Plaster cast: natural or polymer? Gypsum - a large medical encyclopedia Where gypsum is used
Gypsum, or calcium hydrogen sulfate, is a mineral widely used in construction, medicine and sculptural casting. When finished, it is a powder that is mixed with water, after which it gradually dries, acquiring high hardness. Its color can be white, gray or with shades of brown, pink, yellow or red. The hardness of the mineral on the Mohs scale is 2 points.
Gypsum mining
The mineral occurs as inclusions in sedimentary rocks. Its particles are presented in the form of scaly or fine-grained masses. Its deposits are usually found in clayey sedimentary rocks. Outwardly they resemble marble. The mineral is mined using the mining method. Underground deposits are broken off from the total mass by point explosions. The extracted gypsum stone is delivered to the surface and then ground into powder. Initially, it has high humidity, so it is first dried and subsequently baked for several hours. The gypsum coming out of the kiln is completely ready for use.
The technological process may include additional methods for purifying the composition from impurities, which depends on the raw materials used. If the production of gypsum for medical purposes is required, then it is purified more efficiently to improve its binding properties.
Advantages of gypsum as a material
Gypsum has a number of advantages that allow it to significantly surpass the vast majority of other materials used in construction, as well as other fields.
Its undeniable advantages include:
- Light weight.
- Easy mixing when preparing solutions.
- Fast hardening.
- Short drying period.
- Moderate hardness.
The undoubted advantages of gypsum include the possibility of its easy grinding. Thanks to this, you can correct the shape of the product made from it. Depending on the object or surface, this can be done or specially.
The listed properties, which are advantages of the material, may differ depending on the degree of grinding, cleaning and the presence of plasticizers. It is usually classified according to the degree of compression. According to this criterion, there are 12 types of gypsum. This indicator measures the number of kilograms per square centimeter that must be applied to destroy the material. The number in the nomenclature name indicates given quantity kilogram. For example, gypsum marked 5 has an upper compression point of 5 kg/cm².
Where is gypsum used?
There are 3 main areas of application of this material:
- Medicine.
- Sculpture.
- Construction.
Medical use
Purified gypsum powder is used to create a bandage to lock the limbs, which is necessary for the healing of broken bones. To do this, it is diluted in water to prepare a liquid solution. Bandages are soaked in it, which is used to make a dressing. After hardening, the bandage-reinforced solution becomes rigid, completely protecting the plastered limb from unwanted effects.
For medical purposes, only fine grinding of gypsum is used, ensuring high solidity after setting. In addition to being used to treat fractures, it is also used in dentistry. With its help, impressions of teeth are made for the further production of implants. With the advent of more modern non-staining materials this method becomes a thing of the past.
Plaster in sculpture
The use of gypsum has found its application in artistic creativity, in particular the creation of sculptures. For this purpose, high-quality grinding without impurities is used, similar to that used in medicine. There are two ways to use it. The first involves cutting out works from large gypsum stones, and the second involves ordinary casting. Plaster carving is practically no longer used, since the resulting works have external defects, which is due to the heterogeneity of the natural material. In addition, this production method requires great skill and significant time investment. It is much easier to pour gypsum mortar into molds. It hardens quite quickly, thanks to which, having an injection mold, such production can be put on stream.
Gypsum products are far from eternal, because their hardness on the Mohs scale is only 2 points, which is of course less than concrete, which scores 4-5 points. At mechanical impact it is destroyed. Nevertheless, the advantages of gypsum include maintainability, because products made from it can be glued together, and the resulting seams can be easily sanded down with emery cloth. After sanding, defects can be completely hidden with sufficient skill.
Construction use
Most often, gypsum is used to create plasters. Unlike cement or lime compounds, they have a more convenient consistency for work. At an average temperature of +20°, the drying time for such plasters is only 7 days. During this time, they fully gain their strength, which is 4 times faster than in the case of concrete.
Putties are also made from gypsum. They use a finer grinding fraction than plasters, due to which the resulting surface is highly smooth. This is especially important if wallpapering, and even more so painting, is required.
Decorative products for finishing are poured from gypsum. It is made from:
- Wall 3D panels.
- Wall tiles.
- Lepnin.
- Baguettes.
- Columns.
- Pilasters.
- Moldings.
- Ornaments.
- Designer sockets.
The vast majority of gypsum produced for construction purposes is used to make drywall. It is used as a level base for the quick construction of interior partitions and suspended ceilings. Drywall is also used to level out large curvatures in walls.
Using plaster to create decorative elements
Gypsum powder is an excellent material for the production of interior decorations. Most often, 3D wall panels are made from it, as well as various products to imitate ancient architecture. With the advent of polyurethane, such interior items began to be made from it, but gypsum still remains an accessible material that is used if you want to make such decorations with your own hands. For this purpose, 3D molds made of plastic or silicone for casting are offered for sale at quite reasonable prices. When using them, pure gypsum compounds are used. Ideally, the sculptural variety is suitable, but its cost is too high, which is not economically viable. A better choice would be to use granular plaster, sold in stores under the name alabaster.
For production, alabaster is diluted with water in equal proportions. The resulting liquid composition is poured into the mold, after which it is shaken to ensure the release of air bubbles. It is best to install it on a vibrating machine. Its presence allows you to prepare a solution with less water added, which will subsequently have a positive effect on strength. The form is left until the alabaster sets. Usually in the summer, 25-30 minutes are enough for this. After removing the product from it, it is set to dry, and the mold can be reused the required number of times.
Since the mold depth is usually about 20-25 mm, at an air temperature of +20°, complete drying of the casting takes about 3 days. After this, the product can be used for its intended purpose.
When using molds, they must be lubricated to ensure proper casting yield. This can be done with technical petroleum jelly, but the easiest and cheapest way is to use ordinary refined sunflower oil.
Features of working with gypsum plasters
Gypsum-based plasters can be used for application to mineral surfaces. First of all, they are suitable for covering walls made of brick, concrete, aerated concrete, expanded clay concrete, etc. They are also used to level ceilings.
Although gypsum-based plasters and putties have good adhesion, surface preparation with the application of a deep penetration primer is required. This allows you to create an impermeable film between the base and the plaster, preventing the transfer of moisture to the wall or ceiling. This ensures that during the drying period the plaster will have enough water for the normal course of the chemical crystallization reaction between the mixed grinding of gypsum. In the future, this will ensure higher hardness of the material and resistance to mechanical damage.
Typically, gypsum plaster can be applied to a surface with a layer thickness of 0.5 to 3 cm. Some manufacturers offer gypsum mixtures with the addition of special plasticizers and other impurities, making plastering with a large layer thickness quite possible.
Gypsum-based plaster is characterized by less pronounced sliding of the material. Thanks to this, they require less trimming of the burrs. All this contributes to higher labor productivity when using them.
Gypsum is an easily absorbent material, which is why plasters and putties based on it are unsuitable for use in bathrooms. In conditions of high humidity, the possibility of layer destruction increases many times over. To solve this problem, special moisture-proof polymer compositions are produced, but even with their use, cement plasters are still more reliable.
A, m. 1. Mineral white or yellowish color(burnt and crushed is used as a building material, in molding work, for surgical dressings, etc.). Gypsum deposits. Stucco. Plaster figurine. 2. usually plural. Small academic dictionary
Unfortunately, people quite often break something due to an unforeseen incident or in winter, falling on ice. In this case, the properties of plaster and its correct application become an integral part of the treatment of a fracture.
As a rule, a plaster cast is applied within the first hour after the accident. Therefore, medical plaster plays important role both in treatment and in medicine in general.
How to obtain medical plaster
Medical plaster does not immediately look like what most people imagine it to be.
Before we see it in the form of a free-flowing powder, it goes through several stages.
So, initially it is a simple gypsum stone, which is heated in a special stove, but the temperature should not exceed 130-140°C.
After which, the stone loses all moisture and becomes very fragile. This is done in order to turn the stone into a fine powder.
The properties of gypsum and its quality depend on several factors, but the main thing is the time spent in the oven and proper exposure. It is very important to store such plaster in a dry place so that it does not absorb moisture.
What should gypsum be like?
The properties of gypsum are very simple, since it should be white, soft, well sifted, harden quickly, and most importantly, not have lumps.
When applying plaster, the proportions must be observed; as a rule, it is 2 parts of gypsum to part of water. If the proportion is not met, the plaster will not harden and treatment will not begin on time.
What to do if the quality of the plaster has deteriorated
Often hospitals do not use all the plaster in a timely manner and it begins to become damp, but this is not a tragedy.
It happens that the plaster they use is not the best, but you can always make sure that patients feel quality services.
To do this, you need to take plaster, pour it onto an iron layer, and put it in the oven (the temperature should not exceed 120°C), so the plaster will lose moisture.
If you are in doubt, you need to take a mirror, hold it over the plaster, and if it fogs up, then moisture is still present, if not, then everything is in order.
Plaster is most often applied to the lower leg, hand, forearm and feet. Bandages are required to apply a plaster cast. different sizes and related tools.
So, having examined the properties of gypsum and its features, everyone realizes that obtaining gypsum is quite difficult and you need to make an effort, and also make sure that it does not deteriorate.
But it’s better that you just know about it and never encounter its presence on your body.
They are divided into five classes, according to their purpose and hardness:
- Plaster for impressions- Soft and pliable low-hardness gypsum. Used to take partial and full impressions, including those of jaws without teeth. This type of gypsum hardens quickly and has the least expansion.
- Medical plaster- Alabaster gypsum of normal hardness. This type of material is suitable for the production of diagnostic anatomical models, as well as models used for planning orthopedic structures. Gypsum of this class is classified as an auxiliary material, since a model made from it has insufficient strength. Thus, impression plaster and medical dental plaster are used only for technical purposes and not for making working models.
- High strength plaster for models- Class of hard plaster. Used for making removable dentures both the entire dentition and those replacing the missing part of the teeth, for the manufacture of the base of fixed collapsible dentures and other products of this series. Unlike usual medical plaster, the material of this class has sufficient high performance strength.
- Ultra-strong plaster for low expansion models- Gypsum with the highest strength indicators, excellent for making dismountable master models and performing combined work.
- Ultra-strong plaster for models with adjustable expansion rate- Quite a rare variety, intended for the manufacture of models requiring particularly high precision.
To successfully perform dental orthopedic and dental work using dental plaster, it is important to remember certain rules their uses:
- Dental plasters must be stored in a dry place.
Plaster storage containers must be cleaned before each new filling. - Devices and accessories used when working with dental plaster must be clean and free of remnants of previously used plaster.
- One portion of plaster should be the amount needed to fill no more than two or three impressions.
- The use of any hardening accelerators is unacceptable. If necessary, use quick-hardening plaster or increase the mixing time by a few seconds.
- To obtain the desired expansion of gypsum, the ratio of gypsum to water must be very precisely observed.
- Water and gypsum powder should have a temperature of 19-21 ° C.
- The powder must be slowly poured into the water, then allowed to submerge in it, and only after that begin kneading with a spatula.
Machine kneading should not exceed 30 seconds, manual kneading - one minute.
The mixture should be poured into the mold immediately after mixing. It is unacceptable to try to increase the pouring time by vibrating or adding water. - You can remove the plaster model from the impression only when the temperature of the model drops.
Following these instructions will allow you to carry out any dental work using gypsum is comfortable, fast, and economical.
Based on the Department of Orthopedic Dentistry of the Voronezh State Medical Academy was held comparative analysis dental plaster, the task of which is to evaluate the main characteristics of the most common brands of gypsum binders.
High-strength and ultra-strength dental plasters were selected for analysis. The tests were carried out in accordance with GOST R51887-2002.
As a result of the study, parameters were established that determine the quality of dental plaster, ensuring the production of prostheses with high functional and aesthetic properties.
Water consumption. In theory, the required amount of water to convert hemihydrate to dihydrate is 18.6% of the total mass of the binder. But in practice, much more is consumed to ensure the required mobility of gypsum dough: thus, gypsum dough has its own water requirement.
Water requirement is the smallest amount of water required to obtain a given solution consistency. Excess water evaporates from the resulting structure, leaving pores in it that can significantly reduce the strength of the model. Therefore, it is necessary to strive to accurately measure the water to obtain the ideal consistency.
During hardening, hydration of hemihydrate gypsum occurs (the reaction of adding water to the hemihydrate), which releases 29 kJ of heat per kilogram of hemihydrate. The hardening process occurs gradually. Semi-aqueous gypsum forms a supersaturated solution with water, from which the dihydrate is released. Education large quantity dihydrate particles causes the gypsum mixture to compact and thicken, which is the beginning of its setting.
The strength of the finished product depends on many factors: the purity of the raw material (gypsum powder), its structure, methods of its processing, composition and amount of modifying additives. Tensile strength is measured in megapascals: 1 MPa = 10 kgf/cm2.
Direct tests within dental laboratory showed that the highest quality types of gypsum demonstrate high stability on a spatula and a fluid consistency on a vibrating table, which allows you to maximize the number of non-porous pours from one mixing.
Models made from high-quality gypsum binders are resistant to chipping, perfectly replicate the modeled surface, are well polished, sanded and sawed, and when processing the column, the boundaries of the preparation are not damaged. High quality gypsum raw material prevents edges from breaking off when removing the model from the impression, ensuring best result modeling.
Making dental models from plaster:
97. Plaster and plaster casts. Plaster bandages, splints. Basic types and rules for applying plaster casts.
Plaster casts are widely used in traumatology and orthopedics and are used to hold fragments of bones and joints in their given position.
Medical gypsum is a semi-aqueous calcium sulfate salt, available in powder form. When combined with water, the hardening process of the gypsum begins after 5–7 minutes and ends after 10–15 minutes. The plaster gains full strength after the entire bandage has dried.
Using various additives you can speed up or, conversely, slow down the hardening process of gypsum. If the plaster does not harden well, it must be soaked in warm water (35–40 °C). You can add aluminum alum to the water at the rate of 5–10 g per 1 liter or table salt(1 tablespoon per 1 liter). A 3% starch solution and glycerin delay the setting of gypsum.
Since gypsum is very hygroscopic, it is stored in a dry, warm place.
Plaster bandages are made from ordinary gauze. To do this, the bandage is gradually unwound and a thin layer of gypsum powder is applied to it, after which the bandage is again loosely rolled into a roll.
Ready-made non-shedding plaster bandages are very convenient for use. The plaster cast is intended to perform the following manipulations: pain relief for fractures, manual reposition of bone fragments and reposition using traction devices, application of adhesive traction, plaster and adhesive dressings. In some cases, it is permissible to apply skeletal traction.
Plaster bandages are immersed in cold or slightly warmed water, and air bubbles that are released when the bandages get wet are clearly visible. At this point, you should not press on the bandages, as part of the bandage may not be saturated with water. After 2–3 minutes, the bandages are ready for use. They are taken out, lightly wrung out and rolled out on a plaster table, or the damaged part of the patient’s body is directly bandaged. To make the bandage strong enough, you need at least 5 layers of bandage. When applying large plaster casts, you should not soak all the bandages at once, otherwise the nurse will not have time to use some of the bandages within 10 minutes, they will harden and will be unsuitable for further use.
Rules for applying bandages:
– before rolling out the plaster, measure the length of the applied bandage along the healthy limb;
– in most cases, the bandage is applied with the patient lying down. The part of the body on which the bandage is applied is raised above the table level using various devices;
– the plaster cast should prevent the formation of stiffness in the joints in a functionally unfavorable (vicious) position. To do this, the foot is placed at a right angle to the axis of the lower leg, the lower leg is in the position slight bending(165°) in the knee joint, thigh – in the position of extension in the hip joint. Even with the formation of contracture in the joints lower limb in this case it will be supportive and the patient will be able to walk. On upper limb the fingers are placed in a position of slight palmar flexion with the first finger in opposition, the hand is in a position of dorsal extension at an angle of 45° in the wrist joint, the flexor forearm is at an angle of 90-100° in the elbow joint, the shoulder is abducted from the body at an angle of 15–20° at using a cotton-gauze roll placed in armpit. For some diseases and injuries, as directed by a traumatologist, a bandage may be applied in the so-called vicious position for a period of no more than one and a half to two months. After 3–4 weeks, when initial consolidation of the fragments appears, the bandage is removed, the limb is placed in the correct position and fixed with a plaster;
– plaster bandages should lie evenly, without folds or kinks. Anyone who does not know desmurgy techniques should not apply plaster casts;
– areas subject to the greatest load are additionally strengthened (joint area, sole of the foot, etc.);
– peripheral section limbs (toes, hands) are left open and accessible for observation in order to notice symptoms of compression of the limb in time and cut the bandage;
– before the plaster hardens, the bandage must be well modeled. By stroking the bandage, the body part is shaped. The bandage must be an exact cast of this part of the body with all its protrusions and depressions;
– after applying the bandage, it is marked, i.e., the diagram of the fracture, the date of the fracture, the date the bandage was applied, the date the bandage was removed, and the doctor’s name are applied to it.
Methods of applying plaster casts. According to the method of application, plaster casts are divided into lined and unlined. With padding, a limb or other part of the body is first wrapped in a thin layer of cotton wool, then plaster bandages are placed on top of the cotton wool. Unlined dressings are applied directly to the skin. Pre-bone protrusions (area of the ankles, femoral condyles, iliac spines, etc.) are isolated with a thin layer of cotton wool. The first bandages do not compress the limb and do not cause pressure sores from the plaster, but do not fix bone fragments firmly enough, so when they are applied, secondary displacement of the fragments often occurs. Unlined bandages, if not carefully observed, can cause compression of the limb, leading to necrosis and pressure sores on the skin.
According to their structure, plaster casts are divided into longitudinal and circular. A circular plaster cast covers the damaged part of the body on all sides, while a splint cast covers only one part. A variety of circular dressings are fenestrated and bridge-like dressings. A windowed bandage is a circular bandage in which a window is cut out over a wound, fistula, drainage, etc. Care must be taken that the edges of the plaster in the window area do not cut into the skin, otherwise when walking soft fabrics will swell, which will worsen the wound healing conditions. Protrusion of soft tissues can be prevented by covering the window with a plaster flap each time after dressing.
A bridge bandage is indicated in cases where the wound is located throughout the entire circumference of the limb. First, circular bandages are applied proximally and distally to the wound, then both bandages are connected to each other with U-shaped curved metal stirrups. When connected only with plaster bandages, the bridge is fragile and breaks due to the weight of the peripheral part of the bandage.
Bandages applied to various parts of the body have their own names, for example, corset-coxite bandage, “boot”, etc. A bandage that fixes only one joint is called a splint. All other bandages must ensure immobility of at least 2 adjacent joints, and the hip bandage – three.
A plaster splint is applied to the forearm most often for fractures of the radius in typical place. The bandages are laid out evenly over the entire length of the forearm from elbow joint to the base of the fingers. A plaster splint for the ankle joint is indicated for fractures of the lateral malleolus without displacement of the fragment and ligament ruptures ankle joint. Plaster bandages are rolled out with gradual expansion at the top of the bandage. The length of the patient’s foot is measured and, accordingly, 2 cuts are made on the splint in the transverse direction at the bend of the bandage. The splint is modeled and strengthened with a soft bandage. Splints are very easy to turn into circular bandages. To do this, it is enough to strengthen them on the limb not with gauze, but with 4–5 layers of plaster bandage.
A lining circular plaster cast is applied after orthopedic operations and in cases where bone fragments are fused callus and cannot move. First, the limb is wrapped in a thin layer of cotton wool, for which they take gray cotton wool rolled into a roll. It is impossible to cover it with separate pieces of cotton wool of different thicknesses, since the cotton wool will become matted and the bandage will cause a lot of inconvenience to the patient when wearing it. After this, a circular bandage in 5–6 layers is applied over the cotton wool with plaster bandages.
Removing the plaster cast. The bandage is removed using plaster scissors, a file, plaster forceps and a metal spatula. If the bandage is loose, you can immediately use plaster scissors to remove it. In other cases, you must first insert a spatula under the bandage in order to protect the skin from cuts from the scissors. The bandages are cut on the side where there is more soft tissue. For example, a circular bandage up to the middle third of the thigh - along the posterior outer surface, a corset - on the back, etc. To remove the splint, it is enough to cut the soft bandage.
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