T.V.Grineva, E.I.Ippolitova, I.I.Lazareva

«Cathedra» journal, № 7, 2003

Glass ionomers, which appeared in the 1970-s, have very quickly become widely used by dentists, and have taken a respectable place among filling materials.

Glass ionomers have biological compatibility and chemical adhesion to tissues of the tooth, high compressive strength, are subject to minimal shrinkage during solidification, and as a result provide lack of permeability at the tooth-seal edge. The materials of this group are easy-to-use, well tolerated by the patients, and release fluoride for a long time, which reduces risk of recurrent and repeated caries.

Glass ionomers «DENTIS» and «DENTIS ART», which have been developed by JSC «StomaDent», differ from existing national and foreign analogues by their chemical composition, radiopacity, high strength, low solubility, water resistance at initial stage of solidification and acid resistance.

Glass ionomers «DENTIS» and «DENTIS ART» small dispersion powder is a mixture of sublimated polyacrylic acid, fluorined glass and modifier additives, with the average size of particles 2.8 - 3.2 microns. Being mixed with water they form a high-strength multi-component structure.

Glass ionomers «DENTIS» and «DENTIS ART» have relatively long working time – up to 2 minutes, high physical and mechanical characteristics:

One of the most reliable methods of forecasting the conduct of glass ionomers in the oral cavity consists in the analysis of change of the material’s strength over certain periods of time.

The analysis of «DENTIS» strength changes produced the following results:

• in 24 hours: 192 ± 7 MPa
• 7 days: 242 ± 20 MPa
• 24 days: 235 ± 41 MPa
• 3 months: 210 ± 20 MPa
• 6 months: 205 ± 21 MPa.

Graph: Change of compression strength of glass ionomer «Dentis» over time

The results of the analysis allow to conclude that glass ionomer «DENTIS» acquires maximal strength over 7 days and the material’s strength practically does not change in the course of 6 months, which signifies stable strength characteristics and possibility for the material to function long in the oral cavity.

We have analyzed the influence of protective varnish on fillings made of glass ionomer «DENTIS» at the initial stage of solidification.

As a result of tests it turned out that:

1. the strength of samples covered with protective varnish: 128±5 MPa,

2. the strength of samples not covered with protective varnish: 172±14 МПа.

Graph: The influence of protective cover on compression strength of glass ionomer «Dentis»

This result allows to conclude that glass ionomer «DENTIS» is not sensitive to moisture at initial stages of solidification and does not require additional protection of the surface.

The analysis of acid erosion of glass ionomers «DENTIS» and «DENTIS ART» have been carried out via the method of shock stream following the standard procedure. After continuous testing of material samples during 8 hours acid erosion have not been found.

The lack of acid erosion and the results of clinical tests allow to recommend glass ionomers «DENTIS» and «DENTIS ART» for retrograde sealing of root dentin caries.

Of particular interest is analysis of fluoride emission from glass ionomer «DENTIS ART» over certain periods of time in teeth tissues. The analysis was carried out on samples made of molars, which have been removed due to periodontal disease; class I cavities were made in the samples to be restored with glass ionomer «DENTIS ART». After restoration they were placed in polyethylene reservoirs with distilled water, which was changed every day. The reservoirs with the samples were placed in thermostat at +37^oС temperature for various time periods. Three groups of restored tooth samples have been made. The first group was tested 1 month later, 2d group – 3 months later, 3d group – 6 months later.

At the end of this time period the samples were taken out of distilled water, sawn with diamond mill with continuous moisturizing. Glass ionomer «DENTIS ART» was mechanically withdrawn from the samples and the fluoride content in various layers of dentine was measured.

• 1st layer: cavity bottom,
• 2d layer: 0.111 mm from bottom,
• 3d layer: 0.222 mm from bottom.

The analysis have used the method of laser mass-spectrometry on «Enamel-2» device with double focusing and 532 nm wavelength, following the technique used to determine element composition of biological samples in wide dynamic diapason, which allows to define admixtures and trace components.

Graph. Fluoride emission from glass ionomer «DENTIS ART» in the 1^st layer of dentine

Graph. Fluoride content in various layers of dentine

The analysis has shown that:

• glass ionomer «DENTIS ART» is capable to allocate fluoride in dentine,
• the depth of fluoride penetration becomes larger, the longer glass ionomer «DENTIS ART» stays in the cavity,
• fluoride penetrated dentine to the depth of 0.222 mm, and the dentine layer having contact with the filling material contained maximal quantity of fluoride, which allows to suppose that fluoride can penetrate into deeper layers of dentine.

The results of analysis have made it possible to recommend glass ionomers «DENTIS» and «DENTIS ART» for wide use in clinical practice:

• restoration of teeth cavities of III - V classes;
• sealing primary teeth;
• making linings while working with composite materials and amalgam;
• sealing root dentin caries,
• atraumatic restorative tooth treatment (ART)

In order to achieve effective treatment with the use of glass ionomer «DENTIS ART» one has to keep to the following rules:

1. Glass ionomer powder should be mixed with distilled water in exact proportion indicated by the manufacturer. The excess of water leads to the washing-out of aluminum ions and the resulting loss of dimensional cross-linking; and lack of water leads to incomplete hydration and reduced formation of calcium and aluminum ions. In both cases rules violation leads to reduced strength of material, since the formed matrix does not have developed dimensional structure.
2. Before the material is brought in, the prepared cavity should be treated with conditioner, which is the obligatory condition for the creation of chemical bonding of material with the tooth tissues.
3. The material should be introduced in the cavity and the seal should be formed only during working time, which may be identified by the particular shining of the surface of material; otherwise the material structure will be broken and its strength will be sharply reduced.