Materials for bases of removable dentures.doc. Antibacterial material for bases of removable dentures Features of the use of titanium in dentistry

In Russia alone, more than 18 laboratories and 140 dental clinics are already working with this material. The direction is developing intensively.

Now flexible nylon dentures have officially appeared in Ukraine.

Classification of basic dental technical materials:

2.1. Metals and their alloys.

Metals are substances containing a large number of unbound electrons in the crystal lattice, which determines the specific properties of metals - high electrical and thermal conductivity under normal conditions, malleability, opacity, etc.

Metal alloys are macroscopically homogeneous systems consisting of two or more metals

with characteristic metallic properties.

Currently, over 500 alloys are used in dentistry, which are divided into noble and non-precious alloys.

Photo. Gold is a dental technical material.

Classification of alloys based on noble metals:

– gold;

– gold-palladium;

– silver-palladium.

Classification of alloys based on base metals:

– chromium-nickel (stainless) steel;

– cobalt-chromium;

– nickel-chrome;

– cobalt-chromium-molybdenum;

– titanium alloys;

– aluminum and bronze alloys for temporary use.

Alloys of gold, platinum and palladium have good technological properties, are resistant to corrosion, durable, and toxicologically inert.

Alloys of silver and palladium are similar in physical and chemical properties to gold alloys, however, they are inferior to them in corrosion resistance and darken in the oral cavity.

Stainless steels with a nickel content of more than 1% are widely used for the manufacture of dentures, however, according to international standards, such steel is considered toxic.

The basis of the cobalt-chrome alloy is cobalt (66-67%), which has high mechanical qualities, as well as chromium (26-30%), which is introduced to give the alloy hardness and increased anti-corrosion resistance.

Nickel-chrome alloys contain nickel (60-65%), chromium (23-36%), molybdenum (6-11%), silicon (1.5-2%), do not contain carbon, and are used in the technology of metal-ceramic dentures.

Titanium alloys have high physical, chemical and technological properties, and there is an opinion that titanium and its alloys are an alternative to gold.

2.3. Polymers.

Polymers are substances whose molecules consist of a large number of repeating units and are obtained by polyaddition and polycondensation technology.

Classification of polymers:

1. Classification by origin:

– natural or biopolymers (for example, proteins, nucleic acids, natural rubber, etc.);

– synthetic, obtained by polyaddition and polycondensation methods (for example, polyethylene, polyamides, epoxy resins).

2. Classification according to the nature of the substance:

– organic polymers;

– organoelement polymers;

– inorganic polymers.

3. Classification according to the shape of the polymer molecules:

– linear polymers;

– “cross-linked” polymers;

– “grafted” copolymers.

4. Classification by purpose:

– basic (rigid) polymers;

– elastic polymers or elastomers;

– polymer (plastic) artificial teeth;

– polymers for replacing defects in hard dental tissues;

– polymer materials for temporary fixed dentures;

– facing polymers;

– restoration polymers.

Rigid base polymers are used for removable plastic and arched (clasp) dentures.

Elastomers are used as an elastic lining in combined denture bases.

To protect prepared teeth during the manufacture of permanent dentures, temporary fixed dentures based on polymers are used - acrylate, polycarbonate, celluloid.

Polymer facing materials based on ceramic masses, composite materials, and acrylic polymers are used in tooth restoration.

Depending on their purpose, base plastics are divided into four main groups: 1) plastics for bases; 2) plastics for soft base linings; 3) plastics for relining removable dentures and repairing dentures; 4) cold-curing structural plastics used for the manufacture of orthodontic appliances and in maxillofacial orthopedics.

Base materials must meet the following specific requirements:

1) the required consistency of the molding polymer-monomer mass should be achieved in less than 40 minutes;

2) the finished molding mass should be easily separated from the walls of the vessel for mixing the powder with liquid;

3) 5 minutes after reaching the required consistency, the material should have optimal flow properties;

4) water absorption should not exceed 0.7 mg/cm2 after 24 hours of storing the sample in water at 37°C;

5) after drying the sample to a constant weight, stored for 24 hours in water at 37°C, the solubility should not exceed 0.04 mg/cm2;

6) when a plastic sample is exposed to a 400 W ultraviolet radiation source for 24 hours for hot-curing plastics

and 2 hours of cold-curing plastics, slight color changes are allowed;

7) the transverse deflection under a load of 50 N for hot-curing plastics should not exceed 4 mm, and for cold-curing plastics under a load of 40 N should not exceed 4.5 mm.

Depending on their commercial form, structural base plastics are divided into three main types: 1) powder-liquid type plastics; 2) gel type plastics; 3) thermoplastic injection molded plastics.

Plastics typegel.

Gel-type base materials are a ready-made molding compound, usually obtained by mixing a monomer with a polyvinyl acrylate copolymer. The material is supplied in the form of a thick plate, coated on both sides with an insulating polymer film, which prevents the evaporation of the monomer. These materials are manufactured only by the hot-curing method, therefore they do not contain the ingredients of cold-curing redox systems (activators, initiators).

Gels are made on the basis of two-polymer monomer systems. System I is a molding compound obtained by mixing polymethyl methacrylate with methyl methacrylate, system II is a copolymer of vinyl chloride (CH3-CHCI) and vinyl acetate (CH 2 =CH-OCOCH 3) with methyl methacrylate. The physical properties of these two materials are completely different. Gels based on system II are more widely used. The amount of inhibitor and storage temperature are the main factors affecting the shelf life of gel-type materials. When stored in the refrigerator, the gel does not lose its technological characteristics for 2 years. Gel-type materials can be processed into products using compression molding and injection.

Prosthesis basis - This is a plate made of plastic or metal on which artificial teeth and retaining clasps are attached.

The basis of the prosthesis lies on the alveolar process and hard palate and must correspond to the relief of the tissues of the prosthetic bed.

The size of the base of the plate denture depends on the number of remaining teeth, the number and type of clasps. The more natural teeth are preserved in the jaw, the smaller the prosthesis base should be, and vice versa, a decrease in the number of natural teeth necessitates an increase in the boundaries of the prosthesis base.

The size of the prosthesis base is also affected by:

Degree of alveolar process atrophy

The degree of pliability and mobility of the mucous membrane

Pain sensitivity threshold of the mucous membrane

The greater the degree of atrophy and the degree of compliance, the larger the area of ​​the prosthesis base should be.

A number of negative phenomena are associated with the base of a plastic prosthesis.

Covering the hard palate, it causes:

Impaired taste sensitivity

Impaired temperature sensitivity

Speech is impaired

Self-cleaning of the oral mucosa is impaired

Irritation of the mucous membrane appears

Causes a gag reflex

In areas adjacent to natural teeth, gingivitis occurs with the formation of pathological pockets

Border of the prosthesis on the B\jaw:

The border of the prosthesis base is located only within passively moving tissues.

The border of the prosthesis runs along the transitional fold, bypassing the movable buccal cords of the mucous membrane and the frenulum of the upper lip, bypassing the buccal cords. On the palatal side, the base passes along line A, between the hard and soft palate, 1-2 mm short of the blind fossae. On the palatal side, the base overlaps natural teeth - frontal by 1/3 of the height of the tooth crown, chewing by 2/3 of the height of the tooth crown.

Border of the prosthesis on the jaw:

The border of the prosthesis on the lower jaw vestibularly runs along the transitional fold, bypassing the movable buccal cords, bypassing the frenulum of the lower lip, bypassing the retromalar tubercles. If the mucous membrane of the retromalar tubercles is mobile, then the tubercles do not overlap, and if it is not mobile, then they overlap completely. Next, the border of the prosthesis passes to the lingual surface and runs along the maxillary-hyoid line, bypassing the frenulum of the tongue. On the lingual side, the frontal and chewing natural teeth overlap by 2/3 of the height of the tooth crown.

IN oscule bases with occlusal ridges

Having drawn out the models, the technician begins making a wax base with occlusal ridges (bite templates), which are needed to determine and fix the position of the central occlusion in the oral cavity, with subsequent transfer of this position to the articulator or occluder.

Bite patterns include :

Occlusal ridges

Requirements for the prosthesis base:

Must fit tightly to the model

Be positioned exactly along the boundaries of the prosthesis (marked on the model)

Have the same thickness

The edges of the base must be rounded

There should be a metal wire at the base of the lower jaw

Table No. 3

Plastics are divided into self-hardening, or cold-hardening, i.e. hardening at room temperature, and hot-curing plastics, hardening during heat treatment.

The process of setting plastic goes through several stages:

first stage– saturation, consists of mixing powder and liquid, and the presence of both free liquid and powder is not allowed. The optimal volume ratio of monomer to polymer is 1:3;

second stage– sand, the mass resembles sand moistened with water;

third stage– stretching threads, the mass becomes more viscous, and when it is stretched, thin threads appear;

fourth stage– doughy, is characterized by even greater density and the disappearance of stretching threads when broken;

fifth stage– rubbery or the stage of hardening of plastic.

They work with plastic in a dough-like stage. Hot-curing plastics with the correct polymerization mode contain 0.5%, fast-hardening plastics - 3.5% of residual monomer.

The following types of plastics are used in orthopedic dentistry:

1. Acrylates– based on acrylic and methacrylic acids. For several decades they have held the lead in dentistry due to their main properties: relatively low toxicity, ease of processing, chemical resistance, mechanical strength, and aesthetic qualities. Most materials contain polymethyl methacrylate (PMMA) as the main ingredient.

Representatives:

a) “Ethacryl” – a synthetic material based on acrylic copolymer, colored to match the color of the oral mucosa;

b) “Ftorax” is a hot-curing powder-liquid type plastic based on fluorine-containing acrylic copolymers. Consists of powder and liquid. A prosthesis made from Ftorax has increased strength and elasticity and harmonizes well in color with the soft tissues of the oral cavity;

c) “Akronil” – cross-linked and grafted plastic;

d) colorless plastic - based on polymethyl methacrylate, free of stabilizer, containing an antiaging agent (tinuvin). Consists of powder and liquid.

All of the listed plastics are used for the manufacture of bases in clasp and removable laminar dentures, and orthodontic devices. They are hot-curing plastics. Colorless plastic is used for the manufacture of denture bases in cases where a colored base is contraindicated (dye allergy), as well as for other purposes when a transparent base material is needed.

e) “Sinma-74”, “Sinma-M” - plastics produced in the form of white powders of different shades, from bright white to dark brown, and liquid. Hot-curing plastics are used for the manufacture of crowns, small bridges, and facets.

Self-hardening plastics in this group include:

a) “Protacryl”, “Redont 01,02,03” - used for repairs, relining of removable denture bases, as well as for the manufacture of simple orthodontic or orthopedic devices;

b) “Noracryl”, “Acrylic Oxide”, “Stadont”, their distinctive feature is the presence of a range of white colors from gray to brown shades. Used for correction of plastic crowns and bridges;

c) “Carboplast” is a white self-hardening plastic that is used for the manufacture of individual spoons.

2. Elastic plastics are divided into: a) acrylic (“Eladent”, “PM”, “Ufi-gel”); b) silicone (“Ortosil”, “Ortosil-M”, “Boxil”, “Mollosil”); c) polyvinyl chloride (“Ortoplast”, “Elastoplast”); d) urethane dimethacrylate (“Isosite”).

"Eladent" is an elastic plastic based on vinyl acrylic copolymers.

“Ortosil” is a silicone elastic material with a rubber-like consistency that adheres well to plastics. "Eladent" and "Ortosil" are used for the manufacture of two-layer removable dentures when it is necessary to create a soft layer that reduces pressure on the underlying supporting tissues. Depending on the indications, the elastic layer can be placed over the entire surface of the denture, along the boundaries of the denture base, in certain areas of the denture base, under artificial teeth, creating a shock absorber that simulates periodontal disease.

"Boxil" is a plastic based on cold-vulcanized silicone rubber. It is white in color and becomes rubbery after hardening. Designed for the manufacture of boxing mouth guards.

“Orthoplast” is a pink elastic material from which ectoprostheses are made for defects in the soft tissues of the face. Has six shades.

“Elastoplast” is a pink, hot-curing plastic that serves as the basis for boxing mouth guards.

“Izozit” is used as a facing material in the manufacture of metal-plastic structures of dentures. White plastic with a range of shades for dentin, cervical area, incisal edge, which allows you to adjust the transparency and give the teeth a natural appearance.

Used for the manufacture of: bases for removable dentures, maxillofacial and orthodontic devices, various splints, artificial teeth, coatings for metal parts of fixed dentures, crowns, metal-polymer implants.

Elastic plastics, in addition to the general ones, must meet the following specific requirements:

Provide a strong and long-term connection with the base material, which must have minimal adsorbing capacity in relation to saliva and food products;

Due to their high plasticity, they should adhere tightly to the mucous membrane during chewing, not cause irritation and absorb chewing pressure, i.e. create convenience when using a prosthesis;

Should not contain either external or internal plasticizers, which prevents the lining from hardening due to their leaching;

Must have good wettability with no swelling in the oral cavity and constant volume;

The initial softness and elasticity of the lining should be consistently elastic in the oral cavity;

Should not dissolve in the oral cavity;

Must have high wear resistance and color fastness.

Disadvantages of elastic pads include:

Loss of elasticity due to aging of plastic after just half a year;

The impossibility of polishing elastomers, friability, making them unhygienic;

Lack of optimal marginal adhesion of elastomers to rigid base plastics;

It is difficult to process elastomers with a cutting tool, and hence problems arise when correcting the base of the prosthesis.

Violation of the polymerization regime leads to defects in finished products (bubbles, porosity, stains, areas with increased internal stress) , to cracking, warping and breakage of the prosthesis.

There are three types of porosity in plastics: gas, compression and granular.

Gas porosity is caused by the evaporation of the monomer inside the polymerizing molding mass. It occurs when a cuvette with plastic dough in a plaster mold is lowered into boiling water. This type of porosity can also occur when heating a mold with a large amount of mass due to the difficulty of removing excess heat from it, which develops as a result of the exothermic nature of the polymerization process.

Towards compression porosity leads to insufficient pressure or lack of molding mass, resulting in the formation of voids. Unlike gas porosity, it can occur in any area of ​​the product.

Granular porosity occurs due to a deficiency of monomer in those areas where it can volatilize. This phenomenon is observed when the monomer - polymer mass swells in an open vessel. The surface layers are poorly structured and represent a conglomerate of “clumps” or granules of material.

Plastic products always have significant internal residual stresses, which leads to cracking and warping. They appear in places where plastic comes into contact with foreign materials (porcelain teeth, clasps, metal frames, clasp extensions). This is the result of different coefficients of linear and volumetric expansion of plastic, porcelain, and metal alloys.

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Introduction

According to forecasts of the aging population of Western countries, by 2025 more than half of it will be people over 50 years of age. Despite advances in the prevention of dental disease, it is likely that many of these people will require removable full or partial dentures to replace lost teeth. Currently, about 32 million people in North America wear such dentures, and 9 million complete dentures and 4.5 million partial dentures are manufactured annually for prosthetic patients. It is important for these patients to be provided with aesthetically pleasing and highly functional prosthetics as this will improve their quality of life.

Making a removable denture consists of many stages. The first of these is taking an impression, which is followed by a series of technological steps in the dental laboratory. These include obtaining a model, setting the teeth, making a wax model, making a plaster mold in a dental cuvette and removing, boiling, the wax, and then filling the resulting mold space with material for making denture bases or base material.

A variety of materials have been used to make prosthetics, including cellulose-based materials, phenol-formaldehyde, vinyl plastics, and hard rubber. However, they all had various disadvantages:

Materials based on cellulose derivatives were deformed in the oral cavity and had a taste of camphor, which was used as a plasticizer. Camphor was released from the denture, causing stains and blisters to form in the base, as well as discoloration of the denture over several months.

Phenol-formaldehyde resin (Bakelite) proved to be a very difficult, low-tech material to work with, and it also changed color in the mouth.

Vinyl plastics had low strength and fractures were common, possibly due to fatigue of the base material.

Ebonite was the first material used for the mass production of prosthetics, but its aesthetic properties were not very good, so it was replaced by acrylic plastics.

Acrylic plastic (based on polymethyl methacrylate) is currently one of the widely used base materials, since it has good aesthetic properties, this material is cheap and easy to work with. But acrylic plastic is not an ideal material in all respects, since it does not fully meet the requirements for an ideal material for the base of a denture, presented in Table 3.2.1.

But acrylic plastics have become widespread because many of the requirements of Table 3.2.1. they answer. In particular, the technology for manufacturing prostheses from acrylic plastic is quite simple and inexpensive; the prostheses have a good appearance. In addition to its use in complete removable dentures, acrylic plastic is often used for other purposes, such as the manufacture of individual trays for taking impressions, for reproducing the relief of soft tissues on cast metal frames, for repairing dentures, making soft linings for denture bases and artificial teeth.

The curing process in the manufacture of acrylic prosthesis occurs through a free radical polymerization reaction to form polymethyl methacrylate (PMMA).

The conversion (transformation) of a monomer into a polymer includes the traditional sequence: activation, initiation, growth and chain termination.

Hot curing plastics

These materials consist of a powder and a liquid, which, after mixing and subsequent heating, turn into a solid state. The substances included in the powder and liquid are listed in Table 3.2.2. The specific form of application of the material in the form of a powder-liquid system is due to at least three reasons:

Possibility of processing the material in dough form or using “dough” technology

Minimizing polymerization shrinkage

A decrease in the exothermic effect, or a decrease in the heat of reaction.

Polymerization shrinkage is reduced compared to monomer polymerization shrinkage because most of the material (ie beads and granules) is already polymerized.

The polymerization reaction is highly exothermic, as a significant amount of thermal energy (80 kJ/mol) is released when the C=C bonds are converted into -C - C bonds. Since most of the mixture is already in the form of a polymer, the potential for overheating of the material is reduced. Since the maximum polymerization temperature will be lower, the thermal shrinkage of the material will also decrease.

Monomer belongs to the category of volatile and flammable substances, so the container with it must be kept closed at all times and away from sources of open flame. The container is a dark glass bottle, which extends the shelf life of the monomer by preventing its spontaneous polymerization under the influence of light.

Hydroquinone also extends the shelf life of the monomer by instantly reacting with free radicals that may spontaneously form in the liquid, producing stable free radical compounds that are unable to initiate the polymerization process.

Contamination of polymer beads and granules should be avoided because they carry benzoyl peroxide on their surface and only a small amount of polymer is required to initiate the polymerization reaction.

The polymer powder is very stable and has an almost unlimited shelf life.

A crosslinking agent, such as ethylene glycol dimethacrylate ether, is added to the material to improve mechanical properties (Fig. 3.2.1a). It binds in some places to the polymer chain of polymethyl methacrylate and forms a cross-link between this and the adjacent polymer chain through two terminal double bonds (Fig. 3.2.1 b).

Rice. 3.2.1. (a) Ethylene glycol dimethacrylate ether and (b) its cross-linking

Thus, although PMMA itself is a thermoplastic plastic, the inclusion of cross-linking agents in the composition eliminates its subsequent heat treatment.

Cold curing plastics

The chemistry of these plastics is identical to that of hot-curing plastics, except that curing is initiated by a tertiary amine (such as dimethyl-p-toluidine or sulfonic acid derivatives) rather than by heat.

This curing method is less efficient than the hot curing process and produces a polymer with a lower molecular weight. This situation negatively affects the strength properties of the material and also increases the content of residual monomer in it. The color fastness of cold-cured materials is worse than that of hot-cured materials; cold-cured plastics are also more prone to yellowing.

The polymer balls of these materials are somewhat smaller in size than those of hot-curing plastic (the size of the balls in the latter is about 150 microns) in order to facilitate the dissolution of the polymer in the monomer to form a dough-like mass. This state must be achieved before the curing reaction begins, which will change the viscosity of the mixture, and the mass will become excessively dense, preventing the material from being molded.

Lower molecular weight also results in a lower glass transition temperature (Tg), with Tg typically being 75-80°C, but without increasing the material's tendency to deform. Since no external heat source is used to cure the plastic, the amount of internal stress generated in it is lower. However, the material is very susceptible to creep, and this can significantly affect the appearance of deformations of the prosthesis during use.

Cold-curing casting plastics

These plastics are cold-curing and fluid enough when mixed that they can simply be poured into a hydrocolloid mold. They reproduce surface details well, although their other properties are inferior to cold- and hot-curing moldable acrylic plastics, so they are not widely used.

Light-curing base plastics

Visible light curable materials have been introduced previously. In terms of their chemical properties, these materials are more similar to composites for dental restoration than to plastics for the manufacture of denture bases. The material consists of a urethane dimethacrylate matrix, which contains a small amount of colloidal silica to give the material the required fluidity or consistency, and a filler of acrylic beads, which become part of an interpenetrating polymer network structure when it cures. It is widely used as a solid material for denture relining, for making custom impression trays, and for repairing broken dentures.

Fundamentals of Dental Materials Science
Richard van Noort