Types of impression materials. Dental impression materials. Classification of impression materials

Impression materials.

Target. Study the composition, properties and use of impression materials in the clinic and laboratory.

Method of implementation. Group lesson.

Location. Treatment and phantom rooms.

Security.

Technical equipment: multimedia equipment, dental units, instrument trays, impression materials, plaster, spoons, rubber flasks and spatulas.

Tutorials : phantoms of the head and jaws, thematic videos and presentations.

Controls : test questions, situational tasks, questions for testing knowledge control, homework.

Lesson plan.

1. Checking homework completion.

2. Theoretical part. Auxiliary materials, their purpose and classification. Impression materials, requirements for them. Classification of impression materials. Composition and properties of individual impression materials, indications for use in orthopedic dentistry.

3. Clinical part. Demonstration by an assistant of taking an impression with alginate impression material on a case study patient.

4. Laboratory part. Demonstration by an assistant of the technique of mixing elastic impression materials and plaster.

5. Independent work. Taking impressions with alginate masses on a phantom and making plaster models.

6. Analysis of results independent work students.

7. Students solving situational problems.

8. Test control of knowledge.

9. Assignment for the next lesson.

annotation

Auxiliary materials in orthopedic dentistry are usually called materials used at various stages of the manufacture of dentures, splints and devices, but do not constitute the structure itself or its parts.

Classification by purpose:

modeling;

· impression or impression;

· molding;

· abrasive and polishing;

· other (varnishes, acids, alkalis, etc.)

Impression materials

Impression materials are used to obtain an accurate impression of teeth and oral tissues. From this imprint or impression a model can be cast on which designs for full or partial removable dentures, crowns, bridges and inlays are made.

The requirements for impression materials include low shrinkage, high plasticity during introduction into the oral cavity and elasticity after setting, rapid hardening under conditions humidity and oral temperature without negative influence on fabric, exact reproduction of fabric relief, absence unpleasant odor, taste, harmful effects, sterility, insolubility and lack of swelling in oral fluid, good detachability from the model material, no change in impression properties during long-term storage.

Impression materials used in somatology can be divided into several groups (Table 1).

Table 1

Classification of impression materials

Impression materials
Elastic
Hydrocolloid	Elastomeric	Thermoplastic compounds Zincoxyeugenol masses
Alginate materials Agaraceae	Polysulfides Polyesters Silicones

The most commonly used solid impression material is gypsum. It is used at almost all stages of prosthesis manufacturing: for taking impressions, making models, molding materials, soldering.

Impression plaster is a powder to which water is added to form a smooth paste. It contains calcium sulfate hemihydrate (CaS04)2 H20, potassium sulfate to reduce expansion, borax to reduce the rate of hardening and starch, which helps to separate the impression from the plaster model.

To obtain impressions, gypsum powder is mixed with water, and a crystallization process occurs, during which the gypsum changes from a plastic state to a solid state. This process is called grasping.

CaSO4 1/2 H2 O + 3/2 H2 O → CaSO4 2 H2 O

The beginning of setting of gypsum is no earlier than 1.5 minutes, the end is no later than 6 minutes. The setting speed can be adjusted. To speed up the process, increase the water temperature from 30 to 37°C or add substances that catalyze setting (K2SO4, Na2SO4, NaCl, KCl), or use vigorous stirring.

To slow down the setting process of gypsum, inhibitory substances are added: sodium tetraborate, ethanol, glycerin, sugar, starch.

It should be remembered that the faster the setting process of gypsum, the lower the strength of the resulting product and vice versa: the slower the mixture hardens, the higher its strength characteristics.

The gypsum mixture has a very low viscosity, it is hydrophilic and spreads well over the surface of soft tissues, reproducing fine details of the relief with high accuracy. It is better to take impressions with this material using an individual impression tray made of acrylic plastic.

A hardened plaster cast does not shrink, so the time for which the production of a model based on it is delayed does not matter. A release agent should be applied between the plaster impression and the plaster model (usually a sodium alginate solution is used for this purpose).

Zinc oxide eugenol the material is available in the form of two pastes. Basic paste contains zinc oxide, olive oil, linseed oil, zinc acetate and very little, in trace amounts, water; catalyst paste contains eugenol and fillers such as kaolin and talc. The reacting components are zinc oxide and eugenol, which are involved in the curing reaction. Water initiates this reaction, and zinc acetate is added to speed up the process. Oils and fillers are inert components that give the material a plastic consistency.

In order to obtain an impression mass, it is necessary to mix two pastes in equal proportions. The resulting mass has high fluidity and, due to the presence of water in the system, wets well and spreads over the surface of soft tissues. Thus, the material provides a detailed reproduction of the relief of soft tissues without causing their displacement.

This material is mainly used for taking impressions of edentulous jaws, and is also used for making individual trays. The advantage of this material is its dimensional stability and low shrinkage during curing.

Thermoplastic compounds (thermoplastics) When heated they soften and when cooled they harden. Thermoplastics are divided into reversible and irreversible. Reversible thermoplastics retain their plastic properties when used repeatedly, while irreversible thermoplastics lose them.

Paraffin, stearin, gutta-percha, beeswax. By introducing resins (copal, shellac, rosin) an increase in the hardness of the mass is achieved. The introduction of fillers (chalk, talc, zinc oxide, white clay) gives the material a certain structure, reducing its adhesiveness and shrinkage, and reduces the degree of deformation.

Typical representatives of this group of materials are orthocor, Weinstein masses No. 1, No. 2, No. 3; stens, acrodent.

The material is immersed in a water bath for sufficient time to obtain a uniform temperature. Above a temperature of 55-60°C it becomes soft and capable of taking new uniform. When cooled in the mouth to oral temperature, the material hardens and produces an impression. Thus, when making an impression with this material, no chemical reactions occur. To avoid shrinkage deformation, the model should be cast as soon as possible.

Thermoplastic materials are used mainly for taking preliminary impressions of edentulous jaws. Based on the preliminary impression, a model is cast to make a custom tray, which is then used to make a refined impression using a low-viscosity impression material such as zinc oxide eugenol, reproducing fine surface details.

TO elastic materials refers to a large group of substances that, as a result of structuring, acquire elastic, resilient properties. They are divided into hydrocolloid And elastomeric.

The first elastic impression compounds were created in the 1930s based on agar-agar. Agar-agar is a product obtained from certain marine algae(agarophytes), characteristic property which is the ability to produce dense gels. It contains 70–80% polysaccharides (galactose sulfate), 10–20% water, 1.5–4% minerals.

Agar-agar is the main component agar hydrocolloid material. Word " colloid"translated from Greek means glue. If some types of colloids are dried, then the dry residue (phase) can be re-dissolved to obtain a colloid - these are reversible colloids, these include agar impression materials. Others do not dissolve - irreversible colloids; this group includes alginate materials.

Agaraceae impression materials.

The composition and purpose of the individual components of agar impression material are presented in Table 2. As can be seen from this table, to form a gel you only need a small amount of the agar itself.

table 2

Composition of agar impression material

Name	Quantity, (%)	Purpose of the component
		Dispersed phase
		To strengthen the gel
Potassium sulfate		Accelerator for the model
Alkyl benzoate		Protects the shape
Dyes and fragrances		Appearance and taste
		Continuous phase (medium)

The material is produced in a package containing tubes, from which it is squeezed into a special water-cooled impression tray. The spoon is then immersed in a water bath of a certain temperature, where after approximately 8 – 12 minutes it turns into a viscous liquid.

Having received the impression material of a working consistency, the spoon is inserted into the patient’s mouth. From this moment, water cooling begins to be supplied. The water temperature for cooling should be about 13°C. Cooling water circulates in a special impression tray, and after 5 minutes of cooling, the agar should harden. The spoon is then removed from the patient's mouth and an accurate impression of the oral tissues is obtained.

Due to its increased fluidity in the oral cavity and the ability to accurately reproduce the relief of hard and soft tissues, which is associated with the hydrophilic nature of the material, agar gives a very good reproduction of all surface details. The agar impression model should be cast immediately.

Although the material can be used repeatedly and is relatively cheap, its use in the clinic is limited by the following disadvantages: the need to use special equipment, such as water-cooled impression trays and a sectional water bath with a certain temperature, which requires an initial acquisition cost. In addition, the water-cooled tray is quite massive and can create discomfort for the patient.

Alginate impression materials must be sufficiently strong, have a residual deformation of no more than 3%, a curing time at oral temperature of 5–7 minutes, they must have high elasticity, allowing impressions to be taken in the presence of undercuts, and be easy to use.

The main component of alginate impression materials is sodium alginate, which is sodium salt alginic acid (Table 3).

Table 3

Composition of alginate impression material

Name	Quantity, (%)	Purpose of the component
Sodium alginate		Forms a hydrogel
Calcium sulfate dihydrate		Provides calcium ions
Sodium phosphate
Potassium sulfate		To cure the model
Fillers (diatomaceous earth)		Regulates consistency
Sodium silicon fluoride		Controls pH

Modern alginate materials are produced in the form of powders, which, when mixed with water, form a plastic impression material. It is important to strictly observe the correct ratio of powder and water, for which the manufacturer of the material supplies the appropriate measuring cup (measuring spoon) with it. The easiest way to mix the material is in a rubber cup with a spatula, which is usually used for mixing plaster.

The reproduction of surface relief by alginate materials is not as accurate as agar and elastomeric materials, and therefore they are not recommended for taking impressions in the manufacture of crowns and bridges. However, they are very popular in the manufacture of complete and partial dentures.

Elastomeric impression materials

The most commonly used elastomers currently are silicone impression materials.

Silicone impression materials must have the necessary plasticity before structuring, a volumetric shrinkage value of no more than 2% after 6 hours, a curing time (vulcanization) of 4–6 minutes and high impression efficiency (the material must reproduce a groove 0.04 mm wide).

Silicones contain rubber, filler, plasticizer, and catalyst. Materials are produced, as a rule, in the form of a basic paste, a corrective paste and a universal activator.

There are two main groups of silicone impression materials. One group is called condensation cure silicones or C-silicones, and the other is additive curing silicones or A-silicones. Both groups are based on polydimethylsiloxane polymers, which differ in the type of end groups that are responsible for the difference in curing mechanisms.

Thanks to the technique of obtaining a two-layer impression, silicones are capable of very accurately reproducing relief or surface details. To obtain the main impression, the base (main) paste is mixed with the activator in a certain proportion, the material is added to the impression tray and the first impression is obtained. Then the corrective paste, which has a low viscosity, is mixed with the same activator and added to the resulting impression, after which the procedure for obtaining the impression is repeated. The result is a plastic, non-shrinking material - a vulcanization product, the tensile strength of which can be up to 16 kg/cm2.

Polysulfide materials, due to their high precision, are used for taking impressions in the manufacture of bridges and crowns. They are produced in the form of two pastes, basic and catalyst, colored in different colors, which are mixed immediately before taking the impression. The main paste contains polysulfide or mercaptan rubber, and the catalyst paste contains an oxidizing agent, most often lead oxide.

Polysulfide elastomeric impressions have high flexibility and strength, including tear resistance, making the elastic impression easier to remove from the mouth. However, their elasticity is lower than that of all other elastomers. They are prone to cold flow, which can cause distortion of the print when stored under the influence of gravity.

Most often used tiodent– material based on polysulfide rubber. With its help, accurate impressions are obtained with high ductility and low shrinkage. Several models can be cast from one impression.

The disadvantages of this group of masses are the excessive stickiness of freshly prepared paste, a strong odor and the ability to leave stains on the work surface.

Polyester The materials are a set of two pastes, basic and catalyst. The base paste contains low molecular weight polyester with end groups of ethyleneimine, as well as fillers such as fumed silica and plasticizers. The catalyst paste contains an aromatic sulfonic acid ester. When mixing the base paste with the catalyst paste, cationic polymerization occurs.

Polyester materials are used to take particularly precise impressions of several prepared teeth without significant undercuts. The shrinkage of polyester prints per day is only 0.3%, second only to some brands of additive silicones.

The advantages of polyester elastomer materials are that they are easy to mix and more precise than polysulfides and C-silicones. They provide good reproducibility of the microrelief on the impression itself and the model cast from it. If the polyester print is stored in dry conditions, its dimensions will remain stable for a week. Disadvantages are high cost, short work time and high rigidity after curing.

Control questions

1. What materials are considered auxiliary in orthopedic dentistry?

2. What are the requirements for impression materials?

3. What groups are impression materials divided into?

4. List the main properties of solid impression materials.

5. List the advantages of elastic impression materials.

Situational tasks

2. After taking the agar impression, the doctor decided to postpone obtaining the plaster model until the next day. Is this acceptable? Justify your answer.

3. The doctor needs to take an impression of the prepared tooth under the metal-ceramic crown. The doctor has alginate and polysulfide impression materials in stock. What material to choose in this case. Justify.

4. To obtain a diagnostic impression of the dentition, the doctor used zincoxyeugenol impression mass. Evaluate the doctor's actions.

5. The doctor took an impression with polyester mass and placed it in water, postponing making a plaster model based on this impression for several days. Are there any mistakes made? Justify your answer.

Test knowledge control

1. Which group of impression materials does gypsum belong to?

A. hard;

b. elastomeric;

V. hydrocolloid.

2. What increases the hardness of thermoplastic mass?

A. paraffin;

b. gutta-percha;

V. shellac;

g. rosin;

d. white clay.

3. Hydrocolloid materials include:

A. alginate masses;

b. silicones;

V. polyesters;

d. agar materials;

d. zincoxyeugenol masses.

4. What mass do two-layer prints receive?

A. alginate;

b. silicone;

V. thermoplastic;

g. plaster;

5. What are the main advantages of polyester impression materials?

A. precise reproducibility of microrelief;

b. low shrinkage;

V. cheapness;

d. stability of the impression for a long time;

d. high elasticity after curing.

Homework

a) write down the requirements for impression materials;

b) write a classification of impression materials;

c) write down the composition of the agar impression material;

d) write down the composition of the alginate impression mass.

Literature

Main literature:

1. Bazikyan dentistry: textbook / ed. // M.: GEOTAR-Media, 2010. – pp. 542-549.

2. Orthopedic dentistry garage: practical guide/ ed. // Stavropol: Publishing house “Caucasian Region”, 2006. – P. 106-129.

3. Popkov materials science: Textbook. / , // M.: MEDpress-inform, 2009. – P. 125-136.

Additional literature:

1. Abolmasov dentistry: Textbook for students. universities / , // M.: MEDpress-inform, 2009. – P. 75-80.

2. Poyurovskaya materials science: tutorial// M.: GEOTAR-Media, 2008. – pp. 82-104.

The materials used to make impressions (casts) are called impression materials. The design of functionally complete dentures, orthodontic and maxillofacial devices is possible only on the basis of models that are an exact copy of the corresponding sections of the jaws being prosthetized. A model is made by casting an impression obtained from the jaw, so the accuracy of the model primarily depends on the quality of the impression. The quality of the impression, in turn, depends on many factors, the main of which are: the quality of the impression material used, the choice of the technique for obtaining the impression, and the ability of the doctor to correctly use the chosen technique and material.

At the dawn of the development of orthopedic dentistry, beeswax was proposed as an impression material. As an impression material, wax could not even satisfy the requirements of that time made by doctors for materials used to obtain impressions from the area of jaw defects.

The lack of beeswax with the necessary qualities for an impression material prompted dentists to think about the need to search for other materials that have all the properties necessary to obtain impressions in the oral cavity. Clay, gutta-percha and other materials began to be tested as such materials. In 1840, gypsum was used as an impression material, which has not lost its significance to this day.

With the development of dentistry, dental materials science also developed, which has enriched our science with many necessary materials, including impression materials, which can significantly increase the level of dental care for the population.

All impression materials must have certain quality indicators. Currently, they are subject to the following basic requirements.

1. The impression material should not have a harmful effect on the human body and, mainly, should not have a negative effect on the tissues in contact with the impression.
2. Ensure an accurate imprint of the tissues of the prosthetic field (mucous membrane, bone base and teeth), maintain a constant shape after removal from the jaws, removal from the oral cavity and during storage before casting the model.
3. Have good ductility in temperature ranges, not causing burns in the oral cavity.
4. Have an optimal hardening speed, allowing the mass to be introduced into the oral cavity in a plastic state.
5. Have a weak antiseptic effect.
6. Not destroyed when interacting with the oral environment
7. Do not have an unpleasant smell or taste.
8. It is not firmly connected to the plaster of the model, it is easy to separate from it and does not change color.
9. Be accessible, cheap, convenient for transportation and long-term storage.

For ease of study, all materials can be divided into four groups (Table 2):

I - crystallizing impression materials;
II - thermoplastic masses;
III - elastic masses;
IV - polymerizing materials.

BASIC CONCEPTS AND DEFINITIONS.

Imprint called the reverse (negative) image of the surface of hard and soft tissues located on the prosthetic bed and its borders.

Synonymous with the term "imprint" is the definition "cast" who had “citizenship rights” when the main and almost the only material for obtaining them was gypsum. The word “cast” is still found in the vocabulary of dentists and dental technicians, but is gradually becoming an anachronism. Impressions are taken to obtain workers (core), auxiliary (indicative), diagnostic, control jaw models.

The model is an accurate reproduction of the surface of hard and soft tissues located

on the prosthetic bed and its boundaries. On working models manufacture dentures and appliances. The model of the dentition of the jaw opposite to the prosthetic one is called auxiliary, if a defect in the dentition on one of the jaws is replaced. Diagnostic, control are models that are subject to study to clarify the diagnosis, plan the design of a future prosthesis, or record the initial state of the oral cavity before prosthetics and orthodontic treatment.

Impressions are taken using special impression trays, which happen standard And individual . Standard are factory made from stainless steel or plastic for the top and lower jaw. They have different sizes and shapes. The more diverse their choice, the greater the possibilities the doctor has for obtaining an impression.

For individual patients, standard spoons are adapted by lengthening the sides with wax and cutting out holes for the remaining teeth. This avoids difficulties when obtaining an impression. However, standard spoons are not always suitable for this purpose.

In a number of cases (with terminal defects of the dentition, complete loss teeth) must be made individual spoon. As a rule, it is made by a dental laboratory technician either from base plastic or from polystyrene, covering a plaster model of the jaw with it in a thermal vacuum apparatus. The doctor can roll out the quick-hardening plastic dough to a uniform thickness and model an individual spoon on a working model.

The shape and size of the impression tray is determined by the shape of the jaw, the width and length of the dentition, the topography of the defect, the height of the crowns of the remaining teeth, the severity of the edentulous alveolar part and other conditions. If we take into account all possible combinations of these conditions, it turns out that a large number of different trays will be required to obtain impressions with partial loss of teeth. In reality, there are only a few types of standard spoons, which do not always meet the requirements. Therefore, it is often necessary to model the edges of the spoon by modifying them.

A well-chosen spoon makes it easier to take an impression, and the more difficult the conditions for making it, the more carefully you need to select the spoon.

When choosing a spoon, keep the following in mind: The sides of the spoon should be at least 3-5 mm away from the teeth. The same distance should be between the hard palate and the palatal convexity of the spoon. You should not choose spoons with short or long sides that rest against the transitional fold. The best spoon will be the one whose edges, when applied to the dentition during testing, reach the transitional fold. When taking an impression, a layer of impression material 2-3 mm thick will lie between the bottom of the tray and the teeth, the side of the tray will not reach the transitional fold, and the resulting gap will be filled with impression material. This will allow the edge of the impression to be formed by both passive and active movements of the soft tissues. If the edge of the spoon is left standing, this possibility is excluded, since its edge will interfere with the movement of the tongue, frenulum and other folds of the mucous membrane.

When choosing, you need to take into account some anatomical features of the oral cavity. So, on the lower jaw you need to pay attention to the lingual side of the spoon, which should be made longer than the outer one in order to be able to push it deeper soft fabrics floor of the mouth. You should pay special attention to this. Experience shows that most often the lingual edge of the print is not sufficiently embossed for this reason. Before the procedure, the mouth is rinsed with a weak antiseptic solution (potassium permanganate solution, chlorhexidine, the German drug “Duplexol”, the French “PreEmp”).

An impression is considered suitable if the relief of the prosthetic bed is accurately imprinted (including - transitional fold, contours of the gingival margin, interdental spaces, dentition) and on its surface there are no pores or smeared relief with mucus.

The basis for re-taking an impression are the following defects: 1) smearing of the relief due to the quality of the impression material (pull) or the ingress of saliva or mucus; 2) discrepancy between the impression and the future dimensions of the prosthetic bed; 3) lack of clear design of the edges of the print, presence of pores.

Taking an impression may be complicated by a gag reflex. To prevent this, you need to accurately select the impression tray. A long spoon irritates the soft palate and pterygomaxillary folds. In case of a gag reflex, elastic masses should be used, and in a minimal amount. Before taking an impression, it is useful to try on the spoon several times, as if accustoming the patient to it. When taking an impression, the patient is given the correct position (a slight tilt of the head forward, and he is asked not to move his tongue and breathe deeply through his nose. As a distraction, preliminary rinsing with a concentrated solution of table salt can be used. These simple techniques, as well as appropriate psychological preparation, allow a number of cases to eliminate the urge to vomit.

If, with an increased gag reflex, these measures do not produce results, special drug preparation must be carried out. To do this, the mucous membrane of the root of the tongue, pterygomaxillary folds, the anterior part of the soft palate and the posterior third of the hard palate are sprayed with a 10% solution of lidocaine or legacaine (Germany).

However, this may completely remove the protective gag reflex and result in saliva leakage or aspiration of impression material into the larynx. Small doses (0.0015-0.002 g) of the antipsychotic haloperidol (V.N. Trezubov), prescribed 45-60 minutes before the procedure for taking an impression, have a good antiemetic effect.

There are double plastic spoons of the Ivotray type, used for complete dentition, partial and complete loss of teeth. These trays allow you to take an impression simultaneously from the upper and lower dentition, with the mouth closed, with the registration of the central relationship of the jaws.

Distinguish anatomical And functional prints. The first ones are removed with a standard or individual spoon, without the use of functional tests, and therefore, without taking into account the functional state of the tissues located at the boundaries of the prosthetic bed.

Impressions can be taken under measured, arbitrary, chewing pressure. In these cases, especially when viscous, dense impression materials are used, the impression is called compression. In cases where minimal pressure on the moving tissues of the prosthetic bed is required, remove unloading impressions using flowable material and a perforated tray.

In addition, prints are double or double-layer, when a dense viscous material is used for the base of the print. The resulting print is corrected (refined) by a second layer of fluid mass, giving a high-definition print. The first layer turns a standard tray into a custom one (for more details, see the description of silicone impression materials).

REQUIREMENTS FOR IMPRESSION MATERIALS.

The quality of the impression material is of great importance for obtaining an accurate impression. Their main property is plastic , i.e. the ability to fill all elements of the touch surface, and elasticity , i.e. the ability to maintain the given shape when removing the impression from the oral cavity.

The impression mass, like any other medical product, in addition to plasticity and elasticity, must have additional properties that make it acceptable for these purposes. In particular, it is the absence of toxic or irritating effects on fabrics, unpleasant taste and smell, as well as hygiene.

In addition, the impression material must meet the following special requirements:

give an accurate imprint of the relief of the oral mucosa and teeth;

do not deform or shrink after removal from the oral cavity, maintaining its volume for a long time at room temperature;

do not stick to the tissues of the prosthetic bed, do not connect with the plaster of the model, easily separating from them;

do not dissolve in saliva;

do not harden too quickly or slowly, allowing the doctor to carry out all the necessary manipulations, including functional tests;

allow reuse of the mass after its sterilization;

be easy to use;

easy to sterilize, convenient for storage and packaging.

CHARACTERISTICS OF IMPRESSION MATERIALS.

As is known, wax was first proposed as an impression material in the 17th century. The disadvantages inherent in wax forced the search for more advanced materials. In 1840, gypsum was proposed as a new impression material for the oral cavity, and in 1868, the American scientist Stens developed the first thermoplastic impression material, which was later named after him (Stens). Gypsum and stens long years remained universal materials for impressions until the development of elastic impression compounds, which were introduced in our country in 1954.

The group of dental impression materials can be divided into hard, elastic And thermoplastic (reversible).

Hard impression materials.

This subgroup includes gypsum And zinc oxide eugenols(zincoxiguaia-cola) pastes

GYPSUM.

Of all the auxiliary materials used in orthopedic dentistry, gypsum occupies the leading place. It is used at almost all stages of prosthetic manufacturing. It is used to obtain impressions, models,

face masks, as a molding material, for soldering, for installing models in an occluder (articulator), etc.

Natural gypsum is a widespread white, gray or yellowish color. Its deposits are found together with clays, limestones, and rock salt. The chemical composition of natural gypsum is determined by the formula CaSO 4 2H 2 O - calcium sulfate dihydrate. The formation of gypsum occurs as a result of its precipitation in lakes and lagoons from aqueous solutions rich in sulfate salts. The main deposits of gypsum are sedimentary gypsum. IN pure form gypsum is very rare. Its deposits often contain impurities of quartz, pyrite, carbonates, clayey and bituminous substances. The density of gypsum is 2.2-2.4 g/cm3. Its solubility in water is 2.05 g/l at 20°C. Dental plaster is obtained by firing natural gypsum. In this case, calcium sulfate dihydrate loses part of the water of crystallization and turns into calcium sulfate hemihydrate - hemihydrate. The dehydration process occurs most intensively in the temperature range from 120 to 190°C: 2(CaSO 4 2H 2 O) (CaSO 4) 2 H 2 O + ZH 2 O.

Depending on the heat treatment conditions, semi-aqueous gypsum can have two modifications:

α-hemihydrates And β-hemihydrates, which differ in physical and chemical properties.

α-gypsum - is obtained by heating (124˚) gypsum dihydrate under a pressure of 1.3 atm, which significantly increases its strength. It is characterized by high density and strength, water absorption - 40-45%. There are α-modifications with strength indicators 2-3 times higher than the usual one. This gypsum is called super gypsum, autoclaved gypsum, stone gypsum. Special high-strength gypsum is tinted in yellow and is available in sealed packaging, because can actively absorb moisture from the air.

β-gypsum - obtained by heating (165˚) gypsum dihydrate at atmospheric pressure.

In the gypsum production process, heat treatment is essential. If the temperature is not sufficient, some gypsum dihydrate will remain. In case of overheating, complete loss of water may occur, resulting in anhydrite CaSO4. This product sets quickly. The second form is obtained at a higher temperature (from 165 to 520°C). This anhydrite is a slow-setting material. Finally, the third form is formed when heated to 600°C. This produces a non-setting, so-called “dead” plaster.

After firing, gypsum is ground, sifted through special sieves and packaged in

bags made of special paper or in barrels.

Hemihydrate is used in dental practice. Of particular importance are the processes of hardening (setting) of gypsum and the conditions affecting this

When gypsum hemihydrate is mixed with water, dihydrate is formed, and the entire mixture hardens: (CaSO 4) 2 H 2 O + 3 H 2 O → 2 (CaSO 4

This reaction is exothermic, i.e. accompanied by the release of heat.

The setting of gypsum occurs very quickly. Immediately after mixing with water, thickening of the mass becomes noticeable, but during this period the gypsum is still easily molded. Further compaction no longer allows for molding. The setting process is preceded by a short period of plasticity of the gypsum mixture. Mixed to the consistency of sour cream, the gypsum fills the molds well and gives clear imprints.

The plasticity of gypsum and subsequent rapid hardening make it possible to use it to take impressions of jaws and teeth. However, the process of increasing the strength of the gypsum still continues for some time, and the maximum strength of the cast (model) is achieved when it is dried to a constant mass in the environment.

The setting speed of gypsum is influenced by a number of factors: temperature, degree of grinding, mixing method, quality of gypsum and the presence of certain salts in the gypsum. Increasing the temperature of the mixture to +30 - +31 ° C leads to a reduction in the setting time of the gypsum. An increase in temperature from +37 to +50°C has virtually no effect on the setting speed; at temperatures above +50°C, the setting speed begins to drop noticeably, and at temperatures above +100°C, no setting occurs. The fineness of the grind also affects the setting speed. The higher the dispersion of gypsum, the larger its surface. Increasing the surface area of two chemically reacting substances speeds up the process.

The setting speed of the hemihydrate is also affected by the method of mixing it. The more vigorously the mixture is kneaded (stirred), the more complete the contact between the plaster and water will be and, therefore, the faster the setting

Damp gypsum hardens much more slowly than dry gypsum. This plaster is best dried at a temperature of +150 - +170°C. During drying, it is necessary to constantly stir the gypsum, since due to its poor thermal conductivity, uneven heating is possible, which leads to the partial formation of products such as insoluble anhydride, etc.

Salts are of particular importance when working with dental plaster. Salts usually speed up the setting process of plaster. The most effective accelerators are potassium or sodium sulfate, potassium or calcium chloride, solutions of which can be used in 2-3% concentration. With increasing concentration, they, on the contrary, slow down setting. Most often in dental offices a 2-3% solution of table salt is used as an accelerator.

When casting models, accelerators should not be used, since the plasticity of the creamy mass of gypsum is lost in a short time and therefore it is often not possible to cast a high-quality model.

There is usually a tradeoff between the speed of the gypsum setting reaction and the strength of the hardened gypsum. inverse relationship: the faster the setting occurs, the less strength of the resulting product and vice versa, the slower the mixture hardens, the stronger it is. For example, mixing gypsum with a borax solution results in a noticeable slowdown in hardening, resulting in a very durable product.

Strengthening of gypsum castings (models) is carried out using various techniques. After thoroughly drying the plaster (to remove any moisture remaining in the pores), a model is cast and immersed in molten stearin or paraffin. The surface of the product acquires shine and the appearance of ivory. Similar processing is used for the preparation of exhibition or educational exhibits in order to give plaster models a beautiful appearance and increased strength.

Freshly prepared gypsum and a previously hardened gypsum product are firmly connected to each other. This property is used in denture technology, for example, when plastering models in an articulator or cuvette. In cases where a plaster model is obtained from a plaster impression, this property serves as an obstacle to their subsequent separation. In order to avoid this phenomenon, a fat layer is sometimes applied to the surface of the mold. However, the use of fat or petroleum jelly may distort the model. Therefore, a more suitable material for separating the surfaces of the print and the model may be soap solution, into which the impression is immersed for 5-10 minutes. The soap solution forms a thin film and distorts the relief of the model less.

Practice shows that the separation of two plaster products, for example, an impression and a model, can be accomplished without the use of insulating substances. To weaken the connection between them, the print is first immersed in water until completely saturated, i.e. until all the air is expelled from its pores. A saturated impression can no longer absorb moisture from the freshly prepared plaster mass applied to its surface. Thus, the surface of the model will fit tightly to the surface of the print without the penetration of particles of one into the thickness of the other, and they can be separated quite easily by chipping. This is exactly what is done when obtaining plaster models.

To facilitate manipulation when separating casts and models, you can

mix plaster of impression or model with colored water (for example, methylene blue, etc.).

In the work of dental institutions, it is important to follow the rules for storing plaster. Semi-aqueous dental plaster has significant hygroscopicity, absorbing atmospheric moisture, it deteriorates, and its setting becomes worse. Therefore, it is recommended to store plaster in good packaging (metal barrels, thick paper bags), preferably in a dry and warm place on a walkway, and not on the floor. This prevents it from getting damp.

Long-term storage of gypsum, even in a well-closed container and without access to moisture, makes it unsuitable, since the gypsum cakes into lumps and sometimes does not set at all. This is explained by the fact that hemihydrate is an unstable compound and water is redistributed between its particles, in

As a result, more stable compounds are formed - dihydrate and anhydrite 2(CaSO 4) H 2 O → CaSO 4 2H 2 O + CaSO 4.

The fact that gypsum for a long time was the main material for impressions, is explained, firstly, by the lack of alternative masses. Secondly, it was accessible and cheap. In addition, gypsum allows you to obtain a clear imprint of the surface of the tissues of the prosthetic bed; it is harmless and does not have bad taste and odor, practically does not shrink, does not dissolve in saliva, does not swell when wetted with water and is easily separated from the model using the simplest release agents (water, soap solution, etc.)

However, along with its positive qualities, gypsum has a number of disadvantages, resulting in last years it is almost completely replaced by other materials. Plaster is fragile, which often causes the impression to break when removed from the mouth. At the same time, its small details, filling the space between the teeth, are often lost. This lack of gypsum is especially evident in cases where there is divergence and convergence of teeth, their inclination towards the lingual or buccal sides, as well as in periodontitis, when the extra-alveolar part of the teeth increases.

Superhard gypsum (α-hemihydrates) - “Supergypsum” (Russia), “Begodur”, “Begostone”, “Duralit”, “Vel-Mix Stone” and “Supra Stone” (Germany), “Fuji Rock” (Japan) - have a hardening time of 8-10 minutes, while expansion during hardening does not exceed 0.07-0.09%, strength under pressure 1 hour after hardening is 30 N/mm 2, after 1 day - 35-60 N/ mm 2. They are used in the manufacture of dismountable models of jaws combined with conventional plaster. The ratio of powder and water is 100 g per 22-24 ml.

Synthetic superhard plaster, for example, Moldasint (Germany), is characterized by an approximate expansion coefficient after 2 hours of 0.1%. Mixing ratio - 100 g per 20-23 ml, compression resistance - 48 N/mm 2. Supergypsum powders are strictly dosed with water and mixed in vacuum mixers (“Vakuret-S”, “Junior”, “Vamiks-2m”, “Matova-SL”). The forms are filled out by them on vibrating tables (“Vibromister”, “Vibroboy”, “Vibrobaby”, KB-16, -36, -56, all - Germany). This eliminates porosity and underfilling of the model.

ZINCOXIDE EUGENOL PASTES.

Of these materials, the most common is the Czech “Repin”, which consists of two aluminum tubes with white (main) and yellow (catalyst) pastes. The basic paste contains zinc oxide (80%) and inert oils. The catalyst paste contains clove oil (eugenol) - 15%, rosin and fir oil - 65%, filler (talc or white clay) - 15%, accelerator (magnesium chloride) - 4%. Both pastes are mixed in equal proportions. The precipitation reaction that occurs between eugenol and zinc oxide results in hardening of the material, which is accelerated by vigorous mixing, the addition of moisture and increased temperature.

The material is intended for obtaining functional impressions, especially from edentulous jaws. It gives a clear, detailed imprint of the mucous membrane and adheres well to an individual spoon.

However, for all their advantages, zinc oxide eugenol pastes have been replaced by silicone and polysulfide impression materials and are mainly used as a temporary fixation material for fixed dentures.

At different times, zinc oxide eugenol materials “Zero Plus”, “Luralit” (Germany), “Kavex” (Holland), “Dendia” (Austria), and zinc oxide eugenol paste “Dentol” (USSR) were used.

Elastic impression materials.

This group includes alginate, silicone (polysiloxanes), polysulfide (thiokol), polyester masses. The last three subgroups are united by the concept of “synthetic elastomers”.

ALGINATE MASSES.

The widespread use of foreign structuring alginate impression compounds dates back to the early 40s of the current century. This material has gained a strong place in dental practice and has contributed to a significant reduction in the use of plaster. The exceptionally rich variety of alginate materials used in modern clinical dentistry testifies to their great practical importance.

Alginate impression materials are filled, structuring systems. sodium alginate - cross-linking agent. The alginate composition should include the following main components: monovalent cation alginate, cross-linking agent, structuring speed regulator, fillers, indicators and taste and color correcting substances. Sodium alginate (main component) is the sodium salt of alginic acid, a natural polymer of α-mannuric acid.

Alginate-based impression materials were produced in the following form . First group was a set consisting of viscous (5% aqueous solution) sodium alginate and multicomponent powder. Second group alginate materials were produced in the form of paste and powder, which, when mixed, formed an impression compound that hardened at room temperature. Third group- the most common and more advanced alginate materials - are produced in the form of a multicomponent powder to which water is added.

The advantages of alginate impression materials include high elasticity, good reproduction of the relief of soft and hard tissues of the oral cavity, and ease of use. The main disadvantages of these materials can be considered the lack of adhesion to impression trays and some shrinkage over time as a result of water loss. When using alginate materials, it is necessary to strictly adhere to the manufacturer's instructions.

When mixing Stomalgin powder with water, a homogeneous mass is formed. The casts have sufficient hardness and elasticity and are practically not deformed when filled with plaster.

"Stomalgin" is used to take impressions of partial loss of teeth and toothless jaws. It is also used in orthodontic practice to obtain impressions when correcting malocclusions. “Stomalgin” is distinguished by high elastic and strength properties: its residual deformation during compression is 2.5%; tensile strength - 0.15 N/mm 2.

An impression made from the Stomalgin material should be used to obtain plaster models immediately after removal and subsequent washing with water. The model must be cast with liquid plaster without creating unsteady pressure on the impression. The separation of the plaster model from the elastic impression can be done without the use of any tools: it is removed from the model by pulling the edges with your fingers.

In recent years, “Stomalgin-02” has been produced, in which, due to the introduction and composition of triethanolamine, the homogeneity of the material is improved and the elasticity of the material is increased. “Stomalgin-02” is characterized by increased elasticity and allows you to obtain accurate impressions of the relief of the prosthetic field.

Alginate mass “Ipen” (Czech Republic) is prepared by mixing green fine powder (10 g) with water at room temperature (20 ml) for 30-45 seconds. Hardening time is 2.5 minutes.

Chromatic alginate mass “Fraiz” (Poland) is a purple powder, mixed in a ratio of 9 g per 17 ml of water. After 30 sec. After kneading, the color of the paste changes to pink. At this point, the impression tray is filled with paste. The color change to white is a signal to insert the spoon with the mass into the oral cavity. The hardening time of the material at 23°C is 2.5 minutes.

The mass "Kromopan" (Italy) and "Kromopan-2000" also with color indexing of phases (violet, pink, white). The mixing ratio is 9 g per 20 ml. According to the manufacturer, no noticeable distortion of the print occurs within 48 hours after receiving it. This is due to the introduction of an integrated alginate stabilizer into the mass.

There are known Polish masses “Orthoprint” with an antiemetic additive, “Hydrogum” - with a rubber-like effect, as well as “Dupalflex”, “Tricoloralgin”, “Palgaflex” (Germany), “Propalgin” (France). The last mass hardens slowly (3 minutes 45 seconds). Of the American materials, “Geltrate”, “Geltrate Plus”, “Kos Elginate” are common on the Russian market. The “Jeltrate” material is available in three consistencies: normal, dense - used for high arches of the palate and orthodontics, quick-hardening - for taking impressions with an increased gag reflex. The characteristics of normal (fast-hardening) “Jeltrate” are: hardening time -2.5 (1.75) minutes, residual deformation - 2.1 (1.7)%, relative compression -13.3 (13.9)%, fluidity - 1.86 (1.67) g.

SILICONE MASSES.

This group of impression materials has been used since the 50s of the 20th century. Currently, impression materials based on organosilicon polymers - silicone rubbers - are increasingly used in dental practice. The industry today is able to develop silicone impression materials that could meet all the requirements of the theory and practice of dentistry. It is safe to say that the future of impression materials belongs to silicone rubbers.

Apply two types silicone materials that differ in their chemical reactions - polycondensation (C-silicones, or K-silicones - from the English Condensation) and joining or adding (A-silicones, from English additional) .

Polycondensation- this is a polymer synthesis reaction in which a chemical interaction occurs, as a result of which, in addition to polymers, by-product low-molecular substances (ammonia, alcohols, water) are also formed. This reaction underlies the hardening of silicone and polysulfide impression materials.

Condensable materials include basic and accelerating pastes. The basic paste consists of a relatively low molecular weight silicone, dimethylsiloxane, which has reactive hydroxyl end groups. Fillers can be copper carbonate or silica with particle sizes from 2 to 8 mm and concentrations from 35 to 75%, to the level of a thick paste. The accelerator can be a liquid consisting of a suspension of stannous octoate and alkyl silicate, or a paste with the addition of a thickening agent. The reaction proceeds with the formation of rubber with a three-dimensional structure and the release of ethyl alcohol and an exothermic increase of 1°C.

Additional (joining) type of silicone material is represented by pastes of low, medium, dense and very dense consistency and is also polysiloxane. The basic paste consists of a polymer with a moderately low molecular weight and silane groups (-Si-H), from 3 to 10 per molecule,

and filler. The accelerator (or catalyst) is a polymer with a moderately low molecular weight and vinyl end groups, as well as a catalyst - chloroplatinic acid. Unlike polycondensation, the addition reaction does not create a low molecular weight product, but is an ionic polymerization:

Secondary reactions are observed when - OH groups form hydrogen gas. Various products containing platinum or palladium absorb it. Dyes are added to the base and catalyst pastes to determine the completeness and uniformity of mixing of the pastes. A retarder can be introduced - a low molecular weight polymer of the same type as the main paste.

It should be remembered that when mixing two pastes with hands wearing rubber (latex) gloves, sulfur from them can enter the silicone material and reduce the activity of the platinum-containing catalyst. The result of this is a slow or complete absence of hardening of the paste. Therefore, it is necessary to wet the gloves with water or a weak solution of a disinfectant. Vinyl gloves do not have these side effects of latex gloves.

Silicone materials are produced as a set in the form of pastes and liquid slurries, when mixed under normal conditions, vulcanization occurs within a few minutes and an elastic product is formed that does not lose its properties long time. There are options for mixing two infusions. In our country, the impression material called “Sielast-69” is widely known; 03; 05; 21" (Ukraine).

To prepare the mixture, two liquids are added using dropper bottles to the required amount of Sielasta-69 paste, measured using a paper dosage scale placed under a glass plate.

The vulcanization (hardening) time of the impression in the oral cavity is 4-5 minutes, and depends on the amount of paste taken and the number of introduced catalysts, and an increase in the latter leads to faster hardening. The rate of vulcanization is also affected by the ambient temperature. As the temperature rises, the hardening of the print accelerates. The methodology for obtaining models is generally accepted. Before obtaining the model, the impression is placed for 15 minutes. into a saturated soap solution, then washed with water and air dried.

The materials “Sielast-03” and -05 are intended for taking double impressions, for which they include the main and corrective, or clarifying, pastes and a liquid catalyst. More often, a double impression is taken in two stages. In the first of them, the main dense paste is applied to an impression tray lubricated with an adhesive composition (adhesive) and the impression is taken. In this case, in order to create space for the corrective paste, the procedure is carried out either before preparing the teeth, or without removing the provisional crowns, or by first covering the impression material with a strip of thin polyethylene film. Then, after preparation, a pharmaco-mechanical expansion of the gingival groove (pocket) of the supporting teeth is carried out, a linen or cotton thread, or a knitted ring soaked in a vasoconstrictor solution is introduced there. The latter is used “Naftizin” (Russia), “Sanorin” (Czech Republic), “Galazolin” (Poland), “Orostat” (Germany) and other drugs. The first layer of the impression individualizes the standard tray with which it was taken. A layer of paste imprint of the vault of the palate is cut off on it and along the edges of the impression for its free reintroduction into the oral cavity. In addition, the interdental septa are removed to prevent compression of the interdental papillae. And finally, the outlet grooves are engraved from the tooth impressions to the top of the palatal vault, radially, to prevent elastic deformation of the impression. Then the first layer of the print is dried and filled with clarifying paste. The threads are removed from the pockets, and the pockets themselves are dried with a stream of warm air. They can be filled with corrective paste using a special syringe with a curved cannula. You can take an impression without using a syringe by filling the impression with clarifying paste and reintroducing it into the oral cavity.

There is a one-step method for obtaining a two-layer print (sandwich method). At the same time, having filled the spoon with the main paste, the doctor makes indentations in it, in the area of the projection of the supporting teeth. Corrective paste is injected there. It is applied from a syringe to the prepared teeth. After this, a spoon with two pastes is inserted into the oral cavity to take an impression.

One of the best representatives of silicone impression materials is the Japanese “Exaflex”, containing two main pastes (yellow and blue). Mixing them ends when the material is uniformly green in color. There are also 2 pastes for creating a corrective layer, two more pastes for syringe injection of material into periodontal pockets, as well as two pastes for obtaining functional impressions. In addition, the kit includes adhesive glue, retarder, spatulas, and a syringe. The same mass, packaged in juicy cartridges (cartouches) for use in a dispenser pistol with beckoning tips, is called “Examix”. Known sets are multi-purpose ipikon pastes “Koltex/Koltoflex” (Switzerland), “Dentaflex” (Czech Republic), “Kneton/Sitran” and “Tsafo-Tevezil” (Germany).

Silicone impression systems “Detasil” and “Silasof” (Germany) also have cartridge packaging. The last pastes are evenly squeezed out of the cartridges. The priority for using automatic mixing of two pastes belongs to the Canadian company ZM. producing the silicone impression system “ZM Express” with a hardening time of the main and corrective pastes of 6 minutes, and a quick-hardening paste of 4 minutes. Vinylpolysiloxane material "3M Express" has a volume recovery after deformation when removing the impression from the mouth - 99.84%. For comparison, the same figure for polysulfide impression compounds is 99.7%, polyester 99.6%, and for condensation silicone materials - 99.34%.

Physico-mechanical properties of silicone materials. Shrinkage is small. Resident pastes (Germany) a day after receiving the impression have small volumetric changes equal to 0.14–0.60%. Vinyl silicone impression material "Hydrosil" (USA) hardens in 5-5.5 minutes, has a residual deformation - 0.2-0.5%, relative compression - 2-2.5%, detail reproduction - 20 microns, fluidity - 0-0.1%. Another vinyl silicone material intended for occlusal impressions, Regisil (USA), hardens quickly (2.3 minutes), has a shrinkage of 0.2%, a relative compression of 1.3%, and a fluidity of 0.

German silicone impression materials are the most widely represented on the domestic market. Among them are “Optosil II - Xanthoprene”, “DL - Knet”, “Panasil”, “Formasil II”, “Alfasil”, “Gammasil”, “Deguflex”, etc.

Disinfection of silicone impressions is carried out using sodium hypochlorite 0.5%, glutaraldehyde 2.5% (pH - 7.0-8.7), Glutarex, dezoxon 0.1%, hydrogen peroxide 4-6%.

In recent years, a new elastic impression material based on vinyl siloxane rubber has been developed, curing without the release of by-products - “Vigalen-30” and corrective “Vigalen-35”. These materials are practically non-shrinking, which makes it possible to store prints for a long time. Moreover, if necessary, several high-precision models can be cast from one impression.

POLYSULFIDE (THIOCOL) IMPRESSION MATERIALS.

Available in two pastes - basic And accelerator, or catalyst

The polysulfide polymer has a molecular weight of 2000 to 4000 with terminal and non-terminated pendant mercaptan groups (-SH). These groups of adjacent molecules are oxidized by the catalyst, leading, on the one hand, to the expansion of the chain and, on the other hand, to cross-linking of the molecules. The result of the reaction is a rapid increase in molecular weight, turning the paste into rubber. The reaction is slightly exothermic with a typical temperature increase of 3-4°C. Despite the production of rubber within 10 minutes, the reaction continues for several more hours. The stitching of the material prevents noticeable deformation of the impression during its removal. The consistency of the material depends on the amount of filler, the particle size of which is 0.3 mm. Disinfection of polysulfide prints is carried out with a 2% glutaraldehyde solution.

The most active ingredient in catalyst paste, lead dioxide, is always present in it with some magnesium oxide. Bleaching agents are powerless to mask the black color of lead dioxide. Therefore, polysulfide pastes have shades from dark brown to gray-brown. Other oxidizing agents, such as copper hydroxide, can be used as substitutes for lead dioxide. They give mass green color. Disadvantages: unpleasant smell, insufficient elasticity, typo. These facts allow silicone materials to win the competition. Representatives of this group: “COE-flex”, “Permaplastik” (Germany).

POLYESTER IMPRESSION MATERIALS.

Usually used in the form of a paste of medium consistency (main and accelerator). The base paste is a moderately low molecular weight polyester with ethylene rings as end groups. The filler is silica, the plasticizer is glycol ether phthalate. The catalyst paste contains 2,5-dichlorobenzenesulfonate as a cross-linking agent, as well as a filler. Separate tu6a contains a plasticizer - octyl phthalate and about 5% methylcellulose as a filler. Dyes can be added to the base and catalyst pastes. The polyester system is also available in high and low viscosity. The most common representatives of polyester materials are Polyjet, Impregam, Permodine.

THERMOPLASTIC OR REVERSIBLE IMPRESSION MATERIALS. For more than 100 years, dentists have had thermoplastic masses in their arsenal, but in recent years, insufficient attention has been paid to the improvement of these materials due to the fact that the efforts of scientists were aimed at creating and introducing new elastic impression materials based on alginate and synthetic cold-vulcanized rubbers.

The peculiarities of this group of impression materials are that they soften and harden only under the influence of temperature changes. When heated they soften and when cooled they harden. These multicomponent systems are created on the basis of natural or synthetic resins, filler, modifying additives, plasticizer and dyes. Thermoplastic masses are divided into reversible and irreversible. Irreversible materials lose their plasticity when exposed to repeated temperatures and for this reason cannot be reused. A representative of irreversible (or disposable material) is stens.

Paraffin, stearin, gutta-percha, beeswax, ceresin and other materials are also used as thermoplastic substances.

Thermal masses must: 1) soften at a temperature that does not cause pain and burns to the tissues of the oral cavity; 2) not be sticky in the “operating” temperature range; 3) harden at a temperature slightly higher than the temperature of the oral cavity; 4) in a softened state, represent a homogeneous mass; 5) Easy to handle with tools.

Stens is available in the form of round plates of red tones

The material softens at a temperature of 45-55°C (at the same time acquiring the necessary plasticity) and hardens at a temperature of 35-37°C. It is used in dental practice for making preliminary impressions and individual trays.

From a plate softened in a water bath at a temperature of 45-55°C, a roller (for the lower jaw) or a disk (for the upper jaw) is quickly formed with your fingers, distributed over the surface of a standard spoon, inserted into the oral cavity and an impression is obtained, which is then carefully removed from the surface. oral cavity. It is not recommended to reuse the material.

"Acrodent" was produced in the form of rectangular plates of dark pink color with rounded edges.

"Acrodent" softens at a temperature of 55-65°C and loses its plasticity at a temperature of 36°C.

Thermoplastic impression mass (“MST-02”) is produced in the form of dark emerald-colored plates.

Composition (% by weight):

The mass softens at a temperature of 50-60°C, loses plasticity at a temperature of 20-25°C for 3 minutes. and is used to take functional impressions from toothless jaws and to correct (reline) insufficiently fixed dentures on toothless jaws.

Thermal mass "MST-03" is produced in the form of green sticks and is intended for obtaining impressions of cavities for inlays or for making impressions with a copper ring. By analogy with the masses “MST-02”, 03, the material “Ikzekt” (in plates, sticks and cones) is produced in the USA, as well as the German “Xanthigen” and the mass “Kerra”.

To obtain functional impressions using thermoplastic mass, it is necessary to use rigid individual trays, the edges of which exactly correspond to the relief of the transitional fold.

To avoid the formation of defects (bubbles) in the area hard palate and alveolar part, the impression mass should be pressed only against the vestibular edges of the tray and taken with some excess. After carefully shaping the edges of the functional impression, the mass is cooled in the mouth cold water using a syringe or rubber balloon (bulb) or cotton swab. In this case, it is necessary to ensure that the individual tray with the impression mass is tightly pressed to the mucous membrane.

"Stomaplast". It was produced in the form of a greenish mass poured into a metal saucepan. It is an alloy of glycerin rosin ester with castor oil, paraffin, dye and fragrance. It has high plasticity at low temperatures (37-42°C) and, due to this, does not put pressure on the tissues of the prosthetic field and does not deform the edges of the functional impression; it allows you to control and correct, if necessary, its quality by repeated introduction into the oral cavity. Designed for obtaining functional impressions of toothless jaws. Impressions from this material are taken with individual trays, which can be made of self-hardening plastics, but before removing the impression from the oral cavity, the individual tray with Stomaplast is cooled with water (18-20°C). The plaster model is obtained immediately after taking the impression. If this is not possible, then the print is stored in cold water.

"Dentafol" is a thermoplastic compression impression material based on natural resins and polymers, designed to obtain accurate functional impressions from edentulous jaws, especially with significant atrophy of the alveolar ridge. It is also recommended for atrophic mucous membrane of the prosthetic bed.

The model is cast immediately after receiving the impression. The plaster model can be easily separated from the impression if it is immersed in water for a few minutes. hot water. The melting point of "Dentafol" is not higher than 55°C. The fluidity of the mass appears at a temperature of 30°C.

The thermoplastic compound "Kerra" is available in five colors, each of which is intended for its own purpose (correction of the edges of bases and trays, functional impressions, cavity impressions and impressions with a copper ring).

Due to their high density and the presence of “braces” in the print, thermoplastic masses cannot compete with rubber-like materials, elastomers.

Their main purpose today is edging the edges of the prosthesis base, impression tray, and making individual trays.

Final control.

List the properties of materials and give their definitions.

Give a classification of prints and models.

List the rules for choosing a tray, the features of taking an impression, and the criteria for quality control of the resulting impression.

Explain the classification of impression materials.

List physical and mechanical properties of gypsum, zinc oxide eugenol masses. Name the representatives of these groups.

Alginate materials. Properties, features of work, representatives.

Silicone masses. Properties, features of work, representatives.

Thermoplastic masses. Properties, features of work, representatives.

Test control.