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2c. BDS2 CDS DMS > 22. Composite Resins > Flashcards

22. Composite Resins Flashcards

1
Q

L22: What are the ideal mechanical properties of a direct filling material?

A
  • Strength;
  • Rigidity;
  • Hardness;
  • Bonding to tooth/ compatible with bonding systems.
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2
Q

L22: Other than mechanical properties, what other ideal properties are there for direct filling materials?

A
  • Thermal properties;
  • Aesthetics;
  • Radiopaque (opaque to X-rays);
  • Handing/ viscosity;
  • Anticariogenic;
  • Smooth surface finish/ polishable;
  • Low setting shrinkage;
  • Biocompatible.
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3
Q

L22: What are the two main constituents of a composite resin?

A
  • Glass filler particles (hard);

- Resin (soft).

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4
Q

L22: Alongside glass filler particles and resin, what else do composite resins contain?

A
  • Camphorquinone (photo initiator);
  • Low weight dimethacrylates;
  • Silane coupling agent.
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5
Q

L22: Give an example of a type of filler particle:

A
  • Microfine silica;
  • Quartz;
  • Borosilicate glass;
  • Lithium aluminium silicate;
  • Barium aluminium silicate.
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6
Q

L22: What is the conventional particle size for filler particles in a composite resin?

A

10-40 um

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7
Q

L22: What size of filler particles do hybrid composites contain?

A

A range, 0.01-0.1um and 1-10um

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8
Q

L22: What resin monomers are used in composite resins?

A
  • Bis-GMA;

- Urethane dimethacrylates.

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9
Q

L22: What are the key characteristics of resin monomers in a composite resin?

A
  • Difunctional molecule (C=C bonds, to facilitate cross linking);
  • Undergoes free radical addition polymerisation.
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10
Q

L22: How does camphorquinone initiate bonding of composite resin?

A
  • Activated by blue light;
  • Produces radical molecules;
  • These initiate free radical addition polymerisation of Bis-GMA;
  • Changes in resin properties;
  • i.e. increased MW, increased viscosity and strength.
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11
Q

L22: What is the role of low weight dimethacrylates?

A

Improve material - adjust viscosity and reactivity

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12
Q

L22: What is the role of saline coupling agent?

A

Improve bonding - favours glass-resin bonding

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13
Q

L22: What type of restorations are composites used for?

A
  • Where aesthetics are important;
  • Class III, IV and V permanent restorations;
  • Class II - limited occlusal wear;
  • Labial veneers;
  • Inlays, inlays, indirect technique;
  • Cores;
  • Modified forms as luting cements (some dual cured).
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14
Q

L22: What are the three main classification classes for composite resins?

A
  • Filler type;
  • Curing method (light/ self);
  • Area of use;
  • Handling (condensable, syringeable, flowable).
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15
Q

L22: Sometimes a range of filler particle sizes are used to accommodate composite volume, how does this effect the mechanical properties?

A

Stronger, harder, more rigid

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16
Q

L22: What other effects does adding filler particles (to fill volumes) have?

A
  • Improved aesthetics;
  • Increased abrasion resistance;
  • Lower thermal expansion;
  • Lower polymerisation shrinkage;
  • Less heat of polymerisation;
  • Some radiopaque.
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17
Q

L22: What wavelength is blue light (used to cure light-cured composites)?

A

430-490 nm

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18
Q

L22: Why is a certain wavelength of light used to cure composites?

A

Absorption peak at ~ 450nm for camphorquinone

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19
Q

L22: What are the advantages of using light-curing system,s?

A
  • Extended working time, i.e. on-demand set;
  • Less finishing;
  • Immediate finishing;
  • Less waste;
  • Higher filler levels;
  • Less porosity.
20
Q

L22: How does hardness (due to light curing) and depth vary?

A
  • Most blue light absorbed at the surface;

- Hardness decreases with depth.

21
Q

L22: What is the ‘depth of cure’?

A
  • The depth to which the composite resin polymerises sufficiently;
  • (where hardness will be half that of the surface);
  • Indicates increment thickness to use.
22
Q

L22: What is the typical depth of cure for hybrid and bulk composites?

A
  • Hybrid: 2mm;

- Bulk: claim up to 6mm.

23
Q

L22: What are the potential problems with curing bulk fill composites?

A
  • Can curing light be positioned the same as in a lab test?;
  • Can optical rod be placed addicted to tooth/ composite?;
  • Does blue light illuminate material?;
  • Will it polymerise (cure) fully?;
  • What impact does ‘stray’ blue light have on soft tissues?.
24
Q

L22: What are the general potential problems with light curing?

A
  • Light/ material mismatch (overexpose);
  • Premature polymerisation from clinical lights;
  • Optimistic depth of cure;
  • Recommended curing times too short;
  • Polymerisation shrinkage.
25
Q

L22: What are the potential problems with light curing, regarding patients?

A
  • Exothermic reaction (heat release in composite material, conducts to adjacent dentine/ enamel), risk of irreversible damage to pulp;
  • Divergent light beam, may cause thermal damage to tissues.
26
Q

L22: What are the potential problems with light curing, regarding clinicians?

A

Occular damage, safety shields/ glass should be used

27
Q

L22: What are the mechanical property requirements for composite resins?

A

Hardness

(a) strong, 350MPa (fracture stress)
(b) rigid (Young’s modulus), 15GPa

Bond to tooth/ compatible with bonding systems

28
Q

L22: What are the clinical property requirements for composite resins?

A

Large posterior cavity (high strength, high YM, high abrasion resistance

29
Q

L22: How do conventional, microfine and hybrid composites compare?

A
  • Conventional: strong but problems with finishing and staining due to soft resins and hard particles;
  • Microfine: smoother surface (better aesthetics) but inferior mechanical properties (elastic limit and Young’s Modulus);
  • Hybrids: compromise between above two.
30
Q

L22: What is hardness in relation to a composite surface?

A

Resistance to scratching and indentation

31
Q

L22: What is abrasion (wear) in relation to a composite surface?

A

Removal of surface layers when two surfaces make frictional contact

32
Q

L22: Abrasion, of tooth or composite surfaces, can lead to surface roughness, what can this effect?

A
  • Appearance;
  • Plaque retention;
  • Sensation when in contact with tongue.
33
Q

L22: How does surface roughness compare between conventional and microfine composites?

A
  • Conventional: 80um;

- Microfine: 10um.

34
Q

L22: What material properties can affect wear?

A
  • Filler material;
  • Particle size distribution;
  • Filler loading;
  • Resin formulation;
  • Coupling agent.
35
Q

L22: What clinical properties can affect wear?

A
  • Cavity size and design;
  • Tooth position;
  • Occlusion;
  • Placement technique;
  • Cure efficiency;
  • Finishing methods.
36
Q

L22: How does composite bonding to enamel and dentine differ?

A

Enamel: acid etch technique, dentine: universal bonding system

37
Q

L22: What is the typical bond strength of composite to both enamel and dentine?

A

40MPa (dependent on surface preparation of tissue, composite brand and test method)

38
Q

L22: Why is good bonding important?

A
  • Reduce microleakage;
  • Counteract polymerisation shrinkage;
  • To minimise cavity design (small, no need for undercuts);
  • Stress transfer (restoration does not have to withstand full stress, can be transferred to tooth/ bone; if poor bonding to tooth, stress concentrated at interface and more likely to fail).
39
Q

L22: How do mechanical properties compare between microfine and hybrid composites?

A
  • Hybrids better for all properties;
  • Higher compressive strength, elastic stress, tensile strength, flexural strength, elastic modulus, hardness;
  • See L22.
40
Q

L22: How do mechanical properties of composites compare to enamel and dentine?

A
  • Compressive strength similar to (microfine) or greater than (hybrid) enamel and dentine;
  • Tensile strength, slightly greater than dentine and enamel;
  • Elastic modulus much less than enamel, comparable to (hybrid) dentine;
  • Hardness is much less than enamel but similar to dentine.
41
Q

L22: How do the mechanical properties of composites compare to amalgam?

A
  • Amalgam greater compressive strength (just);
  • Comparable tensile strength (amalgam slightly greater);
  • Amalgam twice elastic modulus;
  • Comparable hardness (amalgam slightly greater).
42
Q

L22: Describe the thermal properties of composites.

A
  • Low thermal conductivity, good for protection of the pulp;

- High thermal expansion coefficient, poor so risk of microleakage.

43
Q

L22: How do the thermal expansion coefficients compare of amalgam, composite and GIC; and how do these compare to enamel and dentine?

A
  • Composite highest (worst), then amalgam;
  • GIC comparable to enamel but higher than dentine;
  • Enamel higher (worse) than dentine;
  • Ceramin and gold alloy lower and more comparable to enamel and dentine.

[enamel: 11, dentine: 8, composite: 25-68, amalgam: 22-28, GIC: 10-11, ceramic: 8-14, gold alloy: 12-15]

44
Q

L22: What other advantageous properties do composites offer?

A
  • Aesthetics, good and range of shades;
  • Radiopaque, some are so able to distinguish secondary caries;
  • Smooth surface finish/ polishable (but product/ technique sensitive);
  • Handling/ viscosities, range throughout products (good for different cavities/ uses).
45
Q

L22: What other disadvantages are there to using composites?

A
  • (Most) do not offer anticariogenic properties;
  • (Although low) polymerisation shrinkage still a problem, stresses can develop and make de-bonding likely;
  • Biocompatibility generally ok but some concerns about resins in general (not all monomer polymerised).
46
Q

L22: Which would you use of the following: RMGI, compomer and composite resin, for high, medium and low caries risk patients?

A
  • High risk: RMGI (if frequent attenders);
  • Medium risk: compomer (caries under control, regular attenders);
  • Low risk: composite resin.

2c. BDS2 CDS DMS (12 decks)

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