Determination of central occlusion in case of defects in the dentition. Central ratio of the jaws: definition, methods. Determining the height of the lower face

When casting models and then placing teeth on them, the laboratory technician must rely on the landmarks indicated at the time of determining the central occlusion. it second clinical stage. It consists in establishing the nature of the relationship of the dentition in the horizontal, sagittal and transversal directions.

The spatial relationship of the dentition and jaws during movements of the lower jaw is called articulation.

The closure of the dentition or groups of teeth of the upper and lower jaws during various movements of the latter is called occlusion. Depending on the position of the lower jaw in relation to the upper and the direction of its displacement, there are:

– a state of relative physiological rest;

– central occlusion, or central ratio of the jaws;

– anterior occlusion;

– back occlusion;

– lateral - right and left occlusion.

For the dental technician, the so-called central occlusion is of interest. The general characteristic signs for it for all types of bites (the type of closure of the dentition with the central ratio of the jaws) are:

– closure of the upper and lower teeth with the most complete multiple contact of the tubercles and grooves;

– the coincidence of the midline of closed teeth and the location between the central incisors of both jaws;

– the adjoining of the articular heads by means of discs to the slope of the articular tubercles at their base, to the so-called occlusal point of the joint.

For an orthognathic occlusion (when placing the teeth, the technician most often takes into account this kind of physiological ratio of the jaws) a number of signs are characteristic:

– the upper frontal teeth overlap the lower ones by about 1/3 of the height of their crowns;

– medial-buccal the tubercle of the upper first molars falls into the transverse groove between the buccal tubercles of the lower first molars (the so-called "occlusion key");

– the buccal tubercles of the upper premolars and molars are located outwards from the same-named tubercles of the lower premolars and molars;

– the top of the cutting tubercle of the canine of the upper jaw coincides with the line passing between the canine and the first premolar of the lower jaw;

- each tooth, except for the central incisors of the lower jaw and wisdom teeth, has two antagonists, i.e. the upper tooth merges with the lower and behind of the same name, each lower tooth with the same upper and in front.

Due to these features, the palatine tubercles of the upper teeth fall into the longitudinal grooves of the lower teeth, and the lower buccal tubercles fall into the longitudinal grooves of the upper teeth (Tables 6–9).

With partial secondary adentia, there are three types of ratio of dentition (Fig. 13).

Rice. 13. Options for determining central occlusion in the partial absence of teeth: a - not determined, models are made according to antagonistic teeth; b - determined using wax bases with occlusal rollers, models are made according to prints on wax rollers; c - determined using two wax bases with occlusal rollers, models are made according to prints on wax rollers

Central occlusion with partial absence of teeth is determined using a number of methods (Table 6). The scheme of its definition is presented in Table 7.

Table 6

Methods for determining central occlusion or the central relationship of the jaws and clinical landmarks in the partial absence of teeth

Table 7

Scheme for determining central occlusion with partial absence of teeth

Table 8

Morphological and physiological signs, landmarks and bite elements

VERIFICATION OF THE DESIGN OF THE FSS

Based on the data provided by the doctor, the dental technician, after casting the models with bite ridges into the occluder (articulator), sets the teeth (Table 9).

On the third clinical stage when the patient is admitted, the doctor checks the design of the prosthesis and the quality of the teeth setting (Tables 10, 11).

Table 10

Scheme for checking the design of the FSPP (Scheme OOD)

P ATCHING AND APPLICATION OF SNPP

Finishing the design check, the doctor gives instructions to the dental technician regarding the correction of errors, if any, and determines, in accordance with the conditions, the date for the final production of the prosthesis.

Table 12

OOD scheme for fitting and applying a partial removable lamellar prosthesis and instructing the patient

The patient, on the basis of the available documents, receives a finished prosthesis in the registry. It - final clinical stage. Before handing over the prosthesis to the patient, the quality of the latter is finally checked, it is fitted and applied in the mouth, and instructions are given on the rules for using it and oral hygiene (Tables 12, 13, 14).

Out-of-mouth assessment

Fitting in the mouth

Technical

Estimation after overlay

Doctor's actions

obstructing

Doctor's actions

limitations

imposing a basis

Poor quality

Elimination

The slope is natural

Trying to find a way

Easy to enter and withdraw.

The prosthesis

working and polishing;

lack of

teeth:

insertion of a prosthesis, taking into account

Safety of contact over-

meets

irrational

kov up to

– towards the defect;

defects. Search for places, pre-

basis with mucous

clinical

new

- in oral

obstructing the imposition

prosthetic bed. Preservation

requirements

artifacts, painting

prosthesis. Medica-

direction

prosthesis using a copy

boundaries indicated by the doctor

and maybe

mental image

roving paper, laid-

used

– gas;

prosthesis

between the prosthesis and the natural

for recovery

– granular;

3% solution

natural teeth. Correct-

innovations

– compression

hydrogen peroxide

base metal

or alcohol with

cutter, starting from the side

cash and

next pro-

mucous. If necessary

aesthetic

running wash

bridge this operation

violations

repeat

Degree of conservation

Do not match

Tooth occlusion correction

Tooth match:

individual

cosmetic tre-

in occlusion with the help of

– cosmetic requirements;

features:

novations. Violated

pyro paper. Pro-

– multipoint contacts;

occlusion:

verification of contacts at articu-

- occlusal surface

– value;

lation. Artificial teeth

central occlusion;

grind until equal

- free articulation;

- the position of the front

numbered prints on

– the plate is stable during

thal teeth

carbon paper

function execution;

Location and

- location

Clamp correction

– the shoulder of the clasp has

amount of fixation from-

clasp in relation to

with the help of crampons

in relation to the tooth in accordance with

clasp sprouts in

to the tooth;

in line with aesthetic requirements

plastic

- loose attachment

bovations and restraints

properties;

- poor fixation

– the prosthesis is well fixed

Chapter 2 Clasp prostheses

(main structural elements)

With partial secondary adentia, various types of prostheses are used: bridge-like, removable and clasp. Partial secondary edentulism (PVA)

A symptom complex that occurs in the dentition (ZChS), the main morphological substrate of which is a violation of the integrity of the formed dentition due to loss of teeth caused by various causes (complications of caries, periodontal disease, trauma, etc.).

The goal of the treatment of this pathology is not only the restoration of the integrity of the dentition, but also the normalization of the functions of all components of the FFS, which is possible when using various types of orthopedic structures, depending on the combination of CVA signs.

The main principles of CVA classification are the localization of defects and the severity of adentia.

Indications for the use of clasp prostheses:

1. Bilateral end defects of the dentition.

2. Unilateral end defects of the dentition.

3. Included defects in the dentition in the posterior region with the absence of more than 3 teeth.

4. Defects in the dentition in the anterior section in the absence of more than 4 teeth.

5. Defects in the dentition in combination with periodontal diseases.

6. Multiple defects in the dentition.

Indications for choosing the design of the clasp prosthesis depend not only on the topography of the defects in the dentition, but also on its length, the condition of the supporting teeth, antagonists, the type of bite and the individual characteristics of the patient.

Positive properties of clasp prostheses:

1. The functional efficiency of clasp prostheses is higher than that of

2. Clasp prostheses provide the distribution of masticatory load between the periodontium of the abutment teeth and the mucous membrane of the prosthetic bed.

3. The distribution of the functional load is possible with the help of clasps and other elements.

4. The design of the clasp prosthesis allows you to splint the remaining teeth and eliminate the functional overload of individual groups of teeth.

5. Clasp prostheses reduce the horizontal component of the functional load on the abutment teeth and alveolar processes due to more stable fixation.

6. A slight violation of taste, temperature, tactile sensitivity of oral tissues when using these prostheses.

The determination of the central ratio of the jaws is carried out in the clinic and is a preparatory step necessary for the continuation of laboratory work on the design of dentures.

Determination of the central ratio of the jaws consists of the following steps.

Determining the height of the occlusal ridge for the upper jaw. The lower edge of the occlusal ridge of the upper jaw should be flush with the upper lip or be seen from under it by 1.0-1.5 mm. In the future, the cutting edges of the upper front teeth will be located at this level, which is important for aesthetics and the preservation of natural diction.

Determination of the prosthetic plane along the pupillary line for the anterior teeth and along the nasal line for the posterior teeth.

Determination of the height of the lower part of the face. With the complete absence of teeth, the occlusal height is set, i.e. the distance between the alveolar ridges of the upper and lower jaws in the central

Rice. 186. Landmarks applied to the occlusal rollers for the selection and placement of teeth.

1 - middle line; 2 - smile line; S - lower edge of the occlusal plane; 4 - line of fangs.

Rice. 187. Cross-shaped cuts on the occlusal roller for the upper jaw (a) and their imprints on the roller for the lower jaw (b).

occlusion according to the position of the lower jaw in a state of physiological rest.

Fixation of the central ratio of the jaws.

Application of landmarks on the vestibular surface of wax rollers. On the occlusal rollers, the doctor marks the main guidelines necessary for the dental technician to design prostheses for edentulous jaws (p. 186).

The median line serves for the correct setting of the central incisors and the symmetry of the placement of all teeth. The smile line determines the level of location of the necks of the anterior teeth, i.e. their vertical size, equal to the distance from the level of the occlusal (prosthetic) plane to the smile line. The tubercles of the canines are located on the canine lines, and the distance between the median line and the canine line is equal to the width of the central, lateral incisors and half of the canine on each side. The lines of the smile and fangs determine the choice of the shape, size and type of artificial teeth according to the type of the patient's face, about which the doctor makes a note in the order.

The vestibular surface of the occlusal ridge predetermines the location of the upper lip and its red border, as it is a guide for the location of the vestibular surfaces of the incisors and canines, which will serve as a support for the upper lip. The prosthetic plane guides the dental technician in setting up the teeth in creating sagittal and transversal compensation curves.

The occlusal height is necessary to establish the interalveolar height and position the teeth in this space. Fixing the occlusal height and position of the lower jaw in the central occlusion contributes to the correct orientation of the model of one jaw in relation to the other and is necessary for casting the models into the articulator.

The relief of the design of the vestibular surface of the occlusal ridge of the basis for the lower jaw determines the type of ratio of the dentition; orthognathic, direct, progenic or prognathic.

In order to fold the bases with occlusal rollers from the oral cavity in the position of the found central ratio of the jaws, the doctor makes retention wedge-shaped or cruciform cuts on the upper roller in the region of the first molars on the right and left (Fig. 187). On the sections of the lower roller corresponding to these cuts, a layer of wax 1-2 mm thick is removed and a heated wax plate 2 mm thick is applied. The doctor reintroduces the bases with occlusal ridges into the oral cavity, the patient closes the jaws in the position of central occlusion, and the softened wax of the lower ridge enters the recesses on the occlusal surface of the ridge of the upper jaw base. The bases connected in this way are removed from the oral cavity, cooled, separated and re-introduced into the oral cavity for the final check of the correctness of the determination and fixation of the central occlusion. Wax bases with rollers are cooled, applied to plaster models, the plinths of which are fastened together. In this state, they are received by a dental technician. He sets and plasters the bonded models into the articulator.

This term originates from Latin and means "closing".

Central occlusion is a state of evenly distributed tension of the jaw muscles, while ensuring a one-time contact of all surfaces of the elements of the dentition.

The need to determine the central occlusion is to correctly make a partial or removable denture.

Main features

Experts have identified the following indicators of central occlusion:

1. Muscular. Synchronous, normal contraction of the muscles responsible for the functioning of the lower jawbone.
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 depth 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;
• overlapping elements of the upper row of fragments of the lower one in the front part is 30% of the length;
• the anterior units are in contact in such a way that the edges of the lower fragments rest against 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 lower rows.

Signs of proper row contact

• the rows converge in a single vertical plane;
• incisors and molars of both rows have a pair of antagonists;
• there is a contact of the same units;
• the lower incisors in the central part of the antagonists do not have;
• the upper eighths have no antagonists.

Applies to front 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;
• overlapping of the upper row of fragments of the lower one in the anterior zone occurs to a height of 30% of the total size of the crown;
• the cutting edges of the lower units are in contact with the tubercles of the inner part of the upper ones.

Applies only to the side

• the buccal distal tubercle of the upper row is based in the interval between the 6th and 7th molars of the lower row;
• the lateral elements of the upper row merge with the lower ones in such a way that they fall strictly into the intertubercular furrows.

Methods Used

Central occlusion is determined at the stage of manufacturing prosthetic structures with the loss of several units.

Of great importance in this case is the height of the lower third of the face. 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 preserved and is fixed.

The occlusion index is determined based on the largest possible number of contact zones of the same-named units of the upper and lower rows.

This option is the simplest since it does not require the additional use of occlusal rollers or specialized orthopedic templates.

The presence of three occlusal points between antagonists

This method is used if the patient has retained antagonists in the three main contact areas of the rows. At the same time, a 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 violated, and occlusal wax or thermoplastic polymer ridges are used to correctly compare the casts.

The roller is placed on the bottom row, after which the patient reduces the jaws. After the roller is removed from the oral cavity, imprints of the contact zones of the antagonists remain on it.

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

Absence of antagonistic pairs

The most time-consuming variant of the development of events is the complete absence of elements of the same name on both jaws.

In this situation, instead of the position of central occlusion determine the central ratio of the jaws.

The procedure includes the following steps:

1. Work on the formation of the prosthetic plane, which is positioned along the chewing surfaces of the side units and is parallel to the beam. It is built from the lower point of the nasal septum to the upper edges of the auditory canals.
2. Determination of the normal height of the lower third of the face.
3. Fixation of the mesiodistal ratio of the upper and lower jaw due to wax or polymer bases with occlusal rollers.

Checking the central occlusion with the existing pairs of elements of the same name is performed 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, glued;
• the resulting structure is heated until the wax softens;
• heated templates are placed in the patient's mouth;
• after bringing the jaws together, the teeth leave imprints on the wax strip.

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

If the surfaces of the upper and lower rollers meet during the determination of occlusion, the specialist corrects their contact surfaces.

On the top, wedge-shaped cuts are made, and a certain amount of material is cut off from the bottom, after which a wax strip is glued onto the treated surface. After the rows are brought together again, the strip material is pressed into the cutouts.

Products are removed from the patient's oral cavity and sent to the laboratory for the subsequent manufacture of the prosthesis.

Calculations for orthopedic purposes

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

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

Calculation procedure:

1. At the bottom of the nose, at the level of the nasal septum, the first mark is placed strictly in the center. In some cases, the specialist puts a mark on the tip of the patient's nose.
2. In the center of the chin, a second mark is placed in its lower zone.
3. Measurement is performed between the applied marks height in a state of central occlusion of the jaws. To do this, bases with bite rollers are placed in the patient's oral cavity.
4. Re-measuring between marks, but already 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 normal bite height, which is 2-3 mm, is subtracted from the resting height. And if after that the indicators are equal, we can talk about the normal bite height.

If, when measuring the height, according to the results of the calculations, a negative result is obtained - the lower third of the patient's face is understated. Accordingly, if the result deviates in a positive direction - overbite.

Receptions for the correct setting of the lower jaw

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

The main condition for correct setting is myorelaxation of the jaw muscles.

Functional

The procedure for this method is as follows:

• the patient takes his head back a little until the muscles of the neck tense, which prevents the 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 the index fingers on the patient's teeth, slightly pressing on them and at the same time slightly pulling 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 reducing the jaws, 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 convergence of both rows is achieved.

Instrumental

It is performed using specialized devices that copy the movements of the jaw. 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, this method the apparatus Larina is used and special orthopedic rulers that allow you to fix the movements of the jaw in several planes.

Permissible mistakes

The creation of a prosthetic structure in conditions of malocclusion is the most complex orthopedic procedure, the quality of which is 100% dependent on the qualifications of a specialist, a responsible approach to work.

Violations in determining the position of the central occlusion can lead to the following problems:

overbite

• The folds of the face are smoothed out, the relief of the nasolabial zone is weakly expressed;
• the patient's face looks surprised;
• the patient feels tension when closing the mouth, during the reduction of the lips;
• the patient feels that during communication the teeth knock against each other.

underbite

• The folds of the face are strongly pronounced, especially in the chin area;
• the lower third of the face becomes visually 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, tubercular convergence does not occur.

Permanent lateral occlusion

• overbite;
• offset side clearance;
• 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 rollers during impression taking.
5. Errors and violations on the part of a specialist.
6. Errors in the work of the technician.

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

conclusions

The procedure for determining the position of the central occlusion is only one step in a complex and lengthy procedure for creating a prosthetic structure for the patient. But this stage can certainly be called the most significant and responsible.

It is on the qualifications, professionalism and experience of an orthopedic specialist that the comfort of further operation of the product by the patient and the absence of problems from the temporomandibular joint depend.

After all, various violations in his work, although they can be treated, take a significant period of time, causing discomfort, pain and inconvenience to the patient.

Take care of your teeth, contact your dentist’s office for help in a timely manner in order to maintain the health of the oral cavity and dentition for many years. In addition, taking care of your teeth and gums will help you avoid such unpleasant procedures described in our article.

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Central occlusion and its signs (articular, muscular, dental). Method for determining central occlusion. Various methods of fixing the position of the dentition in the central occlusion. Plastering models in the occluder and articulator.

Central occlusion - multiple fissure-tubercular contacts of the dentition, in which the articular heads are located in the thinnest avascular part of the articular discs in the anterior superior section of the articular fossae opposite the base of the articular tubercles, the chewing muscles are simultaneously and evenly contracted.

Signs of central occlusion:

I. Muscular sign - bilateral uniform contraction of the muscles that raise the lower jaw.

II. Articular sign - the articular head is located on the basis of the slope of the articular tubercle.

III. Dental sign - the maximum number of contact points.

Signs of clenched teeth:

1. Relating to all teeth:

Each tooth has two antagonists, with the exception of the lower central incisors and upper eighth teeth;

The dentitions of the upper and lower jaws end on the same vertical plane;

2. Signs of closure related to the anterior teeth:

The midline of the face coincides with the lines passing through the central incisors;

The upper anterior teeth overlap the lower ones of the same name by 1/3 of the height of the crowns;

Cutting-tubercular contact;

3. Signs related to the lateral teeth:

In the medio-distal direction - the medial buccal cusp of the first upper molar is located between the medial and distal cusps of the first lower, and the distal buccal cusp is located in the interval between the 6th and 7th lower;

In the vestibular-oral direction - the upper lateral teeth overlap the lower ones, the palatine teeth are located in the intertubercular groove of the lower ones.

The upper teeth along the entire perimeter of the dental arch overlap the lower teeth of the same name.

Method for determining central occlusion.

For the manufacture of prostheses, it is necessary to set the dentition in the central occlusion and transfer the appropriate landmarks to the model. The establishment of models in the central occlusion is carried out taking into account the presence and location of antagonistic teeth. There are three typical variants of the state of the dentition in the presence of defects in them, in which central occlusion is established in different ways.

First option. Dental rows with a large number of antagonistic teeth on the right and left. Central occlusion is established based on the maximum number of contact points between the dentition, without the use of wax templates with bite ridges.

Second option. It is characterized by the presence of three occlusal points between antagonistic teeth, however, the number of antagonistic teeth and their topography do not allow placing plaster models in the position of central occlusion without the use of wax bases with bite ridges. The prepared wax base with an occlusal roller is placed on the jaw and the patient is asked to close the dentition. In this way, imprints of antagonist teeth are obtained. If there is no occlusal contact between natural teeth, then the wax roller is cut off until there is uniform contact between them and the occlusal roller in the places of missing antagonistic teeth. Formed on the occlusal roller contact points contribute to the precise establishment of models in the central occlusion of the dentition.

Third option. It is characterized by the absence of antagonistic pairs of teeth. In this case, the central ratio of the jaws is set as follows. First, the height of the lower part of the face is set in a state of relative rest (height of physiological rest). To do this, the prosthetist is asked to lower the lower jaw so that the facial muscles are completely relaxed and the lips close without tension. This position is fixed with a spatula or ruler and proceed to determine the central occlusion. A wax base with an occlusal roller is introduced into the oral cavity and the patient is asked to slowly close the dentition. When closing the dentition, patients often set the lower jaw incorrectly - they shift it forward or to the side.

In order to fix the correct position of the dentition in central occlusion, various methods are used:

In the presence of antagonistic teeth, the position of the central occlusion is checked by closing the teeth. After that, a strip of wax is placed on the occlusal surface of the fitted roller, glued, and then softened hot. Without allowing the wax to cool, the templates are inserted into the oral cavity and the patient is asked to close his teeth. On the softened surface of the wax, imprints of the teeth remain - they serve as a guide for compiling models in a central ratio.

If the occlusal surface of the upper and lower bite rollers closes, then wedge-shaped cuts are made on the occlusal surface of the upper bite roller. A thin layer is removed from the lower roller, opposite the cuts, and a heated strip of wax is attached to it. Then the patient is asked to close his jaws, and the heated wax of the lower roller enters the cuts on the upper one in the form of wedge-shaped protrusions. The rollers are removed from the oral cavity, cooled, installed on the model.

For orthopedic purposes, it is important to know two measurements of the height of the lower face:

The first is measured with the dentition closed in the central occlusion, while the height of the lower part of the face is called morphological, or occlusal;

The second is determined in a state of functional rest of the masticatory muscles, when the lower jaw is lowered and a gap appears between the teeth, this is the functional height.

The anatomical and physiological method for determining the interalveolar height is as follows: the patient makes various movements of the lower jaw, then raises the lower jaw until the upper and lower lips lightly touch. In this position, the orthopedist measures the lower part of the face (in a state of physiological rest). Subtract 2-3 mm from the obtained value - this is the interalveolar height with central occlusion.

To correctly establish the lower jaw, the following techniques are used:

1) ask the patient to swallow saliva while closing the jaws;

2) ask the patient to rest against the soft palate with the tip of the tongue.

In addition to these techniques, it is necessary to place the palm of the right hand on the chin and, while closing the oral cavity, push the jaw backwards, trying not to fix the central occlusion. When the dentition closes, the antagonistic teeth leave imprints on the occlusal ridge, which serve as reference points in the preparation of models.

Then check the occlusal height: it should be less than the height of physiological rest by 2-3 mm. After establishing the central occlusion, the models are plastered in an occluder or articulator.

This article is about central ratio and central occlusion. About bite height and rest height. She will tell you step by step how the doctor works, what methods of determining central occlusion he uses.

Article plan:

1. What is central occlusion and central jaw relation? And what is the difference between them?
2. Steps for determining the central ratio

Detail:

• Methods for determining the lower third of the face. Anatomo-physiological method.
• Methods for fixing the CO after its determination.
• Drawing anatomical landmarks on the finished basis.

Let's start our story.

1) An assigned patient came to the dentist. Today, according to the plan - the definition of the central ratio. The doctor greets his patient and puts on gloves and a mask. He places the patient in a chair. The patient sits straight, leans on the back of the chair. His head is tilted back slightly...

Oh yes! Something needs to be explained to you. Otherwise, we may not understand each other. These are words that will often occur in our story. Their meaning must be known exactly.

Central occlusion and central relation of the jaws

Concepts central occlusion and central ratio often generalized, but their meanings are completely different.

Occlusion- this is the closing of the teeth. No matter how the patient closes his mouth, if at least two teeth are in contact, this is occlusion. There are thousands of options for occlusion, but it is impossible to see or define them all. For the dentist, 4 types of occlusion are important:

• Front
• rear
• Side (left and right)
• and Central

Central occlusion- this is the maximum intertubercular closure of the teeth. That is, when as many teeth as possible for this person are in contact with each other. (Personally, I have 24).

If the patient has no teeth, then there is no central (and no) occlusion. But there is central ratio.

Ratio is the position of one object in relation to another. When we talk about jaw ratio, we mean how the lower jaw relates to the skull.

Central ratio- the most posterior position of the lower jaw, when the head of the joint is correctly located in the articular fossa. (Extreme anterior-superior and mid-sagittal position). There may be no occlusion in the central relationship.

Unlike all types of occlusion, the central ratio does not change throughout life. If there were no diseases and injuries of 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 ratio of the jaws.

Two more definitions are missing to continue the story.

Resting height and bite height

bite height- this is the distance between the upper and lower jaw in the position of central occlusion

Physiological rest height- this is the distance between the upper and lower jaw, when all the muscles of the jaw are relaxed. Normally, it is usually more than the bite height by 2-3 mm.

The bite may be overpriced or understated. Overbite with an incorrectly made prosthesis. Roughly speaking, when artificial teeth are higher than their own. The doctor sees that the height of the bite is less rest height 1 mm or equal to it, or more than it

underestimated- with pathological abrasion of teeth. But there is a variant and improper manufacture of the prosthesis. The doctor sees that the height of the bite is greater than the height of rest. 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 face.

Now you know everything you need, and we can return to the doctor.

2) He received wax bases with bite rollers from the technician. Now he carefully examines them, assessing the quality:

• The boundaries of the bases correspond to those drawn on the model.
• Bases do not balance. That is, they are tightly attached to the plaster model throughout.
• Wax rollers are made qualitatively. They do not delaminate and are of a standard size (in the area of ​​the front teeth: height 1.8 - 2.0 cm, width 0.4 - 0.6 cm; in the area of ​​the chewing teeth: height 0.8-1.2 cm, width 0, 8 - 1.0 cm).

3) The doctor removes the bases from the model, disinfects them with alcohol. And he chills them for 2-3 minutes in cold water.

4) The doctor puts the upper wax base on the jaw, checks the quality of the base in the mouth: whether it holds, whether the boundaries correspond, whether there is a balance.

6) After that, it forms the height of the roller in the anterior section. It all 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 roller) stick out from under it by 1-2 mm. If the lip is thin, the doctor makes the roller protrude by 2 mm. If it is too thick, the roller ends up to 2 mm under the lip.

7) The doctor proceeds to the formation of a prosthetic plane. This is a rather difficult stage. We will dwell on it in more detail.

Formation of the prosthetic plane

"It takes three points to draw a plane"

© Geometry

Occlusal plane

- a plane that passes through:

1) a point between the lower central incisors

2) and 3) points on the outer posterior tubercles of the second chewing teeth.

If you have teeth, then there is an occlusal plane. If there are no teeth, then there is no plane. The task of the dentist is to restore it. And restore correctly.

Prosthetic plane

is the occlusal plane of a complete removable denture. It must pass exactly where the occlusal plane once was. But the dentist is not psychic, he cannot see the past. How will he determine where she had a patient 20 years ago?

After many studies, scientists have found 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 ear tragus. This line is called the Camper horizontal.

Doctor's task- to ensure that the prosthetic plane - the plane of the wax roller on the upper jaw - is parallel to these two lines (Kamper's horizontal and pupillary line).

The doctor divides the entire prosthetic plane into three segments: one frontal and two lateral. He starts from the front. And makes the plane of the frontal roller parallel to the pupillary line. To achieve this, he uses two rulers. The doctor sets one ruler at the level of the pupils, and attaches the second to the wax roller.

He achieves the parallelism of 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 its parallelism with the prosthetic plane. The doctor builds up or removes the wax in the same way as he did in the anterior section.

After that, he smoothes the entire prosthetic plane. For this it is convenient to use

Naish apparatus.

The Naish apparatus is a heated inclined plane with a wax collector.

The basis with bite rollers is applied to a heated surface. Wax melts evenly over the entire surface of the roller, in one plane. As a result, it turns out perfectly even.

The melted wax is collected in a wax collector, which is shaped like a blank for new rollers.

Determining the height of the lower face

Dentists divide the patient's face into thirds:

Upper third- from the beginning of hair growth to the line of the upper edge of the eyebrows.

middle third- from the upper edge of the eyebrows to the lower edge of the nasal septum.

lower third- from the lower edge of the nasal septum to the lowest part of the chin.

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 face (and the height of the bite, respectively):

• Anatomical
• Anthropometric
• Anatomical and physiological
• Functional-physiological (hardware)

Anatomical method

eye detection method. The doctor uses it at the stage of checking the setting of the teeth, whether the technician has overestimated the bite. He looks for signs of overbite: are the nasolabial folds smoothed out, are the cheeks and lips tense, etc.

Anthropometric method

Based on the equality of all third parties. Different authors proposed different anatomical landmarks (Wootsworth: 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, Yupitz, Gysi, etc.). But all these options are inaccurate and usually overestimate the actual bite height.

Anatomical and physiological method

Based on the fact that the bite height is less than the resting height by 2-3 mm.

The doctor determines the height of the face using wax bases with occlusal rollers. 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 points on the patient: one on the upper, the second on the lower jaw. It is important that both are on the center line of the face.

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 on abstract topics, or asks him to swallow his saliva several times. After that, the patient's jaw takes 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 builds up the lower bite ridge. And it measures the distance between the drawn points until it becomes as it should be (resting height minus 2-3 mm).

The inaccuracy of this method is that someone needs a difference of 2-3 mm, while someone has 5 mm. And it's impossible to calculate exactly. Therefore, you just need to assume that everyone has 2-3 mm and hope that the prosthesis will turn out.

Whether the doctor correctly determined the interalveolar height, he checks with the help of 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 by 5-6 mm. If it is wider, then the doctor determined the height incorrectly.

Functional-physiological method

Based on the fact that chewing muscles develop maximum strength only in a certain position of the jaw. Namely, in the position of central occlusion.

If there are bodybuilders among you, you will understand my comparison. When you pump the biceps, if you straighten your arms to half, then lifting a barbell weighing 100 kg will be easy. But if you unbend them completely, then it will be much more difficult to raise it. The same is true for the lower jaw.

In this method, a special apparatus is used - AOCO (Apparatus for Determining Central Occlusion). Rigid individual spoons are made for the patient. They are turned over and inserted into the patient's mouth. A sensor is attached to the lower spoon, into which the pins are inserted. They prevent you from closing your mouth, i.e. set the bite height. And the sensor measures chewing pressure at the height of this pin.

First, a pin is used, which is significantly higher than the patient's bite. And record the pressure force of the jaw. Then use a pin 0.5 mm shorter than the first. And so on. When the height of the bite is even 0.5 mm lower than the optimal one, the chewing force is almost halved. 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.

10) The doctor determines the central ratio of the jaws.

At this stage, one cannot simply tell the patient to close his mouth properly. Even my grandmother often complained that these words were confusing: “And you don’t know how to shut your mouth. It seems, 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. Then he asks the patient to touch the back 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 back edge of the hard palate is.) and swallow saliva. The doctor removes the fingers from the chewing surface of the roller, but continues to push the corners of the mouth. By swallowing saliva, the patient will close his mouth "correctly". So they repeat several times until the doctor is sure that this is the correct central ratio.

11) Next stage. The doctor fixes the rollers in a central ratio.

Fixation of the central ratio of the jaws

To do this, on the roller of the upper jaw, he makes notches (usually in the form of the letter X) with a heated spatula. On the lower roller opposite the notches, the doctor cuts off a little wax, and in its place sticks a heated wax plate. The patient "correctly" closes his mouth. The heated wax flows into the notches. As a result, a kind of key is obtained, according to which the technician will be able to compare the models in the articulator in the future.

There is one more- more difficult - method of fixing the central ratio. It was invented by Chernykh and Khmelevsky.

They stick two metal plates on wax bases. A pin is fixed on the top plate. The lower one is covered with a thin layer of wax. The patient closes his mouth and moves his lower jaw forward, backward and sideways. A pin draws on wax. As a result, different arcs and stripes are drawn on the bottom plate. And the most anterior point of these lines (with the most posterior position of the upper jaw) corresponds to the central ratio of the jaws. On top of the lower metal plate, they glue another one - celluloid. Glue so that the recess in it falls on the most front point. And the pin should get into this recess when the mouth is “correctly” closed. If this happens, then the central ratio is determined correctly. And the bases are fixed in this position.

12) The doctor takes out the bases with a certain central ratio from the patient's mouth. Checks their quality on the model (everything we talked about somewhere above) cools, disconnects. Again introduces into the oral cavity and again checks the "correct" closing of the mouth. The key must go into the lock.

13) The last stage remains. The doctor draws reference lines on the bases. The technician will place artificial teeth along these lines.

Vertically applied to the upper basis median line- this is a line that divides the entire face in half. The doctor focuses on the nasal groove. The median line divides it in half.

Another vertical line canine line- runs along the left and right edge of the wing of the nose. It corresponds to the middle of the canine of the upper jaw. This line is parallel to the midline.

Doctor draws horizontally smile line- this is the line that runs along the lower edge of the red border of the lips when the patient smiles. It determines the height of the teeth. The necks of artificial teeth are made by the technician above this line so that during the smile the artificial gum is not visible.

The doctor takes out wax bases with occlusal rollers from the oral cavity, puts them on the models, connects them to each other and transfers them to the technique.

The next time he sees them with artificial teeth already installed - an almost complete removable denture. And now our hero says goodbye to the patient, wishes him all the best, and prepares to receive the next one.

Determination of the central ratio of the jaws with complete loss of teeth updated: December 22, 2016 by: Alexey Vasilevsky