Without what is it impossible to manufacture dentures in the modern world? Yes, without high-quality impressions (functional and anatomical, which we will analyze further). To make a suitable design, an imprint of the tissues of the upcoming prosthetic bed is needed. Mastering the techniques for obtaining high-quality impressions is a necessary stage in the career of every orthodontist. We will analyze the main classifications of these casts, the methods for obtaining them, as well as the materials used to make them.
What is this?
What are anatomical and functional impressions in dental orthopedics (orthodontics)? This is the name of the reverse (or negative) reflection of the patient's teeth, various soft and hard materials of the oral cavity - the palate, the alveolar process, the transitional folds of the mucous membranes, etc. The impression is obtained using special materials.
The history of anatomical and functional impressions in dentistry began in 1756! Then GermanDr. Pfaff was the first to make such an impression using plain wax as an impression material.
Why are impressions needed?
Why is an impression needed in orthodontics? It is on this basis that a positive model is made, which is an exact copy of the hard and soft tissues of the oral cavity.
Different impressions are used for diagnostic, therapeutic, educational, control and work purposes. Some models are valuable because they help clarify or refute the patient's diagnosis. Some are needed to make a prosthesis. And some allow you to evaluate the effectiveness of orthopedic therapy (impression before and after it).
The so-called working functional impressions are needed for the further production of prostheses by specialists. Auxiliary help to study the "relationship" of the antagonist dentition.
Classification according to Gavrilov
The fundamental gradation in orthodontics is the division into functional and anatomical impressions. What is the difference? The first are created taking into account the functional compliance, the mobility of the matter that covers the prosthetic bed. The second, respectively, without such consideration.
Let's consider the classification of impressions:
- Functional. Most often they are removed from the edentulous jaw. Less often - with the one where some teeth were preserved. The most important purpose is the basis for the manufacture of prostheses for edentulous patients. It is these prints that help determine the optimal ratio of the tissues of the oral cavity and the edges of the prosthesis adjacent to them. This is important for the bestfixing the device, as well as for the correct distribution of the so-called masticatory pressure between the fundamental sections of the prosthetic bed. It is important to note that functional impressions are obtained by functional tests. The latter help to correctly shape the edges of the prints in relation to the position of the movable tissues, which will later be on the border with the prosthesis.
- Anatomical. Additionally, they are divided into main and auxiliary. The first type is removed from the jaw, on which the prosthesis will be installed in the future. The second - from the antagonist jaw (upper or lower), on which there will be no prosthesis. The anatomical type is widely used in orthodontics to display the position of tissues (soft and hard) in the oral cavity. It is useful for making inlays, crowns, bridges and partial dentures.
From the characteristics, an important difference between these varieties stands out. Obtaining functional impressions is important for making a complete denture for an edentulous jaw. Anatomical is more likely to be useful for partial dentures, bridge devices and other smaller structures.
Another important difference between anatomical and functional prints. For the first, standard impression trays are used. And for the second, these instruments are made individually for each patient. To better understand how impressions are taken, functional and anatomical, let's look at what counts as an impression tray.
Impression tray - whatthis?
Impression trays are factory made from plastic or stainless steel. Their shape and volume are determined by many factors at once:
- Patient's jaw.
- Type, breadth of dentition.
- Location of defect.
- Height of the crowns of the remaining teeth.
- The expressiveness of the alveolar processes of the jaw.
Even standard impression trays vary in shape and size. First of all, they are divided into those intended for the upper and for the lower jaw. The removal of functional impressions, as we said, is carried out with individual spoons.
Each of these instruments has a body and handles. The body of the spoon will consist of an alveolar concavity, an outer rim, and curves for the palate. For example, standard impression trays have ten sizes for the upper jaw, nine for the lower jaw.
Using varieties of spoons
When working with elastic materials for impressions, special spoons with holes are used. This is due to the fact that the base does not adhere well to the metal from which the standard spoon is made. Some specialists get out of this situation using their own resourcefulness: they stick a band-aid on the inside of an ordinary metal tool. The elastic base adheres better to its rough fabric surface.
Also, cutting the handles of such spoons with special metal scissors in case of their excessive length is considered medical ingenuity and amateur performance. If the handleon the contrary, it is short, then it is lengthened with a wax plate. But in the collection of a qualified specialist, there are usually standard spoons for any occasion, which saves him from such extreme measures.
The so-called partial spoons are used much less frequently. They are used in relation to jaws with scattered single teeth. The impression is necessary for the manufacture of crowns. Partial spoons are also used for teeth that do not have opposite antagonists.
Individual Spoons
Functional impression with an individual spoon is carried out for edentulous jaws. Such instruments differ in the height of the sides, the expressiveness of the niche for the alveolar processes, and somewhat smaller sizes. The reason is that the print should provide the specialist with more accurate data about the prosthetic bed.
Why do we need individual spoons? As a rule, it is difficult to find two edentulous jaws that are absolutely similar in external characteristics. For accurate fixation of the prosthesis, functional suction is necessary here, which is created by creating a negative pressure. To do this, it is necessary to perfectly match the surface of the prosthesis being made with the tissues of the prosthetic bed that will be in contact with it. Without a precise fit of the edges of the spoon to the borders of the valvular region, this result is difficult to achieve.
How is a custom spoon made? To begin with, using a standard tool in an orthodontic clinic, a complete anatomical cast of the jaw is made. Then already in the laboratory based on itmake an individual model of plastic.
Oxman impression base classification
We figured out the impression trays. The second important component is the materials for the functional impression. According to this classification, they can be divided into the following types:
- Crystallizing masses. This type includes "Dentol" (domestic zinc oxide paste), gypsum, eugenol.
- Thermoplastic masses. These are wax, stens, stomatopast, adhesive, Kerr and Weinstein masses.
- Elastic masses. This category includes stomalgin and algelast.
- Polymerizing masses. Silicone impression bases, ACT-100, styracryl.
Classification of the impression base according to Doinikov and Sinitsyn
Let's imagine another classification common in orthodontics that separates the materials used to take functional and anatomical casts of the jaws.
In the beginning, two groups stand out. The first - according to the physical state of the material:
- Elastic.
- Polymerizing.
- Thermoplastic.
- Solid crystalline.
The second gradation divides materials into categories by chemical nature:
- Alginate.
- Gypsum.
- Silicone.
- Zincoxideeugenol.
- Epoxy.
- Thiokol.
Crystallizing materials
Let's characterize in more detail substances that are more oftenare used in orthodontics for anatomical and functional impressions. It is important to highlight the medical plaster. Its other name is semi-aqueous sulfate s alt. It is obtained from ordinary natural gypsum, subjected to special heat treatment. As a result of this process, the material turns from dihydrate to semihydrous.
The most suitable for dentistry is the alpha modification of medical plaster. It is obtained at elevated pressure and temperature in an autoclave. The substance is distinguished by the best strength and density.
Elastic materials
The basic raw material here is seaweed, from which alginic acid is obtained by technical means. The basis of the material is the sodium s alt of this acid, which swells in water, forming a gel mass. To increase its elasticity and strength, gypsum, barium sulfate, white soot, etc. are additionally added to the impression composition. The gypsum turns the soluble gel into an insoluble one. The remaining components allow the gelation process to proceed more smoothly.
Requirements for functional impressions
The requirements for the resulting model are rooted in the requirements for the materials used to make the cast:
- Softening at a temperature that does not injure the oral mucosa.
- Easy entry/exit from the patient's mouth.
- Quick hardening at a temperature that does not injure the mucous membranes.
- Requirement, which is one of the main wishes of hypersensitive patients, that the mixture should not have an unpleasant smell and taste.
- The material is supplied hygienically, without losing its basic properties required for operation during the sterilization process.
- Impression mixes should be affordable - cost, range, delivery options.
Production of high-quality impressions is a necessary condition for obtaining a perfectly fitting denture. Therefore, considerable attention has been paid to this area in orthodontics. Today, there are special technologies for taking impressions, a wide range of materials and tools necessary for this work.
