Clinical Aspects Of Resin Composite

Question 1

What does composite mean?

Answer 1

Material made of various components that work together

Question 2

Essential component in resin composite

Answer 2

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

Question 3

Composite filler material under EM microscope

Answer 3

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

Question 4

Early dentals materials made of

Answer 4

Poly methyl methacryalte
(What dentures are made of)

Question 5

How was poly methyl methacrylate made

Answer 5

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

Question 6

What happens in an addition polymerisation reaction?

Answer 6

Monomer mol join together without any loss in material

Question 7

Polymerisation reaction

Answer 7

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

Question 8

Why were early acrylic restoration problematic?

Answer 8

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

Question 9

How did they combat shrinkage?

Answer 9

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

Question 10

What is the main resin used in composite now?

Answer 10

Bis-GMA
- thick
- viscous

Question 11

What other polymers take part in the polymerisation reaction?

Answer 11

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

Question 12

Why was the addition of a filler important for composite?

Answer 12

Eg silica

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

Question 13

use of filler particles

Answer 13

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

Question 14

What size filler particles are preferable and why?

Answer 14

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

Question 15

Typical components of modern composite

Answer 15

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

Question 16

Effect of fillers on properties

More filler + larger monomers =

Answer 16

More filler + larger monomers =

Advantages
- Improved mechanical properties
- Less shrinkage

Disadvantages
- Reduced curing depth
- Reduced flowability

Question 17

Properties of composite
Advantages

Answer 17

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

Question 18

Properties of composite
Disadvantages

Answer 18

• 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

Question 19

Clinical indications

Answer 19

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

Question 20

Contra indications - where to not use composite?

Answer 20

Where moisture control cannot be achieved

Subgingival restorations

Where the restoration would come under excessive forces

Question 21

Clinical stages of composite

Answer 21

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

Question 22

Moisture control

Answer 22

Good gingival health

Cotton wool rolls

Rubber Dam

Question 23

Cavity prep

Answer 23

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

Question 24

Removal of unsupported enamel

What is unsupported enamel?

Answer 24

•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

Question 25

What happens if unsupported enamel is left?

Answer 25

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

Question 26

What can we used to remove unsupported enamel?

Answer 26

- greenstone - excavator

Question 27

Why is bevelling important

Answer 27

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

Question 28

Bonding - total etch technique

Answer 28

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)

Question 29

Why dont we want to over dry after washing etch?

Answer 29

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

Question 30

What do we do after using total etch?

Answer 30

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

Question 31

Self etching adhesives

Answer 31

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.

Question 32

Does elf etching technique work on uncut enamel?

Answer 32

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

Question 33

Describe light curing why is it important?

Answer 33

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)

Question 34

Why is distance of the curing light important?

Answer 34

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

Question 35

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

Answer 35

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)

Question 36

After restoration placement what do we do?

Answer 36

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

Question 37

Bulk fill composite materials - what is their purpose?

Answer 37

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

Question 38

Solutions to problems with composite?

Answer 38

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.

Question 39

Two distinct directions that bulk fill materials are going in

Answer 39

Flowable bulk fill Scultable bulk fill

Question 40

Flowable bulk fill - evaluate

Answer 40

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

Question 41

Sculptable bulk fill - evaluate

Answer 41

Advantages - contain different activators to allow deeper light penetration Disadvantages - Less flowable (hence ultrasonics) or used in combination with flowable bulk filler - 4mm layers

Question 42

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

Answer 42

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

Question 43

What is SDR? What benefits does it have?

Answer 43

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

Question 44

Advantages of traditional bulk fill over traditional methods?

Answer 44

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

Question 45

Indications for SDR

Answer 45

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