Functional impression: types, classification, requirements, individual casts, features of application and operation. Methods for making individual spoons in dentistry What is an individual spoon for prosthetics made of
Under any clinical conditions, only a functional impression with an individual spoon should be taken from the edentulous jaw.
Individual spoons can be made from:
1) metal (steel, aluminum) by stamping;
2) plastics:
a) basic (Ftorax, Ethacryl, Jarocryl) polymerization method;
b) fast-hardening (redonta, protacryl) by free molding;
c) standard plastic plates AKR-P;
d) light-curing plastic;
3) solar-cured materials with polymerization in special chambers or using a solar lamp;
4) thermoplastic impression masses (Stens);
Individual spoons are made in the laboratory or directly with the patient.
Making an individual plastic spoon in the laboratory.
In this case, an anatomical cast is taken with a standard spoon and a plaster model is cast on it. On the model, the dental technician draws the boundaries of the future individual spoon.
On the upper jaw, the border of the spoon runs from the vestibular side along the transitional fold, not reaching the deepest point of its arch by 1-2 mm. On the distal side, it overlaps the maxillary tubercles and runs along the line "A" behind the palatine fossae by 1-2 mm.
On the lower jaw, the border of the spoon runs from the vestibular side along the transitional fold, not reaching the deepest point of its arch by 1-2 mm, while bypassing the bands and frenulum of the lip. In the retromolar region, it is located behind the mucous tubercle, overlapping it by 1-2 mm.
On the lingual side, the border of the spoon overlaps the area corresponding to the retroalveolar region (muscleless triangle), not reaching the deepest place of the sublingual space by 1-2 mm and bending around the frenulum of the tongue.
From the foregoing, it can be seen that both on the upper and on the lower jaw, the border of the individual tray is 2-3 mm less than the borders of the prosthesis. This is done in order to leave room for the impression material. The displaced impression material forms the edges of the impression. And, conversely, the distal borders of the tray should be larger than the borders of the prosthesis so that the anatomical formations that are the guidelines for the distal edge of the prosthesis are well imprinted when the impression is taken.
After applying the borders, the dental technician covers the model with Izokol insulating varnish and proceeds to the manufacture of an individual tray from quick-hardening or basic plastic.
For the manufacture of an individual spoon from quick-hardening plastic, the required amount of material is kneaded to the doughy stage and a plate is made from it in the shape of the upper or lower jaw, which is crimped on the model along the outlined boundaries. Then, from small pieces of plastic "dough", a handle is made perpendicular to the surface of the spoon, and not tilted forward. This position of the handle will not interfere with the design of the edges of the print. If on the lower jaw the alveolar part is significantly atrophied and the spoon turned out to be narrow, then the handle is made wider, almost to the premolars: with such a handle, the doctor's fingers will not deform the edges of the impression when they hold it on the jaw
After the plastic has hardened (10-15 minutes), the spoon is removed from the model and processed with cutters and carborundum heads (an individual spoon is not polished), making sure that the edges of the spoon correspond to the boundaries marked on the model. The thickness of the edge of the spoon must be at least 1.5 mm, because. with a thinner edge, it is difficult to obtain the volume of the edge of the print.
An individual spoon can be made from the base plastic by polymerization. To do this, the heated wax plate is pressed tightly over the model, giving it the shape of an impression spoon, the excess wax is cut off with a spatula along the marked boundaries. The wax form of the spoon is plastered into the cuvette in the reverse way and the wax is replaced with plastic.
When making a spoon from AKR-P plastic, standard plates are softened in hot water and crimped according to the model. The excess is cut off with scissors after softening the corresponding area. The handle is made from scraps of material and glued to the spoon with a hot spatula (plastic melts and welds from heat).
Individual spoons made of plastic are hard spoons. They can be used, as well as thermoplastic spoons, for taking compression impressions.
functional impression It is customary to call an impression that reflects the state of the tissues of the prosthetic bed during any movements of the lips, cheeks, tongue. For the first time, the method for its preparation was developed by Schrott in 1864.
Impression classification.
The most popular classification of impressions according to E.I. Gavrilov. It was based on the following basic principles.
1. The principle of the sequence of laboratory and clinical techniques for the manufacture of prostheses. On this basis, prints are preliminary (indicative) and final. Preliminary impressions are taken with a standard spoon. They are used to cast diagnostic models of the jaws, which allow studying the relationship of the dentition, alveolar ridges of the edentulous jaws, the relief of the hard palate and other features that are important for making a diagnosis, drawing up a plan for preparing the oral cavity for prosthetics and the plan for prosthetics itself. The same technique allows you to determine approximately and produce individual spoon . A working model is cast from the final impressions.
2. A method of designing the edges of the impression, allowing the prosthesis to have a closing circular valve, providing one or another degree of its fixation. Accordingly, there are anatomical and functional impressions .
According to the method of decorating the edges of E.I. Gavrilov subdivides functional impressions formatted with:
A) passive movements;
B) chewing and other movements;
C) functional tests.
between anatomical and functional impressions no clear boundary can be drawn. As such, there are no purely anatomical impressions. Receiving an impression with a standard spoon, when forming its edge, functional (though not sufficiently substantiated) samples are always used. On the other hand, functional impression represents a negative display of anatomical formations (palatine ridge, alveolar tubercle, transverse palatine folds, etc.) that do not change their position during movements of the lower jaw, tongue and functions of other organs. Therefore, it is perfectly natural that functional impression has signs of anatomical, and vice versa.
3. The degree of pressure or the degree of squeezing of the mucous membrane.
According to the degree of its squeezing, functional impressions are divided into:
1) compression or obtained under pressure, which can be arbitrary, chewing, dosed;
2) differentiated (combined);
Individual spoons.
Under any clinical conditions, only functional impression individual spoon.
Customized spoons can be made from:
1) metal (steel, aluminum) by stamping;
2) plastics:
A) basic (fluorax, ethacryl, yarocryl) polymerization method;
B) fast-hardening (redont, protacryl) by free molding;
c) standard plastic plates AKR-P;
D) light-curing plastic;
3) solar-cured materials with polymerization in special chambers or using a solar lamp;
4) thermoplastic impression masses (Stens);
5) wax.
individual spoons are made in the laboratory or directly with the patient.
Making an individual spoon from plastic in the laboratory.
In this case, an anatomical cast is taken with a standard spoon and a plaster model is cast on it. On the model, the dental technician draws the boundaries of the future individual spoon.
On the upper jaw, the border of the spoon runs from the vestibular side along the transitional fold, not reaching the deepest point of its arch by 1-2 mm. On the distal side, it overlaps the maxillary tubercles and runs along the line "A" behind the palatine fossae by 1-2 mm.
On the lower jaw, the border of the spoon runs from the vestibular side along the transitional fold, not reaching the deepest point of its arch by 1-2 mm, while bypassing the bands and frenulum of the lip. In the retromolar region, it is located behind the mucous tubercle, overlapping it by 1-2 mm.
On the lingual side, the border of the spoon overlaps the area corresponding to the retroalveolar region (muscleless triangle), not reaching the deepest place of the sublingual space by 1-2 mm and bending around the frenulum of the tongue.
From the foregoing, it can be seen that both on the upper and on the lower jaw individual spoon border passes 2-3 mm less than the boundaries of the prosthesis. This is done in order to leave room for the impression material. The displaced impression material forms the edges of the impression. And, conversely, the distal borders of the tray should be larger than the borders of the prosthesis so that the anatomical formations that are the guidelines for the distal edge of the prosthesis are well imprinted when the impression is taken.
After applying the borders, the dental technician covers the model with Isokol insulating varnish and proceeds to making a custom spoon from quick-hardening or basic plastic.
For making a custom spoon from quick-hardening plastic, the required amount of material is kneaded to the dough-like stage and a plate is made from it in the shape of the upper or lower jaw, which is crimped on the model along the outlined boundaries. Then, from small pieces of plastic "dough", a handle is made perpendicular to the surface of the spoon, and not tilted forward. This position of the handle will not interfere with the design of the edges of the print. If on the lower jaw the alveolar part is significantly atrophied and the spoon turned out to be narrow, then the handle is made wider, almost to the premolars: with such a handle, the doctor's fingers will not deform the edges of the impression when they hold it on the jaw
After the plastic has hardened (10-15 minutes), the spoon is removed from the model and processed with cutters and carborundum heads ( individual spoon do not polish), making sure that the edges of the spoon correspond to the boundaries marked on the model. The thickness of the edge of the spoon must be at least 1.5 mm, because. with a thinner edge, it is difficult to obtain the volume of the edge of the print.
individual spoon can be made from the base plastic by polymerization. To do this, the heated wax plate is pressed tightly over the model, giving it the shape of an impression spoon, the excess wax is cut off with a spatula along the marked boundaries. The wax form of the spoon is plastered into the cuvette in the reverse way and the wax is replaced with plastic.
When making a spoon from AKR-P plastic, standard plates are softened in hot water and crimped according to the model. The excess is cut off with scissors after softening the corresponding area. The handle is made from scraps of material and glued to the spoon with a hot spatula (plastic melts and welds from heat).
Individual plastic spoons are hard spoons. They can be used, as well as thermoplastic spoons, for taking compression impressions.
Advantages and disadvantages of individual plastic impression trays. Plastic spoons are rigid, do not deform in the oral cavity, but, like any laboratory-made spoons (in two visits), they require subsequent correction in the oral cavity. In addition, spoons made in this way give a modified image of soft tissues, since they are compressed and stretched during the anatomical impression.
Wax individual spoons for the upper and lower jaw
Personalized wax spoons can be made both in the laboratory and directly in the oral cavity. Wax spoons according to the CITO method are made in one visit directly on the jaw of the prosthetist. Such spoons are more accurate than individual ones made from an anatomical cast, because they display the soft tissues of the prosthetic bed at rest. The disadvantage of such spoons is that soft wax is deformed during fitting in the oral cavity and when taking an impression (it cannot withstand pressure), therefore, a wax spoon can only be used to remove decompression impressions. individual spoons , regardless of what method and what material they were made of, should be fitted in the oral cavity. A properly fitted spoon sticks to the jaw and does not lag behind it with the movements of the lips and cheeks. In our country, widespread method of fitting individual spoons using Herbst functional tests.
Five samples are used on the lower jaw:
1) swallowing and wide opening of the mouth;
2) movement of the tongue to the sides along the red border of the upper and lower lips;
3) touching the tip of the tongue to the cheeks with a half-closed mouth;
4) movement of the tip of the tongue forward beyond the lips towards the tip of the nose;
5) stretching the lips forward.
Three samples are used on the upper jaw:
1) wide mouth opening;
2) suction of the cheek;
3) displacement of the lips forward (stretching).
Getting a functional impression.
After fitting an individual spoon, they begin to obtain a functional impression.
Taking an impression consists of the following steps:
1) fitting of an individual spoon;
2) applying the impression mass on a spoon;
3) the introduction of a spoon with a mass into the oral cavity;
4) forming the edges of the impression and conducting functional tests;
5) removal of the impression and its evaluation.
It should be taken as a rule that functional impression, providing good fixation of the prosthesis, can only be obtained if the anatomical impression reflects all the structures of the prosthetic field and some functional features of the tissues surrounding the prosthetic bed. Upon receipt functional impression they are only specified.
There are unloading or decompression and compression impressions.
Usually, the value of a compression or unloading impression is associated with the fixation of the prosthesis and its effect on the mucous membrane of the prosthetic bed. However, the value of one or another technique for taking an impression is determined by the influence of the prosthesis on the course of the process of atrophy of the alveolar process.
Unloading (decompression) impressions obtained without pressure or with minimal pressure of the impression mass on the tissues of the prosthetic bed.
The disadvantage of the unloading impression is that the buffer zones of the hard palate are not subjected to compression, and all the pressure from the prosthesis is transferred to the alveolar process, increasing its atrophy.
When receiving a decompression impression, the impression material must reflect without distortion every detail of the oral mucosa so that the microrelief of the prosthesis base exactly matches the surface structure of the prosthetic bed. Therefore, such impressions can be obtained only with the help of impression masses that have a high fluidity and do not require much effort to remove the impression. Such masses include low viscosity silicone pastes: exaflex, xanthoprene, alfazil, as well as zinc oxide eugenol pastes. An impression obtained using liquid gypsum (according to Brahman) usually provides just such a perception of the relief of the surface of the tissues of the prosthetic bed. Some authors believe that if several holes are drilled in the impression tray to drain excess impression material, then the pressure of the impression mass on the mucous membrane can be reduced.
It is known that the fixation of prostheses made from decompression impressions is weak, but they can be used if there are certain indications.
These indications include:
1) significant or complete atrophy of the alveolar processes and mucous membrane;
2) increased sensitivity of the mucous membrane;
3) uniformly pliable mucous membrane of the prosthetic bed.
Compression impressions designed to take advantage of mucosal compliance, so they are removed at high pressure to compress the buffer zones. When talking about a compression impression, they first of all mean the compression of the vessels of the prosthetic bed. The decrease in tissue volume, its vertical compliance are directly dependent on the degree of filling of the vascular bed. The use of compression impressions is recommended in the presence of a loose mucous membrane with good compliance.
A prosthesis made according to a compression impression does not load the alveolar ridge; outside of chewing, it relies only on the tissues of the buffer zones, like on pillows. When chewing under the influence of chewing pressure, the vessels of the buffer zones are emptied of blood, the prosthesis settles somewhat and transfers pressure not only to the buffer zones, but also to the alveolar part. Thus, the alveolar process is unloaded, which prevents its atrophy.
A prosthesis made according to a compression impression has a good fixation, because the pliable mucosa of the valvular zone is in closer contact with the edge of the prosthesis.
The compression impression is taken under continuous pressure. , providing compression of the vessels of the mucous membrane of the hard palate and their emptying. To obtain such an impression, certain conditions must be met:
1) you need a hard spoon;
2) the impression must be taken with a low flow mass or a thermoplastic mass;
3) compression should be continuous, stopping only after the mass hardens. Continuity can be ensured by hand effort (voluntary pressure). But it is more convenient and correct to take a compression impression under the chewing pressure of the muscles that lift the lower jaw, i.e. under bite pressure, which is created by the patient himself, or with the help of special devices that allow you to create a strictly defined pressure (metered) taking into account the individual characteristics of the tissues of the prosthetic bed and chewing muscles.
For obtaining a functional impression use thermoplastic masses, such as Dentofol, Otrocor, Orthoplast, etc.
The convenience of using thermoplastic masses is explained by the following properties:
1) they have an extended plasticity phase, which makes it possible to carry out functional tests necessary to obtain a high-quality impression;
2) during the removal of the impression, they always have the same consistency;
3) they do not dissolve in saliva;
4) evenly distribute pressure;
5) allow you to repeatedly enter the impression into the oral cavity and carry out correction, because new portions of the mass merge with the old portions without deforming the impression.
However, thermoplastic masses have certain disadvantages. These include: inaccurate print due to low fluidity; deformation in the presence of retention points. When cooled with water, they harden unevenly and may deform when removed from the oral cavity.
It should be recognized that when using the above methods of obtaining an impression, in some cases it is not possible to provide a complete functional reflection of the prosthetic field. The tissues of the prosthetic field and the active muscles surrounding it are not the same in relief, relative volume, physiological status during chewing or talking, as well as during the day. The physical and emotional state of a person also has a great influence on the state of the prosthetic bed and the muscles surrounding it. Whatever method of taking the impression is used, further adaptation of the basis of the prosthesis to the tissues of the prosthetic field, the ratio of the dentition and the force of masticatory pressure, as well as the adaptation of the patient and the fitting of the prosthesis for a certain time, is necessary.
The wide variety of clinical conditions encountered for prosthetics necessitates the use of a differentiated impression. One should proceed from the general position that there is no single method shown in all cases. In this regard, the method of obtaining an impression in each specific case must be chosen taking into account the patient's age, constitutional and individual characteristics of the jaw tissues, i.e. in all cases, a differentiated approach is needed. In cases where the tissues of the prosthetic bed in different areas are not the same in their relief and structure, the biophysical properties of each of the elements of the prosthetic bed should be taken into account. When taking an impression, tissues with pronounced spring properties should be under greater load, while tissues of unloaded zones (in the region of the torus, incisive papilla, etc.) should not be excessively loaded.
Selective pressure on the underlying tissues, depending on their anatomical and functional features and biophysical properties, may be important in connection with the need to prevent premature atrophy of the soft and bone tissues of the edentulous jaws by redistributing the masticatory pressure of the prosthesis base.
Therefore, depending on the anatomical and physiological features of the prosthetic bed, it is possible to obtain a display of the mucous membrane in various functional states. At the same time, unloading casts are recommended to be obtained with a thin, atrophic and excessively pliable ("dangling" comb) mucosa. Compression casts are indicated for loose, well-compliant mucosa. The best effect can be achieved only by using differentiated casts obtained with varying degrees of compression of the mucous membrane, taking into account its compliance in different parts of the prosthetic bed.
Requirements for a functional impression:
1) have an accurate and clear imprint of the surface of the mucous membrane of the prosthetic bed without areas and pores washed out by saliva;
2) to have a uniform thickness of the edge and the layer of impression material of the bases of the gaps of the spoon;
3) have an accurate display of the "A" line and blind pits;
4) the edges of the print must be smooth and rounded;
5) the entire impression must be removed from the oral cavity.
Casting of working models.
After receiving the impression, they begin to evaluate it: they check whether the material is pressed in any areas, whether the edges are well-formed, what is their volume. Air pores are not allowed. Then the suction force of the impression is determined. To do this, an impression is introduced into the oral cavity, pressed against the prosthetic bed, and by the handle of the spoon they try to tear it away from the bed. If this is difficult, then this means that the fixation is good. In the event that all requirements are met, the impressions are transferred to the laboratory for further work.
To prevent violation of the valve zone on the model during its opening, the edges of the imprint should be edged. It is carried out as follows. A strip of wax 2-3 mm thick and 5 mm wide is layered 3-5 mm below the edge of the impression. After that, the model is cast in the usual way. The dental technician, cutting off the model, removes excess plaster only within the edging, thereby not violating the sections of the mucous membrane of the transitional fold, in which the edge of the impression was placed. After receiving the model, the wax is removed, and along its edge, a clear functionally designed border and a volumetrically reproduced valve zone remain on the model. If the integrity of the transitional fold is violated, modeling the edge of the prosthesis in accordance with the valve zone becomes impossible, because the marginal closing valve will have defects, which will lead to a violation of the fixation of the prosthesis.
The manufacture of plaster models of edentulous jaws is slightly different from the manufacture of those for removable dentures with partial defects in the dentition. Models with edentulous jaws are specially engraved.
Existing tubercles and nodules are removed from plaster models with a spatula. They are formed from the presence of small bubbles on the surface of the cast. After a general check, the model of the upper jaw is prepared for the creation of a peripheral valve on the palatal surface.
A small layer of gypsum 0.5-1.0 mm deep and of various widths is engraved with a spatula in the transition area of the hard palate into the soft palate. Such an engraving of the model leads to the formation of an elevation at the border of the prosthesis, which is immersed in a pliable tissue. The pressing of soft tissues on the valve zone corresponds to the creation of a palatal valve for the prosthesis on the upper jaw.