1
Q
What are the categories that endodontic materials can be split into? (7)
A
- Instruments
- Irrigants
- Intra-canal medicaments
- Obturation materials
- Sealers
- Pulp capping materials
- Root-end filling materials
2
Q
When are endodontic instruments used?
A
- Used in the mechnical phase of chemomechanical disinfection
3
Q
What are endodontic instruments and what are they used for? (4)
A
- Metal files used to remove soft and hard tissues
- Removes micro-organisms
- Creates spaces for disinfectants/medicaments
- Creates appropriate shape for obturation
4
Q
What are the physical properties of endodontic instruments that we wouls want to consider? (8)
A
- Stress
- Stress concentration point
- Strain
- Elastic limit
- Elastic deformation
- Shape memory
- Plastic deformation
- Plastic limit
5
Q
What is stress?
A
- Deforming force measured across given area
- Tensile/compressive/shear/torsional
6
Q
What is the stress concentration point?
A
- Abrupt changes in the geometric shape of a file that leads to a higher stress at the point
7
Q
Why, when preparing or manufacturing endodontic instruments must the manufacturers pay particular attention to the surface characteristics and the ultimate finish of the instrument?
A
- Because the instruments have quite complex geometric shapes and following manufacturing they might have inherent disruptions in the surfaces which can lead to concentration of stresses at certain points - these are points at which failure of an instrument can occur
8
Q
What is strain?
A
- Response of a material to stress
- Amount of deformation a file undergoes during use
9
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
10
Q
What is elastic deformation?
A
- Reversible deformation that does not excees elastic limit
11
Q
What is plastic deformation?
A
- Permanent bond displacement occurring when the elastic limit is exceeded
12
Q
What is the plastic limit?
A
- The point at which the plastic deformed file breaks
- We want to avoid this at all costs
13
Q
There are 2 types of failure predominantly in instruments. One of them is cyclic fatigue. What is this?
A
- This is when an instrument is freely rotatin within a curved canal
- Because the instrument is rotating what we eventually see is a tension/compression cycle which leads to work hardening and ultimately failure - this is termed cyclic fatigue
14
Q
There are 2 types of failure predominantly in instruments. One of them is torsional fatigue. What is this?
A
- This is the other type of fatigue that we see
- We have an instrument that is in the canal, it binds to the dentinal walls and is rotated
- The bound portion does not rotate like the driven portion of the instrument and we start to see an increase in the rotation with an increase in torque
- So we start to pass through this elastic phase, reach the elastic limit and start to undergo plastic deformation and then ultimately failure
- So torsional fatigue - the binding of an instrument at one point whilst the other portion is rotated will lead to torsion (a twisting force) and then plastic deformation and failure at the end of the plastic phase
15
Q
What are ways in which we can prevent endodontic instrument fracture? (7)
A
- Training and proficiency in the NiTi system of choice
- Create a manual glide path (creates space for the tip of these instruments so we don’t develop torsional fatigue)
- Employ a crown-down instrumentation 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 disable the sutoreverse mode
- Use of rotary files in abruptly curved or dilacerated canals should be avoided
16
Q
There are a large number of instruments that can be used in endodontics. Give examples of classifications of these? (6)
A
- Manually operated (hand instruments)
- Low-speed instruments
- Engine-driven nicket-titanium rotary instruments
- Engine-driven instruments that adapt to canal shape
- Engine-driven reciprocating instruments
- Ultrasonic instruments
17
Q
What are the components of stainless steel? (4)
A
- Alloy of iron, carbon, and chromium
- Nickel may also be present
18
Q
Why would we use stainless steel over carbon steel for endodontic instruments?
A
- The alloy composition of this material inproves the properties over that of carbon steel so prevents rusting
19
Q
Which metal within stainless steel prevents rusting?
A
- 13-26% chromium prevents rusting
- There is a passivation layer of chromium oxide which prevents the degradation of the instrument
20
Q
How are stainless steel endodontic instruments manufactured? (5)
A
- Machined stainless steel wire
- Square/triangular twisted
- Work hardening occurs (twisting of the stainless steel creates work hardening which makes the properties better)
- Machine stainless steel wire into desired shape
- Work hardening occurs (which again improves the physical properties and so makes them better for use in the root canal)
21
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
- Observed work hardening
22
Q
What is Nitinol?
A
- Equiatomic alloy of nickel and titanium
- Exotic metal - does not conform to typical rules of mettalurgy
- Super-elasticity - application of stress does not result in usual proportional strain
23
Q
How can the NiTi crystal structure be altered?
A
- Temperature dependent structures martensite and ausetnite
- Crystal lattice structure altered by temperature or stress
- Characters and porportions determine mechanical properties of the metal
24
Q
What is NiTi like in its martensite form?
A
- It is soft and ductile and easily deformed
25
What is NiTi like in its austenite form?
- Quite strong and hard
26
What is shape memory?
- Shape memory alloys are materials that can be deformed at one temperature but when heated or cooled, return to their original shape
27
What are the components of an endodontic rotary instrument? (6)
- Taper
- Flute
- Leading/cutting edge
- Land
- Relief
- Helix angle
28
What is the taper of an endodontic rotary instrument?
- Diameter change along working surface
29
What is the flute of an endodontic rotary instrument?
- Groove to collect dentine and soft tissue
30
What is the leading/cutting of an endodontic rotary instrument?
- Forms and deflects dentine chips (these are the edges that allow us to cut dentine)
31
What is the land of an endodontic rotary instrument?
- Surface extending between flutes
32
What is the relief of an endodontic rotary instrument?
- Reduction in surface of land (the lands being carved out to create a different behaviour within the root canal
- So lands and reliefs may modify the friction which is in between the instrument and the dentine that it is cutting - so it changes the forces that are applied to the instruments and the ease at which it cuts
33
What is the helix angle of an endodontic rotary instrument?
- Angle cutting axis forms with long axis of file (this affects how the isntrument works within the canal and it may encourage widining in or it may diminish the need for an instrument to drag the user into the canal)
34
What is the function of the positive rake angle?
- Provides the active cutting action of the K3
35
What is the function of third radial land?
- Stabilizes and keeps the instrument centred in the canal and minimises 'over-engagement'
36
What is the function of wide radial land?
- PRovides blade support while adding peripheral strength to resist torsional and rotary stresses
37
What is the function of radial land relief?
- Reduces friction on the canal wall
38
What are the ideal properties of an irrigant? (8)
- 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
39
What is the irrigant we use most often?
- Sodium hypochlorite (NaOCl)
40
Explain sodium hypochlorite?
- NaOCl ionises in water into Na+ and the hypochlorite ion, OCl-
- Establishes equilibrium with hypochlorous acid (HOCl)
- Acid/neutral HOCl predominates
- pH 9 and above OCl- predominates
- HOCl is responsible for antibacterial activity
41
Give examples of properties of sodium hypochlorite? (3)
- Effect on organic material
- Inability to remove smear layer by itself (but it can disrupt the organic component of the smear layer)
- Possible effect on dentine properties (because it can interact with the organic component of dentine)
42
What factors are important for NaOCl function? (5)
- Concentration
- Volume
- Contact
- Mechanical irrigation
- Exchange
43
Why do we need to remove the smear layer to prepare the canal for obturation? (5)
- Smear layer formed during preparation
- Organic pulpal material and inorganic dental debris
- Superficial 1-5 micrometres with packing into tubles
- Bacterial contamination, substrate interferes with disinfection
- Prevents sealer penetration
44
What moight we use to remove the smear layer? (4)
- 17% EDTA
- 10% citric acid
- MTAD (Mixture of a tetracycline isomer, an acid and a detergent)
- Sonic and ultrasonic irrigation (can be used to activate the irrigant and tro improve our efficacy)
- Remeber to watch apical control
45
Which material would we use to remove the smear layer from a canal?
17% EDTA used in the dental hospital
46
Why do we need to be careful with irrigant selection?
- We don't want to mix these irrigants - they do interact
- Have to make sure that once we have used the NaOCl that we withdraw and then we place the EDTA into a canal that has no hypochlorite in it
- Some people use a sterile water rinse between irrigants
- Need to be careful that we don't introduce precipitates which will undo all the hard work we have done
47
What are the possible irrigant interactions which can occur? (3)
- Interaction with NaOCl forms para-chloroaniline
- Cytotoxic and carcinogenic
- Uncertain bioavailability
48
What are the properties of an ideal obturation material? (11)
- Easily manipulated with ample working time
- Dimensionally by tissue fluids stable
- Seals the canal laterally and apically
- Non-irritant
- Umpervious to moisture
- Unaffected by tissue fluids
- Inhibits bacterial growth
- Radiopaque
- Does not discolour tooth
- easily removed if necessary
49
What is the most common core material for root canals?
Gutta-percha
| - one of the oldest dental materials in use today
50
What is gutta-percha produced from?
- PRoduced from juice of trees of sapodilla family
51
What is GP a polymer of?
- Natural rubber and GP are polymers of the same monomer - isoprene
- Trans isomer of polyisoprene
52
GP exists in 2 crystalline forms. What are they?
- Alpha and beta
53
How are alpha and beta GP formed? (5)
- Alpha phase is the naturally occurring form
- Alpha phase heated above 65 degrees celcius and melts into amorphous phase
- Cooled slowly returns to alpha phase
- Cooled rapidly recrystalises as beta phase
- Beta phase used in commercially prepared dental GP
54
Which form of GP is used for dental GP?
- Beta gutta-percha
55
What are the components that make up GP cones? (4)
- 20% GP
- 65% zinc oxide
- 10% radiopacifiers
- 5% plasticizers
56
What are the different forms of GP cones we can get? (4)
- Standardised
- non-standardised
- Size-matched
- Also get thermal obturation materials
57
Can GP be modified?
- GP has been modified in attempts to improve the properties
- Can see we have GP that has been coated with different materials to try to improve interaction with sealers or try to enhance the antimicrobial activity of the cones
- They have been stiffened to improve their handling characteristics
- Probably a lot more to come
58
What are the functions of sealers? (3)
- seals space between dentinal wall and core
- Fills voids 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? (11)
- Exhibits tackiness to provide good adhesion
- Establishes a hermetic seal
- Radiopaque
- Easily mixed
- No shrinkage on setting
- Non-staining
- Bacteriostatic or does not encourage growth
- Slow set
- Insoluble in tissue fluids
- Tissue tolerant
- Soluble on retreatment
60
What is zonc oxide and eugenol? (7)
- Sealer
- Missing vehicle mostly eugenol
- Finely sifted zinc oxide to enhance flow
- Radiopacity < GP
- Can be modified with germicides
- Resin or canada balsam to increase dentine adhesion
- Corticosteroids
61
What is a good property of zinc oxide?
- Effective antimicrobial and may afford cytoprotection
62
What is a good property of resin acids?
- Resin acids 90% component of Rosins affect lipids in cell membrane thus strongly antimicrobial/cytotoxic
- Although toxic, may overall be beneficial with longlasting antimicrobial effect combined with cytoprotective effects
63
Exaplin the setting process of Zinc Oxide and Eugenol? (4)
- Setting is a chamical process combined with physical embedding of zinc oxide in a matrix of zinc eugenolate
- Eugenolate formation constitutes hardening - CaOH accelerates this process so muct be removed from canals
- Free eugenol which remains can act as an irritant
- Lose volume with time due to dissolution - resins can modify this
64
Why can glass ionomer sealers be advantageous?
- Due to their dentine bonding properties
65
Give 3 reasons why me night not want to use glass ionomer sealers?
- Removal upon retreatment is difficult
- Minimal antimicrobial activity
- Little clinical data to support use
66
Which sealer do we use in the dental hospital?
- Resin sealers
| - These are the mainstay of sealers
67
What is a resin sealer
- Epoxy resin
68
How are resin sealers mixed?
- Paste-paste mixing
69
What is the setting of resin sealers like?
- Slow setting - 8 hours
70
Give 2 positives of resin sealers?
- Good sealing ability
| - Good flow
71
What is the toxicity of resin sealers like?
- Initial toxicity declining after 24 hours
72
What is Epiphany?
- Resin sealer
- Dual cure dental resin composite sealer - used with Resilon
- Requires self-etch primer (very difficult to etch effectively in a root canal)
73
Give examples of Epiphany? (5)
- BisGMA
- Ethoxylated BisGMA
- Urethane-dimethacrylate UDMA
- Hydrophilic difunctional methacrylates
- Fillers of calcium hydroxate, barium sulphate, barium glass and silica
74
What is EndoRez?
- It is a UDMA resin-based sealer
| - Hydrophilic
75
Give 3 advantages of EndoRez?
- Good penetration into tubules
- Biocompatible
- Good radio-opacity
76
What is the pH of Calcium Silicate Sealers?
- High pH (12.8) during the initial 24 hours of the setting
77
Are Calcium Silicate sealers hydrophobic or hydrophilic?
- Hydrophilic
78
What properties does having a high pH initially when setting for Calcium Silicate sealers? (2)
- Antimicorbial
| - Osteoinductive
79
What is osteoinduction?
- The process by which osteogenesis is induced
80
Give advantageous properties of calcium silicate sealers? (6)
- Enhanced biocompatibility
- Does not shrink on setting
- Non-resorbable
- Excellent sealing ability
- Quick set - three to four hours - requires moisture
- Easy to use
81
What is one disadvantage of calcium silicate sealers?
- can be quite expensive
82
Why do we not want to be using medicated sealers?
- Sealers containing paraformaldehyde are highly toxic (not acceptable)
- Leand and mercury components removed
- Severe and permanent toxic effects on periradicular tissues
- Sargenti paste, endomethasone, SPAD
83
Give the ways in which pulp capping/ root filling materials can be used? (7)
- Furcation perforation repair
- Root resorption repair
- Apexification
- Pulp cap
- Pulpotomy & pulp regeneration
- Lateral perforation repair
- Apicoectomy
84
Give the characteristics of grey mineral trioxide aggregates? (4)
- Earliest formulations
- Less toxic than Portland cement
- Better setting characteristics
- Tooth discoloration (problem)
85
Give the composition of grey mineral trioxide aggregates? (5)
- Tricalcium silicate
- Dicalcium silicate
- Tricalcium aluminate
- Tetracalcium aluminoferrite
- Bismuth oxide
86
Give the characteristics of white mineral trioxide aggregate? (2)
- Smaller particle size
| - Reduced discolouration
87
Give the composition of white mineral trioxide aggregate? (5)
- Tricalcium silicate
- Dicalcium silicate
- Calcium aluminate
- Bismuth oxide
- Calcium sulphate dehydrate
88
Why can't we use MTA cement in the oral cavity?
- Because it takes so long to set it will be washed out by saliva before it has the chance to set
89
Explain the setting reaction of 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
90
What are bioceramic cements?
- Biodentine is a similar material with some modifications which allow it to set a lot more rapidly so it is great for direct pulp capping
- It can be use to build up the entire restoration for direct pulp capping - so no need for a surface layer
- Sets in an extended time - minutes not hours
- Later you can cut back the biodentine and replace with composite
91
Aome bioceramics are great because they induce osteogenesis. What does this mean?
- The encourage bone formation
| - Probably related to the fact that you get a change in pH and you get hydroxyapatite layer formed on the surface
92
What is a sealer used for?
- To create a fluid-tight seal
