CENTRAL OCCLUSION IS THE POSITION OF THE LOWER JAW RELATIVE TO THE UPPER JAW IN WHICH THERE IS THE MAXIMUM NUMBER OF CONTACTING POINTS OF ANTAGONIST TEETH.
METHOD FOR DETERMINING CENTRAL OCCLUSION. TO MANUFACTURE PROSTHESES, IT IS NECESSARY TO ESTABLISH THE DENTAL ARCHES IN THE CENTRAL OCCLUSION AND TRANSFER THE APPROPRIATE LINKS TO THE MODEL. ESTABLISHMENT OF MODELS IN CENTRAL OCCLUSION IS MADE CONSIDERING THE PRESENCE AND POSITION OF ANTAGONING TEETH.
SIGNS OF CENTRAL OCCLUSION I. MUSCULAR SIGN II. ARTICULAR SIGN III. DENTAL CHARACTER IV. FACIAL SIGN
DENTAL FEATURES CENTRAL INCISAL POINTS OF THE UPPER AND LOWER JAWS COINCIDE WITH THE MIDDLE LINE OF THE FACE; EACH TOOTH (EXCEPT 31, 41, 18, 28) HAS TWO ANTAGONISTS; THE TEETH OF THE UPPER JAW OVERLIKE THE TEETH OF THE LOWER JAW BY 1/3 OF THE LENGTH OF THE CROWN; THE UPPER FIRST MOLAR, CLOSING WITH THE TWO LOWER MOLARS, OVERLOWS 2/3 OF THE FIRST LOWER MOLAR AND 1/3 OF THE SECOND LOWER MOLAR; THE BUCCOAL MEDIAL CURPOSITY OF THE UPPER FIRST MOLAR FALLS INTO THE TRANSVERSE GROOVE BETWEEN THE BUCCHAL CURPOSES OF THE LOWER FIRST MOLAR; THE TEETH OF THE UPPER JAW HAVE A VESTIBULAR INCLINE, AND THE TEETH OF THE LOWER JAW ARE VERTICAL. THESE RELATIONSHIPS ARE CHARACTERISTIC FOR ORTHOGNATIC BITE.
MUSCULAR SIGNS IN CENTRAL OCCLUSION, MAXIMUM MUSCLE EFFORTS DEVELOP, WHICH ARE ACCOMPANIED BY BILATERAL SIMULTANEOUS CONTRACTION OF THE MASTICAL MUSCLES AND ANTERIOR BANDS OF THE TEMPORAL MUSCLES.
FACIAL SIGNS OF THE LIPS CLOSED OVER THE WHOLE EXTENT WITHOUT TENSION; NASOLABIAL AND CHIN FOLDS ARE MODERATELY EXPRESS; THE CORNERS OF THE MOUTH ARE NOT DROPED; THE LOWER THIRD OF THE FACE IS EQUAL TO THE UPPER AND MIDDLE THIRD.
DEPENDING ON THE CLINICAL SITUATION, THERE ARE 4 GROUPS OF DIFFICULTY IN DETERMINING CENTRAL OCCLUSION: I – INTACT DENTAL AREA WITH ORTHOGNATIC BITE OR DENTAL AREA WITH INCLUDED DEFECTS PROVIDED THAT THE EXTENT OF THE DEFECT IS IN FR THE ONTAL REGION HAS NO MORE THAN 4 TEETH, AND THE LATERAL REGION HAS 2 TEETH. II – DENTAL RANKS IN WHICH THE HEIGHT OF THE BITE IS FIXED, THERE ARE ANTAGONISTS, BUT THEY ARE LOCATED IN SUCH A WAY THAT IT IS IMPOSSIBLE TO COMPARE MODELS ACCORDING TO DENTAL CHARACTERISTICS DUE TO THE ABSENCE OF TEETH IN EACH FUNCTIONAL GROUP. III – DENTAL RANKS IN WHICH THERE ARE NO ANTAGONIST TEETH, THE HEIGHT OF THE BITE IS NOT FIXED. IV – TOOTHLESS JAWS.
DETERMINING CENTRAL OCCLUSION IN THE FIRST GROUP OF DIFFICULTY DOES NOT CAUSE DIFFICULTIES. IT CAN BE CARRIED OUT IN THE ABSENCE OF THE PATIENT USING GYPSUM MODELS OF THE JAWS. MODELS ARE EASILY COMPARED BY DENTAL CHARACTERISTICS.
DETERMINATION OF CENTRAL OCCLUSION IN THE SECOND GROUP OF COMPLEXITY. IS CARRIED OUT IN THE PRESENCE OF THE PATIENT. CAN BE CARRIED OUT USING WAX PATTERNS WITH BITE CUTS, OR USING OCCLUSION RETAINERS. THE TEMPLATES WITH BITE BULKS ARRIVE TO THE CLINIC ON PLASTER MODELS. THE DOCTOR TREATS THE TEMPLATES WITH AN ALCOHOL COTTON BALL AND PROCEEDS WITH THEIR APPLICATION. FIRST APPLY THE UPPER TEMPLATE, THEN THE LOWER. A TEMPLATE WITH BITE CUTS IS INSERTED INTO THE ORAL CAVITY. THE PATIENT IS ASKED TO CLOSE TEETH WHILE ATTEMPTING TO ACHIEVE CENTRAL OCCLUSION. IF THE UPPER BITECULOUS IS HIGH, IT IS CUT TO ACHIEVE TIGHT CONTACT OF THE TEETH OF THE ANTAGONISTS, TEETH OF THE LOST ANTAGONISTS AND THE BITEWAY ROLLER OVER ITS ENTIRE EXTENT.
DETERMINING CENTRAL OCCLUSION WHEN TIGHT CONTACT IS ESTABLISHED BETWEEN THE REMAINING TEETH AND THE BITE BETWEEN, WE PROCEED TO DETERMINE THE CENTRAL OCCLUSION. A STRIP OF SOFTEN WAX IS LAYED ON ONE OF THE ROLLERS, AND THE PATIENT IS ASKED TO CLOSE THE MOUTH IN A CENTRAL OCCLUSION POSITION. THE PATIENT DOESN'T ALWAYS CLOSE THE TEETH IN CENTRAL OCCLUSION, SO BEFORE INTRODUCING TEMPLATES WITH BITE CUTS, YOU SHOULD CHECK THE CORRECT CLOSING OF THE TEETH, USING SPECIAL TECHNIQUES: PLACE INDEXES ON THE PATIENT'S TEETH AREA FINGERS AND ASK THE PATIENT TO BITE THEM, WHILE QUICKLY PULLING THE FINGERS TOWARDS THE CHEEKS; ASK THE PATIENT TO SWALLOW SALIVA AND CLOSE TEETH; WE GLUE A SMALL WAX BALL ON A TEMPLATE WITH A BITE CRASH IN THE DISTAL SECTION, ASK THE PATIENT TO TOUCH IT WITH THE TIP OF THE TONGUE AND CLOSE THE MOUTH; WE TURN THE PATIENT'S HEAD BACK AS MAXIMUM AND ASK THE TEETH TO CLOSE; ASK THE PATIENT TO OPEN AND CLOSE THE MOUTH WIDE 10 -15 TIMES AND THEN CLOSE THE TEETH, YOU MAY ADDITIONALLY ASK THE PATIENT TO SWALLOW SALIVA FOR GREATEST ACCURACY;
WAX PATTERNS WITH BITE CUTS ARE REMOVED FROM THE ORAL CAVITY AT THE SAME TIME. THE DOCTOR CHECKS THE CORRECTNESS OF THE STAGE OF DETERMINING THE CENTRAL OCCLUSION ON THE MODELS BY INSTALLING TEMPLATES WITH BITE BULKS ON THEM, AFTER COOLING IN COLD WATER. THE MODELS ARE FURTHER FIXED BY THE DOCTOR IN THE POSITION OF CENTRAL OCCLUSION USING A THREAD, RUBBER BAND, OR USING OTHER MATERIALS AT AVAILABLE.
DETERMINATION OF CENTRAL OCCLUSION IN THE THIRD GROUP OF COMPLEXITY IS CARRIED OUT IN THE PRESENCE OF THE PATIENT AND STARTS WITH DETERMINATION OF THE INTERALVEOLAR HEIGHT. TO DETERMINE IT, THERE ARE 4 METHODS: 1. ANATOMICAL METHOD 2. ANTHROPOMETRIC METHOD 3. ANATOMIC-FUNCTIONAL METHOD (ANATOMIC-PHYSIOLOGICAL) 4. FUNCTIONAL-PHYSIOLOGICAL METHOD
THE ANATOMICAL METHOD WAS PROPOSED FIRST. IT IS KNOWN THAT NORMALLY THE THREE PARTS OF THE FACE ARE RELATIVELY EQUAL. THE METHOD IS BASED ON IMPROVING APPEARANCE AND MAXILLARY FORMATIONS WHILE LEVELING THE HEIGHT OF THE LOWER THIRD OF THE FACE. THE METHOD IS INACCURATE AND UNINFORMATIVE.
THE ANTHROPOMETRIC METHOD IS BASED ON DATA ABOUT THE PROPORTIONS OF INDIVIDUAL PARTS OF THE FACE. ZEISING FOUND A NUMBER OF POINTS THAT DIVIDE THE HUMAN BODY ACCORDING TO THE “GOLDEN” SECTION PRINCIPLE. USING GERINGER'S COMPASSES YOU CAN DETERMINE THE POINT OF THE GOLDEN RATIO. THE DEVICE CONSISTS OF TWO COMPASSES. THEY ARE CONNECTED SO THAT THE LEGS OF THE COMPASSIUM GREATER ARE SEPARATE IN EXTREME AND INTERMEDIATE RELATIONS. ON ONLY ONE LEG, THE LARGER LEG IS LOCATED CLOSE TO THE HINGE, AND THE SECOND IS FARTHER FROM IT. A PATIENT WITH FRONT TEETH IS ASKED TO OPEN THE MOUTH WIDE, THE OUTSTANDING LEG OF THE COMPASSIUM IS PUT ON THE TIP OF THE NOSE, AND THE SECOND LEG IS ON THE MINAL TUBERUS, THEN THE DISTANCE OBTAINED IN THIS WAY WILL BE DIVIDED BY THE MIDDLE LEG AT THE TERM M AND AVERAGE RELATIONS. A GREATER VALUE WILL CORRESPOND TO THE DISTANCE BETWEEN THE SPECIFIED POINTS, BUT WITH CLOSED TEETH OR BITE BULKS. THE ANTHROPOMETRIC METHOD ACCORDING TO WADSWARD-WHITE IS BASED ON THE EQUALITY OF DISTANCES FROM THE MIDDLE OF THE PUPILS TO THE LINE OF CLOSING OF THE LIPS AND FROM THE BASE OF THE NOSE SEPTUM TO THE LOWER PART OF THE CHIN.
ANATOMIC-FUNCTIONAL METHOD AT REST THE LOWER JAW IS SLIGHTLY LOWERED WITH THE LIPS CLOSED, A GAP OF 2-3 MM APPEARS BETWEEN THE TEETH. DURING THE CONVERSATION WITH THE PATIENT, POINTS ARE MADE IN THE AREA OF THE BASE OF THE NOSE AND THE PROJECTING PART OF THE CHIN. AT THE END OF THE CONVERSATION, WHEN THE LOWER JAW IS IN A STATE OF PHYSIOLOGICAL REST, THE DISTANCE BETWEEN THE POINTS IS MEASURED. THEN THE WAX BASES WITH BITE CUTS ARE INSERTED INTO THE MOUTH, THE PATIENT CLOSES THE MOUTH, MOST OFTEN IN CENTRAL OCCLUSION, AND THE DISTANCE BETWEEN THE TWO POINTS IS AGAIN MEASURED. IT SHOULD BE 2-4 MM LESS THAN THE REST HEIGHT. IF THE DISTANCE WHEN CLOSING IS GREATER THAN OR EQUAL TO THE STATE AT REST, THEN THE HEIGHT OF THE LOWER FACE IS INCREASED, EXCESS WAX SHOULD BE REMOVED FROM THE LOWER ROLLER. IF THERE IS A DISTANCE OF LESS THAN 2-4 MM WHEN CLOSING, THEN THE HEIGHT OF THE LOWER FACE IS REDUCED AND A LAYER OF WAX SHOULD BE ADDED TO THE ROLLER.
THE FUNCTIONAL-PHYSIOLOGICAL METHOD IS MORE ACCURATE IN DETERMINING THE HEIGHT OF THE BITE. IT IS PERFORMED USING A SPECIAL APPARATUS TO DETERMINE CENTRAL OCCLUSION. ACCORDING TO THE DEVICE, THE BITE HEIGHT IS SETTED WHICH IS DETERMINED BY THE SENSOR. A SPECIAL PLATE AND PINS OF DIFFERENT LENGTHS ARE INSERTED INTO THE ORAL CAVITY, WHICH WILL CHANGE. THE POSITION IS SELECTED THAT CORRESPONDS TO THE GREATEST PRESSING FORCES OF THE JAWS. THE PRINCIPLE IS BASED ON THE FACT THAT MUSCLES CAN DEVELOP MAXIMUM FORCES ONLY IN A POSITION OF CENTRAL OCCLUSION. AFTER DETERMINING THE INTER-ALVEOLAR HEIGHT, THEY PROCEED TO APPLYING THE TEMPLATES WITH BITE BULKS AND DETERMINING THE CENTRAL OCCLUSION.
DETERMINATION OF THE CENTRAL RELATIONSHIP OF THE JAWS THE CENTRAL RELATIONSHIP OF THE JAWS IN THE ABSENCE OF DENTAL ANTAGONISTS IS CHARACTERIZED BY THE MOST CONVENIENT POSITION OF THE LOWER JAW ACCEPTED WITH ACTIVE CONTRACTION OF THE Masticatory MUSCLES.
FUNCTIONAL METHOD USING FUNCTIONAL CONDITIONS OF THE DENTAL SYSTEM (SWALLOWING, TOUCHING THE TIP OF THE TONGUE WITH THE WAX ROLLER ATTACHED ON THE POSTER EDGE OF THE UPPER WAX PATTERN) OR REFLECTIVE ABDUTION OF THE LOWER JAW WHEN OVERLAYING THE DOCTOR'S FINGERS TURN ON THE ROLLER IN THE AREA OF THE MOLORA TEETH. AT THIS TIME THE PATIENT IS ASKED TO BITE THE BITE, AND THE LOWER JAW REFLECTIVELY MOVES BACK. METHOD BASED ON PRESSURE ON THE LOWER JAW BY THE DOCTOR'S HAND.
INSTRUMENTAL METHOD A NUMBER OF DEVICES DUE TO WHICH THE LOWER JAW MOVES BACKWARDS. AT THE STAGE OF DETERMINING CENTRAL OCCLUSION, IN CASES OF THE ABSENCE OF THE FRONTAL GROUP OF MAXILLARY TEETH, THE following landmarks are applied to the wax rollers: the midline of the face - a landmark for the placement of the central incisors; FANUS LINE - LOWER THE PERPENDICULAR FROM THE POSITION OF THE WING OF THE NOSE TO THE OCCLUSAL ROLLER, WHICH CORRESPONDING TO THE AXIS OF THE FANGS. THESE TWO LINES DETERMINE THE POSITION OF THE FRONTAL GROUP OF TEETH (BETWEEN THE CENTRAL LINE AND THE FANUS LINE 2.5 TEETH ARE INSTALLED - 2 INCISERS AND HALF OF THE FUSK). IN ADDITION, THE “SMILE LINE” IS MARKED AT THE LEVEL OF THE FREE EDGE OF THE UPPER LIP. THE DISTANCE BETWEEN THE TWO LINES IS TO DETERMINE THE HEIGHT OF THE FRONT TEETH.
Lesson 7. Determination of the height of the lower part of the face. Methods for determining and fixing central occlusion. Occluders and articulators. Production of wax bases with occlusal ridges.
Determination of the height of the lower part of the face
Anatomical method– descriptive, the basis for determining the height is the restoration of the correct facial configuration based on the patient’s appearance (the degree of severity of the nasolabial folds, non-retraction of the lips, their calm closure)
Anthropometric method– based on the principle of proportionality of the parts of a person’s face.
Zeising found a number of points that divide the human body according to the principle of the “golden section” ( The whole always consists of parts, parts of different sizes are in a certain relationship to each other and to the whole. ZS - division of a continuous quantity into two parts in such a ratio in which the smaller part is related to the larger one as the larger part is to the entire value; the form, the construction of which is based on a combination of symmetry and the golden ratio, contributes to the best visual perception and the appearance of a feeling of beauty and harmony. Zeising did a tremendous job. He measured about two thousand human bodies and came to the conclusion that the golden ratio expresses the average statistical law. The division of the body by the navel point is the most important indicator of the golden ratio. The proportions of the male body fluctuate within the average ratio of 13:8 = 1.625 and are somewhat closer to the golden ratio than the proportions female body, in relation to which the average value of the proportion is expressed in the ratio 8: 5 = 1.6. In a newborn the proportion is 1:1, by the age of 13 it is 1.6, and by the age of 21 it is equal to that of a man. The proportions of the golden ratio also appear in relation to other parts of the body - the length of the shoulder, forearm and hand, hand and fingers, etc. When the numbers expressing the lengths of the segments were obtained, Zeising saw that they constituted the Fibonacci series - a sequence of numbers in which each subsequent number is equal to the sum of the two previous numbers.)
Finding these points on a person’s face is accompanied by complex calculations and constructions. It is made easier by using a Hering compass, which automatically determines the interalveolar height.
Determination method according to Wadsworth-White: equality of distances from the middle of the pupils to the line of closure of the lips and from the base of the nasal septum to the bottom of the chin.
The simplest way is to divide the face into 3 parts: upper, middle and lower. It is believed that with age the middle section remains relatively unchanged, with which the lower section is compared.
Anatomical and physiological– determination of the height of the relative physiological rest of the lower jaw and the presence of a free interocclusal space. Methodology: the patient is involved in a conversation and asked to count. Upon completion lower jaw is installed in the resting position of the masticatory muscles, and the lips, as a rule, close freely. In this position, the doctor measures the distance between two points marked on the skin at the base of the nasal septum and on the protruding part of the chin. Wax templates are then inserted into the mouth and the patient is asked to close them. The distance is measured again - it should be 2-3 mm less than the resting height.
Central occlusion– multiple fissure-tubercle contacts of the dentition with the central position of the TMJ heads in the articular fossae.
- a state of relative physiological rest (minimal tone of the masticatory muscles and complete relaxation of the facial muscles; the occlusal surfaces of the teeth are separated by 2-4 mm)
- anterior occlusions (sagittal movements of the lower jaw)
- lateral occlusions (right and left)
- distal contact position lower jaw.
Signs of central occlusion
Basic:
1) dental – closure of teeth with the greatest number of contacts
2) articular - the head of the condylar process of the lower jaw is located at the base of the slope of the articular tubercle of the temporal bone
3) muscular - simultaneous contraction of the temporal, masticatory and medial pterygoid muscles (muscles that lift the mandible)
Additional:
1) the midline of the face coincides with the line passing between the central incisors
2) the upper incisors overlap the lower ones by 1/3 of the crown (with an orthognathic bite)
3) each tooth has two antagonists: the upper one is of the same name and distal (except 11, 21), the lower one is of the same name and medially (except 38, 48)
The interalveolar height and the height of the lower third of the face are directly related to central occlusion. Interalveolar height is understood as the distance between the alveolar processes of the upper and lower jaws in the position of central occlusion. With existing antagonists, the interalveolar height is fixed by natural teeth, and if they are lost, it becomes unfixed and should be determined.
From the point of view of the difficulty of determining central occlusion and interalveolar height, A.I. Betelman identified four options for the difficulty of determining central occlusion:
In the first option, when in the alveolar processes of the upper and lower jaws there are three or more pairs of antagonist teeth, located as follows: at least one in the anterior area, and the other two in the lateral areas. In this case, from the parameters of the central center position, as a rule, only the height is determined. Plaster models of prosthetic beds at the laboratory stage are compared in the CO position according to dental characteristics and facets of worn occlusal surfaces of antagonist teeth or using occlusal impressions;
Starting from the second variant of the difficulty of determining the position of the CO, when less than three pairs of antagonists are located in the alveolar processes of the upper and lower jaws, it is necessary to first make bite templates at the laboratory stage and determine the position of the CO at the clinical stage.
And only then, using bite templates, compare models of prosthetic beds in the position of central occlusion (central ratio);
Most difficult option determination of the position of the CS of the jaws are the third, when there is not a single pair of antagonists or they are located only in two areas of the jaws) and the fourth (with complete edentia) options for the location of defects in the dentition.
In the second, third and fourth variants of the location of defects in the dentition of the upper and lower jaws, in order to determine the position of the CS, it is necessary in all cases to always make bite templates
Determination of central occlusion is one of the most important points in prosthetics. In case of complete absence of teeth, the central relationship of the jaws is determined.
Determining central occlusion (central relationship of the jaws) means determining the position of the lower jaw in relation to the upper jaw in three mutually perpendicular planes: sagittal, vertical and transversal. That is, the doctor must convey to the dental technician as accurately as possible the conditions that this particular patient has.
Used in everyday practice anatomical and physiological method for determining central occlusion ( central ratio jaws). The physiological basis of this method is the fact that the occlusal height is 2-4 mm less than the height of relative physiological rest.
The doctor acts as follows:
a wax base with an occlusal roller is made. In it, the basis is the basis of the future prosthesis. And the roller is the future teeth.
The upper base is put on and the occlusal ridge is formed as follows: The upper lip does not protrude or recess. Depending on the length of the upper lip, the edge of the upper lip can protrude from under it by 2 mm, be at its level, or be located above the edge of the upper lip by 2 mm. In general, the cutting edges of the upper central incisors, when the mouth is closed, coincide with the line where the lips close, and when speaking, they protrude from under the edge of the upper lip by 1-2 mm. A person looks older than his age if the cutting edges of the upper incisors are not visible when smiling. The height of the upper occlusal ridge is determined based on these considerations. Having inserted the template into the oral cavity, the patient is asked to close his lips - the line of closure is marked on the roller. Check the height of the roller with the mouth half open - the edge should protrude by 1-2 mm.
A prosthetic plane is formed on the upper roller (a plane that imitates the cutting edges and occlusal surface): in the frontal section, the prosthetic plane is formed parallel to the pupillary line, in the lateral sections - parallel to the nasal line (Kamper's horizontal). To do this, take two rulers: one is installed on the occlusal surface of the roller, the other on the pupillary line (frontal section) and the nasal line (base of the wing of the nose - the middle of the tragus of the ear) line (lateral section). Check the parallelism of the rulers and adjust the rollers if necessary.
The height of the lower part of the face in a state of relative physiological rest is determined (it is approximately equal to the height of the middle part of the face). To determine the state of relative physiological rest, anatomical landmarks are also used: the lips close freely, without tension, the nasolabial and chin folds are slightly pronounced, the corners of the mouth are slightly lowered.
The height of the lower part of the face in the position of central occlusion is approximately calculated (height at rest minus 2-4 mm).
Wax bases with rollers are inserted into the mouth and the lower roller is adjusted to the upper one until the calculated height of the lower part of the face in the position of central occlusion is achieved.
The central occlusion is fixed (the rollers are fastened to each other).
Anatomical landmarks are drawn, indicating to the technique how to place artificial teeth: The median line is drawn as a continuation of the central line of the face, the canine line is drawn vertically from the wings of the nose, the horizontal line is drawn along the border of the upper lip when smiling.
The bases are put on the model and, fastened, sent to the laboratory.
ADD.1 Making wax templates with bite ridges in the absence of teeth.
Methodology:
1. Using a warm spatula, cut off a piece of wax from the plate to the required size according to the model.
2. Wet the model with water.
3. Heat the cut strip of wax on one side.
4. Place the reverse unmelted side on the model.
5. Very accurately crimp the model with your fingers, starting at upper jaw from the palate, and on the lower jaw - from the lingual side and further outward.
6. Strengthen the bases with orthodontic wire with a diameter of 0.8 mm and a length of 2 cm, bending it along inside and according to the shape of the alveolar processes, heat and immerse in the base, topping up with boiling water.
7. Heat the second strip of wax and roll it tightly into a roller.
8. Attach the resulting roller strictly in the center of the alveolar process to the wax template.
9. Using boiling wax, pour the roller onto the base, forming vertical vestibular surfaces, adhering to the dimensions: height - 1.5 cm, width = 1 cm.
10. Make the surface of the rollers smooth, in distal sections make a bevel.
11. Trim the wax base along the appropriate boundaries.
12. Remove the wax from the model and smooth it along the edges.
Requirements for bite pads:
1. The boundaries of the wax templates must correspond to the boundaries of the dentures.
2. Templates must fit tightly to the models.
3. The wax roll should be located strictly in the middle of the alveolar process, the width in the frontal area is 0.8 - 1.0 mm, in the lateral area 1 - 1.5 cm.
Methodology for determining the central relationship of the jaws in the complete absence of teeth on both jaws:
1. Check that the wax templates with bite ridges meet the requirements.
a. The boundaries of the wax templates should correspond to the boundaries of the dentures.
b. The templates must fit snugly to the models.
c. The wax roll should be located strictly in the middle of the alveolar process, the width in the frontal area is 0.8 - 10.0 mm, in the side 1 - 1.5 cm, 2 - 3 mm above the remaining teeth.
2. Determine the interalveolar height using an anatomical and physiological method:
a. Use paper or a ruler. An arbitrary point is placed on the patient’s chin.
b. Then, in a state of physiological rest, this point is transferred to a piece of paper or a ruler.
c. On a ruler or paper, subtract from 1 to 4 mm, depending on the age of the patient (the tone of the masticatory muscles), to obtain the height of the bite.
3. Using a dental spatula, trim the frontal section of the upper bite ridge parallel to the pupillary line, ensuring that it is 0.5 - 1 mm below the edge of the upper lip.
4. Trimming side sections bite ridges parallel to each other and the tragonasal line.
5. We make locks on the surface of the roller.
6. We trim the lower bite ridge, ensuring its contact along the entire plane with the upper ridge; the height of the ridges should correspond to the height of physiological rest (i.e. 2 - 3 mm above the bite height) - we control it with a ruler.
7. Using a dental spatula and an alcohol burner, heat the bite ridges by 2–3 mm.
8. Heated bite ridges are inserted into the oral cavity and close the dentition in a position of central occlusion.
9. After the wax hardens and checks that the height of the bite and the central relationship of the jaws are correctly fixed, approximate lines are applied to the rollers: midline, line of teeth closure, canine line, smile line.
10.Wax templates are removed from the oral cavity.
Requirements for bite ridges after determining central occlusion:
1. The bite ridges should fit snugly on the models.
2. The bite ridges must be securely glued together.
3. The bite ridges must securely fix the models in the position of central occlusion.
4. Indicative lines must be clearly drawn on the bite ridges: midline, teeth closure line, canine line, smile line.
ADD.2 use wax templates with bite ridges or, as they are sometimes called, occlusal ridges. On plaster models, along the boundaries marked with a chemical pencil, templates or bases are first made from dental wax. In the area of dentition defects, rollers are installed, the width of which in the lateral sections should be no more than 1-1.2 cm, and in the area of the front teeth - 0.6-0.8 cm. The height of the rollers in the area of the front teeth is approximately 1.5 cm , in the molar area 0.8 cm and should be 1-2 mm greater than the height of the teeth. And the occlusal surface is formed approximately along the occlusal plane of the entire dentition.
With a fixed bite and the presence of antagonists at the occlusal ridge, central occlusion is determined as follows. Wax templates with bite ridges are treated with alcohol, rinsed in cold water, inserted into the mouth and the patient is asked to slowly close his teeth. If the rollers interfere with the closure of antagonist teeth, determine the amount of separation of the teeth and cut off the wax by approximately the same amount. If, when the teeth are closed, the ridges are separated, then, on the contrary, wax is layered on them until the teeth and ridges are in contact. The position of central occlusion is assessed by the nature of the closure of the teeth, typical for each type of occlusion. To accurately establish the lower jaw in centric relation, special functional tests are used. The best results are obtained by swallowing. However, in some patients with restless behavior it is useful to secure this test as follows. Before asking the patient to swallow, it is necessary to relax the muscles that lower and raise the lower jaw. To do this, the patient is asked to open and close his mouth several times, relaxing the muscles as much as possible. At the moment of closing, the lower jaw should move easily, and the teeth should be set exactly in the position of central occlusion. After preliminary training and achievement of the usual closure, strips of wax are placed on the occlusal ridges, glued to the roller and heated with a hot dental spatula. Wax rollers with bases are inserted into the oral cavity and the patient is asked to close his teeth in the same way as during training, i.e. the muscles that lift the mandible should be relaxed, and in the final closing phase the patient should make a swallowing movement. On the softened surface of the wax, impressions of the teeth of the opposite jaw are obtained, which serve as a guide for establishing plaster models in the position of central occlusion.
If the antagonists are the occlusal ridges of the upper and lower jaws, you should first achieve simultaneous closure of the teeth and ridges by first cutting or layering the wax. It is necessary to pay attention to the location of the occlusal plane of the ridges. It must coincide with the occlusal plane of the dentition or be a continuation of it. The occlusal plane of the ridges is a guideline when modeling the closure surface of prostheses. After determining the height of the rollers on the occlusal surface of the upper roller, I make "?: wedge-shaped cuts at an angle to each other. A thin layer of wax is cut off from the lower roller and a new, preheated strip is glued in its place. The patient is asked to close his teeth, controlling the accuracy of the lower jaw setting to the position of central occlusion. The heated wax of the lower roller fills the cuts on the upper one and takes the form of wedge-shaped protrusions. The rollers are removed from the oral cavity, cooled, the clarity of the resulting imprints is assessed and reinserted into the mouth to control the accuracy of determining the central relationship of the jaws. If the protrusions enter into wedge-shaped notches, and signs of teeth closure correspond to the position of central occlusion, therefore, the clinical approach satisfies everyone necessary requirements. Once convinced of this, the doctor removes the rollers from the oral cavity, cools them and places them on the model. Before plaster placement in the articulator, the models are made in the position of central occlusion and the resulting relationship is compared with the nature of the closure of the teeth in the oral cavity. Having once again verified the accuracy of the manipulations performed, the models are fixed in the articulator for the further stage of manufacturing a partial removable laminar denture.
The technician fixes the models into an articulator or occluder.
An occluder is a device that reproduces only the vertical movements of the lower jaw (opening and closing the mouth).
Occluders consist of two wire or cast frames, hingedly connected to each other. The lower frame is curved at an angle of 100 - 110 degrees and imitates the angle and ramus of the lower jaw. In the rear section of the frame there is a platform for resting the pin that holds the interalveolar height.
The upper frame is located in a horizontal plane and has a vertical pin that rests against a platform on the lower frame. The models are plastered into the occluder as follows.
Preparing the model for plaster: making cuts on their base and soaking in water, create a pile of plaster on the table, lower the lower frame of the occluder into it, and, having covered it completely with plaster, place the models in the space of the occluder. In this case, pay attention to the position of the models relative to the front edge of the occluder frames, its midline and the plane of the table. Having covered the lower model with plaster, create a mound of plaster on the base of the upper model and lower the upper frame of the occluder. If the bite height is not fixed, it is necessary to ensure that the height pin is supported on the platform of the lower frame of the occluder. When the plaster hardens, its excess is cut off, the wax strips holding the models together are removed, and the occluder is opened. Then the wax bases with occlusal ridges are removed, and the relative position of the models in the central occlusion remains fixed in the occludator.
Articulators - These are mechanical devices that are designed to reproduce the movement of the lower jaw relative to the upper jaw.
There are various articulators, but they are all divided into four main types:
Simple articulated articulators;
Average anatomical or linear-planar;
Semi-adjustable;
Fully adjustable or universal.
In a simple hinge articulator, only hinge movements can be performed, and any lateral movements are excluded. Therefore, it is possible to use such an articulator only as a visual aid for students.
In average anatomical articulators, the value of the articular and incisal angles is fixed. You can change the relationship of the incisors, but there is no way to adjust the lateral displacements. Medium anatomical articulators can be used for the manufacture of single crowns and, if necessary, for the manufacture of a complete removable denture for edentulous jaws.
The mid-anatomical articulator from Girrbach has a fixed Benet angle of 20*, a fixed sagittal angle articular path - 35*.
Semi-adjustable articulators allow adjustment of the Bennett angle and the sagittal joint path angle. The intercondylar distance is usually 110 mm. Semi-adjustable articulators contain mechanisms that reproduce articular and incisal paths, which can be adjusted based on average data, as well as individual angles of these paths obtained from patients.
Fully adjustable or universal articulators - adjusted to individual jaw position data, which is transferred to the articulator using a facebow.
This stage consists of establishing the relationships of the dentition in the horizontal, sagittal and transversal directions.
Central occlusion is the position from which the lower jaw begins its path and in which it ends. Central occlusion is characterized by maximum contact of all cutting and chewing surfaces of the teeth.
Interalveolar height is the distance between the alveolar processes of the upper and lower jaws in the position of central occlusion. With existing antagonists, the interalveolar height is fixed by natural teeth, and if they are lost, it becomes unfixed and should be determined.
From the point of view of the difficulty of determining central occlusion and interalveolar height, all dental rows can be divided into four groups. IN first group includes dentitions in which antagonists have been preserved, which are located in such a way that it is possible to compare models in the position of central occlusion without the use of wax bases with occlusal ridges. Co. second group These include dentitions in which there are antagonists, but they are located in such a way that it is impossible to compare models in the position of central occlusion without wax bases with occlusal ridges. Third group consist of jaws on which there are teeth, but there is not a single pair of antagonist teeth (unfixed interalveolar height). IN fourth group includes jaws devoid of teeth.
In the first two groups, with preserved antagonists, only central occlusion should be determined, and in the third and fourth interalveolar height And central occlusion (central relationship of the jaws).
In the presence of antagonist teeth, the definition of central occlusion is as follows:
On models, the doctor warms up the occlusal surfaces of the rollers and, while the wax is warm, introduces wax bases with occlusal rollers into the patient’s oral cavity. Then the doctor asks the patient to close the dentition until the antagonist teeth come into contact. At the same time, to prevent the lower jaw from moving forward or to the sides, it is necessary to use one of the following techniques:
while closing the jaws, ask the patient to tilt his head back, reach the back third of the palate with the tip of his tongue, or swallow saliva. In the softened wax, teeth from the opposite jaw will leave clear imprints, which can be used to compare models in the position of central occlusion in the laboratory. In those areas where there are no antagonist teeth, softened wax rollers will connect to each other, fixing the bases in the desired position. The described method of fixing wax bases with occlusal ridges is called “ hot".
With absence large quantity teeth, when the occlusal ridges are large, or when making prosthetics for toothless jaws, the doctor uses another method called "cold". In this case, the doctor makes cuts (locks) on the occlusal surface of the upper ridges in two different directions, and cuts off a thin layer of wax from the lower ridges, instead of which he places a heated strip of wax. Then wax bases with occlusal ridges are introduced into the patient’s mouth, who is asked to close his jaws, controlling the position of the central occlusion. This method eliminates the strong heating of the rollers, which, if extended, can become deformed in the oral cavity.
Determining the central ratio of the jaws means determining the most functionally optimal position of the lower jaw in relation to the upper jaw in three mutually perpendicular planes - vertical, sagittal and transversal.
The stage of determining the central relationship of the jaws in the oral cavity is carried out in a certain sequence.
1. Fitting the wax base with occlusal ridges on the upper jaw:
· formation of the vestibular surface of the upper occlusal ridge (the future vestibular surface of the dentition of the upper jaw). In this case, the doctor focuses on appearance patient (recession or protrusion of lips, cheeks, symmetry of natural facial folds and anatomical formations);
· 
determining the height of the upper occlusal ridge (to determine the level of the upper jaw incisors). When the lips are in a calm position, the cutting edge of the front teeth is located at the level of the lip incision or 1-2 mm lower. The line on which the cutting edges of the teeth will be located should be parallel to the line connecting the pupils - the pupillary line.
· creation of a prosthetic plane. In this case, the doctor focuses on the pupillary line in the frontal region and the nasal-ear lines in the lateral regions.
Pupillary line is a line connecting the patient’s pupils.
Naso-auricular line (Kamper horizontal) is a line connecting the center of the tragus of the ear and the lower edge of the wing of the nose.
To make the doctor’s work more convenient in this case, there is a device called N.I. Larina.
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:
- 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 base.
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
Concepts central occlusion And centric relation are often generalized, but their meanings are completely different.
Occlusion- This 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
Central occlusion– this 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 centric relation.
Ratio- This is the location of one object in relation to another. When we talk about jaw relationship, we are talking about how the mandible 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 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.
Resting height and bite height
Bite height– this is the distance between the upper and lower jaw in the position of central occlusion
Bite height - the distance between the upper and lower jaws in the position of central occlusion Height of physiological rest 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 There may be an overbite overpriced or understated. Overbite with an incorrectly manufactured prosthesis. Roughly speaking, when artificial teeth higher than their own. The doctor sees that the bite height is less rest height by 1 mm or equal to it or more than it
The lower third of the face is significantly larger than the middle third Understated– 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.
6) After this, 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 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 dots: 1) Between the central incisors
2) and 3) Posterior buccal cusp of 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- 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 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.
Determination of the height of the lower part of the 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 very bottom of the chin.
The lower third of the face is significantly larger than the middle thirdAll 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
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 barbell weighing 100 kg. 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-physiological method. It is the simplest and relatively accurate.
10) The doctor determines 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 your mouth “correctly” the doctor puts 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.
Fixation of the central relationship of the jaws
To do this, he makes notches on the upper jaw roller (usually in the form of the letter X) using a heated spatula. On the lower roller, opposite the notches, the doctor cuts off a little wax, and in its place glues a heated wax plate. The patient closes his mouth “correctly”. The heated wax flows into the notches. The result is a kind of key by which the technician will be able to compare models in the articulator in the future.
Notches in the form of the letter X There is one more- more difficult - method of fixing the central ratio. It was invented by Chernykh and Khmelevsky.
They glue two metal plates onto the bases with wax. There is a pin attached to 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 to the sides. And the 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 relationship of the jaws. On top of the lower metal plate they glue another one - celluloid. Glue it so that the recess in it is at the very front point. And the pin should fall into this recess when the mouth is “correctly” closed. If this happens, then the central relation is determined correctly. And the bases are fixed in this position.
12) The doctor takes out bases with a certain central ratio from the patient’s mouth. Checks their quality on the model (everything we talked about somewhere above), cools it, disconnects it. Inserts it into the oral cavity again and again checks the “correctness” of closing the mouth. The key must fit into the lock.
13) The last stage remains. The doctor puts indicative lines on the bases. The technician will place the artificial teeth along these lines.
Midline, canine line and smile line Apply vertically to the upper base midline- this is the line that divides the entire face in half. The doctor focuses on the philtrum. The midline divides it in half.
Another vertical line - canine line- runs along the left and right edges of the wing of the nose. It corresponds to the middle of the maxillary canine. 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 technician makes the necks of the artificial teeth above this line so that the artificial gum is not visible when smiling.
The doctor takes out wax bases with occlusal ridges from the oral cavity, puts them on the model, connects them to each other and hands them over to the technician.
Next time he will see them with artificial teeth already installed - almost complete removable denture. And now our hero says goodbye to the patient, wishes him all the best, and prepares to accept the next one.
Determination of the central relationship of the jaws with complete loss of teeth updated: December 22, 2016 by: Alexey Vasilevsky
An integral clinical stage of prosthetics is the calculation of central occlusion.
From this article you will learn about all the important factors that should be taken into account in order to correctly record the CO, what stages of the procedure and determination methods are used, what control of correctness means.
Signs
Central occlusion can be characterized by muscle, articular and dental characteristics.
For muscle signs characterized by uniform tension of several muscle groups at the same time (masticatory, temporal, medial).
For articular signs characteristically, the articular convexity of the lower dentition is adjacent to the posterior slope of the articular tubercle.
For dental signs Characteristic features of jaw compression in comparison with all teeth, as well as frontal and lateral.
Features of contact for all teeth are as follows:
- the middle line between the frontal incisors corresponds to the line of the face;
- a large number of fissure-tubercle joints of both jaws;
- contact of teeth with corresponding antagonizing pairs.
Signs of connection of anterior teeth:
- the presence of connecting contacts between the edges of the lower incisors and the palate of the upper;
- overlap of the upper frontal teeth about a third of the lower ones;
- placement of the front teeth of both jaws in an identical sagittal plane during their compression.
Signs of contact of the lateral incisors:
- overlap of the buccal tubercles of the upper (left or right) incisors with identical tubercles of the lower ones;
- transverse arrangement of the palatal convexities of the upper teeth between the oral convexities of the lower ones.
Methods
In case of partial absence of teeth, prosthetics are performed, which involves determining the central occlusion. Incorrect fixation of central proportions can lead to many undesirable aesthetic and functional consequences.
The CO can be determined in the following ways:
- If antagonistic pairs are present on both sides, then occlusal ridges made of wax are used to calculate the central ratio.
In order to install the CO, a wax roller is carefully placed on the lower row of teeth and adjusted to the upper one. Then the mesiodistal position of the jaws is determined.
- If antagonists are located at three occlusion points(front, left and right).
Since the lower line of the chin is fixed by natural teeth, centric proportions are established without the use of occlusal ridges.
This technique for calculating the CO consists of fixing maximum quantity chewing contacts. It is permissible to use this technique in the absence of two lateral or four frontal teeth.
- If there are no antagonistic pairs at all, then occlusion is not traced. Therefore, in order to find out the CO, it is necessary to establish and record the following parameters - determining the lower point of the face, measuring the mesiodistal location of the jaws and the occlusal surface.
To determine the correct location of the teeth in the central comparison, the following technique is used:
- if antagonistic pairs are present, occlusion is checked by closing the jaw.
To do this, a softened warm strip of wax is glued to the chewing surface of the fitted roller and inserted into the growth cavity, after which the patient quickly clenches the jaw until the wax has cooled.
As a result of such actions, an impression is formed on the wax strip, according to which the design of the prosthesis is made in a central comparison;
- when the chewing surfaces of the upper and lower rollers come into contact, produce wedge-like cuts on the upper roller.
A small layer is cut off from the bottom roller, then a warm strip of wax is applied on top. When the patient clenches his teeth, the wax pad of the lower roller in the form of wedge-like protrusions is inserted into the grooves of the upper one.
Measurements for orthopedic purposes
The height of the lower point of the face is great importance in orthopedic dentistry.
Measurements of this area are necessary to achieve the best esthetic results, to improve dental contacts in normal functioning conditions, as well as to create space in the vertical plane.
Dentists are required to determine the size of the lower face using the following methods:
- Anatomical. The essence of this method is to measure the contours of the face. When a fixed bite is lost, the anatomical structures around the mouth become deformed.
To return the correct contours of the face, one should take into account the fact that when measuring the interalveolar height, the patient must completely close his lips without straining them. This method is usually used in conjunction with the other two.
- Anthropometric. This method consists of measuring the proportions of individual areas of the face. In practice it is used extremely rarely. It can only be used if the patient has a classic face type.
- Anatomical and physiological. This method is based on the study of anatomical and physiological data.
To measure the height of the lower point of the face, the patient needs to move the lower jaw, and then lift it and slightly close the lips.
In this position, the specialist makes the necessary measurements and subtracts three millimeters from the resulting figure. This sets the height of the lower point of the face in the central comparison.
Techniques for correct positioning of the lower jaw
Many specialists use certain techniques to accurately calculate the lower jaw in the CO.
For example, the patient is required to clench his jaw and swallow saliva. The second technique is that the patient should touch the soft palate with his tongue.
In addition, the patient needs to touch right hand(palm) to the chin, close your mouth, and while doing this try to push your jaw back (without fixing the central point).
When the patient closes his mouth, imprints formed by antagonizing pairs remain on the bite ridge, which are subsequently used to create prosthetic structures.
Errors allowed
Errors when calculating CO are classified into groups.
Errors in the vertical plane (increasing or decreasing the bite)
As the bite increases, the patient experiences tense clenching of the lips, a slightly surprised facial expression, an elongated chin, and teeth chattering when speaking.
To eliminate this error, with an increased bite height due to the lower teeth, the rollers should be remade only for the lower row.
If the height is increased by the upper incisors, new ridges are required only for the upper jaw. Next, you need to calculate the CO again and set up the teeth.
When the bite is lowered, the patient notices clearly visible nasolabial wrinkles, chin skin folds, sunken lips, drooping tips of the mouth, and slight shortening of the chin.
When understated only due to the lower teeth, the rollers are remade for the lower jaw. But if the height is reduced due to the upper incisors, both rollers are remade. After this, the CO is redefined.
Errors in the transversal plane
If the lower jaw is not fixed in the central alignment, but in the frontal, posterior or lateral (right, left).
In frontal position a prognathic bite, tubercular contact of the lateral incisors, and a small gap between the front teeth can be seen.
When positioned laterally– increased bite, slight gap between displaced teeth.
Errors when the lower jaw is extended
The most common mistake is fixing the lower jaw pushed forward when measuring the CO.
To correct it, converted ridges are installed on the sides of the lower jaw. If the lower jaw is displaced back, new ridges are installed on the entire lower surface of the teeth.
Due to the fact that patients often fix their jaw in an incorrect position, it is not so easy to establish an accurate CO.
If there is no contact between some antagonistic pairs, this can be explained by the following factors:
- Incorrect fit of wax rollers or uneven softening. Most often, defects occur due to uneven closing of the rollers when installing the central heating center.
The main signs of these defects are the lack of contact between the lateral teeth on one or both sides.
They can be eliminated by applying a not too heated wax strip to the chewing surface of the teeth. After which, you need to fix the bite again.
- Deformation of wax rollers. When they are removed from oral cavity and installed on the model, loose contact with the latter is monitored.
Signs of this error are an increase in the bite, a gap between the front teeth, and an uneven tubercular connection of the chewing teeth. The error is eliminated with the help of bite rollers with rigid bases.
- Anatomical defects in the oral cavity. In such cases, it is advisable to determine the CO using rollers made on rigid bases.
The video presents Additional Information on the topic of the article.
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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