Composite Resins

Question 1

When were composite resins patented?

Answer 1

1960s

Although greatly improve performance in more recent times

Question 2

Name a challenge about composite resins

Answer 2

Technique sensitive

Question 3

Properties of ideal direct restorative material

Answer 3

Safe for dental team and patient
Aesthetic
Durable, chemically stable, tasteless
Poor conductor of heat
Minimal tooth prep
Easy to use
Cost effective

Question 4

Properties of typical composite resin

Answer 4

Safe if handled correctly (& used in correct location)
Aesthetic
Durable, chemically stable, tasteless
Porr conductor of heat (good insulators)
Minimal tooth prep (do not need undercut due to adhesive bonding strategies)
Technique sensitive (not easy to use)
Not cheap but highly effective (durable)

Question 5

What is a composite material?

Answer 5

Where two or more materials (metals, ceramics & glasses, polymers) are combined in such a way to produce improved properties
E.g. fibreglass is a tough glass-fibre reinforced polymer used in wide range of applications

Question 6

Composite ‘rules’

Answer 6

In a composite, component materials are largely unchanged by the presence of others (unlike a soln)
There must be some form of interfacial bonding between components (unlike a mixture)

Question 7

How do composites work?

Answer 7

Different components bring diff. properties to final material
E.g. fibreglass: thin glass fibre filler is strong but brittle, & polymer matrix is tough but flexible.
Additional toughness may be imparted by crack deflection. Fillers also change other properties e.g. light scattering.

Question 8

Composition of dental composite resins

Answer 8

Matrix component typically mixture of methacrylate resins (most commonly bis glycidyl methacrylate or bisGMA, but others as well)
Filler typically a silica (SiO2) powder
Modern dental composites usually contain a photoinitiator (most commonly camphorquinone)
-Polymer formed from monomers, filler and photoiniatiator (and some pigment), fillers become trapped in polymer matrix

Question 9

How is bisGMA formed?

Answer 9

By reaction of glycidyl methacrylate with bis-phenol A

Question 10

Rafael Bowen

Answer 10

Inventor of dental composite

-Reality more complex: key patents also held by ICI Ltd

Question 11

Setting

Answer 11

May set by chemical cure or light activation (polymerisation)
Chemical cure: 2 pastes mixed (an activator with free-radical initiator)
-this approach obsolete in restorative materials
Light activated systems contain a photoinitiator; setting initiated by exposure to appropriate lamp
-camphorquinone most common, activated at 470nm- hence visible blue light used

Question 12

Dental composite resins and water

Answer 12

Hydrophobic so need bonding system to adhere to hydrophilic tooth tissue
-no intrinsic ability to bond to tooth

Question 13

Cons of composites

Answer 13

Hydrophobic will not bond directly to hydrophilic dentine or enamel
Polymerisation shrinkage

Question 14

What has changed since 1960s in evolution of composites?

Answer 14

Way we cure the resins (initiation of polymerisation)
Size of filler particles
Bonding to tooth tissue

Question 15

What size fillers do we now use?

Answer 15

Nanofillers: 0.01 - 0.01p μm

We have moved down size over time

Question 16

Advantages of smaller filler sizes

Answer 16

> resistance to wear & potentially greater strength
ability to polish
translucency
Combined with changes in filler volume, potential to decrease polymerisation shrinkage

Question 17

Coupling agents

Answer 17

Improve adhesion of resin to filler surfaces to > strength and toughness
-chemically coat filler particle surfaces

Question 18

What are used to coat fillers?

Answer 18

Silanes have been used for > 50 years

Question 19

Disadvantages of silanes

Answer 19

Age during storage
Lose potency
Sensitive to water: water absorbed into composite restorations results in hydrolysis of silane bond and eventual loss of properties

Question 20

Common silane agents

Answer 20

Vinyl triethoxysilane

Gamma or 3-methacryloxypropyltrimethoxysilane

Question 21

Overcoming polymerisation shrinkage

Answer 21

It is inevitable
Risk of bulk placement:
-inadequate cure at depth
-weak or incomplete interface with tooth tissue = microleakage and secondary caries
Composites should be placed and cured in layers to reduce shrinkage and stresses, gives good marginal integrity

Question 22

Layering techniques

Answer 22

2mm is considered reasonable thickness of individual composite layer
Oxygen inhibition is an additional complcication

Question 23

Three phases in composite resin system

Answer 23

Organic phase (resin matrix)
Dispersed phase (inorganic filler)
Interfacial phase (coupling agent)

Question 24

Organic phase (resin matrix)

Answer 24

Monomer, initiator, inhibitors, pigments

Forms polymer backbone to provide tensile strength

Question 25

Dispersed phase (inorganic filler)

Answer 25

Glass, quartz, colloidal silica

Improves mechanical properties (wear and compressive strength) and decreases shrinkage

Question 26

Interfacial phase (coupling agent)

Answer 26

Provides adhesive bond between organic and dispersed inorganic phases

Question 27

Resin monomers in composites

Answer 27

The main resin monomer in all composites is bisphenol A-glycidyl methacrylate (bisGMA)
Other monomers are added, for example to reduce viscosity and improve mixing:
-triethylene glycol dimethacrylate (TEGDMA)
-urethane dimethacrylate (UDMA)
It may be that new resin monomers will be incorporated in future innovations

Question 28

How do composites set?

Answer 28

Free-radical polymerisation

-leads to polymerisation shrinkage

Question 29

Photo initiators

Answer 29

e.g. camphorquinone
Diff manufacturers today utilise range of photoinitiators in their products
Intended to aid efficiency of photoinitiation of polymerisation, and should match output of light curing unit

Question 30

When did the first composites enter dental market?

Answer 30

1960s

• early versions were macrofilled composites
• high wear rate, polymerisation shrinkage, technique sensitivity (bad)

Question 31

Development of microfilled composites

Answer 31

1970s

• increased wear resistance, more highly polishable surface
• technique sensitive

Question 32

Introduction of hybrid composites

Answer 32

By mixing of filler particles of various sizes

-improved mechanical properties, good polishability

Question 33

Introduction of nanofilled composites

Answer 33

Early 2000s

• with dispersed nanoscale filler
• simplified but effective bonding systems reduced sensitivity and impvoed clinical success

Question 34

Claimed advantages of nanofilled over conventional composites

Answer 34

Potentially superior fracture toughness, high strength, and excellent wear resistance
High polishability and low polymerisation shrinkage
> continuity between nanoscopic tooth structure and nonfillers to provide more stable and ‘natural’ interface
> surface to volume ratio allow high filler loading to give workable consistencies
Nanosized fillers are able to scatter or absorb visible light which increase translucency