Composite Resin

Question 1

What are composite?

Answer 1

A solid formed from two or more distinct phases that have been combined to produced properties superior to or intermediate to those of individual constituent.

Question 2

Uses of composite ? 7

Answer 2

1. Direct or indirect restorative material
2. Fiber reinforced composite posts
3. Luting agents
4. Core build up in post endodontics restoration
5. Pits and fissure sealants
6. Bonding of orthodontics brackets
7. Splinting of mobile teeth

Question 3

Basic composition?

Answer 3

1. Matrix- continous phase
2. Filler- dispersed phase
3. Coupling agents

Question 4

Other constituents of composite?

Answer 4

1. Activator-initiator
2. Pigments
3. inhibitors
4. UV absorbers

Question 5

What is dental resin based composite?

Answer 5

Dental resin based composite is structure composed of three major components : a highly cross-linked polymeric matrix reinforced by a dispersion of glass, mineral or resin filler particles and/or short fiber bound to the matrix by coupling agents.

Question 6

What is resin matrix?

Answer 6

The resin matrix in most dental composite is based on a blend of aromatic and/or aliphatic dimethacrylate monomers such as bis-GMA and urethane dimethacrylate (UDMA)to form highly cross-linked,strong, rigid and durable polymer structures.

Question 7

Most widely used resin matrix?

Answer 7

1. Aliphatic / aromatic dimethyl acrylate monomers-Bis-GMA
2. TEGDMA
3. UDMA

Question 8

Most recently used resin matrix?

Answer 8

Silorane monomers

Question 9

Example of high density monomers?

Answer 9

1. BISGMA

2. UDMA

Question 10

advantages of high density monomers.

Answer 10

1. Low polymerisation shrinkage due to large molecular volume of this monomer
2. High cross linking improved properties
3. High strength and rigidity

Question 11

Disadvantages of high density monomer?

Answer 11

Due to high density these monomers are viscous and difficult to manipulate

Question 12

How to overcome the high density monomers viscosity?

Answer 12

TEGDMA(dilutent monomer) + BISGMA(viscous) -> decrease viscosity ->easy to manipulate and paste like consistency

Question 13

Functions filler

Answer 13

1. Improve the mechanical properties
2. Decrease polymerisation shrinkage
3. Decreases thermal expansion and contractions
4. Decrease water sorption
5. Radioopacity
6. Control of workability/viscosity

Question 14

Examples of fillers?

Answer 14

1. Quartz
2. Silica
3. Glasses with heavy metals
4. fluoride releasing fillers

Question 15

Properties of quartz?4

Answer 15

• chemically inert
• very hard and difficult to grind
• difficult to polish
• abrades opposing tooth

Question 16

Properties of silica? 2

Answer 16

• less harder than quartz

- non crystalline structure

Question 17

Properties of glasses with heavy materials?4

Answer 17

• radio opaque
• less inert
• slowly leach out
• shorter lifetime

Question 18

Characteristics of fluoride releasing fillers

Answer 18

• ability to release fluoride

- Ytterbium trifluoride and Ba-Al-fluorosilicate

Question 19

Effect of filler size and distribution?

Answer 19

• the composite properties are improved to a great extent by increasing the filler loading
• this can be achieved by particle and distribution

Question 20

Filler size and aesthetics

Answer 20

Larger particles> scattering of light> opacity> decreasing curing depth > rough surface texture > stains, plaque

Small particle > less scattering light > less opacity > increase curing depth > smooth surface texture > higher aesthetics

Question 21

Classification by filler particles size

Answer 21

1. Macrofilled
2. Small (fine) particle composite
3. Midfilled
4. Minifilled
5. Microfilled composite
6. Hybrid composite
7. Nanofilled composite

Question 22

What is the function of coupling agents?

Answer 22

• These bond the filler particles to the matrix
• improves properties of resin
• prevent leaching

Question 23

How coupling agents improves properties of resins?

Answer 23

They improve properties of resin by transferring stresses from plastic resin matrix to stiff filler particles

Question 24

Most commonly used coupling agent?

Answer 24

Organosilanes-gamma methacryloxypropyl trimethoxysilane

Question 25

What is the used of activation/initiations system?

Answer 25

Both monomethacrylate and dimethacrylate polymerise by the addition polymerisation mechanism initiated by the free radicals. Free radicals can be generated by chemical activation or by external energy activation.

Question 26

Most common photoinitiator?

Answer 26

Camphorquinone

Question 27

Characteristics of camphorquinone?

Answer 27

- most common photoinitiator - absorbs blue light - 400-500nm range

Question 28

How visible light activates?

Answer 28

- initiator reacts with amine activator - form free radicals - initiates addition polymerisation

Question 29

Types of polymerisation mechanism?

Answer 29

1. Chemically activated | 2. Light activated

Question 30

How chemically activated resins supplied?

Answer 30

Chemically cured composites are supplied as two pastes, one of which contains the benzoyl peroxide initiator and the other an aromatic tertiary amine activator.

Question 31

Mechanism of chemically activated resin

Answer 31

-when the two paste are mixed together the amine reacts with the benzoyl peroxide to form free radicals and addition polymerization is initiated.

Question 32

How the addition polymerisation occurs?

Answer 32

``` 1. Induction A. Activation B. Initiation 2. Propagation 3. Chain transfer 4. Termination ```

Question 33

Advantages of chemically cured composite?

Answer 33

1. Convenience and simplicity 2. Long term storage stability 3. Manipulation of working / setting time by varying proportion 4. Degree of cure equal through out if mixed properly 5. Marginal stress build up during curing is much lower than for photocured due to slower cross linking

Question 34

Disadvantages of chemical cured composites

Answer 34

1. Mixing causes air entrapment leading to porosity which might weaken the material and increase staining 2. Aromatic amine accelerators oxidise and turn yellow with time-colour instability 3. Difficult to mix evenly

Question 35

Two types of light used in light cured resins

Answer 35

1. UV light | 2. Visible light

Question 36

Characteristics of uv light cured

Answer 36

- used before - limited penetration of light into resin - lack of penetration through the tooth structure - caused damage to retina

Question 37

What kinds of paste in light cured?

Answer 37

Single paste

Question 38

What contain in the single paste of visible light cured composite ?

Answer 38

-photoinitiator A. Camphorquininone-0.2 wt % B. Dimethyl aminecethyl metacrylate 0.15 wt % - amine accelator

Question 39

How polymerisation occurs in light cured composite?

Answer 39

1. Exposure to light(400-500nm) 2. Excites photosensitizer 3. Photosensitizer reacts with amine 4. Free radical formed 5. Addition polymerization starts

Question 40

Advantages of light cured composites?

Answer 40

- no mixing needed - no aromatic amine accelerator , thus greatly improved colour stability - ‘command’ setting (upon exposure to an intense blue light). This means that working time is controlled, at will , by the clinician - small increment of composite can be polymerised at a time allowing the use of multiple shades within a single restoration and accommodations for shrinkage within each increment as opposed to bulk shrinkage

Question 41

Disadvantages of light cured composite?

Answer 41

- limited cure depth :necessary to build up in layers of about 2mm - marginal stress buildup during curing is much higher in self cured resin - mildly sensitive to normal room illumination - special lamp is needed to photo initiate curing - poor lamp accessibility in posterior and interproximal areas,require extra exposure time - darker shades require longer exposure time

Question 42

Factors involves in photocuring?

Answer 42

``` 1. Curing lamps A. LED lamps B. QTH lamps C. PAC lamps D. Argon laser lamps 2. Depth of cure and exposure time 3. Safety precautions ```

Question 43

Amounts of photon absorbed by initiators depend on

Answer 43

- wavelength - light intensity - exposure time

Question 44

Curing depth should be kept

Answer 44

2-3mm

Question 45

Exposure time depend on

Answer 45

Intensity of curing unit | -higher the intensity lesser the exposure time