lateral elements do not contact normally, tubercle reduction does not occur.
Permanent lateral occlusion
- Overbite;
- clearance on the offset side;
- shifting the bottom row to the side.
Reasons for such problems
- Incorrect preparation of wax templates.
- Insufficient softening of the material for taking impressions and impressions.
- Violation of the integrity of wax forms due to their premature removal from the oral cavity.
- Excessive jaw pressure on the ridges during impression taking.
- Errors and violations on the part of the specialist.
- Errors in the work of the technician.
The video provides additional information on the topic of the article.
Formation of the prosthetic plane
“To draw a plane you need three points”
© Geometry
Occlusal plane
- a plane that passes through:
1) the point between the lower central incisors
2) and 3) points on the external posterior tubercles of the second chewing teeth.
Three points: 1) Between the central incisors 2) and 3) Posterior buccal cusp of the second molar
If you have teeth, then there is an occlusal plane. If there are no teeth, then there is no plane. The dentist's task is to restore it. And restore correctly.
Prosthetic plane
Like the occlusal plane, only on a denture
- this is the occlusal plane of a complete removable denture. It should run exactly where the occlusal plane once was. But the dentist is not a psychic; he cannot see the past. How will he determine where she had a patient 20 years ago?
After many studies, scientists have established that the occlusal plane in the anterior jaw is parallel to the line connecting the pupils. And in the lateral section (this was discovered by Camper) - a line connecting the lower edge of the nasal septum (subnosal) with the middle of the tragus of the ear. This line is called the Camper horizontal.
The doctor’s task is to ensure that the prosthetic plane - the plane of the wax ridge on the upper jaw - is parallel to these two lines (Kamper’s horizontal and the pupillary line).
The doctor divides the entire prosthetic plane into three segments: one frontal and two lateral. He starts from the frontal section. And makes the plane of the frontal ridge parallel to the pupillary line. To achieve this he uses two rulers. The doctor places one ruler at the level of the pupils, and attaches the second to the wax roller.
One ruler is installed along the pupillary line, the second is glued to the bite block
He achieves parallelism between the two rulers. The dentist adds or cuts wax from the roller, focusing on the upper lip. As we described above, the edge of the roller should evenly protrude from under the lip by 1-2 mm.
Next, the doctor forms the lateral sections. To do this, the ruler is installed along the Camper (nose-ear) line. And they achieve parallelism with the prosthetic plane. The doctor builds up or removes wax in the same way as he did in the anterior section.
The ruler along the Camper horizontal is parallel to the occlusal plane in the lateral section
After this, he smoothes the entire prosthetic plane. It is convenient to use for this
Naisha apparatus.
The Naisha apparatus is a heated inclined plane with a wax collector.
The base with bite rollers is applied to the heated surface. The wax melts evenly over the entire surface of the roller, in one plane. As a result, it turns out perfectly smooth.
The melted wax is collected in a wax collector, which is shaped like a blank for new rollers.
Next, the doctor proceeds to determine the height of the lower part of the face. And again a little theory.
Determination of the height of the lower part of the face
Dentists divide the patient's face into thirds:
The upper third is from the beginning of hair growth to the line of the upper edge of the eyebrows.
The middle third is from the upper edge of the eyebrows to the lower edge of the nasal septum.
The lower third is from the lower edge of the nasal septum to the very bottom of the chin.
The lower third of the face is significantly larger than the middle third
All thirds are normally approximately equal to each other. But with changes in the height of the bite, the height of the lower third of the face also changes.
There are four ways to determine the height of the lower part of the face (and the height of the bite accordingly):
- Anatomical
- Anthropometric
- Anatomical and physiological
- Functional-physiological (hardware)
Anatomical method
Determination method by eye. The doctor uses it at the stage of checking the teeth setting to see if the technician has overestimated the bite. He looks for signs of overbite: whether the nasolabial folds are smoothed, whether the cheeks and lips are tense, etc.
Anthropometric method
Based on the equality of all third parties. Different authors have proposed different anatomical landmarks (Wootsword: the distance between the corner of the mouth and the corner of the nose is equal to the distance between the tip of the nose and the chin, Jupitz, Gisi, etc.). But all these options are inaccurate and usually overestimate the actual height of the bite.
Anatomical and physiological method
Based on the fact that the height of the bite is 2-3 mm less than the resting height.
The doctor determines the height of the face using wax bases with occlusal ridges. To do this, he first determines the height of the lower third of the face in a state of physiological rest. The doctor draws two dots on the patient: one on the upper jaw, the second on the lower jaw. It is important that both are on the center line of the face.
The doctor draws two dots on the patient
The doctor measures the distance between these points when all the patient's jaw muscles are relaxed. To relax him, the doctor talks to him about abstract topics, or asks him to swallow his saliva several times. After this, the patient’s jaw takes a position of physiological rest.
The doctor measures the distance between the points in a position of physiological rest
The doctor measures the distance between the points and subtracts 2-3 mm from it. Remember, normally it is this number that distinguishes physiological rest from the position of central occlusion. The dentist trims or extends the lower bite ridge. And measures the distance between the drawn points until it becomes as it should (rest height minus 2-3 mm).
The inaccuracy of this method is that some people need a difference of 2-3 mm, while others need 5 mm. And it is impossible to calculate it accurately. Therefore, you just need to assume that it is 2-3 mm for everyone and hope that the prosthesis will work.
Whether the doctor has correctly determined the interalveolar height is checked using a conversational test. He asks the patient to pronounce sounds and syllables (o, i, si, z, p, f). When pronouncing each sound, the patient will open his mouth to a certain width. For example, when pronouncing the sound [o], the mouth opens 5-6 mm. If it is wider, then the doctor determined the height incorrectly.
When pronouncing the sound “O”, the distance between the teeth (ridges) is 6 mm
Functional-physiological method
It is based on the fact that the masticatory muscles develop maximum strength only in a certain position of the jaw. Namely, in the position of central occlusion.
How does chewing force depend on the position of the lower jaw?
If there are bodybuilders among you, you will understand my comparison. When you pump your biceps, if you extend your arms halfway, it will be easy to lift a 100 kg barbell. But if you straighten them completely, then lifting it will be much more difficult. The same is true for the lower jaw.
The thicker the arrow, the greater the muscle strength
This method uses a special device - AOCO (Apparatus for Determining Central Occlusion). Hard individual spoons are made for the patient. They are edged and inserted into the patient's mouth. A sensor is attached to the lower spoon, into which pins are inserted. They make it difficult to close your mouth, i.e. set the bite height. And the sensor measures chewing pressure at the height of this pin.
AOCO (Apparatus for Determining Central Occlusion)
First, a pin is used that is significantly higher than the patient's bite. And record the force of jaw pressure. Then use a pin 0.5 mm shorter than the first one. And so on. When the bite height is lower than optimal even by 0.5 mm, the chewing force is reduced by almost half. And the desired bite height is equal to the previous pin. This method allows you to determine the bite height with an accuracy of 0.5 mm.
Our dentist uses the anatomical and physiological method. It is the simplest and relatively accurate.
9) Next, the doctor fits the lower roller to the upper one. They should fit snugly against each other. There should be no steps.
10) The doctor determines the central relationship of the jaws.
Causes
Reasons why the distance between the jaws becomes smaller:
- changes in the surface of the teeth;
- teeth grinding, which changes the condition of the enamel;
- habit of chewing on one side;
- removal of molars;
- lack of substances important for the normal functioning of the body;
- unqualified installation of prostheses.
To professionally make dentures, many measurements will be required, including the patient’s jaw at rest.
Determination of the central relationship of the jaws
At this stage, you cannot simply tell the patient, close your mouth correctly. Even my grandmother often complained that these words were confusing: “And you don’t know how to shut your mouth. It seems that no matter how you close it, everything is right.”
To close the mouth “correctly,” the doctor places his index fingers on the bite ridges in the area of the chewing teeth of the lower jaw and at the same time pushes the corners of the mouth apart. Next, he asks the patient to touch the posterior edge of the hard palate with his tongue (It is better to make a wax button in this place - not all patients know where the posterior edge of the hard palate is.) and swallow the saliva. The doctor removes his fingers from the chewing surface of the roller, but continues to move the corners of the mouth apart. When swallowing saliva, the patient will close his mouth “correctly.” They repeat this several times until the doctor is absolutely sure that this is the correct central ratio.
11) Next stage. The doctor fixes the rollers in a central ratio.
