resin composite restorations

what is composite resin?

an esthetic restorative material that is used to restore both anterior and posterior teeth

what does the word composite mean?

a material made by combining two or more different materials that do not dissolve in each other, and each material keeps its own properties, producing a material with better overall properties (stronger, more wear-resistant, and more esthetic) than either material alone.

why are composite resins popular?

they have have undergone many improvements over the years and are now widely used because they:

• Match the natural tooth color (esthetic).

• Bond directly to tooth structure.

• Can be used for both anterior and posterior restorations.

• Require more conservative tooth preparation than amalgam.

what does resin composite consist of?

• an organic resin matrix

• inorganic filler particles

• an organic coupling agent

what is the organic resin matrix?

the continuous phase (main body) of the composite resin into which all the other components are mixed.

what are some examples of high molecular weight monomers?

• Bisphenol glycidyl methacrylate (BisGMA) monomer

• Urethane dimethacrylate (UDMA) monomer

what are high molecular weight monomers?

comprising mostly of BisGMA, or UDMA or a mix of both, they are extremely viscous and thick monomers. they decrease the amount of filler than can be added and are difficult to handle

what is the most commonly used high molecular weight monomer?

Bisphenol glycidyl methacrylate (BisGMA) monomer

what is an example of low molecular weight monomer?

triethylene glycol dimethacrylate (TEG-DMA)

why are low molecular weight monomers added?

ones such as TEG-DMA are added as dilutant to provide more fluidity for the material

what are the advantages of low molecular weight monomers?

• decreases viscosity

• increases fluidity

• increases wettability, which helps resin flow and adapt to tooth

• improves mechanical properties

• allows for more filler particles to be incorporated

what are the disadvantages of low molecular weight monomers?

• increases polymerization shrinkage

• increases water sorption as it is more hydrophilic

what does the organic resin matrix consist of?

1. high molecular weight monomers

2. low molecular weight monomers

3. activator / inhibitor system

4. inhibitors

5. pigments

matrix monomers in direct resin composite systems can be polymerized how?

1. chemical curing (auto or self curing)

2. photo chemical through light activation

3. dual-cured through both mechanisms

what is chemical curing?

also known as self or auto curing, it is not used today. it is chemically polymerized system comprised of a two paste system

what is photo (chemical) curing?

also known as light curing, it comprises of one paste only. the paste contains a photo sensitive chemical, such as camphorquinone (diketone), which absorbs visible light and hardens

what is dual curing?

combines light and chemical curing. they begin with the photochemical reaction and continues chemically

what are inhibitors?

they are prevent spontaneous polymerization, which increases the shelf life and working time of the material

what are pigments?

contains metal oxide pigments to provide composite with different shades and opacity to match the color and translucency of the tooth

what are inorganic fillers?

the dispersed phase, which is added to improve the strength, wear resistance and optical characteristics of the material

what are the advantages of inorganic fillers?

they decrease:

• polymerization shrinkage

• coefficient of the thermal expansion

• water sorption

what are the disadvantages of inorganic fillers?

increases viscosity

what are the types of inorganic fillers?

it is formed of inorganic silica either in:

• crystalline forms such as quartz

• non-crystalline form such as glass

why does most inorganic silica comprise of silicate glass now?

quartz silica is stronger and harder but more difficult to finish and polish

as filler particle size decreases, what increases?

polishability and wear resistance of composite

as the filler loading (% of filler content) increases, what occurs?

enhancement mechanical properties of composite

the ideal composite would be what?

highly filled with very small particles

why is loading composites with a large amount of small filler difficult?

they have a large total surface area and more resin is needed to coat the particles, making the composite very viscous and difficult to handle

what is the coupling agent used for?

bind the filler particles to the organic resin matrix. one end will bond to silica filler particles and form siloxane bonds with the hydroxyl (-OH) groups on the filler surface and the other end will bond with the organic matrix by copolymerizing with resin monomers such as Bis-GMA and UDMA

what are the functions of the coupling agent?

it binds filler to resin, allowing for proper stress transfer between them, which increases strength and rigidity as well as wear resistance of the composite

how does the coupling agent provide hydrolytic stability?

by preventing water from penetrating along the resin filler interface

how are resin composites classified according to size?

1. macrofilled composites

2. microfilled composites

3. hybrid composites

4. nanofilled composites

macrofilled composites

1. 75-80% inorganic filler by weight

2. average particle size is 8µm

3. large particle size and extremely hard filler

4. rough surface structure, strontium and barium glass making it radiopaque

microfilled composites

1. polishable

2. smooth lustrous surface similar to tooth enamel

3. particle size is 0.01 - 0.04 µm

4. contains 35-60% inorganic filler by weight

5. some of the physical and mechanical properties are inferior, good wear resistance

6. low modulus of elasticity, which allows the restoration to flex

7. high resin content results in an increased coefficient of thermal expansion and lower strength

what are microfilled composites used for?

• class I for low stress restorations

• class III for buccal and lingual surfaces

• class V

hybrid composites

1. combines the properties of conventional and microfilled

2. contains 75-85% inorganic filler by weight

3. particle size is 0.4-1 µm

4. physical properties is superior to that of conventional

what are hybrid composites used for?

it is used for moderate stress where strength and wear resistance is more important than surface luster:

• class I

• class II

• class IV

nanofilled composites

1. contains filler particles that are extremely small, 0.005-0.01µm (5-10nm)

2. because of these small particles are so small, manufacturers can pack a high amount of filler into the resin, resulting in good physical properties and esthetics

3. they are highly polishable

what are the types of nanofilled composites?

1. completely nanofilled resins

2. nanohybrid resins

completely nanofilled resins

contain nano-meter sized particles throughout the resin particles

nanohybridge resins

consists of large partials surrounded by nanometer sized particles

how are composites classified based on according filler loading and consistency?

• packable composite

• flowable composite

what is packable composite?

also referred to as high density or condensable composites, they are composites with high filler loading and large particle sizes, and they also have good fracture resistance

what are some disadvantages of packable composites?

• poor adaptation to cavity walls as well as between successive increments (layers)

• poor wear resistance due to large filler particles

what are flowable composites?

a low filled composite with low viscosity

what are the main advantages of flowable composite?

increased adaptability and elasticity

when are flowable composites used?

• cervical lesions (class V)

• as a liner/base under composite restorations to provide an elastic layer that can absorb polymerization shrinkage stresses

what are some disadvantages of flowable composite?

since they contain less filler:

• lower strength.

• lower hardness.

• lower wear resistance.

• inferior mechanical properties overall.

Therefore, they should not be used alone in large stress-bearing restorations.

how are composites classified based on the type of resin matrix?

1. regular methyl methacrylate resins matrix

2. silorane resin matrix

what is silorane resin matrix?

it is a recently introduced low-shrinkage composite is based on the silorane resin. it does not contain methacrylate resins. silorane resin is more hydrophobic than conventional methacrylate resin so this decreases wettability and adaptation

how is composite classified based on technique of polymerization?

1. chemical cure composite

2. light cure composite

3. dual cure composite

how is composite classified based on technique of packing?

1. incrementally packed composite

2. bulk-fill composite

what are some types of bulk-fill composite?

1. conventional consistency bulk-fill composite

2. flowable bulk-fill composites

what are the advantages of resin composite?

1. superior esthetic quality

2. satisfactory physical and mechanical properties

3. bond to the tooth using adhesive systems. adhesive bonding helps strengthen the remaining tooth.

4. conservative prep, more so than amalgam

5. has low thermal conductivity

6. easy to repair

what are the disadvantages of resin composite?

1. questionable adaptation to the tooth structure due to high polymerization shrinkage and poor wettability to tooth structure

2. may exhibit high occlusal wear in areas of high occlusal stress, especially in composite restoration of those replacing all occlusal contacts

3. hydrolytic instability in the oral fluids

4. high technique sensitivity

5. conventional composites lack anticariogenic (anti-cavity) effects by fluoride release

what are some indications for composite resin?

1. classes I, II, III, IV and V restorations

2. core buildups

3. conservative composite restorations (preventive resin restorations)

4. esthetic enhancement procedures such as veneers, tooth contour modifications and diastema closures

what are some contraindications of composite?

1. an operating area that cannot be adequately isolated

2. class V restorations that are not esthetically critical

3. patients with bad oral hygiene and high caries index

how does cavity preparation design for composite differ from amalgam?

rather than mechanical retention, it bonds to enamel and dentin using adhesives, so, its cavity design is more conservative

the adhesive cavity design is characterized by what?

1. preservation of tooth structure. the cavity outline is limited only to defective enamel and dentin, with no extension in depth or width

2. rounded line and point angles

3. beveled cavosurface angle. the enamel walls forming the boundaries of the cavity are beveled to a 45 degree short bevel

what is the advantage of a bevel in cavity design?

1. increases the surface area of enamel available for bonding, with better marginal sealing and stronger micromechanical retention

2. exposes the ends of the enamel rods rather than the sides which provides for a more retentive etching pattern with micropores in enamel prisms and macropores in interprismatic substance following acid etching

3. better esthetics because a beveled margin creates a gradual transition between the tooth and composite.

what can be made within the bevel?

small round indentations, or scallops, to further increase the surface area

when is a bevel contraindicated?

1. stress bearing areas such as occlusal surfaces of posterior teeth

2. in areas of composite if it is finished in thin margins to avoid chipping

3. the gingival wall since the enamel is very thin in this area and it will chip if it is beveled

how do amalgam and composite compare?

for cavity preparation, resin composite is relatively easy and less complex than amalgam. however, manipulation and steps of application of resin composite are more difficult and technique sensitive, requiring a meticulous and skillful operator to obtain a durable and successful composite restoration