8 - Dental Composites: aesthetic restorative materials Flashcards
LOs
Composite restorative materials
Examples of where composite restorative materials are used?
1
what are dental composites made from/ how many materials
2
what happens to the characteristics of the constituent materials on combining them
1
- 2 or more constituent materials
- that are not miscible and have significantly different physical or chemical properties
2
- On combining the two, the resultant material has characteristics different from the individual components
- usu have better properties than individual components
COMPOSITE RESTORATIVE MATERIALS
Indications + contraindications?
1
reasons why composite is so widely used in restorative dent?
(Advantages?)
2 - EXTRA INFO
recommended types of resin composite for:
- Class 1&2
- Class 3&4
- cervical lesions
Dental composites
What are the Major constituents?
What are the minor constituents?
resin phase of dental composites
1
what do they consist of?
2
commonly used monomers in dental composites
- structure
- consistency (hard to mix with filler particles?)
DILUENTS
1
Examples of diluent monomers
2
why may they be added to resin monomers (EG Bis GMA)
3
function of diluent monomers
See slide 8
Viscosity modifiers (diluent molecules)
1
function
2
What is the effect of cross linking
- Have low molecular weight
- can also act as cross linking agents
Effect of cross linking: a cross linked polymer is generally stronger and total water uptake/interaction with fluid is minimised
MINOR COMPONENTS
1
EGs
2
What does an inhibitor do?
3
EG of common inhibitors
Colours are added to give rise to a variety of shades
Stabilisers - help for storage
FILLER PARTICLES IN DENTAL COMPOSITES
1
Usu made from?
2
How do the filler particles influence the properties of the composite
3
What size filler particles are usu used in composites
4
Advantages/ benefit of using filler particles in composites (IMAGE)
- major constituent of dental composites
1
- quartz
- fusillica
- other glasses such as aluminosilicates or borosilicates
2
- type, conc + size of filler + particle size distribution all help determine the properties of the composite
3
- usu use smaller filler particles in dent composites to improve properties of composite
- modern composites are all hybrid composites - blend of diff sized filler particles
- can range from 5-10 microns and are blended with sub-micron particles
- this blending allows improvement in efficiency of filler loading
4
ADDITONAL benefits mentioned to the pic:
-Increasing filler content - coefficient of thermal expansion decreases so higher filler content in composite, the net coefficient of thermal expansion will be much lower and easier to match with tooth tissue but still mismatch with the tissue - can lead to percolation of fluids down the margins when pt consumes hot or cold liquid - can eventually lead to marginal leakage and failure
- improves surface hardness - Higher filled composites preferred over composites with low filer content
Resins typically soft whilst inorganic fillers eg quartz or silica have high hardness so blending of two to form the composite helps to improve the surface hardness of the composites
Also mentioned refractive indices (slide 12)
SILANE COUPLING AGENTS
1
Why do we use silane coupling agents
2
How do they help this?
EXTRA INFO FOR UNDERSTANDING
- dental composites comprise of an inorganic filler + organic polymer matrix
- so there is no inherent affinity between these two distinct phases
- it is v important to improve ashesion of the filler with polymer matrix to avoid debonding in service
- to do so, molecules that are bifnucional such as silane coupling agents is used to treat the filler particles
IN RH image
- filler particles have been treated with this molecule - one end of molecule has a carbon carbon double bond
- other end has 3 hydroxyl groups attached to silicone
(This is commonly used silane coupling agent)
- when you interact this molecule or condense it with inorganic particles , the hydrophilic end condenses with the inorganic particles
- when polymerisation occurs, this group undergoes polymerisation
Overall
- have enhanced adhesion between the ceramic phase (inorganic phase) and organic phase
PHOTOINITIATORS
1
Most common one used? (Colour)
2
What colour and range of light does it absorb?
3
How does it work?
4
Does the colour of the photo-initiator effect the colour/ shade of the composite?
5
EXTRA
- minor but important constituent in dental composites
4
No
Dental composites: SETTING REACTION
1
Type of reaction?
2
How may the free radicals be generated?
3
2 types of curing reactions
1
- free radical addition polymerisation reaction
- Methacrylates undergo addition polymerisation
2
- heat
- light
- chemical activation
3
A - CHEMICAL REACTION
B - PHOTOINITATORS
Dental composites: SETTING REACTION
1
What do chemically activated reactions comprise of
2
How do chemically activated reactions work?
Don’t know whether madeeha has put correct answers so need to google nad check slide 15
1
- Two paste systems
- PASTE 1 = initiators such as benzoyl peroxide BPO
- PASTE 2 = Amine
2
- reaction starts as soon as 2 are mixed + produce free radicals + polymerisation commences
- limited working time (ISO standards = recommended of at least 90 seconds)
- rate of set is uniform throughout the bulk of the material causing a gradual rise in viscosity @ room temp
EXTRA
- ISO recommends that these materials should form a hard solid within 5 minutes at 37 degrees (as being set in mouth
Dental composites: SETTING REACTION
1
What do photo-initiated reactions comprise of
2
Disadvantage of camphorquinone
3
Alternatives to camphoriquinone
4
What is the matrix phase?
1
- One paste system
- photoinitiators such as camphorquinone
- amine activator in the same paste
2
- is a bright yellow solid present
- hard to obtain different shades
3
trimethylbenzoyl-diphenyl-phosphine oxide (TPO) is being currently tested as an alternative and some composites are using a combination of the two
4
- ‘Matrix’ is the phase formed on polymerisation of the methacrylate monomers
- weakest + least wear resistant phase
- can absorb fluids
- is responsible for shrinkage and thermal properties are of importance to suit dental applications
EXTRA
- don’t halve a limited working time
- viscosity does not increase until exposed to photoinitation
- so plenty of placing and manipulation time
- once composite exposed to photoinitation source, material sets V rapidly
CURING
1
Disadvantages of chemical activation
(HINT - when mixing)
2
Photoinitiation / light activation - what does the degree of the cure depend on?
(Other writing on page, not underlined = extra)
PHOTOPOLYMERISATION
1
When does the polymerisation reaction begin?
2
What causes the free radicals to form?
3
What happens after free radical formation?
4a
Free radical addition polymerisation can terminate by what 2 methods?
4b
And in this case what termination reaction occurs?
4a
- 2 free radicals combining
- by disproportionation of free radical
4b
- disproportionation of free radicals
PHOTOPOLYMERISATION
1
How can the extent/ degree of polymerisation be determined?
2
- what is this termed as?
3
- what is the usu % range of degree of polymerisation/ conversion (NEED TO KNOW STAT OR DELETE Q??)
PHOTOPOLYMERISATION
1
What usu forms on polymerisation of dental composites?
2a
What causes linear polymers to occur?
2b
And what causes cross linking to occur?
3
How does cross linking affect/influence dental composites?
4
What is Autoacceleration or Trommsdorrf-Norrish effect/Gel effect?
5
During Autoacceleration/ Trommsdorrf-Norrish effect/Gel effect there is a rapid increase in rate of polymerisation. How does this affect the temp?
TEGDMA/EGDMA - has 5 functional groups
Need to check whether this slide matches qs below that madeeha has made and add extra info I have included
5
can cause temp to rise if heat dissipation is not possible
PROPERTIES OF DENTAL COMPOSITES
- affected by different factors
Overall
- type + amount of filler influences the mechanical properties
- study from 2011
- ## take home message = even with slight difference in filler content, there is a big difference in mechanical properties
Degree of Conversion (DC)
1
How does DC effect properties of dental composites
2
What can you use to determine DC?
3
How does DC effect micro hardness?
4
Does higher DC mean better or worse mechanical properties?
5
How does increasing DC affect water uptake + monomer diffusion?
Higher molecular weight = better mechanical properties
Highly cross linked = higher hardness
EFFECT OF MONOMERS & FILLERS ON DC
1
How do monomers affect DC
2
How do filler affect DC
The different monomers used in a dental composite and the type of filler both influence the degree of conversion
1
- viscosity of the resin monomers: plays a significant role in degree of conversion
DEGREE OF POLYMERISATION/ CONVERSION
What happens if DC is not adequate?
If degree of polymerisation is inadequate:
Check which of the above q is right
-
CROSSLINKING
1
Does cross linking affect physical properties of dental composites?
2
What does increasing the crosslinking lead to?
3
Do cross linked networks dissolve in solvents? What happens?
- can affect aesthetics as will reduce interaction with surrounding fluids thus decreasing bacterial ingress or staining
EXTRA (Also mentioned in previous FCs)
- most dental composites contain viscosity modifiers or diluent molecules
= low molecular weight dimethacrylate monomers
- which can undergo polymerisation + cross link the network
POLYMERISATION SHRINKAGE
- plays a significant role in restoration failure
1
How may it cause failure?
2
Why can marginal leakage / micro leakage cause restoration failure?
Polymerisation shrinkage can often result in the failure of a restoration because :
1
- shrinkage can compromise the marginal seal + rupture adhesive bonds made between the tooth restorative interface
- THIS CAUSES GAP FORMATION which can cause:
* secondary caries formation
* Marginal leakage
* post op sensitivity
2
- oral fluids contain bacteria
- hence slow ingress of oral fluids can lead to ingress of bacteria
- bacteria form within these interfaces
- can cause post op pain OR marginal staining due to ingress of oral fluids (aesthetic failure of restoration)
SHRINKAGE + SHRINKAGE STRESS
1
What is C factor / configuration factor?
2
1
- ratio of bonded to free area can give an indication of the interfacial stresses that will be set up
This is referred to as c factor/ configuration factor
2
DEPTH OF CURE
1
What is depth of cure?
2
What should we do to avoid undercurring?
3
What does curing depth depend on?
- TIME
- if you cure over a few more seconds it will not harm but you don’t need to do it for more than the recommended time
COMPOSITE INTERACTION WITH FLUIDS
What can it cause?
- can cause loss of ionic specials - that is from the filler phase (not so common)
Ignore the extra on diagram
CLINCAL CONSIDERATIONS
Summary
CLINCAL CONSIDERATIONS
Summary
COMPOMERS
- essentially are like composites
- have additional component of aluminofluorosilicate glass or basic glasses
- so that a secondary reaction can be effected such as an acid base reaction
- the idea was If a composite could adhere to tooth tissue the compomer would have a superior properties than composite
- HOWEVER still required a bonding agent
Currently phased out from clinical use Because there are no particulate advantages over other existing type of restorative materials
Compomers chemistry
Compomers
Advantages and disadvantages
RECENT DEVELOPMENT IN DENT
NANOCOMPOSITES
1
Size of nano particles?
2
EG of nano particle
3
Properties of nanocomposites
DATA ON DIFF TYPES OF COMPOSITES
- Flexural Strength
- Polish Retention
FLEXURAL STRENGTH
- nano composite similar to hybrid composite
- microfine is much lower
DIFF COMPOSITES AFTER BRUSHING
Benefits of high polish retention
FLOWABLE COMPOSITES
MAKE Q
- 1 of the principles of MI dent is to retain tooth struc as much as possible hence come across lots of smaller cavities
- if you use dental composites, it may not be able to flow as well in a small cavity, hence may not be able to flow very well in a small cavity therefore adaptation to walls of cavity may be compromised
HENCE
- flowable composites were developed so that you could overcome the flow problems of hybrid composites
HOWEVER FLOWBALE COMPOSITES GIVE RISE TO (IMAGE)
FLOWABLE COMPOSITES
1
why were they developed?
2
How was this achieved?
3
what does doing this result in?
4
how’re these problems being overcome/ recommendations
- so that you could overcome the flow problems of hybrid composites
- to have a greater flow + lower viscosity
2
- by reducing the amount of filler in a hybrid composite
- approx 20-25%lower filler content than a hybrid composite
3
IMAGE
4
- recommended more as liners and fissure sealants due to the problems and small restoration
- not really for big restorations
FLOWABLE COMPOSITE vs HYBRID COMPOSITES
1
Do flowable or hybrid composites have better mechanical properties?
Why?
- hybrid composites have better mechanical properties
BECAUSE - less filler in flowable composites hence rigidity is lower
PRE-WARMING OF COMPOSITES
1
Why may we prewarm hybrid composites?
2
Why would heating hem cause this change?
How do we pre-warm composites?
What temp do they heat to?
- using calset heating device
- can heat to 3 diff temp: 27, 54, 68 degrees
EXTRA
- usu when heat don’t reach high temp of 68 degrees
(EG when heat to 60, the temp in composite was us around 45 or so)
PREWARMING COMPOSITES STUDIES
Make Q’s
Pre-warmed composite resin and the fit of ceramic restorations STUDY
MAKE Q’s
BULK FILLED COMPOSITES
More recent development
Make Q
Make q for diagram
