cons sheet # 14 - Danah kanaan

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cons sheet # 14 - Danah kanaan

Post by Shadi Jarrar on 27/1/2011, 12:18 am

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Composite restorations



* Composite is a material that combines two different phases a matrix (organic polymer risen) in which a (inorganic) filler material is dispersed.

In 1962 Bowen developed a polymeric restorative dental material reinforced with silica particles known as composite.

Good mechanical properties are achieved when a strong bond between the organic resin & the inorganic filler is made which can be done by coating the filler material with sylane coupling agent.

The inorganic filler significantly enhances the physical properties of the composite by:

1. Increases its strength

2. Reduces the coefficient of thermal expansion (CTE)
The more the filler particles the less the CTE

3. Affects the surface roughness/ texture
We need a restorative material that provides a smooth surface in order to prevent retention of plaque & stains.

4. Adds radio-opacity ( to differentiate it from carries which are radio lucent)

5. Increases the viscosity of the material
The more filler particles the more the viscosity

6. Decrease the polymerization shrinkage ( most important & common problem encountered with composite restorations)
Usually the filler doesn’t shrink in contrast to the matrix which does, due to the fact that it’s a polymer so during its polymerization reaction it changes from a monomer to a polymer causing the shrinkage.
This shrinkage forms a gap between the wall of the cavity & the restoration which causes the restoration to become leaky & as a result recurrent caries.



** Classification of composite material:


I. Based on the size, content of the filler material ( three types )

a) Macrofill / conventional
b) Microfill
c) Hybrid


II. Based on the curing/ polymerization method:

a) Light cure ( one paste that polymerizes when exposed to light)
b) Self cure (two pastes base & catalyst)


III. Based on the viscosity :

a) Flow-able composite ( low viscosity)
b) Packable composite ( high viscosity)



Mcarofill / conventional composite

- Inorganic filler : 75-80 % by weight
- Average particle size : 8 micron
The large size & extreme hardness of the filler particles provides excellent physical properties but due to the fact that with time the matrix around the filler undergoes wear its causes surface roughness.

• clinical implications of rough surface restoration:
1. Discoloration
2. Not esthetical
3. Accumulation of plaque



Microfill composite

- Inorganic filler : 35-60 %
- Average particle size : 0.01 – 0.04 micron
- Not heavily filled so the amount of matrix will increase
- Physical properties are inferior to those of macrofill
• Note: Used only for class V because it won’t face a lot of occlusal stress & gives a very smooth surface which is desired near the gingival area.
It’s also a flexible, elastic material so if there were forces acting on the tooth’s root causing it to flucture/ move the composite will move with the tooth & not deboned.


Hybrid composite

- Inorganic filler: 75-85 % ( greatest % & very good physical properties)
- Average particle size : 0.4 – 1 micron
- The higher filler content makes hybrid composite superior in physical properties to both macrofill µfill, while the smooth will ensure smooth surface (though not smoother than the micro but its smooth enough).



Flow able composite

- low viscosity
- low filler content
- inferior physical properties ( strength, wear resistance)
- higher polymerization shrinkage
- easily handled
- favorable wet ability
Uses:
1. small class VI restoration
2. Pits & fissure sealants
3. marginal repair material
When a tooth restored with composite gets chipped at the marginal ridge
4. linear for conventional or hybrid composite



Packable composite
Composite with handling characteristics similar to composite

- rarely used but if desired for class II
- highly viscose
- low polymerization shrinkage
- Not superior to hybrid


Self cured composite

- Base & catalyst ( chemical reaction )
- Once mixed setting starts

Drawbacks:
1. limited working time
2. incorporation of bubbles during mixing
3. color instability


Light cured composite

- Most commonly used
- Longer working time
- Color stable
- Less porosity



** Physical properties:


I. Linear Coefficient of Thermal Expansion ( LCTE)
Is the rate of dimensional change of a material per unit change in temperature?

- The closer the LCTE of the material to the LCTE of the tooth structure, the less the chance to create an opening at the junction when temperature changes occur.
- Composite exhibits LCTE 3 times of that of the tooth structure. ( no material has the same LCTE as the tooth structure)

Note:
The Dr. asked whether amalgam has a higher or lower LCTE.
I googled it & it said that both have almost the same LCTE compared to the tooth structure! (Though not sure)

- Gaps will form but, we can avoid them by bonding to an etched tooth surface which reduces the negative effect resulting from the difference of LCTE between the tooth & the composite.



II. Water absorption
Is the amount of water absorbed per unit volume
- risen absorbs more water than filler
- the more the filler percentage the less water absorption




III. Solubility
Loss of weight per unit volume due to the solutions in the oral fluid.

- Most composites are not soluble




IV. Wear resistance
Material’s ability to resist surface loss as a result of abrasive contact.

- Affected by :
1. filler’s particle size & content
2. Location in dental arch ( posterior more, anterior less)
3. Surface texture ( smoothness of the restoration surface)

- Wear resistance necessary in poster teeth & occlusal surface
- Surface texture is important in anterior & gingival areas ( class V )



V. Modulus of elasticity
Measure of the stiffness of the material

- High modulus of elasticity  more rigid




VI. Polymerization shrinkage ( most important)

- Gaps could occur if the polymerization shrinkage is stronger than the bonding strength of the composite to dentine.
- A bond formed between composite & enamel is stronger than that formed with dentine so higher shrinkage will occur in dentine areas.
- When a composite restoration is well bonded to the enamel if shrinkage takes place a fracture will occur in the enamel instead of the junction area.
- To minimize the high stress of shrinkage :
1. Use incremental build up ( each increment not more than 2 mm)
2. soft start polymerization ( using light cured composite)
3. Stress breaking line ( using flow able composite)



• An important clinical factor is configuration factor ( C factor ) which equals :
Number of bounded surfaces / number of non-bounded surfaces

Examples: the C factor for

Class 1 = 5
Class 2 = 2
Class 4 = ¼
Class 5 = 5




• Indications for using composite:
1. Classes 16
2. Cement for crowns
3. Sealant & conservative cavities
4. Esthetic enhancement


• Contraindications for using composite :
a) absolute  isolation factor ( working area must be free of saliva & moisture)
b) relative  occlusal factor ( high stress areas)


• Advantages:
1. good esthetics
2. more conservative
3. low thermal conductivity
4. repairable ( can add to it )
5. bond to tooth structure ( less micro leakage, staining & reinforces tooth structure)


• Disadvantages :
1. polymerization shrinkage
2. time consuming
3. finishing & polishing is difficult
4. difficulty is establishing contact in posterior teeth
5. technique sensitive
6. wear
7. high coefficient of thermal expansion
8. expensive





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Danah kanaan









Last edited by Shadi Jarrar on 27/1/2011, 8:53 pm; edited 1 time in total
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Shadi Jarrar
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Re: cons sheet # 14 - Danah kanaan

Post by Dyala Al-Armouti on 27/1/2011, 8:11 pm

#14
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Dyala Al-Armouti

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