Resin compositesBy Dr. Dida Boru

April, 2014

A composite: a combination of two or more chemically different materials with distinct interface between them and having properties better than those of the components acting alone.

Resin composite: a restorative dental material containing ◦ Organic resin matrix◦ Inorganic filler particles◦ Coupling agent◦ Other components

Resin composite

Are high molecular weight monomers◦ Bisphenol A glycidyl methacrylate (bis-GMA)◦ Urethane dimethacrylate

Terminal methacrylate groups provide sites for free radical polymerization

Disadvantages of bis-GMA ◦ Color instability◦ High viscouscity ( decreased by adding TEGDMA

or EGDMA)

1. Organic resin particles

May be Colloidal silica: inert

◦ Low cofficient of thermal expansion◦ Improved condensability and polishibality

Barium silicate:medium hardness◦ Is very radiopaque

Quartz: most widely used filler material throughout 1970’s◦ Very stable and inert◦ Disadvantages lack of radiopacity

Abrasiveness High cofficient of thermal expansion Wear opposing tooth

Zinc silicate Lithium aluminium silicate

2. Inorganic fillers

The greater percentage of the filler content, the better the physical properties

Classification of filler particle size◦ Macro fillers: 10-100 microns◦ Midi fillers: 1-10 microns◦ Mini fillers: 0.1-1 microns◦ Micro fillers: 0.01-0.1 microns◦ Nano fillers: 0.005-0.01 microns

Generally the smaller the average particle size, the easier it will be to polish

Cont…

Its primary purpose is to bond filler particles to organic resin matrix

Improve physical properties of resin composite.

Most commonly used coupling agent are organosilanes (Gamma methacryloxy propyltrimethoxy silane)

3. Coupling agent

Polymerization initiators◦ For chemically activated: benzoilperoxide and

tertiary amines◦ For light activated: diketone photoactivators

(camphoroquinone) are used Polymerization inhibitors: monomethyl ether

of hydroquinone◦ to prevent spontaneous polymerization under

normal storage condition Uv radiation absorbers:

◦ added to improve color stabilty by absorbing electro magnetic radiation.

4. Other ingredients

Based on filler particles size: ◦ Traditional (convectional)◦ Small particle macrofilled resin composite (fine

particles)◦ Microfilled resin composites◦ Hybrid resin composites (blend)

Based on polymerization method◦ Chemically activated◦ Light activated

Types of direct filling resin composites

Filler : 70-80%◦ 20-50 micron size

Disadvantages: ◦ Roughness ◦ Staining and discoloration

Traditional (convectional)

Filler: 70-80%◦ 1-5 micron size

Good compressive and tensile strength (fracture resistant)

Polished nicely Recommended for large (2mm or larger)

diastema closure and for class IV cavity

Small particle macrofilled resin composite (fine particles)

Filler: 35-50%◦ 0.02-0.04 microns

Polish to high luster and produce excellent esthetic result

Should not be used in high stress bearing area

Physical properties are generally inferior to those of small particles macro filled resin composites

Good choice for class V cavity

Microfilled resin composites

The most commonly used nowdays Filler: 70-80%

◦ 0.04 and 1-5 microns sized Are usually radiopaque Physical properties are intermediate to that

of Traditional and Small particle macro filled resin composite

Fracture resistant

Hybrid resin composites (blend)

Two paste system Base: contain benzoyl peroxide Activator (catalyst): Contain tertiary amine Disadvantage

◦ Contain porosity

Chemically activated (self cured)

Ultraviolet light activated: ◦ contain benzoin methyl ether and tertiary amines

which when activated by UV light produce free radicals

Visible light activated: ◦ contain camphoroquinone (0.25%) photo initiator

and tertiary amines in single paste

Light activated (light cured)

Advantages of visible light resin composites over self cured composites◦ Longer working time◦ Shorter chair time◦ Greater degree of polymerization◦ Reduced porosity◦ Greater color stability

Cont…

Disadvantages◦ Non uniform polymerization secondary to limited

depth of penetration by the curing light Following light activation resin composites

continue to undergo polymerization for up to 24 hours

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I. Incremental addition of resin composite• Ensures completeness of polymerization• Reduces polymerization shrinkage stress

II. Resin layer should not exceed 2mm in depth

III. Minimum of 40 seconds exposure timeThe most desirable finish surface for a

composite resin can be provided by aluminum oxide disks

Contraindications for composite include varnish and zinc oxide-eugenol

Principles of proper polymerization technique

Dr. michael Bounocore developed acid etching technique using 85% phosphoric acid in 1955

Purposes◦ Increases surface energy◦ Chemically cleans tooth structure◦ Creates micropores for micromechanical retention

Standard acid etching of enamel is application of 37% phosphoric acid for 15 seconds with 15 seconds rinsing and 15 seconds drying

Acid etching technique

Other acids used ◦ Pyruvic acid ◦ Nitric acid

Depth of enamel caused by enamel etchin is approximately 10-15 microns

Bonding agent is used instead of acid etchant to open dentinal tubule ◦ EDTA

Cont…

Resin composite undergo volumetric shrinkage of 1.6-5.7% during polymerization due to monomer shrinkage

Most detrimental effect of shrinkage is microgap formation which results in ◦ Sensetivity ◦ Secondary caries◦ Staining ◦ Pulpitis and necrosis

Polymerizatin shrinkage

Indications◦ Class III cavity (except distal cavity on canines)◦ Class IV cavity◦ Cavity V cavity ◦ Filling gaps (diastemas) between teeth◦ Veneering ◦ Minor reshaping of teeth

◦ Partial crowns on single teeth ◦ As Pit and fissure sealant◦ Cementation of crowns

Indication and contraindications of resin composite

Contraindications ◦ Class II cavity ◦ Class I cavity ( only indicated if requirements

fulfilled)◦ Cavity on distal surface of canines

Resin composite is indicated for posterior tooth restoration if:◦ Restoration is not in occlusal contact◦ Isthmus is less than 1/3 of buccolingual

intercuspal dimension◦ Cusps are not involved◦ Margins are not involved

Treatment area must isolated well

Requirement for succesfull posterior resin composite

Esthetics Low thermal conductivity No mercury or galvanism Conserves tooth structure Easily shaped prior to polymerization

Advantages when compared to amalgam filling

Time consuming to place Micro leakage Post treatment sensitivity Excessive wear Low strength Highly sensitive to moisture

Disadvantages