Nanocomposites in dentistry: nanohybrid and microhybrid

The issue of high-quality composite materials used for dental restoration, has always been sharp. To dental composites high demands are made. They must have sufficient mechanical strength to be used not only on the anterior but also on the chewing teeth.

Have good aesthetic properties, low polymerization shrinkage, low coefficient of thermal expansion.

Be technologically advanced, make it easy to manipulate color shades. It became possible to combine all these properties in one composition relatively recently, after the development and introduction of new dental restorative materials, which include nanocomposites.

What are nanocomposites?

Nanocomposites are multiphase materials in which at least one phase (filler) has a fraction size of 0.1 to 100 nm (1 nanometer is equal to 0.001 microns). Dental nanocomposite materials are typically a combination of an inorganic filler and an organic matrix.

As the latter, various resins are used with additives - polymer inhibitors, catalysts, photoinitiators, light absorbers, dyes.

Before the advent of nanotechnology in dentistry, orthodontists had already used formulations whose particle sizes fit into the nanoscale. These are the so-called microfilic composites. Their average particle size is 0.04 μm, which corresponds to 40 nm.

However, along with positive properties - good polishability, high color fastness and low abrasive wear - microfilic composites also have significant disadvantages. The main one is insufficient mechanical strength, which does not allow using them for filling and restoring chewing teeth. Another disadvantage of these materials is the adhesion of microparticles, which leads to an inhomogeneous composite structure.

With regard to dental composites, there is such a pattern. The finer the filler particles, the higher its polishability and aesthetics, but the lower the strength, and vice versa. Dental scientists were constantly looking for new materials to break this vicious circle.

The beginning of the use of nanocomposites in dentistry marked a new era in the development of formulations for the restoration and treatment of teeth. The first nano-filled composite was presented by 3M ESPE in Vienna at the international dental exhibition in autumn 2002.

The main properties of composite dental materials are the size of the filler particles and the degree of filling of the matrix. The first parameter affects the abrasion resistance, polishability, color stability. The degree of filling determines the strength, thermal expansion, and polymerization shrinkage of the composite.

The degree of filling in traditional microfilic composites is 35–60% by weight. This is a low value, which does not allow obtaining a material with the required strength properties. In dentistry, nanocomposites are highly filled compounds (more than 60%), which makes it possible to use them for the restoration of not only anterior, but also chewing teeth.

Traditional dental formulations and nanocomposites behave differently in use. The first have filler particles leaving the surface under the action of an abrasive load of the restored tooth, they leave behind small craters that reduce shine and aesthetics renovated place. When nanocomposites are abraded, due to their small particle size, a crater does not form, due to which the brilliance and appearance of the tooth does not change.

In the early days, nanotechnology was only used in dentistry to make adhesives. Subsequently, they began to be used for the production of restoration and filling composition.

Types of nanocomposites

The main differences between these compositions are determined by the type, size and structure of the filler. The following are used as starting materials for the production of nanoparticles:

• titanium silicate;
• quartz;
• zirconium silicate;
• heavy salts;
• polymers;
• some metal oxides.

According to the structure and size of the filler, two main groups of nanocomposites are distinguished:

• nanohybrid compositions, which are a modification of traditional microhybrid (microfilic) composites by introducing nanoparticles into their structure;
• true nanocomposites based solely on nanofillers.

Nanocomposites also differ in:

• method of polymerization (chemically or light-cured);
• release form (in syringes or capsules);
• the number of color shades;
• transparency and a number of other features.

Nanohybrid composites

Traditional microhybrid composites contain small (about 0.04 μm) and large (up to 1 μm) particles. Due to the tendency to sticking, fine particles are unevenly distributed in the matrix, which leads to a deterioration in polishability and a decrease in aesthetics. To eliminate this drawback, nanoparticles with a size of 20-70 nm were introduced into the traditional composite. Unlike the fine fraction of conventional composites, nanoparticles do not stick together and are evenly distributed over the matrix. This ensures the homogeneity of the composition.

As a result of the modification, nanohybrid composites are obtained, which, in comparison with traditional materials, have higher strength and improved aesthetic characteristics. Large particles provide high strength of the composite. The fine fraction, which fills the gaps between the coarse ones, provides excellent polishability and high aesthetics of the restoration site.

The latest nanocomposites (Estet-X, for example) contain 3 sizes of filler - midparticles, miniparticles and nanoparticles. The ratio of these phases is strictly controlled. Such compositions are called "microarray".

True nanocomposites

More promising dental composites are those in which the entire filler is nanoparticles. Such compositions are called "true" or "nanocluster".

Nanoparticles in true composites are present in 2 types.

• in the form of nanomers with sizes of 20... 75 nm.
• in the form of nanoclusters, the sizes of which vary from 0.6 to 1.4 microns.

Nanoclusters are nothing more than agglomerations of nanomers. Existing technologies make it possible to control their size and structure. This is very important because the fundamental properties of dental nanocomposites depend on it. Strength is provided by large particles, while polishability and aesthetic appearance are provided by small particles. By controlling the size and distribution of large and small nanoparticles in the matrix, it is possible to obtain a material with desired properties.

Nanocluster composites have a very high filling - up to 87%. This results in good strength and low material shrinkage. At the same time, the polishability, abrasive wear resistance and aesthetics of the restored teeth remain high. In the process of wear, nanoclusters wear out gradually, splitting off nanoscale by nanoscale from themselves. Therefore, there are no visible cavities on the surface of the material, as is the case with traditional composite compositions.

Properties and features

The development of nanocomposites made it possible to get out of the vicious circle that existed earlier in relation to dental compositions, when the achievement of high aesthetic parameters was achieved at the cost of reducing strength, and vice versa. Now you can combine the required properties in one material.

Nanocomposites are distinguished by:

• high strength and reliability of the restoration;
• excellent polishability, long-term dry gloss retention.
• low shrinkage during polymerization - 1.6-1.9%, which is significantly lower than that of traditional composites;
• high degree of matrix filling - up to 87% by weight;
• manufacturability, good handling properties;
• a large number of color shades.

The disadvantages include the high price and insufficient knowledge of clinical manifestations.

The area of ​​use of nanocomposites is practically unlimited. They are used for:

• filling any carious cavities;
• restoration of enamel defects in case of fragmentary erosion;
• restoration of aesthetics anterior teeth;
• installations temporary fillings;
• overlays straight veneers;
• teeth splinting;
• restoration of metal-plastic and metal-ceramic crowns and facets;
• manufacture of overlays and inlays;
• build-up of tooth stumps on anchor pins;
• as a sealant.

For polymerization, mainly light irradiation is used.

Manufacturers of nanocomposites

Among the manufacturers who produce the material, such foreign brands can be distinguished.

ZM ESPE

ZM ESPE (USA) is one of the leaders in the development of innovative solutions in the field of dentistry. The company produces materials and instruments for orthopedics and dental therapy.

Filtek Supreme XT restorative material belongs to true nanocomposites, that is, only nanoparticles are used as a filler. The composition has high polishing and strength properties, retains a dry shine for a long time. It is used in the restoration of chewing and anterior dental units, the manufacture of direct veneers, splinting and the formation of tooth stumps.

Dentsply

The American company DENTSPLY sells its products in 120 countries.

One of the products is the Ceram X nano-hybrid formulation, which uses ceramics and nanoparticles as fillers.

The main purpose is anterior restoration. Uniform transparency and high aesthetic characteristics are achieved with a minimum number of color shades.

Voco

The VOCO company (Germany) produces materials for orthopedic, restorative and preventive dentistry. VOCO products are bought in more than 100 countries around the world.

The Grandio composite is manufactured using nanotechnology to achieve 87% fullness by weight. Methacrylate is used as a matrix. Curing is done with halogen light. The composition is available in capsules and syringes. Grandio VOCO meets all the requirements for modern dental nanocomposites.

Vivadent

Initially a Swiss company, and now an international syndicate Vivadent produces a wide range of restorative and therapeutic dental compounds, supplying them to 120 countries around the world.

One of the company's products, the Tetric EvoCeram nanohybrid light-curing composite, is designed for filling and restoring anterior and chewing dental units. The shade-coded option facilitates the dentist's work and maximizes the aesthetic effect.

Kerr

The company of the same name, founded in the United States in 1891 by the Kerr brothers, has now become an international company producing products that are in demand in many countries of the world. Including in Russia.

Premise nanohybrid composition contains particles of 3 sizes - nanofiller 0.02 microns, glass filler 0.4 microns and polymerized particles 30-50 microns. This made it possible to ensure high filling (84%) and low shrinkage (1.6%) of the composite.

Pentron

Pentron's Simile nanohybrid composite is a versatile material for the treatment and restoration of posterior and anterior teeth.

The composite has high strength, excellent polishability and many shades, allowing you to achieve absolute color harmony with the natural enamel of the tooth.

Schiitz Dental Group

The German company Schiitz Dental Group, in addition to many other materials for dentistry, produces the restorative nanocomposite NanoPaq. The exceptional strength and reliability of the restoration is ensured by a high fill rate of up to 82%.

The composition of NanoPaq has 4 transparency classes - highly transparent, low-transparent, medium-transparent and completely matte. The nanocomposite manufacturing technology allows you to control the level of transparency with the possibility of obtaining any intermediate version.

Conclusion

Modern dental restorative and filling materials, which primarily include nanocomposites, open up wide opportunities for dentists and orthodontists in the treatment, restoration and correction of anterior and posterior teeth.

Thanks to the nanofiller, a set of characteristics is provided that cannot be obtained using traditional formulations. The main ones are high polishability, mechanical strength, abrasion resistance, ideal aesthetic qualities.