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Clinical Skills A > Tooth Coloured Materials 1 > Flashcards

Tooth Coloured Materials 1 Flashcards

1
Q

Definition of composite?

A

-A product with at least 2 distinct phases.
-Purpose is to combine 2 or more materials to produce one with superior properties
-Dental composite contains inorganic filler and an organic binder

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2
Q

Adv of TCM

A

-Aesthetics
-Conservation of tooth structure
-Adhesion to tooth structure
through a bonding system
-Low thermal conductivity
Alternative to amalgam

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3
Q

DISadv of TCM

A

-Technique sensitivity
-Polymerization shrinkage leading to marginal leakage, secondary caries and postoperative sensitivity
-Decreased wear resistance

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4
Q

How is it set?

A

Via free radical addition polymerisation

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5
Q

What is free radical addition polymerisation?

A
  • Activation–> Chemical (Organic amine + organic peroxide) and Light (Camphorquinone + blue light (450-490nm),
    Check your light!!)
  • Initiation
  • Propagation
  • Termination
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6
Q

Acrylic restorations when first placed?

A

Polymerisation is highly exothermic
Bond to dentine is poor as dentine is wet and acrylic is hydrophobic

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7
Q

Polymerisation shrinkage leads to-

A

Poor bond to tooth so easily pulled away from dentine
Which leads to;
-Poor retention
-Staining
-Sensitivity
-Secondary caries

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8
Q

Monomers

A

Binds the filler particles together and provides workability.

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9
Q

Bis-GMA Monomer

A
  • Extremely viscous bc of large benzene rings
  • Viscosity is lowered by adding TEGDMA which:
    —freely movable
    — increases polymer conversion
    —increases crosslinking
    —increases shrinkage (bc of new bonding types form mono to poly)
    —increases filler incorporation
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10
Q

What is a resin composite composed of?

A

3 main components:
- (1) the resin matrix comprising: (i) a monomer system, (ii) an initiator system for free radical polymerization, and (iii) stabilizers for maximizing the storage stability of the uncured resin composite and the chemical stability of the cured resin com-posite;
- (2) the inorganic filler consisting of particulates such as glass, quartz, and/or fused silica; and
- (3) the coupling agent, usually an organo-silane, that chemically bonds the reinforcing filler to the resin matrix

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11
Q

What is conversion?

A

Degree to which a monomer is converted to a polymer.

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12
Q

What does curing do?

A

converts monomers to polymers - from soft/liquid to a solid state.

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13
Q

Relevance of correct curing technique?

A

To reduce the degree of polymerization shrinkage, improving clinical and esthetic success of composite resin restorations.

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14
Q

Curing phases?

A

pre-gel, gel point and post-gel

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15
Q

Gel point def

A

An abrupt change in the viscosity of a solution containing polymerizable components

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16
Q

What happens at gel point?

A

The resin presents a high modulus of elasticity, loses its flowing ability and transmits the stress yielded by polymerization shrinkage to the tooth-restoration interface

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17
Q

Depth recommended when curing and why?

A

2mm to minimise stress transfer

18
Q

Role of fillers?
Examples of fillers?

A

to reduce shrinkage upon curing.
strontium glass, barium glass, quartz, borosilicate glass, ceramic, silica, prepolymerized resin are used.

19
Q

Filler Classification

A
  • Irregular or spherical in shape depending on the mode of manufacture.
20
Q

Adv of spherical particles

A
  • Spherical particles are easier to incorporate into a resin mix and to fill more space leaving less resin.
  • One size spherical particle occupies a certain space.
    Then adding smaller particles fills the space between the larger particles to take up more space.
  • More space taken = less resin remaining and so less shrinkage on curing.
21
Q

Inorganic fillers - PROS

A

Reduce:
- Polymerisation shrinkage
- Water sorption
- Thermal expansion
Increase:
- Compressive/tensile strength
- Modulus of elasticity
- Abrasion resistance

22
Q

The coupling agent- Role

A

Usually an organo-silane, that chemically bonds the reinforcing filler to the resin matrix

23
Q

Properties

A

Comp. Strength 170-260MPa (Enamel 100-380, Dentine 250-350)

Tensile Strength 30-55MPa (Enamel 10, Dentine 20-50)

Coeff. Therm. Exp.20-77 (Enamel 11.4, Dentine 8.3)

Polymer Shrinkage 3%

24
Q

Flowable composites

A

Their percentage filler content by weight (50% to 70%) is less than that of traditional hybrid composite resins which gives them a lower viscosity

25
Indications of a flowable composite
-Class V restorations -Micropreparations -Extended fissure sealings -Adhesive cementation of ceramic restorations -Blocking out cavity undercuts -Initial (base) layer in any classification
26
Flowable composite con
The flowable composite resins have lower filler volumes and thus they exhibit increased shrinkage and wear with decreased strength.
27
Packable Composites (Macrofilled Hybrids):
These composites are firm and can be packed into a preparation. - Generally contain larger filler particles or even fibres to improve packing qualities. Because of their high viscosity they are more difficult to sculpt and voids are more common.
28
Acid etching process
- An acid (mostly 30-40% phosphoric acid) is applied and rinsed off. - pH is 0.2 (very strong acid) and decalcification occurs in 5-8 seconds - Etching decalcifies portions of enamel rods - Calcium salts are dissolved which exposes interprismatic and prism areas for interlocking tag formation with the bonding resin. - This is purely mechanical bonding, not true adhesion. Bond strength ~20 MPa.
29
Why is it difficult to bond to dentine?
Dentine is a hydrated moist tissue and resin is hydrophobic.
30
Bonding agents role?
Allows the hydrophobic composite to bond to the dentine.
31
What is a smear layer?
Created by any mechanical cutting of dentine. Essentially dentine debris of variable thickness. In addition smear plugs are formed which block dentinal tubules.
32
What does the smear layer do?
Can protect dentine and ultimately the pulp from penetration of bacteria. Eliminates diffusion of dentinal fluid. Impairs bond of composite to dentine. It’s self is only relatively loosely bound. Can harbour bacteria.
33
Bonding mechanism of resin to enamel and dentine
An exchange process involving replacement of minerals (removed from either of the hard dental tissues) by resin monomers, which, upon setting, become micro-mechanically interlocked in the created porosities.
34
Dentine hybrid later with resin- describe hybridisation?
Hybridisation ~ the infiltration of resin monomers into the collagen fibrillar matrix of demineralised dentin, followed by polymerisation. It is a process that creates a molecular-level mixture of adhesive polymers and dental hard tissues – the hybrid layer.
35
Acid etching benefits
Improves the retention of the restoration Increases the surface area of the dentine Removes “smear layer” from prep Allows for penetration of bonding agent into dentin Protect pulp exposures before using!
36
Acid etching steps :
Phosphoric acid (35-37%) gel or liquid Isolate teeth, apply etchant, wait (5-15 seconds) Rinse – don’t desiccate! – blot prep to remove water
37
Primer steps
2nd step Improves wettability of prep Penetrates etched dentin tubules Applied in a thin layer; thinned with air; blot May require light-curing
38
Bonding steps
- Un-filled or lightly filled resin - Adhesive bonds to collagen fibers in dentin – mechanically “locks-in” – “Hybrid Layer” - Applied in a thin, uniform layer - Light-cured 10-20 seconds Dental composite then applied
39
Current application technique
Current approaches involve either applying these 3 steps separately or together: Etch and rinse, prime and bond Self-etch primer and bond
40
Acid etching good for enamel/ dentine
Yes! for both removes/modifies smear layer and exposes dentinal tubules
41
Final stage- resin application?
Final stage, application of the hydrophobic resin and cure, resulting in a three step process Simplified two-step etch-and-rinse adhesives combine the primer and adhesive resin into one application

Clinical Skills A (5 decks)

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