Classification of dental composites

Depending on a type of polymerization reaction: self-cured composites; light cured; heat-cured (used for indirect inlays or onlays).

Filler particles’ size: macro-filled (particles’ size - 1-100 mcm); micro-filled (particles’ size 0,04-0,4 mcm); hybrid composites (particles’ size 0,04-100 mcm).

By filling rate: highly filled (more than 65% of inorganic filler); low-filled (less than 65% of inorganic filler).

Clinical indications: I type – composite materials for loaded restorations; II type - composite materials for unloaded restorations.

Self-cured composites contain an initiator package which consists of benzol peroxide, that is activated by tertiary aromatic amines (N, N₂-dihydroxyethyl-р-toluidin) with formation of free radicals that initiate polymerization reaction. Self-cured materials use the reaction between their two components: between the catalyst paste (which contains benzol peroxide) and accelerating base paste (which contains tertiary amines) for creation of free radicals. The speed of polymerization depends on the quantity of initiator, temperature and presence of inhibitor of polymerization. Advantage of the self-cured composites is equal polymerization disregarding the cavity depth and thickness of filling.

Light cured composites use photosensitive matter camphorochinon and amine activator (N, N-dimethylaminoethyl methacrylate) as an initiator. They form with diketon, which is activated when acquiring the energy of light, complex, which dissociates with formation of reactive free radicals. Intensive decomposition of camphorochinon starts under the influence of light with wavelengths 400-500 nm. Polymerization time depends on quantity of initiator, curing time and light intensity. Darker shades and opaque shades have a longer curing time and slower polimerization reaction. Polymerization also depends on the curing light characteristics, distance from the light to the composite, curing time, characteristics of initiator package. At the initial stage polymerization may be inhibited by oxygen, which has a bigger reactional ability for radicals, than a monomer has. The outer-surface layer of hardened composite is not completely polymerized. This layer is called “oxygen inhibited layer”. Its thickness depends on the depth of oxygen diffusion. Some substances that have such characteristics, can bind to the active groups of monomer molecules instead of oxygen, but then the polymer chain breaks up, because such molecule does not add next monomer molecules. Such substances inhibit the polymerization of composite resin. Phenols have such properties (eugenol in particular).

Disadvantage of all composite resins is polymerization shrinkage. It is caused by shortening of distance between molecules of monomer when the polymer link is formed. Intermolecular distance before the polymerization is around 3-4 Angstrom (Vander Waals forces), after polymerization it is about 1,54 Angstrom.

In self-cured materials polymerization reaction speeds up with the rise of temperature, that is why it starts by the walls of the cavity, and polymerization shrinkage is noticed in the center or on the surface of a filling. In light cured composites polymerization starts at the site of initial contact of the ray with the composite’s surface, that is why the shrinkage is noticed at the opposite side of the filling.

Macro-filled composites - materials with the filler particles size 1–100 mc (usually 20–50 mc) (Evicrol (Spоfa Dental), Consize (3M ESPE), Adaptic (DentSplay), Visio-Fill, Visio-Molar and other).

Advantages: great compression strength; chemical stability; good marginal adaptation.

Disadvantages: minimal polishing ability;subjected to discoloration.

Mainly used for class I and II cavities, class V cavities in posterior teeth. They are used for the sites where great mechanical strength is needed, and esthetics is not a primary consideration.

Micro-filled composites — materials with the filler particles size 0,04–0,4 mc (Isopast (Vivadent), Degufill-SC, Degufill-M (Degussa), Durafill (Kulzer) and other).

Advantages: great esthetics;good polishing ability;colour stability.

Disadvantages: low mechanical strength (low filler content).

Mainly used for class III, V cavities and lesions in sites, where the stress is minimal.

Hybrid composites - materials with the filler particles size is between 0,04 to 100 mc (Valux Plus (ЗМ), Spectrum (DentSplay), Charisma (Kulzer) and other). Most of hybrids contain 80-85% of filler.

Advantages: great compression strength;chemical stability;great esthetics;colour stability; minimal shrinkage.

Used for cavities of all classes, for partial crown restoration and for reconstruction of occlusion.

Classification of dental composites (by R.W. Phillips, 1991)

Type of filling material	Filler particles size, mcm
Ordinary	8-12
With small particles	1-5
Microfilled	0,04-0,4
Hybrid

Дата добавления: 2014-01-05