Composite filling materials and compomers. Types filling techniques for primary and permanent teeth

Amalgam

It is an alloy of mercury with one or several metals.

1. Structure: silver 65%, tin 29%, copper 6-20%, zinc 2%, mercury of 3 %.

2. Advantages: plasticity, hardness at t-37º, high durability, insignificant contraction.

3. Disadvantages: changes colour of a tooth, the factor of thermal expansion exceeds the similar indicator of solid tissues of a tooth, high heat conductivity.

4. Use: cavity sealing of the I-st, II-nd classes by Black, V-th class of chewing teeth.

Metal seating materials concern amalgams (silver, gold, copper).

Properties of amalgams depend on metals in an alloy. Silver and tin cause amalgam expansion at hardening. Addition of copper to amalgam raises hardness of a seal. Zinc is added into the structure of amalgam for protection from oxidation. Considerable influence on properties of an amalgam is rendered a way of manufacturing, the size of particles and their form. The amalgam that has small particles is stronger, gives smaller contraction, has homogeneous structure. Particles can be of the needle and spherical form. At amalgam creation 2 processes take place simultaneousy - alloy dissolution in mercury and creation of new phases. Amalgam sawdust consists of two components: inter-metal combination Ag₃Sn (gamma - phase) and fusible mix - Ag₃Sn + Sn. More silver is in an alloy - more content Ag₃Sn, that is gamma - phase. In the course of creation of a firm amalgam, parts of Ag₃Sn and tin react with mercury, and the part of initial gamma - phase remains. Thus two new phases are created: gamma –1 and gamma –2 [Ag₂Hg₃ (gamma -1), Sn₈Hg (gamma - 2)].

The matrix of solid amalgam is gamma - 1 (Ag₂Hg₃), and parts of gamma - phase Ag₃Sn interspersed in a matrix - are filler. Other connections of gamma -2 phase (Cu₃Hg₄, Sn₇Hg₁₅) are placed in the matrix. Durability of an amalgam increases, when the quantity of gamma – phases increases. Process of amalgam's hardening can be accompanied with contraction, and creation of new phases (gamma - 1 and gamma -2) leads to expansion then the second contraction comes.

Amalgams of new generation have no gamma – 2 phase. Gamma –2 phase reduce hardness of a seal and increase corrosion.

Topicality: nowadays a great number of dental material (self-cured and light-cured composite materials, compomers) are used for filling carious lesions in deciduous and permanent teeth in children. It is necessary to know the composition of the material, its advantages and disadvantages, mixing technique and its special peculiarities and recommended indications.

Objective: to study basic properties and methods of use of dental composites and compomers.

Plan of lecture:

1. Сomposite material (self-cured and light-cure): composition, properties, methods of appliance.

2. Adhesive systems.

3. Flowable composites, condensable («packable») composites.

4. Compomers.

Dental composites — are a group of restorative materials widely used in dentistry for their improved physical properties and aesthetics.

Dental composites typically consist of: a resin-based organic matrix and an inorganic filler. It also includes silane, catalyst, pigments.

Оrganic matrix. Every composite has a resin-based oligomer matrix.

Monomer or oligomer is a bisphenol A-glycidyl methacrylate (BIS-GMA), which has a high molecular mass and is a base for composites. It was first used by Dr. Rafael L. Bowen in 1962 and is sometimes called “Bowen’s resin”. Other monomers can be used, such as UDMA — urethane dimethacrylate, ТЕGDМА — triethyleneglycol dimethacrylate and others.

During the polymerization reaction molecules of monomer form the polymer chains.

Inhibitor, catalyst package, initiator package and light absorbing agent (in light-cured composites only), pigments are added to the material composition.

Inhibitorofpolymerization (monomethyl ether hydrochinon) is added to the matrix in order to prolong the shelf life and working time of a composite.

Catalyst - is a substance that provides the connection of monomer molecules, used for the start, acceleration and activization of polymerization.

An initiator package begins the polymerization reaction of the resins.

An inorganic filler. Quartz, barium glass, silicone dioxide silica, ceramic powder and others may be used as fillers in composite materials. The filler gives the composite wear resistance, consistency, radioopacity, polymerization shrinkage and thermal expansion of composite and translucency.

Configuration, size and shape of particles of the filler may vary. They modify composite’s properties, that is why classification of dental composites is based on the size of particles of the filler.

Surface active matter (silane, dressing, from French – аррreter – to soak). From chemical point of view – silica organic compound. Filler’s surface is treated with silane. Silanes are bipolar linking agents, which bond chemically to filler on one side and to organic matrix on the other. A coupling agent such as silane is used to enhance the bond between the matrix and the filler. Due to this process composites aquire mechanical and chemical stability, water sorbtion decreases, wearing resistance increases.

UV absorbent is added in order to lower the composite’s dependence on sun light.

Дата добавления: 2014-01-05