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Clinical Skills - Chemistry & Clinical Aspects of Dental Materials > Clinical Aspects Of Resin Composite > Flashcards

Clinical Aspects Of Resin Composite Flashcards

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1
Q

What does composite mean?

A

Material made of various components that work together

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2
Q

Essential component in resin composite

A

Filler particles embedded in a matrix made of resin
The 2 are linked together by a silane couponing agent

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3
Q

Composite filler material under EM microscope

A

Filler takes up a lot of space and resin fills in gaps between filler particles

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4
Q

Early dentals materials made of

A

Poly methyl methacryalte
(What dentures are made of)

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5
Q

How was poly methyl methacrylate made

A

Poly methyl methacrylate made from the polymerisation of of methyl methacrylate (small mol)
- imitator and activator (addition polymerisation reaction)

1930’s - developed
1950’s - used for tooth coloured filling materials

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6
Q

What happens in an addition polymerisation reaction?

A

Monomer mol join together without any loss in material

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7
Q

Polymerisation reaction

A
  1. Starts with the production of free radicals
  2. Free radicals cause double bonds on carbon group and methyl methacrylate to break down leaving an active site which then can cause a chain reaction for other methy methacrylate to join to it
  3. As this occurs the monomer mol get closer together
  4. There is a visible and measurable shrinkage within the material because in initial state methyl methacrylate is a liquid so the monomer mol can but around but after polymerisation, they are bound tightly together
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8
Q

Why were early acrylic restoration problematic?

A

Polymerisation is highly exothermic

Bond to dentine is poor as dentine is wet and acrylic is hydrophobic

Poor bond to tooth so easily pulled away from dentine causing gaps

Which leads to;
Poor retention, Staining, Sensitivity, Secondary caries

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9
Q

How did they combat shrinkage?

A

If larger mol of methyl methacrylate is used, there is less shrinkage

Because larger mol already occupy a lot of space per molecule so fewer polymerisation reaction to occur within the same vol of material

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10
Q

What is the main resin used in composite now?

A

Bis-GMA
- thick
- viscous

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11
Q

What other polymers take part in the polymerisation reaction?

A

Diligent monomers (smaller) - TEGDMA
- help Bis-GMA be more flowable

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12
Q

Why was the addition of a filler important for composite?

A

Eg silica

  • take up space so fewer polymerisation reactions occur therefore, less shrinkage
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13
Q

use of filler particles

A

Play no part in the setting reaction

• Take up the space of the resin – so less resin – less shrinkage
• Add advantageous properties to the material
• Increase wear resistance
• Strength
• Radio-opacity
• Allows different colour composite

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14
Q

What size filler particles are preferable and why?

A

The larger the particle the higher the strength at the expense of aesthetics

• Small particles make for a weaker material, give better polishability but hard to add a very large amount so more shrinkage

• Most composites contain a mixture of different size filler – a “hybrid” – more space can be taken up if smaller particles are added with larger particles

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15
Q

Typical components of modern composite

A

Bis-GMA - Main polymerisable monomer

TEGDMA - Diluent monomer

Camphorquinone (CQ) - Initiator (Forms free radicals but requires presence of DMAEMA)

Silica filler -
- strength
- wear resistant
- colour
- radiopacity

Silane coupling agent - Binds filler to matrix

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16
Q

Effect of fillers on properties

More filler + larger monomers =

A

More filler + larger monomers =

Advantages
- Improved mechanical properties
- Less shrinkage

Disadvantages
- Reduced curing depth
- Reduced flowability

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17
Q

Properties of composite
Advantages

A
  • strong
  • hard wearing
  • easy to place
  • easy to polish
  • good aesthetics
  • less destructive prep than amalgam, crowns or veneers
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18
Q

Properties of composite
Disadvantages

A
  • hydrophobic (have to create a dry area to use composite)
  • polymerisation shrinkage
  • time consuming (rubber dam etc)
  • does not bond to tooth requires a separate bonding agent
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19
Q

Clinical indications

A

Tooth coloured restorations are required
- Preferably there is enamel to bond to on all sides of the cavity
- Where Moisture control – saliva, gingival crevicular fluid and blood can be kept away from the cavity
- Where Occlusal forces are not excessive
- Posterior teeth, large restorations, patients with strong bite / parafunctional habits

Restore following Trauma and caries
Build up teeth following toothwear
Build up teeth prior to crowning
Improve the shape and colour of teeth cosmetically

20
Q

Contra indications - where to not use composite?

A

Where moisture control cannot be achieved

Subgingival restorations

Where the restoration would come under excessive forces

21
Q

Clinical stages of composite

A
  1. Select Shade (before rubber dam - blue changes colour perception and tooth changes colour after drying)
  2. Moisture Control
  3. Cavity Preparation
  4. Bonding
  5. Placement
  6. Light Curing
  7. Finishing / Polishing
22
Q

Moisture control

A

Good gingival health

Cotton wool rolls

Rubber Dam

23
Q

Cavity prep

A

Clear caries from ADJ
Remove infected dentine
Protect pulp if very close to exposure
Remove unsupported enamel
Bevel labial surfaces

24
Q

Removal of unsupported enamel

What is unsupported enamel?

A

•Enamel usually is connected to the dentine beneath.
•As enamel has a crystalline structure it is not strong if not connected to dentine. It comes apart easily between prisms.
•The prisms run perpendicular to the surface

25
Q

What happens if unsupported enamel is left?

A

Caries tends to spread at the ADJ undermining the enamel (hence cavities occur)

If left unsupported the shaded enamel prisms may crumble in the future leaving a gap that can lead to secondary caries

26
Q

What can we used to remove unsupported enamel?

A
  • greenstone
  • excavator
27
Q

Why is bevelling important

A

After removing unsupported enamel for smooth surface caries the edge may be bevelled to improve surface area and colour transition

45 degree further reduction of the enamel

Helps transition from colour of tooth to colour of restoration so there isn’t a sudden change

28
Q

Bonding - total etch technique

A
  1. Apply acid etch 37% phosphoric acid on all surfaces emails and dentine and extending onto the edge of the cavity onto uncut enamel
  2. Wash after 10-20 secs with 3 in 1
  3. Keep slightly damp surface (small blow with 3 in 1)
29
Q

Why dont we want to over dry after washing etch?

A

We are relying on collagen fibres in dentine which have been exposed to etch to stand upwards and will be gripped onto once the adhesive is applied

Over drying the collagen fibres will cause them to collapse, reducing the bonding strength

30
Q

What do we do after using total etch?

A

When using total etch technique apply adhesive that have prime and bond in one on all surfaces
To prevent pooling gently air dry and light cure for 10-20 seconds

31
Q

Self etching adhesives

A

There are some adhesives that include an acidic component and etch the tooth themselves.

The Bond to enamel although effective has been shown to improve if the enamel is etched first and therefore sometimes a “selective etch” technique is advocated.

32
Q

Does elf etching technique work on uncut enamel?

A

Not as effective for uncut enamel so etch applied to these surfaces first and self etch adhesive bonds itself to cut surfaces and dentine
This is called a selective etch technique

33
Q

Describe light curing why is it important?

A

Activated polymerisation process

Light of 450 – 490 nM

Sets material when you are ready

Limited depth of cure – 2mm max, less for very dark composite shades (If building up a tooth with composite, it has to be placed in increments of 2mm at a time curing at each layer)

34
Q

Why is distance of the curing light important?

A

The further the light is away from composite materials, the less bright the light is hitting the material

35
Q

How to we avoid getting the composite in areas we don’t want it?

A

Matrix strip and wedge to prevent bonding two adjacent teeth together and to help shape proximal surfaces

For posterior teeth - use metal matrix band (ensure curing from the occlusal surface)

36
Q

After restoration placement what do we do?

A

Finishing – removal of excess material, creating the correct shape for the restoration
- Finishing burs (short white stone)
- Abrasive discs
- inter-proximal strips

Polishing
Using abrasives to achieve a high polish
- Polishing “points”
- “Soflex” Discs

37
Q

Bulk fill composite materials - what is their purpose?

A

Overcoming a significant problem with composite
- poor results in class 2 (posterior) subgingival restorations
- secondary caries occurring

Poor adaptation, bond failure, shrinkage
A composite with a higher curing depth than 2mm is required

38
Q

Solutions to problems with composite?

A

Need a material that allows deeper curing than 2mm, and adapt better to the cavity and not shrink during curing.

Materials have been developed that allow deeper curing by having either less filler (flowable Bulk Fill) which allows the light to penetrate further or using different activators (Sculptable Bulk Fill) that can allow deeper curing as they use different coloured lights eg purple – can cure up to 4mm seep halving the time taken to cure.

39
Q

Two distinct directions that bulk fill materials are going in

A

Flowable bulk fill

Scultable bulk fill

40
Q

Flowable bulk fill - evaluate

A

Advantages
- less filler so light can penetrate further
- contain modulators to compensate for shrinkage reducing stress

Disadvantages
- more polymerisation / shrinkage
- not as strong / wear resistant (poor mechanical properties)
- need ‘capping layer’ of normal composite over the top

41
Q

Sculptable bulk fill - evaluate

A

Advantages
- contain different activators to allow deeper light penetration

Disadvantages
- Less flowable (hence ultrasonics) or used in combination with flowable bulk filler
- 4mm layers

42
Q

Why is flowable bulk fill preferred and how is the problems it involves overcome?

A

Less filler =
more flowable and better adaptation (no voids left around edges of restoration)

but this is done at the expense of the strength and increase shrinkage

Strength problem is overcome by placing 2mm of regular composite on top

Shrinkage problem is overcome by having a special functional polymer that breaks as shrinkage stress rises thus releasing stress

43
Q

What is SDR?

What benefits does it have?

A

SDR is a Bulk Fill Flowable Posterior Composite Material
(up to 4mm cure depth)

Contains a modulator which causes the chain to break apart so stress can be released (delaying the gel point) - material stays liquid for longer as its curing than a normal composite would

This allows the shrinkage to happen from the surface which prevents the restoration from being pulled away from. The sides and bottom of the cavity as it’s curing

44
Q

Advantages of traditional bulk fill over traditional methods?

A

Quicker
Fewer voids (flowable and goes into all gaps)
Less technique sensitive
Fewer incidents of post operative sensitivity

45
Q

Indications for SDR

A

Class I & II bulk fill bases
Fissure Sealant
PRR – all in one
Core build up (Inc Nayyar technique)
Ideal for use in paediatric dentistry

Clinical Skills - Chemistry & Clinical Aspects of Dental Materials (8 decks)

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