L2 - Resin based composites Flashcards
What is resin based composite
type of synthetic material that is used in dentistry for restorative or adhesive purposes
Two components of RCs
Organic resin and inorganic filler particles
big con of using amalgam when directly restoring in the mouth
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
reasons on increasing demand for RCs in general
- 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
2 types of dental restoration and meaning
Direct restoration - directly repairs in the mouth
Indirect restoration - - do the repairs outside of the mouth then put in the mouth using adhesives
why are RCs useful
- Restores function
- Replace parts of missing teeth
- Aesthetics
Resin composite is comprised of several components which are?
- an organic resin polymer matrix,
- inorganic filler particles,
- silane coupling agent
- initiators/accelerators pigments
what is PMMA
Polymethyl methacrylate is a polymer used in dental restorations like dentures
advantages of using PMMA
Non degradable – doesn’t break down
Easy to manipulate the shape
Biocompatible
Excellent optical properties purposes
how is PMMA biocompatible
tasteless,
odourless,
non-toxic,
non-irritating,
resistant to microbial colonisation
what does it mean by having excellent optical properties
it can easily be cured by the light. Likewise, it can be translucent for aesthetic purposes
What are the cons of using PMMA
- High exo reaction
- Poor mechanical properties
- Absorbs water
- Polymerisation shrinkage
- Large thermal coefficient of thermal expansion
what does it mean by polymerisation shrinkage
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.
what does it mean by Large thermal coefficient of thermal expansion
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
why is it that its bad to have high exo reaction
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.
What is MMA
Methyl Methacrylate (MMA) is the monomer of PMMA
pros of using MMA
Colourless liquid (important for aesthetics)
Immiscible with water but miscible with organic solvents
cons of using MMA
- 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)
what did bowen invent for compossite resin
Bis-GMA and filler agents
whats the structure of Bis-GMA
Bis-GMA is a monomer with methyl methacrylate groups bound to the Bisphenol (Main) structure
why MMA groups are added to the Bis-GMA
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
what are the problems of using resins
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
why is the loading of filler particles into the resin important
It provides mechnical properties against stress.
how can we reduce the visocity of the resin
using viscosity controllers
what are monomers that can be used in the resinmatrix and which ones are base monomers and viscosity controller
Base monomers:- have high MW and viscosity
Bis-GMA
BisEMA
UDMA
Viscosity Controllers: - have low MW and visocity
MMA
EGDMA
TEGDMA
Components in the organic resin matrix
Base monomer
Visocity controllers
Inhibitor
Pigments, dyes (inorganic)
Activator (light) and (photo)intiator
why is an inhibitor added to the resin matrix in RCs?
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
two types of curing in regards to activitor and initiator
Chemical cure
Light cure
how does a chemical cure work
two paste composites are mixed together which harden the material
cons of using chemical curing
-Introduces porosity when mixing the cure which could leads to gaps
- reduced mechanical properties
Limited working time
pros of using Light curing
-no mixing needed
-Increased working time
-increased colour stability
-improved mechanical properties
- only activated by the visible blue light /UV light
Cons of using just resin
- poor mechanical properties
-poly shrinkage
-high coefficient of thermal expansion
wateruptake
concerns over cytotoxicity (claims unfounded)
How can we improve so we can overcome the disadvantages of just resin
Using Composite resin
what is A composite
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)
why is a coupling agent important in RC
provides chemical bonds between the resin and filler particles which could resist cracks and gaps in the restoration
advantages of having filler-resin bonds
-more flexible whilst putting stress on filler particles
-improves physical and mechanical properties
-prevent water penetration int he material
