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BaB > L2 - Resin based composites > Flashcards

L2 - Resin based composites Flashcards

1
Q

What is resin based composite

A

type of synthetic material that is used in dentistry for restorative or adhesive purposes

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2
Q

Two components of RCs

A

Organic resin and inorganic filler particles

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3
Q

big con of using amalgam when directly restoring in the mouth

A

you have to cut into the tooth, making line cuts so the amalgam can be filled in. This means the tooth tissue is filed away

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4
Q

reasons on increasing demand for RCs in general

A
  • Aesthetic
    -It is a minimally invasive as it can be cemented on top rather than cutting into the enamel
    -Environmental concerns over mercury pollution from using silver amalgam
    -Claims over mercury poisoning / cytotoxicity so people got scared
    -Banned the use of mercury in all industries in EU
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5
Q

2 types of dental restoration and meaning

A

Direct restoration - directly repairs in the mouth
Indirect restoration - - do the repairs outside of the mouth then put in the mouth using adhesives

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6
Q

why are RCs useful

A
  • Restores function
  • Replace parts of missing teeth
  • Aesthetics
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7
Q

Resin composite is comprised of several components which are?

A
  • an organic resin polymer matrix,
  • inorganic filler particles,
  • silane coupling agent
  • initiators/accelerators pigments
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8
Q

what is PMMA

A

Polymethyl methacrylate is a polymer used in dental restorations like dentures

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9
Q

advantages of using PMMA

A

 Non degradable – doesn’t break down
 Easy to manipulate the shape
 Biocompatible
 Excellent optical properties purposes

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10
Q

how is PMMA biocompatible

A

tasteless,
odourless,
non-toxic,
non-irritating,
resistant to microbial colonisation

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11
Q

what does it mean by having excellent optical properties

A

it can easily be cured by the light. Likewise, it can be translucent for aesthetic purposes

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12
Q

What are the cons of using PMMA

A
  • High exo reaction
  • Poor mechanical properties
  • Absorbs water
  • Polymerisation shrinkage
  • Large thermal coefficient of thermal expansion
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13
Q

what does it mean by polymerisation shrinkage

A

the monomers in the resin are polymerised, removing water and creating double carbon bond. This reduces the net volume of the resin

This could lead to gaps around the restoration.

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14
Q

what does it mean by Large thermal coefficient of thermal expansion

A

the mouth experiences hot and cold temperatures when eating or drinking. The material will contract or expand due to its fluctuating temperatures. This could lead to gaps and cracks in the dental restoration

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15
Q

why is it that its bad to have high exo reaction

A

if there is a direct restoration in the mouth, the polymerisation reaction of PMMA gives out heat, leading to possible damage and necrosis of the tissues.

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16
Q

What is MMA

A

Methyl Methacrylate (MMA) is the monomer of PMMA

17
Q

pros of using MMA

A

Colourless liquid (important for aesthetics)
Immiscible with water but miscible with organic solvents

18
Q

cons of using MMA

A
  • Irritant > can cause contact dermatitis
  • High coefficient of thermal expansion
  • High shrinkage on curing
  • Exothermic process (54.3k – J/mol)
  • High curing temperatures (necrosis of tissues)
19
Q

what did bowen invent for compossite resin

A

Bis-GMA and filler agents

20
Q

whats the structure of Bis-GMA

A

Bis-GMA is a monomer with methyl methacrylate groups bound to the Bisphenol (Main) structure

21
Q

why MMA groups are added to the Bis-GMA

A

improves bond strength and stability. There were some methyl group in the Bis structure which made it difficult to rotate so the material is quite stiff and needed high energy to break the structure

22
Q

what are the problems of using resins

A

it has high viscocity due to high proportion of H bonds. This made the loading of filler particles more difficult. It is also sticky and hard to manipulate

23
Q

why is the loading of filler particles into the resin important

A

It provides mechnical properties against stress.

24
Q

how can we reduce the visocity of the resin

A

using viscosity controllers

25
Q

what are monomers that can be used in the resinmatrix and which ones are base monomers and viscosity controller

A

Base monomers:- have high MW and viscosity
Bis-GMA
BisEMA
UDMA

Viscosity Controllers: - have low MW and visocity
MMA
EGDMA
TEGDMA

26
Q

Components in the organic resin matrix

A

Base monomer
Visocity controllers
Inhibitor
Pigments, dyes (inorganic)
Activator (light) and (photo)intiator

27
Q

why is an inhibitor added to the resin matrix in RCs?

A

Inhibitor like Hydroquinone reacts with any free radicals to form stable compounds so it doesn’t initiate the polymerisation reaction beforehand.

Rdaical can be formed by normal light, radiation or heat in normal setting

28
Q

two types of curing in regards to activitor and initiator

A

Chemical cure
Light cure

29
Q

how does a chemical cure work

A

two paste composites are mixed together which harden the material

30
Q

cons of using chemical curing

A

-Introduces porosity when mixing the cure which could leads to gaps
- reduced mechanical properties
Limited working time

31
Q

pros of using Light curing

A

-no mixing needed
-Increased working time
-increased colour stability
-improved mechanical properties
- only activated by the visible blue light /UV light

32
Q

Cons of using just resin

A
  • poor mechanical properties
    -poly shrinkage
    -high coefficient of thermal expansion
    wateruptake
    concerns over cytotoxicity (claims unfounded)
33
Q

How can we improve so we can overcome the disadvantages of just resin

A

Using Composite resin

34
Q

what is A composite

A

a Material that has two different phases where they have different properties

or i.e a combo of two chemically different material

like stainless steel (its a metal and ceramic mixed together)

35
Q

why is a coupling agent important in RC

A

provides chemical bonds between the resin and filler particles which could resist cracks and gaps in the restoration

36
Q

advantages of having filler-resin bonds

A

-more flexible whilst putting stress on filler particles
-improves physical and mechanical properties
-prevent water penetration int he material

37
Q
A

BaB (4 decks)

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