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BDS3 CLINICAL DMS > Endodontic Materials > Flashcards

Endodontic Materials Flashcards

1
Q

What is the function of endodontic instruments

A

mechanical phase of chemomechanical disinfection

metal files used to remove soft and hard tissues

removes microorganisms

creates spaces for disinfectants/medicaments

creates appropriate shape for obturation

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2
Q

What are the important physical properties for endodontic instruments

A 
stress
stress concentration point
strain
elastic limit
elastic deformation
shape memory
plastic deformation
plastic limit
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3
Q

What is stress

A

deforming forecasters measured across a given area

can be shear/compressive/tensile/torsional

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4
Q

What are stress concentration points

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

amount of deformation a file undergoes during use

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6
Q

What is elastic limit

A

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

in day to day use we try to keep it in the elastic region but sometimes we get to the plastic region when we see unwinding of files

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7
Q

What is elastic deformation

A

reversible deformation that does not exceed elastic limit

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8
Q

What is plastic deformation

A

permanent bond displacement occurring when elastic limit is exceeded

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9
Q

What is the plastic limit

A

the point at which a plastic deformed file breaks

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10
Q

What are the two types of failure for endo instruments

A

cyclic and torsional fatigue

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11
Q

What is cyclic fatigue

A

when the file is rotated in a curved canal, on one side it undergoes compressive force while the other undergoes tension force and because it is rotating we see the generation of tension/compression cycles resulting in work hardening, cyclic fatigue and eventually failure

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12
Q

What is torsional fatigue

A

when the instrument is in the canal it binds to the wall and is rotated but the bound portion doesn’t rotate like the driven portion of the instrument

This results in a torque making the instrument exceed the elastic phase, reach the elastic limit and undergo plastic deformation and then ultimate failure

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13
Q

What are ways we can prevent instruments fracture

A

training and proficiency in the NiTi system of choice

create a manual glide path
employ a crown down

instrument technique to ensure straight line access

use an electric speed and torque controlled motor

NiTi files should be used in constant motion using gentle pressure

avoid triggering or disabling the autoreverse mode

use of rotary files in abruptly curved or dilacerated canals should be avoided

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14
Q

How can instruments be classified

A

manually operated
low speed instruments
engine driven nicke titanium rotary instruments
engine driven instruments that adapt to canal shape
engine driven reciprocating instruments
ultrasonic instruments

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15
Q

What is the alloy composition of stainless steel instruments

A

iron carbon chromium

may have nicke l

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16
Q

What is the function of chromium in the stainless steel

A

it creates a passivation layer of chromium oxide which prevents rusting

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17
Q

How are the stainless steel instruments created

A

they are made of machined stainless steel wire
they are square or triangular
they are twisted and this results in work hardening
it is machined into the desired shape and this results in work hardening also

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18
Q

What is work hardening

A

strengthening of a metal by plastic deformation

crystal structure dislocation

dislocations interact and create obstructions in crystal lattice

resistance to dislocation formation develops

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19
Q

What is nitinol

A

equiatomic alloy of nickel and titanium

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20
Q

What is special about nitinol

A

exotic metal and does not conform to typical rules of metallurgy

it displays super elasticity where the application of stress does not result in usual proportional strain

this is related to the forms that the NiTi can take e.g austenite and martensite

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21
Q

What is the crystal structure of NiTI

A

it can transition from austenite to marsenite based on temperate

this changes the mechanical properties of the metal

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22
Q

What are the mechanical properties of martensite

A

soft, ductile and easily deformed

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23
Q

What are the mechanical properties of austenite

A

quite strong and hard

used in production of endo materials

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24
Q

What is shape memory alloys

A

materials that can be deformed at one temp but when heated r cooled they return to their original shape

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25
Q

What is the benefit of NiTi in terms of its two phases

A

can be warmed up to change to A-phase and get a broader instrument that can occupy a larger space and so good for debridement

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26
Q

What are the components of an endodontic rotary instrument

A 
taper
flute
leading/cutting edge
land
relief
helix angle
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27
Q

What is a taper

A

diameter change along the working surface

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28
Q

What is the flute

A

groove to collect dentine and soft tissue

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29
Q

What is the leading/cutting edge

A

forms and deflect dentine chips

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30
Q

What is land

A

surface extending between flutes

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31
Q

What is relief

A

reduction in surface of land

this modifies the friction between instruments

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32
Q

What is the helix angle

A

angle cutting axis forms with long axis of file

this effects the nature of how the instrument works in the canal

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33
Q

Describe the wide radial land

A

provides blade support while adding peripheral strength to resist torsional and rotary stresses

34
Q

What is the radial and relief

A

land is diminished in surface area so can reduce friction between the canal wall and instrument

35
Q

What is the third radial land

A

stabilizes and keeps the instrument centre in the canal and minimizes over engagement

36
Q

What is the positive rake angle

A

provides the active cutting action of the K3

37
Q

What are the properties of irritants

A 
facilitates removal of debrirs
lubrication
dissolution of organic and inorganic matter
penetration to canal periphery
kill bacteria/yeasts/viruses
biofilm disruption 
biological comaptibility
does not weaken tooth structure
38
Q

How does sodium hypochlorite work

A

it ionizes in water into Na+ and hypochlorite ion

it establishes an equilibrium with hypochlorous acid

39
Q

What condition does HOCl predominate in the equilibrium

A

acid / neutral

40
Q

What condition does OCl- predominate in the equilibrium

A

ph 9

41
Q

What is HOCl responsible for

A

antibacterial activity

42
Q

What does sodium hypochlorite effect

A

organic material

unable to remove smear layer by itself (inorganic component)

possible effect on dentine properties

43
Q

What are factors important for hypochlorite function

A 
concentration 
volume
contact
mechanical agitation
exchange
44
Q

How is the smear layer formed

A

happens during prep
made of organic pulpal material and inorganic dentinal debris

superficial 1-5 micrometers with packing into tubules

made of bacterial contamination, substrate and interferes with disinfection

prevents sealer penetration

45
Q

How is the smear layer removed

A

17% EDTA
10% citric acid
MTAD
sonic and ultrasonic irrigation

46
Q

What should be known about EDTA

A

can’t use with hypochlorite

don’t want to create precipitates

47
Q

What are possible irritants

A

sodium hypochlorite
EDTA
chlorhexidine digluconate (0.2 or 2%)
sterile saline

48
Q

When do we use chlorhexidine digluconate

A

used if sodium hypochlorite contraindicated such as a perforation site

49
Q

If chlorhexidine and NaOCl are mixed what forms

A

chloroaniline
cytotoxic and carinogenic

uncertain bioavailability

50
Q

What are properties of an ideal obturation material

A 
easily manipulated with ample working time 
dimensionally stable by tissue fluids 
seals the canal laterally and apically
non irritant
impervious to moisture
unaffected by tissue fluids
inhibits bacterial growth
radiopaque
does not discolor tooth
sterile
easily removed if necessary
51
Q

What is the most common core material

A

GP

52
Q

What is Gp

A

natural rubber and gutta percha are polymers of isoprene

53
Q

How does Gp exist

A

as 2 phases - alpha and beta

54
Q

What is the alpha GP phase

A

naturally occurring form
when heated above 65 degrees it melts into amorphous phase
cooled slowly returns to alpha phase
cooled rapidly recrystalises as beta phase

55
Q

What is the beta phase used in

A

commercially prepared dental GP

56
Q

What is the composition of Gp cones

A

20% gp
65% zinc oxide
10% radiopacifiers
5% plasticizer

57
Q

Wha are the different types of GP cones

A

standardised
non standardised
size matched

58
Q

What is the function of a sealer

A

seals space between dentinal wall and core

fills void and irregularities in canal, lateral canals and between GP points used in lateral condensation

lubricates during obturation

59
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 pretreatment
60
Q

What is zinc oxide and eugenol made of

A

the mixing vehicle is mostly eugene
finely sifted zinc oxide is used to enhance flow
radiopacity is less than GP
can be modified with germixides
has Rosin or canada balsam to increase dentine adhesion
has corticosteroids

61
Q

What is zinc oxide and eugenol effect as

A

an antimicrobial and may afford cytoprotection

62
Q

What does zinc oxide and eugenol contain that allows for its antimicrobial character

A

resin acids in the Rosin affect lipids in the cell membrane

although toxic, amy overall be beneficial with antimicrobial effect combined with cytoprotecitve effects

63
Q

What is the setting of zinc oxide and eugenol

A

chemical process combined w physical embedding of zinc oxide in a matrix of zinc eugenolate

eugenolate formation constitutes hardening - CaOH acerbates this process so must be removed from canals

free eugonel which remains can act as an irritant

lose volume this time due to dissolution - resins can modify this

64
Q

Describe benefits and disadvantages of GI sealers

A

advocated due to dentine bonding properties

removal upon pretreatment is difficut

minimal antimicrobial activity

little clinical data to support use

65
Q

Describe goods and bads of epoxy resin sealers

A

slow setting - 8 hours
good sealing ability
good flow
initial toxicity declining after 24h

66
Q

Describe the goods and bads of calcium silicate sealers

A

high pH during the initial 24h of setting

hydrophilic

enhanced biocompatibiltiy

does not shrink on setting

non resorbable

excellent sealing ability

quick set - 3 to four hours -requires moisture

easy to use

67
Q

What is grey MTA made of

A 
tricalcium silicate
dicalcium silicate
tricalcium aluminate
tetracalcium aluminoferrite
bismuth oxide
68
Q

What are characteristics of grey MTA

A

earliest formulations
less toxic than portland cement
better setting characteristics
tooth discoloration

69
Q

What are characteristic of white mTA

A

smaller particle size

reduced discoloration

70
Q

What is white mTA made of

A 
tricalcium silicate
dicalcium silicate
calcium aluminate
bismuth oxide
calcium sulphate dehydrated
71
Q

What is the setting reaction of MTA like

A

they are hydraulic cements (require water for setting)
they’re composed of several phases
when mixed with water there is a chemical reaction that occurs between these phases and water

72
Q

Why is the fact that zinc oxide loses volume with time due to dissolution a negative thing

A

we want stability and the problem is they dissolve with team so the apical seal can be diminished can can result in problems

73
Q

What is the negative to epiphany resin sealers resin sealers

A

they require a self etch primer and its hard to do this effectively in the RC space

74
Q

What are the components of dual cure resin composite sealers (epiphany)

A 
used with resilon
bisGMA
UDMA
hydrophilic difunctional methacrylates
fillers of CAOH, barium sulphate, barium glass and silica
75
Q

What is the advantage of UDMA resin based sealers

A

they are hydrophilic so can get good penetration into tubules
biocompatible
good radiopacity

76
Q

What is the main bio ceramic cement

A

MTA

biodentine

77
Q

What is so good about bioceramics

A

they induce osteogenesis and encourage bone formation
this is related to the change of pH
hydroxyapatite layer forms on the surface
cementum forms directly on top of MTA

78
Q

What are the 3 stages of MTA setting

A

mixing
dormancy
hardening

79
Q

What are issues with MTA

A

extended setting time (modifications made)
handling difficult
works best in areas where its hard to control moisture e.g large open apex
do not work in oral cavity as takes so long to set it will be washed away by saliva
discoloration

80
Q

What makes biodentine good

A

quicker setting
direct pulp capping
reduced staining

BDS3 CLINICAL DMS (9 decks)

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