Advertising on the portal

A method for reproducing registered occlusal positions on computer three-dimensional models of dentition and orientation of computer three-dimensional models in space. Accurate bite registration: increasing the predictability of prosthetic results

First clinical stage: examination of the patient, diagnosis, choice of prosthesis design, obtaining working and auxiliary or two working impressions. Taking impressions in the manufacture of removable dentures is carried out according to generally accepted methods.

First laboratory stage: obtaining plaster models and comparing them, if possible, in the position of central occlusion. If it is impossible to compare the models, wax bases with occlusal ridges are prepared.

Second clinical stage: determination of central occlusion of the jaws. From the point of view of the difficulty of determining central occlusion and interalveolar height, four groups of dentition defects should be distinguished. The first group includes dentitions in which the antagonists have been preserved and 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. The second group includes dentitions in which there are antagonists, but they are located in such a way that it is impossible to place the models in the position of central occlusion without templates with rollers. The third group consists of jaws that have teeth, but they are located in such a way that there is not a single opposing pair of teeth. In this group, it is necessary to determine the interalveolar height in the position of central occlusion. The fourth group includes jaws devoid of teeth.

With a fixed bite and the presence of antagonists, central occlusion is determined as follows: wax templates with bite ridges are treated with alcohol, introduced into the oral cavity and the patient is asked to slowly close his teeth. If the rollers interfere with the closure of antagonist teeth, then the amount of separation of the teeth is determined and the wax is cut off to approximately the same extent. 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 a given type of occlusion. A strip of wax is placed on the occlusal ridge, glued to the ridge and heated with a hot dental spatula. Wax bases with a roller are introduced into the oral cavity and the patient is asked to close his teeth. 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 position of the occlusal plane of the ridges. It must coincide with the occlusal plane of the dentition. After determining the height of the rollers, wedge-shaped cuts are made on the occlusal surface of the upper roller with a spatula at an angle to each other. A thin layer of wax is cut off from the bottom roller and a new, preheated thin strip is glued in its place. The patient is asked to close his teeth, controlling the accuracy of placing the lower jaw in 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 mouth, cooled, the accuracy of the impressions obtained is assessed and reinserted into the mouth to control the accuracy of determining the central relationship of the jaws. If the projections fit into the wedge-shaped cuts, and the signs of teeth closure correspond to the position of the central occlusion, therefore, the clinical approach satisfies all the necessary requirements. Once convinced of this, the doctor removes the rollers from the oral cavity, cools them, installs them on the model and sends them to the laboratory.

The greatest difficulties arise when determining the central relationship in a non-fixed bite or in the presence of signs of a decrease in interalveolar height in a fixed bite. In addition to determining central occlusion, accurate registration of the interalveolar distance is required here. The initial value in this case is the height of the lower third of the face at rest.

At the end of this clinical stage, the doctor determines the color, shape, style and size of artificial teeth, focusing on the patient’s age, gender, profession, jaw shape, degree of atrophy of the toothless alveolar processes, size of the upper lip and dentition defect.

Second laboratory stage: plastering of models into an occluder or articulator in the position of central occlusion and placement of artificial teeth. At the same laboratory stage, clasps are prepared if they were not made in the previous one.

Third clinical stage: checking the design of the prosthesis and the correctness of determining the central relationship of the jaws. The doctor carefully checks the working models for cracks, defects and blurred contours of the prosthetic bed. Pays attention to the tightness of the wax templates to the prosthetic bed and the correspondence of the boundaries of the prosthesis. The color, size and shape of the teeth are assessed, the size of the incisal overlap and the severity of the cusps are studied. The position of the teeth relative to the middle of the alveolar ridge and the density of occlusal contacts are checked. On plaster teeth, the location of the elements of the retaining wire clasp and the position of the process in the base of the prosthesis are assessed. The wax reproduction is removed from the model and placed in a flask with a cold weak solution of potassium permanganate or wiped with alcohol, after which the prosthesis is inserted into the oral cavity.

After applying a prosthesis with a wax base to the jaw, its stability, the boundaries of the base, the location of the clasps, the correspondence of the color of artificial and natural teeth, and the size of the latter are checked. Then they help the patient set the jaws in the position of central occlusion. If all opposing teeth (artificial and natural) close tightly and evenly, then the central occlusion is determined correctly. To check the tightness of the closure, you need to insert a spatula between the teeth and try to separate them. There should be close contact between the teeth. If there are no errors, the prosthesis is transferred to the laboratory for final production.

Third laboratory stage: final modeling of the wax base and its replacement with a plastic one, grinding and polishing of the prosthesis.

Fourth clinical stage: fitting and application of the prosthesis in the oral cavity, alignment of articulatory balance.

Fifth clinical stage: correction of removable lamellar prosthesis.


Related information.


Diseases of the teeth, tissues surrounding the teeth, and damage to the dentition are quite common. Abnormalities in the development of the dental system (developmental anomalies) are no less often observed, which arise as a result of a variety of reasons. After transport and industrial injuries, operations on the face and jaws, when a large amount of soft tissue and bone is damaged or removed, after gunshot wounds, not only the form is impaired, but the function also suffers significantly. This is due to the fact that the dental system mainly consists of the bony skeleton and the musculoskeletal system. Treatment of lesions of the musculoskeletal system involves the use of various orthopedic devices and dentures. Establishing the nature of the injury, disease and drawing up a treatment plan is a section of medical practice.

The production of orthopedic devices and dentures consists of a number of activities that are performed by an orthopedic surgeon together with a dental laboratory technician. The orthopedic doctor carries out all clinical procedures (preparing teeth, taking impressions, determining the relationships of the dentition), checks the designs of prostheses and various devices in the patient’s mouth, places the manufactured devices and prostheses on the jaws, and subsequently monitors the condition of the oral cavity and dentures.

A dental laboratory technician performs all laboratory work on the manufacture of prostheses and orthopedic devices.

The clinical and laboratory stages of manufacturing prostheses and orthopedic devices alternate, and their accuracy depends on the correct execution of each manipulation. This necessitates mutual control of the two persons involved in the implementation of the intended treatment plan. Mutual control will be the more complete, the better each performer knows the technique of making prostheses and orthopedic devices, despite the fact that in practice the degree of participation of each performer is determined by special training - medical or technical.

Denture technology is the science of the designs of dentures and methods of their manufacture. Teeth are necessary for crushing food, i.e. for the normal functioning of the chewing apparatus; in addition, teeth are involved in the pronunciation of individual sounds, and, therefore, if they are lost, speech can be significantly distorted; finally, good teeth decorate the face, and their absence disfigures a person, and also negatively affects mental health, behavior and communication with people. From the above, it becomes clear that there is a close connection between the presence of teeth and the listed functions of the body and the need to restore them in case of loss through prosthetics.

The word “prosthesis” comes from the Greek prothesis, which means an artificial part of the body. Thus, prosthetics aims to replace a lost organ or part of it.

Any prosthesis, which is essentially a foreign body, must, however, restore the lost function as much as possible without causing harm, and also replicate the appearance of the organ being replaced.

Prosthetics have been known for a very long time. The first prosthesis, which was used in ancient times, can be considered a primitive crutch, which made it easier for a person who had lost a leg to move around and thereby partially restore the function of the leg.

The improvement of prostheses went both in terms of increasing functional efficiency and in approaching the natural appearance of the organ. Currently, there are prostheses for legs and especially for arms with rather complex mechanisms that more or less successfully meet the task. However, prostheses are also used that serve only cosmetic purposes. An example would be ocular prostheses.

If we turn to dental prosthetics, we can note that in some cases it gives a greater effect than other types of prosthetics. Some designs of modern dentures almost completely restore the function of chewing and speech, and at the same time, in appearance, even in daylight, they have a natural color, and they differ little from natural teeth.

Dental prosthetics has come a long way historically. Historians testify that dentures existed many centuries BC, as they were discovered during excavations of ancient tombs. These dentures were frontal teeth made of bone and secured with a series of gold rings. The rings apparently served to attach artificial teeth to natural ones.

Such prostheses could only have cosmetic value, and their manufacture (not only in ancient times, but also in the Middle Ages) was carried out by persons not directly related to medicine: blacksmiths, turners, jewelers. In the 19th century, specialists involved in dental prosthetics began to be called dental technicians, but in essence they were the same artisans as their predecessors.

The training usually lasted several years (there were no set deadlines), after which the student, having passed the appropriate exam at the craft council, received the right to work independently. Such a socio-economic structure could not but affect the cultural and socio-political level of dental technicians, who were at an extremely low stage of development. This category of workers was not even included in the group of medical specialists.

As a rule, no one cared then about improving the qualifications of dental technicians, although individual workers achieved high artistic perfection in their specialty. An example is a dentist who lived in St. Petersburg in the last century and wrote the first textbook on dental technology in Russian. Judging by the contents of the textbook, its author was an experienced specialist and educated person for his time. This can be judged at least by his following statements in the introduction to the book: “A study begun without theory, leading only to the proliferation of technicians, is worthy of reproach, because, being incomplete, it produces workers - merchants and artisans, but will never produce a dentist - an artist as well as an educated technician. The art of dentistry, practiced by people without theoretical knowledge, cannot in any respect be equated with that which would constitute a branch of medicine.”

The development of denture technology as a medical discipline has taken a new path. In order for a dental technician to become not only a performer, but also a creative worker capable of raising denture equipment to the proper height, he must have a certain set of special and medical knowledge. The reorganization of dental education in Russia is subordinated to this idea, and this textbook is based on it. Dental prosthetic technology has the opportunity to join the progressive development of medicine, eliminating handicrafts and technical backwardness.

Despite the fact that the object of study of dental technology is mechanical equipment, we should not forget that the dental technician must know the purpose of the equipment, its mechanism of action and clinical effectiveness, and not just its external forms.

The subject of study of denture technology is not only replacement devices (prostheses), but also those that serve to influence certain deformations of the dentofacial system. These include the so-called corrective, stretching, and fixing devices. These devices, used to eliminate all kinds of deformities and consequences of injuries, become especially important in wartime, when the number of injuries to the maxillofacial area increases sharply.

From the above it follows that denture technology should be based on a combination of technical qualifications and artistic skill with basic general biological and medical principles.

The material on this site is intended not only for students of dental and dental engineering schools, but also for old specialists who need to improve and deepen their knowledge. Therefore, the authors did not limit themselves to just describing the technological process of manufacturing various prosthetic designs, but considered it necessary to also give the basic theoretical prerequisites for clinical work at the level of modern knowledge. This includes, for example, the question of the correct distribution of chewing pressure, the concept of articulation and occlusion and other points that link the work of the clinic and laboratory.

The authors could not ignore the issue of workplace organization, which has become of great importance in our country. Safety precautions were also not ignored, since work in a dental laboratory is associated with occupational hazards.

The textbook provides basic information about the materials that a dental technician uses in his work, such as gypsum, wax, metals, phosphorus, plastic, etc. Knowledge of the nature and properties of these materials is necessary for a dental technician in order to properly use them and further improve them .

Currently, in developed countries there is a noticeable increase in people's life expectancy. In this regard, the number of people with complete loss of teeth is increasing. A survey conducted in a number of countries revealed a high percentage of complete tooth loss in the elderly population. Thus, in the USA the number of toothless patients reaches 50, in Sweden - 60, in Denmark and Great Britain it exceeds 70-75%.

Anatomical, physiological and mental changes in elderly people complicate the prosthetic treatment of edentulous patients. 20-25% of patients do not use complete dentures.

Prosthetic treatment of patients with toothless jaws is one of the important sections of modern orthopedic dentistry. Despite the significant contribution of scientists, many problems in this section of clinical medicine have not received a final solution.

Prosthetics for patients with toothless jaws aims to restore normal relationships between the organs of the maxillofacial area, providing an aesthetic and functional optimum so that eating is enjoyable. It is now firmly established that the functional value of complete dentures mainly depends on their fixation on edentulous jaws. The latter, in turn, depends on taking into account many factors:

1. clinical anatomy of the edentulous mouth;

2. a method for obtaining a functional impression and modeling a prosthesis;

3. features of the psychology of patients undergoing primary or repeated prosthetics.

When starting to study this complex problem, we first focused our attention on clinical anatomy. Here we were interested in the relief of the bone support of the prosthetic bed of toothless jaws; relationships between various organs of the edentulous oral cavity with varying degrees of atrophy of the alveolar process and their applied significance (clinical topographic anatomy); histotopographic characteristics of edentulous jaws with varying degrees of atrophy of the alveolar process and surrounding soft tissues.

In addition to clinical anatomy, we had to research new methods for obtaining a functional impression. The theoretical prerequisite for our research was the position that not only the edge of the prosthesis and its surface lying on the mucous membrane of the alveolar process, but also the polished surface, the discrepancy of which with the surrounding active tissues leads to a deterioration in its fixation, is subject to targeted design. A systematic study of the clinical features of prosthetics for patients with edentulous jaws and the accumulated practical experience allowed us to improve some ways to increase the effectiveness of complete removable dentures. In the clinic, this resulted in the development of a three-dimensional modeling technique.

The debate has not been settled that acrylate base materials have a toxic, irritating effect on the tissue of the prosthetic bed. All this makes us wary and convinces us of the need for experimental and clinical studies of the side effects of removable dentures. Acrylic bases break unreasonably often, and finding out the reasons that cause these breakdowns is also of some practical interest.

For more than 20 years we have been studying the listed aspects of the problem of prosthetics for toothless jaws. The site summarizes the results of these studies.

1589 21 ARTICLES

Diagnostic plaster casts of the jaws are made to create a replica of the patient's jaw. They are often also used to clarify the diagnosis. Using them, it is possible to obtain data on the peculiarities of the location of teeth, which is necessary for obtaining comfortable orthodontic structures and removable dentures. How are diagnostic jaw models made?

Making a plaster model of the jaw is an important stage in diagnostics and prosthetics. First, the doctor takes impressions using modern methods and materials. Later, with the help of plaster, it is possible to recreate plaster models of the jaws, which should closely replicate the main features of the patient’s real tissues.

After this, both plaster jaws are placed in an articulator, which simulates the movement of the jaws. You can easily buy a plaster model of the jaw at dental clinics. It will be possible to contact specialists if any diseases arise or the need to resort to prosthetics. Diagnostic jaw models must be of high quality. They necessarily provide information about the alveolar processes, tubercles, palate, frenulum and other soft tissue formations of the oral cavity. With the help of a high-quality plaster model of the jaws, you can clarify many controversial situations that arise during examinations and dental treatment.

Dental laboratory

    Own laboratory

    The FDC clinic has its own dental laboratory, equipped with the latest technology, so even the most labor-intensive orthopedic work is performed in the shortest possible time.

    Laboratory in France

    If necessary, exclusive work can also be performed in the most prestigious dental laboratory in France, Bourbon Atelierd’ Art Dentaire (Nice)

Enjoy European quality and style,
without leaving Moscow

The convenient location of the French dentistry and the availability of guarded free parking make visiting the Clinic as simple and convenient as possible in a big city.

Location within walking distance
from Moscow City

Near the metro station Ulitsa 1905 Goda

Articles on the topic

Clarity SL braces

Installation of vestibular ceramic braces Clarity - the last word in the treatment of malocclusion. Inconspicuous, aesthetic, safe and highly effective - that’s what Clarity braces are. All work is performed by experienced French orthopedists.

Teeth whitening trays

Teeth whitening trays are transparent covers on the teeth that, when used, release a special whitening composition that dissolves stains and reduces the yellowness of tooth enamel. These devices can be used at home as an effective means of teeth whitening.

Distal bite

Correction of distal bite in children and adults. Treatment of all stages of the disease. Modern techniques: trainers and mouthguards. Quick results. Clinic of French dentistry in Moscow. French specialists, Russian hospitality and European technologies.

Mesial bite

Treatment and correction of mesial occlusion in children and adults at the French Dentistry Clinic in Moscow. Experienced specialists from France, modern technologies and Russian hospitality. We take on the most difficult cases.

Mouth guards for teeth protection

Mouthguards for protecting teeth are used by athletes and people in traumatic professions. They are also used for bruxism (teeth grinding). They protect jaws and teeth from damage and pathological abrasion of enamel.

Invisible braces

Installation of invisible braces of all types. Complete correction of dental malocclusion. While maintaining the aesthetics and visual appeal of your smile. Clinic of French dentistry in Moscow. Modern technologies, European quality.

Crossbite

Correction of crossbite in children and adults. Experienced specialists from France will not give your malocclusion a chance. Modern painless techniques, American and European devices and treatments.

Non-ligating (self-ligating) braces

All types of self-ligating (ligature-free) bracket systems. European level of service, individual approach to each patient, modern technologies, short treatment time. Clinic of French dentistry in Moscow.

STB braces

Lingual braces STB – painless installation, short treatment time, any defects. French Dentistry Clinic in Moscow - only French specialists, only proven reliable technologies, only high-quality treatment!

Ormco braces

Ormco braces in a French dental clinic in Moscow. We correct any defects and imperfections in the dentition. We take on the most difficult cases. All procedures are absolutely painless and do not take much time. We know what effective treatment is!

Deep bite

Treatment of gingivitis of all forms and types. Clinic of French dentistry in Moscow. Professional approach, quick cure, no side effects, increased comfort and coziness, friendly attitude towards patients.

Plastic braces

Plastic braces of all colors and shades, reinforced plastic. High treatment efficiency and excellent aesthetics – that’s what modern plastic braces are. Clinic of French dentistry in Moscow.

Open bite

Correction of open bite in children and adults. Treatment of all stages. Modern techniques: trainers, braces and mouthguards. Clinic of French dentistry in Moscow. French specialists, European technologies and Russian hospitality.

Braces and myths associated with them

Malocclusions are not only found among children. Every second adult has one or another orthodontic deviation, some of which require correction using braces.

Making a plaster model from a plaster cast consists of the following operations: I) preparing a plaster cast; 2) casting a plaster model; 3) separation of the cast from the model; 4) model processing.

Preparation of a plaster cast consists of creating conditions for easy separation of the cast from the model and preventing its damage. To do this, the cast is immersed in cold water for 15-20 minutes in order to saturate it with water and obtain a passive state in relation to the liquid plaster of the cast model. Otherwise, the dry plaster of the cast will absorb the water from the liquid plaster of the model and they will be firmly connected. It is not recommended to cover the surfaces of a plaster cast with any insulating material due to the risk of distorting the accuracy of the relief of the tissues of the prosthetic bed.

Preparation of a plaster functional cast of an edentulous jaw consists of creating an edging from a wax plate 3-4 mm thick, located 2-3 mm below the edge of the cast along its entire periphery. This will help maintain the thickness and boundaries of the edge of the impression, which is important for creating a closing valve along the edges of the prosthesis and its good fixation on the edentulous jaw.

The cast taken out of the water is lightly shaken and filled with small portions of liquid plaster, pouring it first onto the most prominent areas of the cast. In this case, to prevent the formation of pores in the model and to completely fill all the recesses of the cast, it is necessary to constantly shake the cast or place it on a vibrating base (table).

Having filled the cast with liquid plaster slightly above its edges, pour a mound of plaster onto the table and, turning the cast upside down with a spoon, immerse it in this mound. At the same time, make sure that the surface of the spoon is parallel to the plane of the table, and the height of the base of the model is at least 1.5-2 cm. Without waiting for the plaster to completely harden, the edges of the model are formed. When casting a plaster model from a plaster functional cast, the edges of the model are shaped, focusing on the edge of the wax edging.

Plaster models made from high-strength gypsum cast from medical plaster casts have a coefficient of volumetric expansion of 0.43%, and models from medical plaster cast from elastic casts have a coefficient of volumetric expansion of 0.35%. This must be taken into account when making prostheses that require great precision.

Casting a plaster model using a thermoplastic cast is no different from that described above. In this case, there is no need to pre-soak the impression in water, but rather rinse it to remove mucus and saliva.

The casting of a plaster model according to the impression obtained using alginate impression mass is carried out immediately or no later than 20 minutes after its removal from the oral cavity. In this case, the impression must be placed in a solution of potassium-aluminum sulfate (potassium alum) to eliminate traces of alginic acid, which interferes with the setting reaction of the gypsum. After washing the cast with running water, the model is cast using the usual method. Obtaining a plaster model from double (two-layer, refined) casts, where silicone or thiokol mass is used as the second layer, does not require haste due to their low shrinkage. Such casts can be cast on the 2nd day.

After the plaster of the model has hardened (after 1-2 hours), first the tray is separated from the cast, and then, after removing excess plaster along the edges of the model, they begin to release it. In this case, you need to know the type and topography of dental defects in order to prevent tooth breakage.

The release of the plaster model from the plaster cast begins from the vestibular side, from the smallest piece, which is determined by the visible fracture lines. Holding a dental spatula in your right hand and resting your finger on the model and your hands on the table, insert the sharp end of the spatula into the fracture line and, acting as a lever, break off a piece. In this way, the entire vestibular wall is released.

To remove the palatal part of the cast (the thickest and most massive), it is necessary to create additional wedge-shaped cuts in different directions and, by inserting a spatula into them, separate all parts of the cast from the model with light blows of a hammer. In some cases, you can use coronal scissors to chip away the plaster in small pieces.

The freed model is carefully trimmed along the edge of the base, forming a base where all surfaces have smooth contours and merge into one another at a certain angle.

The base of the mandible model is the same shape as the base of the maxilla model, without the notch on the lingual side, which weakens the strength of the model.

The model is released from the plaster functional cast by lightly tapping the surface of the cast with a hammer; When a crack appears, remove the impression plaster with a spatula.

To free the plaster model from the thermoplastic cast, it is immersed in hot water (+50-60 °C), after the mass has softened, one of the edges of the cast is lifted and again lowered into hot water so that the water penetrates into the inner layers. Then carefully separate the thermoplastic mass from the model. To completely clean the model from traces of thermoplastic mass, take a piece of it, soften it in hot water and, pressing it to the model, collect all the remaining mass. Finally, you can wash the model with ether or monomer.

The separation of the plaster model from the alginate cast is carried out 50-60 minutes after its casting and complete hardening of the plaster. In this case, to avoid breaking teeth, they use a sharp scalpel, cutting the impression mass into pieces and sequentially freeing the model. Delay in separating the model from the alginate impression results in hardening and shrinkage of the impression material.

For separating a double (two-layer) cast from a plaster model. It is enough to immerse the model in warm water (+40-^ + 50°C) to soften and remove the thermoplastic mass, and a thin layer of elastic mass (sielast) is easily pulled off the model.

If one or more of the model's plaster teeth break, they can be glued back to their original place using nitrocellulose glue or cement.

A plaster model can be used to make a prosthesis if its base height is at least 1.5 cm and there is no damage to the working surface (pores, various inclusions, breaks and fractures). Otherwise, it is necessary to take the impression again and make a new model.

To increase the hardness of the plaster model, boil it in a 20-30% aqueous solution of sodium tetraborate for 5-10 minutes or lubricate its surface with this solution using a cotton swab.

Plaster models of increased hardness can be treated by using marble gypsum (super gypsum) for these purposes, which is used in the process of making clasp and metal-ceramic prostheses.

In the process of manufacturing porcelain crowns, inlays, and half-crowns, the supporting teeth of the model must have increased strength. To obtain them, cement, amalgam, gallodent, low-melting metals, etc. are used.

To obtain a plaster model, it is necessary to collect a cast, accurately place its parts in a spoon, and then glue them together and to the spoon with molten wax.

The collection of the impression begins no earlier than 30-40 minutes after removing it from the oral cavity, so that the moisture on the surface of the impression can evaporate.

Before placing parts of the cast in a tray, it is necessary to very carefully clean their surface adjacent to the tray, as well as the inner surface of the tray, from small particles of plaster that interfere with the accurate preparation of the cast.

The largest parts of the cast are placed first, and then the small ones. All parts of the cast must be accurately placed in the tray so that there is no gap anywhere between the tray and the outer surface of the cast. There should be no gaps on the inner surface of the cast, between its parts. The outer edges of the assembled impression are glued to the impression tray with hot wax. Pouring wax within the prosthetic field is not allowed; the slightest inaccuracy made during gluing the cast leads to distortion of the model.

The method of obtaining a plaster model involves filling a cast or impression with liquid plaster, which is why this process is called model casting.

To make it easier to separate the cast from the model, it must be coated with an insulating substance. For these purposes, a number of substances are used that are applied to the surface of the impression. For this purpose, soap alcohol, kerosene with stearine and a number of other substances have been proposed. However, practice has shown that any insulating substance leaves a layer on the cast, resulting in an inaccurate model. Therefore, it is better to immerse the glued cast in cold water for 6-8 minutes; it fills all the pores, so that the model plaster does not adhere to the cast plaster.

For greater strength of the model, the plaster with which the cast is poured should have the consistency of sour cream.

The cast begins to be filled with small portions of plaster, and it is poured first onto the most convex part of the cast. The impression is shaken constantly to remove air bubbles. This is repeated until the entire cast is filled with plaster.

When the entire cast is filled, a mound is made from the remains of the plaster, which is placed on the cast; the latter is turned down and, together with the mound, pressed against a smooth object (glass, metal plate, etc.); The result is models with a wide base-stand, convenient for work. Thus, the model consists of two parts:

  • 1) the working part corresponding to the prosthetic field, i.e. the location of the future prosthesis,
  • 2) a stand that serves to stabilize the model.

Please note that the height of the stand should be at least 2-2.5 cm; This is of particular importance in the case of a deep sky, since the thinning of the model in this place can lead to the dream being pressed through during pressing under pressure from the press.

After the plaster has hardened, the edges of the model are trimmed with a spatula (Fig. 14).

Separating the cast from the plaster model. The cast is separated from the plaster model 8-10 minutes after casting, that is, when the plaster of the model begins to generate heat. This is the most favorable moment for separating parts of the cast from the model. The cast is removed very carefully to avoid damage to the model. First of all, you should free the teeth, guided by the dental formula, which indicates where and which teeth are located. To separate, use a dental spatula, inserting it shallowly along the fracture line of the cast, and using a lever-like movement, separate parts of the cast from the model. When all the teeth are freed, they tap the cast with a horn or metal hammer until a specific hollow sound of emptiness appears, meaning that a gap has formed between the cast and the model; After this, the model is completely separated from the cast. If, when separating the cast from the model, a tooth breaks off, which has retained the clear contours of the fracture line, you can glue it to the model using a special liquid glue (a solution of celluloid in acetone). Gluing with cement is not recommended due to the fact that it prevents the exact fit of the tooth to the model.

In case of more serious damage to the model, for example, separation of part of the alveolar process, fracture of the model, scratches in the area of ​​the prosthetic field, etc., the impression should be retaken.

Separation of impression material from the model. When casting a model from an impression, no insulating substance is required so that the impression can be easily separated from the plaster model. After the plaster has hardened, the impression with the model is immersed in hot water for several minutes; The impression mass softens and is easily separated from the model.