W2 CR & AMAL Flashcards
What basically is a composite resin?
Ceramic filled polymers which is set by resin polymerisation.
How does composite bond to the tooth?
Chemically bonds to tooth through an ion exchange mechanism known as free-radical polymerisation
Can it release fluoride?
Yes
What types of composites are available?
Packable and flowable (filled and unfilled)
Describe the organic matrix
(Bis-GMA), UDMA, TEGDMA composite made of matrix —> unfilled resin
Describe the phase in Organic Matrix (unfilled resin)
Phase that polymerises forming a solid mass that bonds to tooth.
What are two disadvantages of the Organic Phase? (Unfilled)
- Weakest and least wear resistance phase.
2. Absorbs water stain and discolour.
What elements/components are in the Inorganic Filler?
- Silica Particles
- Quartz
- Glass (Ba,Sr,Zr)
Is the inorganic Filler, filled resin or unfilled?
Filled resin, permitting it is made up of matrix and filler. –> Filled Resin
What does the Coupling Agent do?
Chemically bonds and stress absorber
What the setting reaction?
Free radical polymerisation
What is the setting period of composite resin?
3-40 sec
Does it thermally expand?
Yes
Does it wear?
Dependent on contract stress, duration and oral environment
How does it bond to the enamel?
ion exchange
Describe the composition of composite
Organic matrix (Bis-GMA) + UDMA + TEGMA (unfilled)
Inorganic matrix Glass, Quarts, Silicia (filled)
Coupling agent
Accelerator/initiator
What is the impact if water contamination on this material?
Would not bond to tooth, as the material is hydrophobic
Would i be able to see this material on a radiograph?
Yes, because it is radio-opaque
Indication of composite resin
Pits and fissure seals
Anterior restorations
Luting material
Splinting of teeth
Contraindications of composite resin
Root caries
Moisture isolation
Potential allergy
What is the difference between packable and flowable?
Flowable has less viscosity than packable allowing it to flow into pits and fissures.
How do you bond composite to enamel?
Etching margins with 37% phosphoric acid to create dissolution of outer surface of enamel rods is called micromechanical bonding
Resin then penetrate into the microporosities and develop resin tags.
Technique sensitive affected by moisture contamination
How do you bond composite to dentine?
3 step process
Etch (do not etch dentin)
Primer
Adhesive
Describe the importance of the Depth of Cure
Important for light activated materials. Inadequate incremental placements and light cure can cause
marginal leakage
recurrent caries
pulpal sensitivity
restoration failure due to polymerisation shrinkage,
Describe the importance of the Depth of Cure
Important for light activated materials. Inadequate incremental placements and light cure can cause
marginal leakage
recurrent caries
pulpal sensitivity
restoration failure due to polymerisation shrinkage,
Do composites absorb water and expand?
Yes, this reduces mechanical properties such as hardness and wear resistance
Can composites change colour?
Yes, by extrinsic (mouthwash, tea) or instrinsic (physiochemical)
What is the quality of radiopacity?
It improves property and enables clinicians to detect recurrent caries and marginal defects on xrays
What are the mechanical properties of composite resin
Wear: depends on the contact stress, duration, chemical environment.
Increased filled volume increases hardness, wear resistance and fracture toughness.
Polymerisation shrinkage: is reduced by incremental placement, use of GIC as liner or base to act as a shock absorber reducing volume of composite
How many types of composite resin are there?
3
Self cure
Dual cure
Light-cure
What are the indications for composite resin?
Direct and indirect restorative material
Anterior restorations
Pits and fissure sealants
Luting agents
What are the contraindication for composite resin?
High occlusion load
Root caries
Where moisture control is difficult
Large proximal restorations
What are the advantages of composite resin?
Aesthetics
Conservation of tooth structure
Decreased microleakage
Radiopacity
What are the disadvantages of composite resin?
Polymerisation shrinkage
Time consuming
Expensive
Technique sensitive
What are the indications for amalgam?
High occlusal load bearing teeth
Ease of placement
Aesthetics not important
What are the properties of amalgam
Strength
Dimensional Change
What is the basic chemistry of amalgam?
The reaction between silver alloy and mercury is called amalgamation. When high-copper alloy particles contact the mercury, the copper, silver, tin and other elements dissolve into the mercury.
New solids products begin to crystallize then hardening. Reaction products are called the matrix.
What is the clinical handling of amalgam?
- Mixing (trituation)
- Condensation
- Carving
- Finishing: polishing carries out of a 24> after placement
What are the indications for amalgam?
Large restorations
High occlusal load bearing teeth
Moisture tolerant
What are the contraindications for amalgam?
Use in deciduous teeth
Anterior teeth
Small class I and II restorations where moisture isolation is possible
What is the advantage of amalgam
Ease of use
Easily to manipulate
Inexpensive
Excellent wear resistance
What is the disadvantage of amalgam?
Non-aesthetic
Tarnish and corrosion
Galvanic shock
Discolouration of tooth
What are the classifications of amalgam?
Particle composition
Partical shape:
Spherical, lathe-cut, or admixed (sphereical and lath-cut).
Irregular: provides more resistance to packing, but strong
Spherical is more easily condensed.
What is the chemistry of amalgam?
Gamma phase (Y)
Gamma 1 Y1 and gamma 2 Y2.
Gamma 2 increases corrosion, creep and lowers strength. Modern amalgam → low gamma 2 phase due to higher presence of copper.
+ Eta phase: tin copper combination
Copper acts to convert gamma 2 to gamma 1 and formation of silver-copper alloy. Ag + Cu + Y2 = Y1+ Cu/Sn
What is the composition of amalgam?
Silver, Copper, Tin, Zinc
Describe the strength of amalgam
Strength - amalgam must withstand oral mechancial forces. ↑ compressive and tensile stress results in occlusion exceeds this will fracture.
Tensile strenth is approx 12.5% of compressive strength
Describe dimensional change
Expansion may result in post-placement sensitivity or protrusion from the cavity, if it contracts it will leave gaps between the restoration leaving it prone to leakage and recurrent decay.
Describe what Creep is?
Break down of the margins of the restoration - resulting i a fracture. Low copper amalgams have more breakdown at margins.
Describe tarnish and corrosion?
Tarnish results in discoloured restoration, not aesthetic.
Corrosion is a chemical reaction that can pentrate to the body of amalgam - leading to failure.
