This article is about centric relation and centric occlusion. About bite height and resting height. She will tell you step by step how the doctor works, what methods he uses to determine central occlusion.
Article outline:
- What is central occlusion and central jaw relation? And what is the difference between them?
- Stages of determining the central ratio
Details:
- Formation of the prosthetic plane
- Methods for determining the lower third of the face. Anatomy - physiological method.
- Methods for fixing the CO after its determination.
- Drawing of anatomical landmarks on the finished basis.
Let's begin our story.
1) The appointed patient came to the dentist. Today the plan is to determine the central ratio. The doctor greets his patient and puts on gloves and a mask. He sits the patient in a chair. The patient sits upright, leaning on the back of the chair. His head is slightly thrown back...
Oh yes! Something needs to be explained to you. Otherwise, you and I may not understand each other. These are words that will appear often in our story. Their meaning needs to be known exactly.
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.
TMJ functioning problems
| Click to sign up for a FREE consultation |
Disruption of the work and function of the joints and muscles of the lower jaw is called TMJ dysfunction. The pathology is caused by the occurrence of a defect in the teeth, increased wear and tear and an abnormal bite of a person.
The main clinical manifestation of dysfunction is clicking and clattering of teeth when opening the mouth. In more advanced cases, pain occurs in the ears, jaw, and painful sensations begin during chewing and yawning.
The main method for diagnosing TMJ dysfunction is radiography, which reveals dysfunction of the jaw and joint.
Treatment consists of a comprehensive effect on the condition of the jaw, which the dentist carries out based on knowledge of the biomechanics of its work.
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.
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.
Purpose of the dental system
The biological mechanics of the dental system and its understanding lead to timely recognition of pathologies of teeth and soft tissues of the oral cavity. The normal functioning of the temporomandibular joint largely depends on the structure and normal functioning of the periodontium - the soft tissues surrounding the tooth cavity.
The anatomy and physiology of the structure of the periodontium determines the biomechanics of the structure and the characteristics of the periodontium. In addition, periodontal biomechanics helps in the functioning of other organs.
Knowledge of the laws of biological mechanics of the jaw and joints helps to design and use features, as fundamental knowledge on the topic of prosthetics and dental implants. Knowledge of the anatomical features of the jaw is necessary in the manufacture of structures and dental materials.
Devices have been developed that almost completely repeat the movements of the jaw and make it possible to reproduce anatomically similar structures to the human jaw. Popular devices include the occluder, facebow, and articulator. The latter design plays an important role in the fitting and creation of individual prostheses.
If disorders of the lower jaw occur, disruptions in articulation, speech, nutrition and swallowing occur. Today, a system of articulation of movements has been developed, led by such authors as Ganau, Gisi, Monson. These authors most accurately described the biomechanics of mandibular movements.
The authors claim that dysfunction of the lower jaw, as well as sore neck muscles, necessarily lead to breathing problems. Different angles of inclination of the lower jaw determine human health.
Occlusion is a condition characterized by full contact of both jaws, which ensures complete chewing of food. Therefore, the contact of teeth is a determining factor for the characteristics of chewing mechanisms.
The work and action of the lower dentition during chewing is due to the synchronous work of all muscles and joints. The work occurs under the influence of the central nervous system. In this case, displacements that occur spontaneously occur under the influence of the neuromuscular structure.
Conscious movements of the dentition include the moment food enters the mouth and swallowing food. The remaining movements that occur after eating food are the result of unconscious motor functions of the body.
The lower part of the human masticatory apparatus is the only moving bone in the human body. However, the connecting and muscle tissue, which sets the mechanism in motion, is of great importance in the structure of the masticatory row and in the normal functioning of the muscles.
In the structure of the lower dentition, there are several muscle groups that are responsible for various movements of the jaw.
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.
Directions of movement of the lower jaw
During the movement of the lower jaw, sagittal, vertical and transversal displacement of its heads occurs.
Vertical displacement is necessary to open and close the mouth. In this case, the movement, depending on the force, occurs with varying strength, which determines the degree of movement of the head.
The sagittal axis of displacement is the ability to move the lower jaw back and forth. In this case, the forward movement of the jaw and the biomechanism of the head of the articular part at the moment of movement is called the sagittal path of the joints.
Transverse is the ability of the jaw to move left or right. In this case, certain muscle groups move. For example, the direction of the masticatory apparatus to the right determines the left direction of the lateral muscles, and vice versa.
Without knowledge of how muscles and joints work, the dentist cannot regulate the normal functioning of the masticatory apparatus, which means he will not be able to manufacture and install suitable dentures and implants.
