Composition and properties of fast-hardening plastics in dentistry

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Technologists have thoroughly studied the physical properties of medical plastics, which has made it possible to widely introduce fast-hardening material into the practice of dentistry, orthodontics and maxillofacial surgery.

Orthodontic appliances are designed to correct abnormalities of the jaw system. However, the design of the devices will not function properly without fast-hardening materials.

In addition, acrylic substances are used to make dental crowns used in prosthetics.

General overview

Rapid-hardening plastics are also called self-hardening. In medical practice, the adaptation of this type of material has technologically changed the process of creating structures.

Peculiarities:

the ability of the material to undergo accelerated polymerization at everyday room temperature, or human body temperature;
high level of compatibility of the material with other forms of substances;
there is no destructive effect of the material on the oral mucosa.

In addition, medical compounds are used to repair damaged prosthesis bases.

Also, materials of this type make it possible to restore a combined non-removable structure directly in the oral cavity .

Composition and properties

Quick-hardening plastic masses are used in orthodontics in various variations, most often in the manufacture of removable and non-removable appliances and their parts.

Each factory package contains a powdery substance (varieties of acrylic), liquid (methyl methacrylate with various additives) and activators.

When these three components are combined, a solid dental material for prosthetics is formed, and polymerization occurs.

Functional features of the constituent elements:

Powder is an ether polymer of methacrylic and acrylic acids with various metal additives. This substance also contains dyes and plasticizers. The powdery substance is the basis for creating materials.
The liquid consists of ether compounds of methacrylic acid, chemical compounds similar in composition - monomers and various additives.
Monomer is an ethereal transparent consistency with a strong characteristic odor.
Improper storage can cause self-polymerization, so it is important to tightly seal the bottle and add an inhibitor to prevent the substance from hardening. The function of this substance is to polymerize the composition without heating.
Fillers are able to add viscosity to the powder, increase the strength of the composition and protect polymers from rapid wear. In addition, there are antimicrobial fillers that prevent the formation of microorganisms in polymers.

High quality medical plastics must be packaged in kits containing liquid and powder.

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New trends in the production of base polymers

In the last few years, there has been a tendency to introduce aesthetic fibers into the structure of hot-curing base polymers. They look more advantageous, but they are inferior to the standard ones in terms of physical and mechanical properties. “Veins” in the structure of polymers lead to the formation of microvoids and reduce the density of the material. Oxygen in microvoids increases the number of monomers. Therefore, such polymers with improved aesthetic characteristics should be used only when indicated - in rare cases.

Despite certain disadvantages, acrylic plastics remain the most common material for the production of removable denture bases. Their main advantages are low price, manufacturability and lack of need for expensive equipment.

Advantages and disadvantages

The materials are used in medicine for various purposes. Versatility is associated with a set of good basic physical and chemical properties.

The advantages of the material in orthodontics are undeniable:

do not have harmful effects on the body;
the material is highly durable and can withstand strong mechanical stress;
the ability to eliminate the breakdown of a fixed prosthesis directly in the oral cavity;
the ability of the material to quickly self-polish (harden) under normal conditions, which simplifies the process of filling teeth;
has a color similar to the natural color of the dental crown;
a fast, simplified material processing technique that reduces the time required for manipulations in the patient’s oral cavity.

However, there are also disadvantages:

inexpensive types may have an unaesthetic appearance;
may darken during prolonged use;

If the consistency is not prepared correctly, the material becomes insufficiently strong and is susceptible to chipping.

Classification of polymers

Polymers used in prosthetic dentistry belong to one of three groups. Each of them is subject to different hygienic, toxicological, aesthetic, and technological requirements.

Basic, or basic polymers in dentistry are used for the manufacture of artificial teeth and bases for removable dentures.
Auxiliary - needed for impressions, molding and modeling.
Clinical polymers include sealants, restoratives, and adhesives.

Features of application

It is necessary to use products for medical purposes only if mixed in the correct proportions.

Features of the use of materials:

The liquid is mixed with the powdered composition until a viscous substance is formed. Excess monomer can lead to increased material shrinkage, porosity and poor coloration.
The mixed composition is tightly closed. Over a half-hour period of time, the mass swells and goes through several stages: sandy, viscous, dough-like, rubbery.
The polymerization mode occurs when immersed in water or heated and the presence of an activator. The individual regimen must correspond to the description on the packaging.
It is important to follow the instructions exactly, because if the polymerization process is shortened, there will be an excess of monomer, which will provoke inflammatory processes in the mucous membrane. If overheated, it will become excessively brittle.
During the production of prostheses, the formation of porosity in the material is possible. This phenomenon occurs during accelerated polymerization and when there is a lack of monomer.

If the proportions are observed, the listed phenomena and deformation can be avoided. Depending on the stage of swelling, specialists use the material for filling, making devices, and making impressions.

The video discusses the properties of quick-hardening plastic for the manufacture of prostheses.

Method for making a temporary splint from quick-hardening plastic

Several methods have been proposed for the manufacture of temporary splints from quick-hardening plastics.
We present the method described by M.R. Marey. To make a splint using this method, it is necessary to make an aluminum mold in the form of a groove, concave in the shape of the dental arch. The mold is made from an aluminum plate 1 cm wide, 0.25-0.30 mm thick and 13-14 cm long (Fig. 168). In the absence of a plate, it can be obtained by flaring ordinary aluminum wire 2-3 mm thick. In order to obtain the shape of the groove, the plate is stamped on a lead tile with wire 3-3.5 mm thick (Fig. 168). Before bending the mold along the dental arch, it is annealed on the flame of an alcohol burner. This makes it soft and pliable. Its edges are bent with crampon tongs so that they do not bend inward, but, on the contrary, diverge outward. The latter circumstance allows you to subsequently remove the mold from the hardened tire without much difficulty. Applying a splint consists of the following technical techniques:

1. Applying a ligature to the teeth to be splinted. As a ligature, take a plastic thread (fishing line) 0.3-0.4 mm thick, which is tied with a triple knot on the vestibular surface of the tooth (Fig. 168). The ends of the thread are cut short.

2. Preparation of dough from quick-hardening plastic.

3. Formation of the tire. The prepared dough of quick-hardening plastic is placed in a mold pre-greased with Vaseline and pressed against the teeth so that the ligature nodes are immersed in the plastic. Excess plastic that extends beyond the edges of the mold is removed with a spatula. After the plastic has hardened, the aluminum mold can be easily separated from the tire with a spatula. Irregularities and sharp protrusions on the tire are removed with carborundum heads. The splint should not lie on the gum, and applied to the lower row of teeth should not interfere with the closure of the teeth. The splint ligatures should not be inserted into the gum pocket.

Source

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Plastics have the ability to quickly harden under normal conditions, so they are widely used in medical practice for filling, manufacturing and repairing devices.

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