Dental Composite



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Dental material

Lec. 5


9-3-2011
Dental Composite
Definition: tooth color restorative material
It has advantages and disadvantages we will talk about them later on.
Application of dental composite
1- Fractured tooth

2- Caries legion

3- Spacing between teeth


Scientifically, it defined as:
Products which consist of two distinct phases normally formed by blending together result in a compound have different structures and properties.
*note that the sitting reaction of composite is polymerization.
Composite mean more than one phase or material
*Why do we mix them together?

To achieve some properties this cannot be achieved from either of the

component by itself.

History

They were developed in the 1960s (relatively new) once they evolved they replaced quickly over the tooth color restorative materials such as fabricate restoration and acrylic resin restoration.


Fabricate and acrylic resin restoration can be near from normal tooth color but they are not good as composite.
Nowadays, people turn to use composite than silver filling because they want to look nicer.
Component of composite:
1-Matrix

2- Fillers
Matrix

- Its resin material

- Its main property is stickiness

- Just to bind the fillers togather

-Help to fix the composite on the tooth structure.

- Its not a cure chemical bonding its a micro-chemical bonding



Fillers

- They are added to the matrix just to reinforce the matrix.

Because the matrix by its self is a weak phase.

* The matrix by its self has 4 different elements:




  1. principle monomer

  2. diluents monomer

  3. activator /initiator system

  4. Celine coupling agent

* Principle monomer is one of two things:




  1. bis GMA (bisphenol A glycidyl methacrylate)

  2. UDMA (urethane dimethacrylate)

These the two main monomer we use for the composite


* diluent monomer:

- It dilutes the viscosity of the principle monomer.


Since the principle monomer is very viscous by its self, we need something to reduce its viscosity. Thus, is achieved by the diluent monomer which is commonly is TEG DMA (triethylene glycol dimethacrylate)

* The functional group of both the principle and the diluent monomer is carbon-carbon double bond


Remember! When there is a monomer with

Carbon-carbon double bond, it will turn into single bond through polymerization.

* Activator/ initiator system

They are 2 different ways to initiate the polymerization:


1- Light cure system

2- Chemical cure system

(we will talk about them later on)
* Celine coupling agents:
- Its aim is to bind the fillers to the matrix

*Polymerization reactions:


They are two types of reaction:


  1. additional polymerization: the double bond is change into single bond but there is no byproduct




  1. condensation polymerization: the double bond is released with a byproduct


advantages of the matrix;
1-it’s the moldable phase of the composite. Because it allow the filling material to take the shape of the tooth or the shape we want it to be
So, the matrix can be shaped but the fillers can't be shaped


  1. This moldability is happened at ambient temperature (room temperature)

Disadvantages of the matrix:


  1. matrix phase are many and it’s the weakest phase

  2. it has low-wear resistance

Because inside the oral cavity, the teeth are moving against each other, eating process and food bolus are there. This will affect the tooth and the filling material


 If the amount of the matrix is big, there will be too much wear on the composite and that will decrease the life time of the filling material inside the oral cavity.
So, it should stayed dimensionally the same so that it can be durable


  1. Another problem of the matrix is that it absorb water.

This will change its size, weak it and change the physical property of the filling material.




  1. its stain and discolor

Stain come form chocolate and coffee. It enter the matrix with water
More matrix phase  more discoloration
To avoid the discoloration of the matrix, manufacturer try to decrease the matrix phase and increase the filler content

Type of fillers


  1. naturally exciting fillers : quartz, its very hard, inert and it doesn’t react in the oral environment (chemically stable)




  1. synthesizing fillers: bio engineer glass

we manufacture them and modify them to a certain size and shape for

using in the oral environment


Advantages of fillers


  1. decrease the negative properties of the matrix

adding more fillers more hardness of the composite and that hardness with more wear resistance




  1. decrease the co-efficient of thermal expansion

Co-efficient of thermal expansion is: a unit change in length of the filling material related to the unit change in temperature

Because the temperature in the oral cavity is not static, we need a material with co-efficient at least matching the tooth structure


If there were no matching, the tooth expansion and contraction in different rate will result in gapping between the restorative material and the tooth structure
Gaps mean space and microleakage like saliva and bacteria and that will result in caries and sensitivity of the patient tooth.


  1. decrease the setting contraction

during polymerization, composite material will decrease in mass ( contraction upon setting)


So, adding more fillers, will decrease the contraction
4- fillers particles can be modified to have the optimal characteristics, we can make them more opaque or more translucent
Caries

Dental caries are either on the tooth structure or between the composite and the tooth structure. No caries on the composite


Lactic acid for example, is a byproduct of bacteria. It demineralizes the tooth structure but doesn’t do anything with the composite

* Composite come in tubes or syringes from the manufacturer that contain monomers, diuent, coloring agents and other chemical substance participate in the reaction



The only thing that we do at the clinic is to initiate the reaction.
The type, concentration, particle size and particle size distribution of the fillers affect the physical and the mechanical properties of the composite.
Classifying of the composite
The finishability of the composite is determined by the filler content. So, classifying of the composite is according to the size of the filler particle but more less in the matrix



  1. large size filler particle: affect the surface finish of the composite and make it rough




  1. Small size filler particle: make a very smooth surface finish of the composite

we can add more filler to a composite with small size particle. Because, the more the content, the good the physical property of the composite



*wear resistance
Also depend on the size of the particle
1- Big fillers particle on the surface : friction with the tooth structure and/or food bolus will result in removing these large filler particle from the matrix huge dimensional change
2- Small filler particle on the surface: because they are small and tightly packed together, the wear developed is the same degree on all particles. Thus, will not removed the particle from the matrix and will resist the wear on the surface and the surface loss will be less than that of the 1st case
.
Composite can be prepared by:


  1. chemical cure system

  2. light cure system

  3. dual cure system(both chemical and light)



Chemical cure system


Comes in two jars or two different paste on have the activator and the other have initiator
The activator is usually tertiary amine (dimethyl-p-toludine) and the initiator is benzoyl peroxide

.
They come in two different color so that we can know if the proper mixing happened or not and that is by getting a one homologous color when mixing.


It’s a chair side mixing

chair side mixing mean that while the patient is on the chair and his/her tooth is ready for filling, we do mixing the material and apply it in patient mouth


We also have an inhibitor in the system to inhabit the polymerization reaction
once we mix the two paste together, polymerization begins and the material start to get harder that we will not be able to shape it or even put it in the oral cavity
 So, we use the inhibitor to expand the working time so that we can put it in the oral cavity and shape the way we want.

Both the inhibitor and the initiator produce free radicals. These radicals will de stabilize the double bonds in the composite

.

The inhibitor doesn’t react with the double bond till the initiator come.



So, the affinity of the inhibitor is higher than the initiator


Disadvantages of chemical cure system
During mixing the two paste, there is a chance of the air bubble to be incorporated in the reaction and this will weaken the material

Light cure system

Its one paste material and there is no chair side mixing

So, we directly use it from the tubes to the oral cavity and
Polymerization starts once we cure it with the light. So it has an expanded working time
Since there is no mixing, the paste in this system is thicker(more fillers) and that’s mean a stronger restoration
 light cure material are stronger than the chemical cure material because of two reasons:


  1. more fillers

  2. no mixing(since mixing may be incorporated with air bubbles)

The light used in this system has a certain characteristics. The most important is the weave length.


The wave length of the light should match the initiator in the light cure system
the commonly used initiator in the light cure system is diketone Anthraquinone which is activated by the blue visible light of a wavelength of 470 nm


Visible light curing unit


As the light is very bright, direct viewing of the light source will damage the human eye even indirect viewing is contraindicated. Avoiding the light is achieved by the yellow protector and there are also specific type of glasses the dentist can wear to avoid this kind of damage

We said before that the inhibitor expand the working time

In addition to that, it extend the storage life time


 most of the material are not used immediately but within 6 months to 1

year. So, as long as its stored, we don’t want any polymerization. This

would come from any accidental light that will not result in a complete

polymerization but it will decrease its plasticity


Notice that complete polymerization is only achieved with the proper light

curing
Depth of cure


It’s a certain depth of the composite that the light can penetrate through
If we were using too much composite, the light will not reach the deep part of it.

The depth of cure is usually 2mm

It depends on:


  1. Type of the composite we use

  2. Time of light exposure

  3. Shade of the composite (shade composite required more exposure time because they are pigmented

We said before that the depth of cure is usually 2mm. So, Any depth is more than 2mm will not be cured


Sometimes, we may have 6mm depth. This problem is solved by the incremental addition of the composite (adding the composite layer by layer)


The thickness of each layer is determined by the depth of cure and each layer is cured with the light separately
Advantages of the incremental addition :


  1. assure adequate polymerization

  2. minimize polymerization shrinkage

the shrinkage of each layer is compensated from the next added layer


composite with much shrinkage develop more stress on the wall of the tooth
composite shrinkage is approximately 2% and its occur after polymerization takes place

No spacing result from the incremental addition as it happened in case we put the composite as one piece


Air inhibition
When polymerization is completed , the surface layer(outer layer) of the composite is in direct contact with the atmosphere and that will result in inhabitation of polymerization of this layer because of the O2 in the atmosphere

It occur in both system (chemical and light cure system)


The air inhabited layer help in bonding the layers together
How..?!

In incremental addition when we make a curing for the 1st layer, this will result in an inhabited layer on the surface of this layer which will result in a double bond still un reacted. Adding the 2nd layer which is also still having the double bond unreacted will react with the previous one and bind to it


The last layer added in incremental addition will still unreacted

( inhabited layer). So, to avoid that we cover it with a protective layer that should be translucent (transmit light). This layer is usually known as a miller strip.

The miller strip should be removed after polymerization. Because we only want the filling material to be in the oral cavity and by doing that we eliminate the inhabited layer
Another way to get rid off the inhabited layer, is by building the composite slightly more and then we removed the extra inhabited layer so that we only have a completely polymerized composite
We can differentiate the inhabited layer by feeling it which appear softer because its un cure and sticky and slimy

In case we have a fracture in a very old filling and we want to repair it. 1st, we should know in polymerization not all the double bond in the composite is turned into single bond. Only 50% of the double bond will turn into a single bond and the other 50% will still unreacted.


As long as we have double bond in the composite, we still have the ability to add more composite
Its one of the advantages of the composite being an additive material . this known as a DGREE OF CONVERSION.
Shade of composite
Depending on the fillers product, there are two types;


  1. more-opaque used to hide the natural tooth color

  2. more-translucent  may result in blue color staining on the composite

We usually use a translucent composite for the insical edge.


How to detect the composite restoration..??!
Clinically, it feels softer than the enamel
When Taking an x-ray photo of a tooth, we will see some areas are dark (transmit light) and other areas are white (reflex light)
The white color area called radio-opaque

The black color area called radio-lucent



Usually, caries appear radio-lucent while composite appear radio-opaque (by adding a barium and/or heavy element on the filler particles of the composite)


Again, we should remember that the Fillers are the most important determinant of the physical and chemical property of dental composite.
يتـــبع.....
Done by: Mohammad Al-Garalleh


Good luck


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