Subtleties of determining central occlusion and possible errors

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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.

Main features

Experts have determined the following indicators of central occlusion:

1. Muscular. Synchronous, normal contraction of the muscles responsible for the functioning of the lower jaw bone.
2. 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.
3. 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.

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Methods used

Central occlusion is determined at the stage of manufacturing prosthetic structures when several units are lost.

This is necessary to ensure the normal functioning of the product and eliminate the occurrence of deviations and problems in the functioning of the temporomandibular joints.

In this case, the height of the lower third of the face is of great importance. However, in the absence of a large number of units, this indicator may be violated and must be restored.

If the patient has partial adentia, several options for determining the indicator are used.

The presence of antagonists on both sides

The method is used when antagonists are present in all functional areas of the jaws.

In the presence of a large number of antagonists, the height of the lower third of the face is maintained and fixed.

The occlusion index is determined based on as many contact zones as possible of the same units of the upper and lower rows.

This option is the simplest, as it does not require the additional use of occlusal ridges or specialized orthopedic templates.

Presence of three occlusion points between antagonists

This method is used if the patient still has antagonists in the three main contact zones of the rows. At the same time, the small number of antagonists does not allow normal positioning of plaster casts of the jaw in the articulator.

In this case, the natural height of the lower third of the face is disrupted, and occlusal ridges made of wax or thermoplastic polymer are used to correctly match the casts.

The roller is placed on the bottom row, after which the patient brings his jaw together. After the roller is removed from the oral cavity, imprints of the antagonist contact zones remain on it.

These prints are subsequently used by technicians in the laboratory to position the casts and create a fully functional and correct, from an orthopedic point of view, prosthesis.

Absence of antagonistic pairs

The most labor-intensive scenario is the complete absence of the same elements on both jaws.

In this situation, instead of the position of central occlusion, the central relationship of the jaws is determined .

The procedure includes the following steps:

1. Work on the formation of a prosthetic plane , which is positioned along the chewing surfaces of the lateral units and is parallel to the beam. It is built from the lower point of the nasal septum to the upper edges of the ear canals.
2. Determination of the normal height of the lower third of the face.
3. Fixation of the mesiodistal relationship of the upper and lower jaws using wax or polymer bases with occlusal ridges.

Checking central occlusion with existing pairs of elements of the same name is carried out by closing the teeth and is carried out as follows:

• a thin strip of wax is placed on the already prepared and fitted contact surface of the occlusal roller and glued;
• the resulting structure is heated until the wax softens;
• heated templates are placed in the patient’s oral cavity;
• After bringing the jaws together, the teeth leave imprints on the wax strip.

It is these fingerprints that are used in the process of modeling central occlusion in the laboratory.

If, during the process of determining occlusion, the surfaces of the upper and lower rollers close, the specialist adjusts their contact surfaces.

Wedge-shaped cuts are made on the upper one, and a certain amount of material is cut off from the lower one, after which a wax strip is glued to the treated surface. After the rows are brought together again, the strip material is pressed into the cutouts.

The products are removed from the patient’s mouth and sent to the laboratory for subsequent production of a prosthesis.

conclusions

In conclusion, it can be noted that central occlusion must be determined by a qualified specialist, taking into account the anatomical and physiological characteristics of the dentition.

Only after a thorough check of the central organ, detection and correction of errors, can wax casts be plastered into the articulator and sent to the laboratory for the manufacture of prostheses.

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What is bite height and how important is its correct determination?

Calculations for orthopedic purposes

In the process of creating prosthetic structures for malocclusion, an orthopedic specialist takes measurements of the heights of the lower third of the patient’s face using an anatomical and physiological method.

To do this, the height of the bite is measured in a state of complete reduction of the jaws, with central occlusion and in a state of physiological rest.

Payment procedure:

1. At the lowest point of the nose , at the level of the nasal septum, the first mark is placed strictly in the center. In some cases, the specialist places a mark on the tip of the patient's nose.
2. in the center of the chin , in its lower zone.
3. Between the applied marks, the height is measured in the state of central occlusion of the jaws. To do this, bases with bite ridges are placed in the patient’s oral cavity.
4. Repeated measurements are taken between marks , but in a state of physiological rest of the lower jaw. To do this, the specialist must distract the patient so that he really relaxes. In some cases, the patient is offered a glass of water. After a few sips, the muscles of the lower jaw really relax.
5. The results are recorded. However, the standardized indicator of normal bite height, which is 2-3 mm, is subtracted from the height at rest. And if after this the indicators are equal, we can talk about normal bite height.

If, when measuring height, the calculation results yield a negative result, the lower third of the patient’s face is underestimated . Accordingly, if the result deviates in a positive direction, the bite is overestimated .

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General overview

The technique for constructing the bite height is based on determining the intermaxillary distance when the dentition is closed. The indicator under consideration is of significant importance, determining how correct the anatomical structure of the jaw and the position of the teeth are.

A change in the height of the bite, caused by the loss of one or more units, or a displacement of the central axis, leads to a disruption of the natural balance, and entails associated disorders, which include:

• Recession of lips;
• Deepening of nasolabial folds;
• Advancement of the mandibular region;
• Reducing the height of the lower part of the face.

In addition to disrupting aesthetics, such defects act as negative factors that complicate orthodontic and orthopedic treatment.

Techniques for correct positioning of the lower jaw

Correct positioning of the patient's jaw in the position of central occlusion involves the use of two methods of placement: functional and instrumental.

The main condition for correct placement is muscle relaxation of the jaw muscles.

Functional

The procedure for carrying out this method is as follows:

• the patient moves his head back slightly until the neck muscles tense, which prevents protrusion of the jaw;
• touches the tongue to the back of the palate, as close to the throat as possible;
• at this time, the specialist places his index fingers on the patient’s teeth, lightly pressing on them and at the same time slightly moving the corners of the mouth in different directions;
• the patient imitates swallowing food, which in almost 100% of cases leads to muscle relaxation and prevents jaw protrusion;
• When bringing the jaws together, the specialist touches the surfaces of the teeth and holds the corners of the mouth until it is completely closed.

In some cases, the procedure is repeated several times until complete muscle relaxation and correct reduction of both rows are achieved.

Instrumental

It is performed using specialized devices that copy jaw movements. It is used only in extremely serious situations, when bite deviations are significant and it is necessary to correct the position of the jaw using the physical efforts of a specialist.

Most often, when carrying out this method, the Larin apparatus and special orthopedic rulers are used, which make it possible to record jaw movements in several planes.

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

1. Incorrect preparation of wax templates.
2. Insufficient softening of the material for taking impressions and impressions.
3. Violation of the integrity of wax forms due to their premature removal from the oral cavity.
4. Excessive jaw pressure on the ridges during impression taking.
5. Errors and violations on the part of the specialist.
6. Errors in the work of the technician.

The video provides additional information on the topic of the article.

Factors of abnormal development

Among the factors that can cause a change in the natural height of the bite are:

• Increased abrasion of tooth enamel;
• Chronic bruxism;
• Incorrect distribution of load on the jaw apparatus;
• Partial or complete edentia;
• Metabolic disorders and demineralization of bone tissue;
• Mistakes made during dental prosthetics.

Identifying the original source of the problem is an important point on which the effectiveness of the chosen treatment method depends. When planning prosthetics, it is necessary to conduct a comprehensive examination of the maxillary region.