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BDS3 - dental material science > Endodontic Materials > Flashcards

Endodontic Materials Flashcards

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1
Q

What is stress?

A

Deforming force measured across a given area.

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2
Q

How do you calculate stress?

A

stress= F/A

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3
Q

What are the 4 different types of stress?

A

Tensile
Compressive
Shear
Torsional.

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4
Q

What is an instruments concentration point?

A

Abrupt changes in the geometric shape of a file that leads to a higher stress at that point.

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5
Q

What is strain?

A

Response of a material to stress. The amount of deformation that a file undergoes.

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6
Q

How do you calculate streain?

A

strain= deltaL/L

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7
Q

What is the elastic limit?

A

A set value representing the maximal strain that when applied to a file, allows the file to return to original dimensions.

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8
Q

What is elastic deformation?

A

Reversible deformation that does not exceed the elastic limit.

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9
Q

What is shape memory?

A

Shape memory alloys are materials that can be deformed at one temperature but when heated or cooled, return to their original shape.

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10
Q

What is plastic deformatiob?

A

Permanent bond displacement occurring when the elastic limit is exceeded.

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11
Q

What is the plastic limit?

A

The point at which a plastic deformed file breaks.

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12
Q

What is cyclic fatigue?

A

When an instrument is placed into a root canal and is freely rotating in a curvature. This generates tension and compression cycles which leads to cyclic fatigue= instrument failure. (work hardening then failure is cyclic fatigue).

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13
Q

What is torsional fatigue?

A

When an instrument binds to dentinal walls, other side is rotated, leads to torsion, leads to elastic deformation.

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14
Q

What is stainless steel?

A

It is an alloy of iron, carbon and chromium. Nickel might also be present! 13-26% of chromium prevents rusting and there is a passivation layer of chromium oxide.

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15
Q

Does work hardening improve or disadvantage an instruments physical properties?

A

Improves.

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16
Q

How is machined stainless steel wire manufactured?

A

Square/triangular wire is twisted and work hardening occurs.

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17
Q

How is machine stainless steel wire into desired shape manufactured?

A

Work hardening occurs.

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18
Q

What is work hardening?

A

Strengthening of a metal by plastic deformation. There is a dislocation in the crystal lattice structure- these dislocations interact and create obstructions in the crystal lattice. Some resistance to dislocation formation develops and work hardening (creates break points so dislocations cant slide within the material) occurs.

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19
Q

What is nitinol?

A

It is an equiatomic alloy of nickel and titanium
It is an exotic metal (does not conform to typical rules of mettalurgy
It has super elasticity- the application of stress does not result in the usual proportional strain.

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20
Q

WHAT IS THE PROPERTIES OF NiTi IN MARTENSITE FORM?

A

IT IS SOFT AND DUCTILE AND EASILY DEFORMED.

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21
Q

WHAT IS THE PROPERTIES OF NiTi IN AUSTENITIC FORM?

A

STRONG AND HARD.

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22
Q

What percentage of taper does a K file have?

A

2 %.

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23
Q

What is the taper component on an endodontic instrument?

A

Diameter change along working surface.

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24
Q

What is the flute component on an endodontic instrument?

A

Groove to direct dentine and soft tissue.

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25
Q

What is the lands component on an endodontic instrument?

A

Lands modify friction and change the forces applied to an instrument.

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26
Q

What is the leading/cutting edge component on an endodontic instrument?

A

Forms and deflects dentine chips.

27
Q

What is the land component on an endodontic instrument?

A

Surface extending between flutes.

28
Q

What is the relief component on an endodontic instrument?

A

Reduction in the surface of land.

29
Q

What is the helix angle component on an endodontic instrument?

A

Angle cutting axis forms with long axis of file.

30
Q

What irritant do we use for endodontic irrigation?

A

Sodium hypochlorite.

31
Q

What are the four features of an endodontic instrument?

A
  • Positive rake angle (provides the active cutting action of the K3)
  • Third radial land (stabilises and keeps the instrument centered in the canal and minimises over engagement)
  • Wide radial land (provides blade support while adding peripheral strength to resist torsional and rotary strength)
  • Radial land relief (reduces friction on the canal wall).
32
Q

What are properties of an irrigant?

A 
Facilitate removal of debris
Lubrication 
Dissolution of organic and inorganic matter
Penetration to canal periphery
Kill bacteria/yeast/viruses
Biofilm disruption
Biological compatibility
Does not weaken tooth structure.
33
Q

How does sodium hypochlorite work?

A

NaOCl in water ionises in water into NA+ and the hypochlorite ion OCl-. It then establishes equilibrium with hypochlorous acid (HOCl) and the acid/neutral HOCl dominates and ph9 and above the OCl- predominates. HOCl is responsible for antibacterial activity

-sodium hypochlorite has an effect on organic material and has the inability to remove the smear layer by itself but it has a possible effect on dentine properties.

34
Q

What factors are important for NaOCl function?

A
  • concentration
  • volume
  • mechanical aggregation
  • contact
  • exchange.
35
Q

How is the canal prepared before obturation?

A
  • Smear layer formed furing prep
  • Organic pulpal material and inorganic dentinal debris
  • Superficial 1-5 um with packing into tubules
  • Bacterial contamination, substrate and interfers with disinfection
  • Prevents sealer penetration.
36
Q

What materials can we use to remove the smear layer?

A
  • 17% EDTA
  • 10% citric acid
  • MTAD (mix of tertracycline isomer, an acid and a detergent)
  • Sonic and ultrasonic irrigation.
37
Q

What substance can you use to wash out a hypochlorite accident?

A

Sterile saline.

38
Q

What irrigant can you use if sodium hypochlorite is contraindicated?

A

Chlorhexidine digluconate.

39
Q

What is the trade name for sodium hypochlorite?

A

Parcan.

40
Q

What is the main property of chlorhexidine digluconate?

A

Antimicrobial.

41
Q

What is the trade name for chlorhexidine digluconate 0.2% and 2%?

A

Corsodyl 0.2%

Gluco-chex 2%.

42
Q

What are the interactions with irrigants?

A

Interaction with NaOCl forms para-chloroaniline. It is cytotoxic and carcinogenic with an uncertain bioavailability.

43
Q

What are the properties of an ideal obturation material (common exam question)?

A
  • easily manipulated with ample working time
  • dimensionally by tissue fluids stable
  • non-irritant
  • seals the canal laterally and apically
  • impervious (doesn’t allow fluid to pass through) to moisture
  • unaffected by tissue fluids
  • inhibits bacterial growth
  • radiopaque
  • does not discolour tooth
  • sterile
  • easily removed if necessary.
44
Q

What is gutta perca?

A

It is the most common core obturation material that is produced from juice of trees of the sapodilla family. It is natural rubber and gutta perca are polymers of the same monomer isoprene. It is a transpolymer of polyisoprene.

45
Q

What are the two phases that gutta perca exists in?

A

Alpha and beta phase. The alpha phase is the naturally occuring form and when heated to above 65 degrees it melts into an amorphous phase. When cooled rapidly it recrystalises as beta phase. The beta phase is used in commercially prepared dental gutta perca.

46
Q

What is the composition of a gutta perca cone?

A

20% GP
65% zinc oxide
10% radio-pacifiers
5% plasticisers.

47
Q

What is modified gutta perca?

A

It is impregnated and coated with bioceramic nanoparticles. This allows for a true chemical bond between the sealer and the GP points. Points also undergo a proprietary stiffening process and are laser verified for tip and taper accuracy.

48
Q

What are the functions of a selaer?

A

Seals space between dentinal wall and core. It fills the voids and irregularities in canal, lateral canals and between GP points used in lateral condensation/ Lubricates during obturation.

49
Q

What are the properties of an ideal sealer?

A 
Exhibits tackiness to provide good adhesion
Establishes a hermetic seal
Radiopacity
Easily mixed
No shrinkage on setting
Non-staining
Bacteriostatic or does not encourage growth
Slow set
Insoluble in tissue fluids
Tissue tolerant
Soluble on re-treatment.
50
Q

Why are glass ionomer sealers not frequently used for a sealer?

A

It is hard to remove upon re-treatment and it has minimal antimicrobial activity. It is advocated due to dentine bonding properties.

51
Q

What are resin sealers?

A 
Epoxy resin
Paste-paste mixing
Slow setting (8 hours)
Good sealing ability
Good flow
Initial toxicity declining after 24 hours.
52
Q

What is endorez?

A

UDMA resin-based sealer. It is hydrophilic and provides good penetration into tubules. It is biocompatible and has good radio-opacity.

53
Q

What is epiphany resin sealer and what are the components?

A

A dual cure dental resin composite sealer used with Resilon. It requires a self etch primer.
BisGMA
Ethoxylated BisGMA
Urethane-dimethacrylate UDMA
Hydrophillic difinctional methacrylates
Fillers o calcium hydroxide, barium sulphate, n=barium glass and silica.

54
Q

What are the characteristics of calcium silicate sealers?

A 
High pH (12.8) during the initial 24 hours of the setting
Hydrophillic
Enhanced biocompatibility
Does not shrink on setting
Non-resorbable
Excellent sealing ability
Quick set- 3-4 hours- requires moisture
Easy to use.
55
Q

Why are medicated sealers not used?

A

Sealers containing paraformaldehyde not acceptable
Lead and mercury components removed
Severe and permanent toxic effects on peri-radicular tissues
Sargenti paste, endomethasone, SPAD.

56
Q

What are the characteristics of the grey mineral trioxide aggregate and what are the components?

A

Is the earliest formulations
Less toxic than portland cement
Better setting characteristics
Tooth discolouration

Tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite and bismuth oxide.

57
Q

What are the characteristics of the white mineral trioxide aggregate and what are the components?

A

Smaller particle size
Reduced discolouration

Tricalcium silicate, dicalcium silicate, calcium aluminate, bismuth oxide and dehydrated calcium sulphate.

58
Q

What is biodentine?

A

Biodentine- allows MTA to set more rapidly- direct pulp cap or build up entire restoration for direct pulp capping with no lining, reduced staining so good for anterior teeth.

59
Q

What is the most important characteristics of an ideal root filling?

A

A biologically acceptable chemical and mechanical treatment of the root canal system to promote healing and repair of the peri-radicular tissues.

60
Q

What is the setting reaction of MTA?

A

Hydraulic cements
Composed of several phases
When mixed with water a chemical reaction occurs between these phases and water (hydration)
White and grey MTA undergo different setting reactions
Extended setting times
Modifications to change characteristics
Requires water for set
MTA cannot be used as will be washed away by saliva.

61
Q

What is the setting process for zinc oxide eugenol?

A

Setting is a chemical process combined with physical embedding of zinc oxide in a matrix of zinc eugenolate
Eugenolate formation constitutes hardening- CaOH accelerates this process to must be removed from canals
Free eugenol which remains can act as an irritant
Lose volume with time due to dissolution- reins can modify this.

62
Q

What can be added to zinc oxide eugenol to increase dentine adhesion?

A

Rosin or canada balsam

*mixing vehicle is mostly eugenol and its radipacity is less than GP. It can be modified with germicydes.

63
Q

What are the benefits and negatives of zinc oxide eugenol?

A

ZnO effective antimicrobial and may afford cytoprotection
Resin acids 90% component of Rosins affect lipids in cell membrane thus strongly antimicrobial/cytotoxic
Although toxic, may overall be beneficial with long lasting antimicrobial affect combined with cytoprotective effects.

BDS3 - dental material science (9 decks)

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