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BDS3 CLINICAL DMS > Endodontic Materials > Flashcards

Endodontic Materials Flashcards

(80 cards)

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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
What is the benefit of NiTi in terms of its two phases
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
26
What are the components of an endodontic rotary instrument
``` taper flute leading/cutting edge land relief helix angle ```
27
What is a taper
diameter change along the working surface
28
What is the flute
groove to collect dentine and soft tissue
29
What is the leading/cutting edge
forms and deflect dentine chips
30
What is land
surface extending between flutes
31
What is relief
reduction in surface of land | this modifies the friction between instruments
32
What is the helix angle
angle cutting axis forms with long axis of file this effects the nature of how the instrument works in the canal
33
Describe the wide radial land
provides blade support while adding peripheral strength to resist torsional and rotary stresses
34
What is the radial and relief
land is diminished in surface area so can reduce friction between the canal wall and instrument
35
What is the third radial land
stabilizes and keeps the instrument centre in the canal and minimizes over engagement
36
What is the positive rake angle
provides the active cutting action of the K3
37
What are the properties of irritants
``` 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
How does sodium hypochlorite work
it ionizes in water into Na+ and hypochlorite ion it establishes an equilibrium with hypochlorous acid
39
What condition does HOCl predominate in the equilibrium
acid / neutral
40
What condition does OCl- predominate in the equilibrium
ph 9
41
What is HOCl responsible for
antibacterial activity
42
What does sodium hypochlorite effect
organic material unable to remove smear layer by itself (inorganic component) possible effect on dentine properties
43
What are factors important for hypochlorite function
``` concentration volume contact mechanical agitation exchange ```
44
How is the smear layer formed
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
How is the smear layer removed
17% EDTA 10% citric acid MTAD sonic and ultrasonic irrigation
46
What should be known about EDTA
can't use with hypochlorite | don't want to create precipitates
47
What are possible irritants
sodium hypochlorite EDTA chlorhexidine digluconate (0.2 or 2%) sterile saline
48
When do we use chlorhexidine digluconate
used if sodium hypochlorite contraindicated such as a perforation site
49
If chlorhexidine and NaOCl are mixed what forms
chloroaniline cytotoxic and carinogenic uncertain bioavailability
50
What are properties of an ideal obturation material
``` 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
What is the most common core material
GP
52
What is Gp
natural rubber and gutta percha are polymers of isoprene
53
How does Gp exist
as 2 phases - alpha and beta
54
What is the alpha GP phase
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
What is the beta phase used in
commercially prepared dental GP
56
What is the composition of Gp cones
20% gp 65% zinc oxide 10% radiopacifiers 5% plasticizer
57
Wha are the different types of GP cones
standardised non standardised size matched
58
What is the function of a sealer
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
What are the properties of an ideal sealer
``` 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
What is zinc oxide and eugenol made of
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
What is zinc oxide and eugenol effect as
an antimicrobial and may afford cytoprotection
62
What does zinc oxide and eugenol contain that allows for its antimicrobial character
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
What is the setting of zinc oxide and eugenol
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
Describe benefits and disadvantages of GI sealers
advocated due to dentine bonding properties removal upon pretreatment is difficut minimal antimicrobial activity little clinical data to support use
65
Describe goods and bads of epoxy resin sealers
slow setting - 8 hours good sealing ability good flow initial toxicity declining after 24h
66
Describe the goods and bads of calcium silicate sealers
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
What is grey MTA made of
``` tricalcium silicate dicalcium silicate tricalcium aluminate tetracalcium aluminoferrite bismuth oxide ```
68
What are characteristics of grey MTA
earliest formulations less toxic than portland cement better setting characteristics tooth discoloration
69
What are characteristic of white mTA
smaller particle size reduced discoloration
70
What is white mTA made of
``` tricalcium silicate dicalcium silicate calcium aluminate bismuth oxide calcium sulphate dehydrated ```
71
What is the setting reaction of MTA like
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
Why is the fact that zinc oxide loses volume with time due to dissolution a negative thing
we want stability and the problem is they dissolve with team so the apical seal can be diminished can can result in problems
73
What is the negative to epiphany resin sealers resin sealers
they require a self etch primer and its hard to do this effectively in the RC space
74
What are the components of dual cure resin composite sealers (epiphany)
``` used with resilon bisGMA UDMA hydrophilic difunctional methacrylates fillers of CAOH, barium sulphate, barium glass and silica ```
75
What is the advantage of UDMA resin based sealers
they are hydrophilic so can get good penetration into tubules biocompatible good radiopacity
76
What is the main bio ceramic cement
MTA | biodentine
77
What is so good about bioceramics
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
What are the 3 stages of MTA setting
mixing dormancy hardening
79
What are issues with MTA
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
What makes biodentine good
quicker setting direct pulp capping reduced staining

BDS3 CLINICAL DMS (9 decks)

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