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BDS 3 Duplicated > Dental Materials > Flashcards

Dental Materials Flashcards

1
Q

What is a dental impression used for?

A

Recording the intra-oral structures

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2
Q

What information do we receive from the dental impression?

A

Negative imprint of the oral structures from which a positive reproduction can be formed

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3
Q

What is the process of a conventional impression?

A
  1. Material is mixed
  2. Loaded into impressions tray
  3. Inserted into mouth
  4. Allowed to set
  5. Remove from mouth
  6. Permits a cast to be made
  7. Device is made of this cast
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4
Q

What are the 2 main uses for dental impressions?

A

Study casts and construction of dental appliances

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5
Q

Name some forms of dental applicances?

A
  • Orthodontic appliances
  • Removable dentures
  • Mouth guards and bleaching trays
  • Inlays and onlays
  • Crowns
  • Bridges
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6
Q

What are the requirements for an impressions tray?

A
  • Rigid and non-flexible under load
  • Extend sufficiently to support the impression material
  • Fit loosely around dental arch avoiding soft tissues
  • Adequate means of retention of impression material in tray
  • A handle
  • Decontaminated
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7
Q

Name the 2 main material types of trays?

A

Plastic and Metal

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8
Q

Problems caused by a non-rigid impressions tray?

A
  • Tray shape is altered intra-orally
  • Distorts the impression material
  • Cast inaccurate
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9
Q

Name the 2 main ways impression trays ensure the impression material stays in the tray?

A 
Trat design:
- perforations
- rim-lock
Tray adhesives:
- types
- usage
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10
Q

How do perforations ensure retention?

A

Material extruded through holes retaining the material to tray mechanically

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11
Q

How does rim-lock ensure retention?

A

Retentive feature around extent of tray

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12
Q

What are tray waves and how do they improve retention?

A
  • Periphery waves

- Helps to contain the fluid impression material in stock impression trays

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13
Q

What is greenstick and how does it improve retention?

A
  • Rigid impression material

- Contains the fluid impression material in impression tray

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14
Q

What are the chemical constituents and purposes of the constituents of greenstick?

A
  • Resin and waves for consistency control
  • Stearic acid as a plasticiser
  • CaCO3 as a filler, colouring agent and controlling rigidity
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15
Q

How is greenstick prepared?

A
  • Transition temp at 55-60C

- Softened by hot water or flame

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16
Q

What is the typical tray adhesive used with alginate?

A

10-12% toluene in 45-50% isopropanol

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17
Q

What is the mechanism of action of a tray adhesive?

A
  • Based on contact technology
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18
Q

What is the process of tray adhesive use? but, when should they never be used with?

A
  • Applied to tray and allow to dry
  • used sparingly
  • Periphery covered
    Never on metal trays
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19
Q

Name the 2 main presentations of tray adhesive?

A

Spray and paint on

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20
Q

What are the benefits of special trays?

A
  • Permits equal thickness of impression material

- Dimensional change of impression material theoretically the same in all dimensions

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21
Q

What are special trays made from?

A

Polymethylmethacrylate or Shellac

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22
Q

What are the specific spacing of the perforations according to material used?

A

3mm - alginate
2mm - C-silicone
1mm - impression paste

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23
Q

Name the 10 most important properties of impression materials?

A
  1. easy to handle
  2. compatible with oral fluids
  3. reproduce detail accurately
  4. good tear resistance
  5. no adverse effects
  6. pleasant taste
  7. easily removable
  8. easy decontamination
  9. remain dimensionally table
  10. compatible with all model construction materials
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24
Q

What is the process of impression decontamination?

A
  1. Immediately after removal rinsed under cold running water
  2. Tray and material immersed in water-based disinfection solution (MFI)
  3. Impression then rinsed gently with tap water (over-disinfection can lead to changes)
  4. impression placed in sealed polythene bag and sent to lab
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25
What is alginate chemcially?
Irreversible hydrocolloid
26
What is a colloid?
A substance which is distributed evenly through a material
27
What 2 phases can alginate be in?
Dispersed and continuous
28
What is the chemical equation for alginate?
Sodium and potassium salts + alginic acid forms alginate
29
What are the chemical constituents of alginate and their function? ***
- K/Na alginate - dissolves in water to form a hydrogel with Ca - CaSO4 dihydrate - reacts with soluble Na alginate to form insoluble Ca alginate - Borate - reduces inhibition of setting of plaster - Silicate powder - filler controls consistency and flexibility - NaPO4 act as a retarder by reacting with Ca - Na silicofluoride - controls pH - Glycols - reduces powder dustiness - Peppermint - taste
30
What is the process of alginate setting reaction?
- Potassium (sodium) alginate + calcium sulphate dihydrate + water → calcium alginate + potassium (sodium) sulphate - NaPO4 retards setting - Set after PO4 runs out
31
What is the mixing, working and setting times of alginate?
Mixing: 45-60s Working: 45s (fast) 75s (reg) Setting: 1-4.5 mins
32
How to reduce permanent deformation when using alginate?
- Reducing amount of compression - Reducing time the impression is under compression - Allowing time for recovery before pouring model
33
How to improve dimensional stability with alginate?
- Allow the alginate to heal over bench - Control relative humidity - Proper storage - Syneresis (contracts on standing) - Imbibition (wrap in damot tissue and place in bag)
34
What are the 3 factors which affect the strength of alginate?
- P/L ratio = weaker - insufficient spatulation (improper dissolving) - over speculation (disrupts formation of Ca alginate gel)
35
What are the advantages and disadvantages of alginate as an impressions material?
``` Adv: - easy slow - reproduce detail - fast set - minimal tissue displacement - cheap - tolerable Dis: - poor dimensional stability - poor tear strength - distorts if unsupported 0 3mm thickness required - easy to include air in bag ```
36
What are the indications of use for alginate?
Less accuracy and detail is required: - study cast - denture construction - removable ortho - teeth opposing an indirect cast restoration
37
How to properly prepare the alginate mixture?
- shake container - dispense metered volumes - use correct bowl and spatula - add powder to water - mix in a 8-figure motion - swipe material against bowl side to reduce air incorporation
38
What are some useful clinical tips fr alginate use?
- ensure smooth impression surface - smear into fissures - place some on palate - evert lips and retract cheeks - ensure centrality - hold still - ensure full set - remove quickly from mouth
39
What are the common failures of poor alginate mixtures?
- Grainy - Treating - Bubbles - Chalky model - Distortion
40
What is the reason for a grainy alginate?
- inadequate or prolonged mixing | - ratio too low
41
What is the reason for alginate tearing?
- Inadequate bulk | - premature removal
42
What is the reason for external bubbles on alginate?
Air incorparation
43
What is the reason for a chalky alginate?
- Inadequate cleaning - Excess water in impression - Premature removal
44
What is the reason for a distorted alginate?
- Delayed pouring of impression - Tray movement - Premature removal
45
Name a commercially available alginate product?
Tropicalgin by Zhermack
46
How can gypsum improve the quality of an alginate impression? but what is necessary to remember?
- Good surface quality and detail gain - Avoid water interaction with gypsum - Set gypsum not in contact with alginate for periods of serval hours
47
What is the defintion of a dental cast?
Replica of the structures in the oral cavity
48
What are dental plasters and dental stones based on?
Gypsum CaSO4 dihydrate Crystalline in form
49
Explain the process of production for Plaster of Paris?
Heating crystalline gypsum to between 110-130 in open vessel Forms Beta-Ca sulphate hemihydrate Add water reverting back to dihydrate Highly exothermic reaction
50
Describe the appearance of beta-Ca sulphate hemihydrate?
Porous powder Irregular shaped particles Not closely packed together
51
How does the the crystalline hemihydrate from impact the plaster?
Determines the precise type of plaster produced
52
Explain the process of dental stone?
Dihydrate is heated to 125C under pressure in presence of water vapour
53
Describe the appearance of alpha-Ca sulphate hemihydrate
Unformorm shaped particles | Reduced porosity
54
What are the 5 chemical constituents for dental stone?
``` CaSO4 hemihydrate Water KSO4 Borax NaCl ```
55
What is the function of KSO4 in the dental stone mixture?
``` 2% Accelerates setting time by half Crystallises quickly Encourages further crystal growth 4% decreases expansion ```
56
What is the function of Borax in the dental stone mixture?
2% Retards the set Leads to formation of Ca salts of the borate Deposited on the dihydrate crystals preventing further crystal growth
57
What is the function of NaCl in the dental stone mixture?
Reduces expansion Extra sites for crystal growth Keeps crystals closer together
58
What is the function of CaSO4 dihydrate in the dentals tone mixture?
0.5-1% Provides nuclei of crystallisation Acts as an accelerator
59
Explain the dental stone setting process?
Water is added to hemihydrate poder Converted to dehydrate As solubility of dihydrate is low a supersaturated solution rapidly forms Stability of this solution is low, the dihydrate crystals start to precipitate out Process continues as more hemihydrate is dissolved in water
60
What are the compressive strength properties of dental stone?
``` 12-45 MPa Compressive strength Greater porosity - Low CS B-hemihydrate - Low CS Further water lost to atmosphere over time After 7% water lost - 60 MPa gained ```
61
What are the surface hardness and abrasion properties for dental stone?
Higher hardness values assoc with higher compressive strength With water loss to atmosphere hardness also increases Open crystal structure is stable once set but is porous permitting water up take Leads to surface degradation of the model
62
Describe how you could increases the abrasion resistance of a dental stone cast?
``` Impregnation: Epoxy resin Methylmethacrylate Glycerin Haderning solutions containing 30% colloidal silica (increases hardness) ```
63
What are the reproduction of detail properties for dental stone?
Not ideal for very fine detail ISo requires 0.05mm line using a specific consistency of mixed materials But considered sufficient for most dental applications
64
What are the hygroscopic expansion properties for dental stone?
Stone is immersed in water during set Crystals can grow more freely Degree of expansion is greater Affect relatively insignificant
65
What are the volumetric change on setting properties fro dental stone?
Theoretically expected Slight setting expansions is always observed Expansion is due to crystal growth of dihydrate and the set materials having micro porosities Models will be fractionally oversized and prosthesis too big
66
What is the difference in setting expansion between plaster and stone?
Plaster: - 0.3-0.4% Stone: - 0.05-0.3%
67
What are the working and setting time properties for dental stone?
2-3 minute working time | 2-3 minute setting time
68
What is the definition of working time?
The point at which the material can be manipulated into the impression satisfactorily
69
How can the manufacture manipulate the setting time for htypsum?
KSO4 Borax NaCl CASO4 dihydrate
70
Indications for dental stone (gypsum)?
Study casts for general diagnosis Working casts: - denture full and partial - ortho appliances
71
What is the definition of a working cast?
Cast onto which the restoration is constructed in the lab
72
What is the definition of a study cast?
Cast is intended to be used for treatment planning purposes
73
How compatible is a gypsum-based material?
Compatible with all commonly used impression materials
74
How can you adjust the behaviour of the dental stone material?
P:L ratio Water temperature Degree of spatulation of the mixture
75
What adverse reactions to the dental stone will excess water procedures?
Aid mixing Slow setting time Weakened plaster
76
What occurs if you increases the temp of the water added to the mixture for gypsum-based impression materials?
Solubility of the hemihydrate and dihydrate increases Mobility of the Ca and SO4 ions increases so set is accelerated Results in combo of both small accelerate in rate of reaction and a reduction in setting time
77
What are the adverse reactions of changing spatulation speed and time for dental stone?
Particles are wetted thoroughly so a smooth mix forms Increasing speed or time of spatulation reduces setting time, as crystal nuclei are disrupted forming more crystal sites and more rapid precip of dihydrate Greater setting expansion
78
What is the definition of a silicone impression material?
Elastomeric impression material Condensation reaction with ethyl alcohol given off Hydrophobic
79
Name the 5 constituents of silicone impression material?
``` Dimethyl siloxane Colloidal silica or CuCO3 Stannous octoate Alkyl silicate Colloidal silica ```
80
What is the function of dimethyl siloxane in silicone impression material?
low Mr silicone which has reactive terminal hydroxyl end groups
81
What is the function of CuCO3/Colloidal silica in silicone impression material?
Filler, as silicone polymer is liquid | FIller particles between 5-10 um
82
What is the function of Stannous octoate in silicone impression material?
Accelerator
83
What is the function of Alkyl silicate in silicone impression material?
Accelerator
84
What is the function of Colloidal silica in silicone impression material?
Thickening agent
85
Explain the reaction for condensation silicones?
Condensation reaction with ethyl alcohol given off 3D silicone matrix is formed on setting Marked shrinkage on polymerisation Not as accurate as addition silicones due to setting reaction Slight exothermic Poured ASAP Accurate proportioning difficult leads to variability
86
What is the function of alkyl silicate in the silicone material and what occurs if the amount is reduced?
``` Creates cross linking Reduced amount causes: - weaker material - decreased tear resistance - increased permanent set Moisture sensitive (setting inhibited) ```
87
Why does stannous octoate has a limited shelf-life? (silicone)
Oxidises Alkyl silicate not stable in presence of tin ester Minimal shrinkage as bulk of material is filler
88
How much does silicone shrink?
Proportional to the amount of polysiloxane present
89
Name the 3 presentation of condensation silicones?
Putty Putty and light body Paste/Paste
90
Explain the mixing technique for condensation silicone?
Mixed with low viscosity paste accelerator | Kneaded into mass of putty
91
Give 1 trade name for condensation silicones?
Lab Putty (Coltene Whaledent)
92
What are the indications for condensation silicone?
Where dimensional stability is not crucial: - fixed prosthodontics (putty and light body) - removable prosthodontics (putty) (reline and rebase) Produce wax replicas of denture
93
Name the 2 types of impression composition materials?
Greenstick | Red cake
94
Give a description of greenstick?
Rigind non-elastic impression material Used for border moulding of impression trays especially the post dam Mucocompressive
95
When to avoid greenstick?
Allergy to colophony (asthma)
96
Give a description of red cake?
Thermoplastic Impression Compound (Trade name) Sheets or sticks Indicated for first impression of the edentulous arch
97
What are the chemical constituents and purposes of the constituents of red cake?
- Resin and waves for consistency control - Stearic acid as a plasticiser - CaCO3 as a filler, colouring agent and controlling rigidity
98
What are the properties for red cake?
``` Transition temp between 55-60C Hot water both or over naked flame Overheating can create volatile compounds Or leaching from overheating Full softening is essential Mucocompression gained Highly viscous Dimensional stability poor 1/5% ```
99
Explain the process of how to use red cake chairside?
``` Boiling water Line dish with gause Leave for 1 min to soften Place into impression tray Place back in bath to soften Bit back Check to see if safe for intra-oral Place Take impression Cool impression to keep dimension ```
100
Why do we need to use occlusal registration?
Not possible to relate the dental arches to each other due to lack of index teeth Casts can't be related to each other
101
What is the aim of occulsa registratyion?
Records the relationship of the dental arches to each other intraorally which can then be used to relate the casts extraorally
102
Name 3 types of occlusal registration materials?
A-silicones/polyether Higher methacrylates Waxes
103
Give a description of a-silicones/polyether bite reg pastes?
Easy to manipulate and move May 'bounce' usually syringed in a gun and allowed to set
104
Give 2 names of bite reg paste commercial products?
Jet Bite Blue, Coltene Whaledent, Silicone | Memosil 2, Heraeus Kulzer, Silicone
105
Give a description of higher methacrylates?
``` Based on (poly)methylmethacrylate Fluid/dough form Sets to a solid Rigid Highly accurate Can get into undercuts Used as a dough or coping + dough ```
106
What is the definition of coping?
Thin layer of material which covers the preparation to the margins
107
How to use higher methacrylates in bite registration?
Mix dough, place on coping, patient bites Removed when material set Can be replaced on model to indicate occlusal relationship
108
Give 1 example of a commercial name for a higher methacrylate?
DuraLay II (Reliance)
109
What can higher methacrylates show?
Dough, removed and measured | Indicates amount of interocclusal clearance
110
What is the definition of an addition silicone impression material
Elastomeric impression material Termed after setting reaction addition polymerisation reaction Hydrophobic
111
Name the 6 constituents for addition silicone impression materials and their functions?
Polymethyl hydrogen siloxane - polymer Siloxane prepolymers - cross linking polymer Quartz - filler Divinyl polydimethylsiloxane - polymer Chloroplatinic salt - catalyst Surfactant and retards - reg of setting and aids to wetting of hydrophobic silicone
112
How can the amount of filler change the category of the addition silicone impression material?
Heavy Universal Light-body
113
What 2 pastes are needed to form an addition silicone impression material?
Base paste | Catalyst paste
114
What must both pastes share for an addition silicone impression material?
The same consistency to facilitate mixing
115
What is the function of surfactants for an addition silicone impression material?
Address the hydrophobicity of the polysiloxanes Facilitates wetting of the surface of the preparation and the soft tissues Aids pouring of the model as wet stone has an affinity for the hydrophilic surface of the impression
116
What reaction will occur if the mixture has moisture contamination for an addition silicone impression material?
Rolled edge of preparation margins
117
Describe the setting reaction for an addition silicone impression material?
Polymethyl hydrogen siloxane in one paste + vinyl-terminated polysiloxane on the other paste Addition polymerisation reaction
118
Explain the setting reaction chemistry for an addition silicone impression material?
Hydrogen from the hydrogen siloxane backbone links with the vinyl group on the other siloxane chain Forming cross-link polymer No byproducts
119
What type of catalyst is present for an addition silicone impression material and what must you avoid interacting with it?
Platinum Sulphur containing materials such as latex gloves Results in weakened material Latex-free gloves
120
Describe the good properties of an addition silicone impression material?
Highly hydrophobic V good dimensional stability (best) Many models can be poured
121
Describe the bad properties for the use of an addition silicone impression material?
Too accurate and not compensated for during the investment and casting process Too small a die producing a small cast
122
When will the addition silicone impression material increase in stiffness and why?
After 2-3 hrs due to further crosslinking
123
How to mitigate the poor tear resistance of an addition silicone impression material?
Leave in the mouth for longer
124
How to mitigate the bad interaction of the addition silicone impression material to the oxygen inhibition layer of resin-based composite materials?
Apply a layers of separator on recently placed resin-based composite materials
125
Name 3 advantages and disadvantages for an addition silicone impression material?
``` Adv: - good detail reproduced - excellent dimensional stability - high patient acceptance Dis: - hydrophobic - too accurate - tear resistance poor - expensive ```
126
Name the 2 indications for an addition silicone impression material?
Fixed and removable cast restorations Good if distance between lap and surgery is far Suitable for the same indications as alginate More surface detail and long term dimensional stability
127
Name the 5 types of presentation for addition silicone impression materials?
``` Putty Heavy-bodied Universal bodied Light-bodied Extra light-bodied pastes ```
128
Give 1 example of a commercially available addition silicone impression material?
Affinis Coltene Whaledent
129
What is the effect to a model if addition silicones release hydrogen gas as a by product?
Porosity on the die material
130
What can be used to absorb the hydrogen for an addition silicone impression material?
Palladium
131
How to pour a cast for a gypsum based material or epoxy?
Leave for 30 mins before pouring cast | And leave overnight if epoxy is to be sued to make the die
132
What are the 2 main constituents of an impression paste?
Zinc oxide | Eugenol-based impression
133
Name the 2 main indications for an impression paste?
Making working impression of edentulous arches | Denture relining material
134
What spacing does impression paste need in a special tray?
1mm | Used in thin sections
135
Name the 2 pastes used in an impression paste?
Base | Catalyst
136
Name the constituents for the base paste of an impression paste and their function?
Base: - Zinc oxide - reactive component - Inert oils - plasticiser and reduced irritation of eugenol - Zinc acetate - acclerator
137
Name the constituents for the catalyst paste of an impression paste and their function?
Catalyst: - eugenol - reactive component - Mg/CaCl - accelerator - Talc/Kaolin or silica - inert fillers - Gum rosin - binder (50%) - Lanolin/resinous balsam - viscosity and flow regulator
138
What is the function of gum rosin of an impression paste?
Binder Gives the paste body Reduces the risk of separation of the components Thermoplastic and so can be softened in hot water aiding is removal from the plaster model
139
What catalyses the setting reaction for an impression paste?
Water
140
Describe the setting reaction of impression paste?
Similar to ZOE
141
Describe the process of the setting reaction of the impression paste?
Sets slowly passing through a thickening phase after which it is hard to manipulate Further phases of hardening occur before the impression should be removed Setting reaction accelerates with the increases in oral temp and humidity Check for set on mixing pad
142
Name 3 good properties of the impression paste?
Rigid impression produced Good fine detail reproduced Mucostatic impression
143
Name 3 bad properties of the impression paste?
Lacks elasticity leading to breakage or distortion when removed from undercuts Adheres to dry surfaces Small dimensional change (0.15% shrinkage)
144
Describe the process of mixing impression paste?
``` By hand Using paper pad Clarident spatula Paste/paste system Each paste a different colour Ensures mixed thoroughly ```
145
Describe the best practice to remove the impression paste from the spatula to the tray?
Warm spatula above temp rosin soften and wipe
146
What strange sensations can impression paste give to a paitient?
Tingling or mild burning sensation intra-orally
147
How to avoid the impression paste sticking to the patients extraoral tissues?
Apply petroleum jelly to extraoral features | A lot
148
Give 1 example of a commercially available impression paste?
Impression paste by SS White
149
What material can be sued to make a working model?
Gypsum-based
150
How long will a gypsum-based material cast take to set?
At least 1 hr
151
How to remove the impression paste from the gypsum-based model?
Immersed in warm water to remove the impression
152
What type of cast can an impression paste only be sued with?
Gypsum-based model | No separating medium is required
153
What are the indications for impression plaster?
USed to record endentulous ridges
154
Name 5 good properties for impression plaster?
``` Good surface detail Tolerated by patient Small setting expansion Good dimensional stability Hydrophilic ```
155
Name 3 bad properties for impression plaster?
Sets ridigly and is very brittle Must be fractured to release it from undercuts Pieced back together so that the cast may be poured (no recovery from deformation)
156
Describe the setting reaction and constituents for impression plaster?
Similar to plaster of PAris with the beta-CaSO4 hemihydrate More KSO4 included to control expansion Borax is needed to retard the set KSO4 also acts as accelerator Requires a higher water to powder ratio when used as an impression material Runnier mix if compared to pouring a model Setting is exothermic
157
Name 2 disadvantages of impression plaster?
Salivate excessively and can damage surface detail | Hard to tolerate the upper impression as material flows quite readily during early setting reaction
158
Describe the mxijgn process for impression plaster?
Hand Correct P:L Powder sifted into water and left for short time before mixing Powder particles fully wetted
159
How must the powder for an impression paste be stored?
Airtight tin to stop water entering the tin
160
What sized spacing is needed for impression plaster in a special tray?
1mm
161
How long is the working time for impression plaster?
2-3 mins
162
How do you insert the tray with impression plaster as the impression material?
Tray moved side to side on insertion so material can flow
163
How to decontaminate impression plaster?
Decontamination procedure follow manufacturer's instructions
164
When casting impression plaster what should you use as a separator?
A separating medium Solution of Na alginate painted onto impression used Prevents plaster used for model adhering to the impression plaster
165
What is the definition of a wax?
``` Type of lipid Insoluble in water Soluble in non-polar solvents Melt above 45C Plastic at ambient temps ```
166
Name the 5 bases to make a wax?
``` Animal/vegetable fat Gums FAs Oils Resins ```
167
What is the melting point, hardness and role in dental wax for Carnauba?
Organic 84-91 High Increases melting range and hardness
168
What is the melting point, hardness and role in dental wax for Ouricury?
Organic 79-84 High Increases melting range and hardness
169
What is the melting point, hardness and role in dental wax for Candelilla?
Organic 68-75 High Increases hardness of paraffin wax
170
What is the melting point, hardness and role in dental wax for Beeswax?
Organic 62-68 Medium Common base for many waxes
171
What is the melting point, hardness and role in dental wax for Japan Wax?
Organic 53 Medium/low May be substituited for beeswax
172
What is the melting point, hardness and role in dental wax for Paraffin?
Synthetic 40-51 Medium Common base wax
173
What is the melting point, hardness and role in dental wax for Ozokerite
65-69 Medium/high Great affinity for oils and raises melting temp
174
What is the melting point, hardness and role in dental wax for Ceresin?
77-93 Medium/High Increases melting range
175
What is the melting point, hardness and role in dental wax for Montan?
72-90 Medium/high Increases melting range
176
What is the melting point, hardness and role in dental wax for Barnsdahl?
70-74 Medium/High Increases melting range and hardness and reduces paraffin wax flow
177
Origin of the Carnauba wax?
Copernicia palm
178
Origin of Ouricury wax?
Feather palm
179
Origin of the Candelilla wax?
Euphorbia antisyphilitica
180
Origin of the Japan wax?
Really a fat containing glycerides of palmitic and stearic acid From sumac tree Lacquer
181
What is the definition of a lacquer?
Clear or coloured varnish that dries by solvent evaop to produce a hard and durable finish
182
Origin of Spermaceti wax?
Sperm whale
183
Origin of bees wax?
Bees
184
Why can natural waxes have very varying properties within the same wax?
Source difference | Time obtained
185
What is the definition of mineral waxes?
Derived from refining petroleum products Available as paraffin wax Show volumetric contraction (10-16%) during cooling and solidification
186
What is the defintion of microcrystalline waxes?
``` Derived from heavier oil fractions produced during petroleum distillation Higher MP Less volumetric contraction Tougher Formed into plates Oil reduces hardness ```
187
Give 4 examples of microcrystalline waxes?
Ceresin Ozokerite Montan Barnsdahl
188
Which substances can you later to alter the overall properties of a wax?
Gums Fats Resins
189
Why do dental waxes have a melting range?
As there are many different constituents on the eax which melt at different temps
190
What is a key property a dental wax must have?
Change rapidly from solid to liquid
191
What to consider when mixing a dental wax?
Amount and mode of thermal expansion | Ensure the properties of the wax blended is suitable for each application
192
What are the physical properties of waxes?
Compressive strength and elastic moduli are relatively low | Beeswax weakest and carnauba wax strongest and most elastic
193
How can flow of wax be adjusted?
Change in temperature below MP | Flow controlled by composition
194
How long should be left between completion of wax pattern and investment?
Short as possible as, wax shouldn't be left to stress relieve Wax can rebound and loss its shape
195
What are the indications for baseplate and modelling wax?
``` Base of denture Bite blocks (occlusal rim) ```
196
Name the 5 constitients of baseplate wax?
``` Paraffin waxes (ceresin + beeswax and some carnauba was as hardener) Al/Cu particles as strengtheners Resins Oils Colouring agents ```
197
What are the properties of baseplate wax?
FLow determined by climate present in DImensional stability not crucial Beeswax permits surface to be smoothed and contoured MP < 100 Residue wax on teeth can interfere with bonding and interlocking of resin with artificial teeth
198
What is the only successful application of wax?
Bite rims to record jaw relationship
199
What is the definition of shellac?
``` Derived from insects Thermoplastic Rigid when solid Waxes can be added More stable at mouth temps ```
200
What are the properties of an acrylic base plate?
More rigid Better retention More expesnive
201
Indication for acrylic base plate?
Fit and retention of prototype and therefore final denture
202
What is a clinical tip for using wax bite black?
Pass wax through cold water between spells in mouth Reduces expansion Returns to original size and shape
203
What is the definition of Moyco beauty wax?
Record occlusal relationships Strengthened to overcome distortion Brittle
204
What is the definition of sticky wax?
Beeswax mixed with natural resins (dammar) Firm and brittle once cet fracture > flex FLows when melted Hold casts together with metal prior to mounting
205
Name 4 denture base materials?
Wax Shellac Acrylic Metal
206
Name 4 types of cast metal used for denture base?
Cobalt-Chromium Nickel-Chromium Pure titanium Titanium
207
Name 3 materials denture teeth can be constructed from?
PMMA (polymethylmethacrylate) Bis-GMA Ceramic
208
What are the good properties of PMMA denture teeth?
Highly cross-linked resin Good hardness and wear resistance Resists crazing Good abrasion resistance
209
What are the optical considerations for denture teeth choice?
``` Aesthetics are key Need to be translucent and opalescent Shade guide Denture teeth should fluoresce like natural teeth under UV light Different shapes and sizes ```
210
Name the 2 types of construction methods for PMMA denture teeth?
Inject into mould | Built up in layers
211
Explain the process of inject into mould construction method for PMMA denture teeth?
Injected into a mould (acrylic powder is softened by heating and forced into the mould under pressure further divided into dough and injection moulded
212
Explain the built up in layers construction method for PMMA denture teeth?
Best aesthetics
213
What are the good properties of ceramic denture teeth?
Excellent aesthetics | Good wear resistance
214
What are the bad properties of cermaic denture teeth?
Hard so can't be adjusted easily If adjusted lose surface glaze Glaze can't be replaced Brittle Unnatural chattering and clicking on contact Retention to denture base via diatoric hole on undersurface of teeth (mechanical) PMMA is forced into retention holes No chemical bond between teeth and denture allowing teeth to detach during lifetime Silane can be used to create chemical union but is unreliable
215
What are the contraindications for ceramic teeth?
Reduced ridge support as more force is transmitted to the ridge Need sufficient bulk for strength contraindicated where little interocclusal clearance is present
216
What occurs if the denture teeth are poorly bonded to the denture base?
Stress concentrations Debonding of the tooth Better quality teeth (highly corss-linked) have a decreased ability to bond
217
How can highly cross-linked teeth achieve a better bond to the denture base?
Build the tooth with less crosslinking in the bonding area
218
How to enhance chemical adhesion for a denture tooth?
Resin at base of tooth can be softened with a monomer | chemicals must be compatible
219
How can micromechanical retention be achieved for a denture tooth?
Roughening
220
Which curing method is better for union between denture tooth and base
Heat is better | Cold is other option
221
What can you treat denture teeth to enhance bond strength?
4-META
222
What properties must the denture teeth and base share to enable compatibility?
Modulus of elasticity Coefficient of thermal expansion This prevents crazing and cracking around the base
223
Explain the process of processing of a denture?
``` Convert the wax prototype into finished acrylic appliance Invested Boiled out Acrylic placed into plask Cured Flash removed Polished ```
224
How to flask acrylic?
Gypsum bonded investment material used such as binder is beta Ca SO4 Low temp
225
Explain the process of flasking during the denture processing process?
Waxed up denture is sealed onto a master model Invested in plaster of PAris in a splint metal flask Plaster has set the flask is open end and boiling water is used to remove the wax Done thoroughly to remove all traces of wax Wax will act as a separator and stop bonding between denture teeth and denture base
226
When flasking what is essential to take care with?
Not to disturb any teeth or clasps | Only held by mechanical interlocking or undercuts
227
Why is a separator applied during the flasking stage?
Prevents the resin dough impregnating the gypsum which would create a rough surface Reduces water ingress into acrylic, which would lead to crazing
228
Name an example of a separator and its function?
``` Na alginate K alginate NH3 alginate Forms an insoluble Ca alginate coating on surface of plaster Eliminates water ingress ```
229
What is the definition of a denture adhesive?
It is a glue that stick the prosthesis to the supporting oral mucosa Attempts to improve the retention and function
230
Name the 3 main materials in a denture adhesive?
Gelatin Pectin Gum
231
How are denture adhesives thickened?
With cellulose or a filler such as MgO2
232
What materials can be added to a denture adhesives to give antibacterial properties and reduce surface tension?
Hexachlorophene | Na lauryl sulphate
233
Name the 3 presentations of denture adhesives?
Paste from tube Powder Pads
234
Name 2 commercially available denture adhesives?
Fixodent by P&G Oral Health | Poligrip by GSK
235
Why is good denture hygiene important?
Bacteria and fungi may colonise the surfaces of a denture | Can cause infection of the soft tissues/damage
236
Name the 3 main materials for a denture cleanser?
``` Na hypochlorite (kill bacteria and fungi) Citric acid (breakdown biofilm) Na perborate (forms an alkaline peroxide solution when in contact with water) ```
237
What is the function of a dental cleanser?
Bactericidal | Fungicidal
238
Name the 3 types of presentations for denture cleansers?
Paste Tablet Powder
239
What are the side effects of Na hypochlorite on the denture?
Bleach denture white
240
Na hypochlorite ratio for denture cleansing?
1 tsp to a tumbler of water for 20 mins | Do not use with metal dentures
241
Explain the process of cleaning a denture?
``` To remove food debris and plaque Soft brush with cold water No toothpaste as abrasive Fill sink with water to reduce risk of shattering Toilet soap as preference ```
242
Name 1 commercially available denture cleanser?
Milton Sterilising fluid by Milton
243
Name the 8 requirements of a denture base resin for a dentist?
Adequate strength to withstand occlusal loading Easy to manipulate and process No toxic fumes or dust during processing Remain unstained and unaffected by fluids and temperature changes in the oral cavity Simple to repair Maintain its shape, form and aesthetics in normal function Biocompatible Radiopaque
244
Name the 6 requirements of a denture base resin for patients?
Fit well and be comfortable in use Not traumatise the tissues Easy to clean Aesthetically pleasing both immediately on placement and in the longer term Allow good heat diffusion to retain normal perception of thermal stimuli Permit food to be tasted normally so that food can remain appealing
245
What is the GS denture base material?
PMMA | Polymethymethacrylate
246
Name the 4 formulations of PMMA?
Gel Sheet Blank P:L
247
How is PMMA formed?
Polymer formed from the addition reaction of monomer methylmethacrylate
248
What advantages does PMMA have in a powder and granule formulation?
Increases SA:V enabling more mixing | 150um
249
Name the 6 chemical constituents of PMMA and their functions?
``` (Poly)methylmethacrylate (principal component) Benzoyl peroxide (initiator) Ti/Zn oxide (increases opacity) Inorganic pigments Mercuric sulphide Cadmium sulphide Ferric oxide (varies colour, respectively: Red, Yellow. Brown) Dibutyl phthalate (plasticiser) Dyed synthetic fibres – nylon or acrylic (simulate anatomical structures such as capillaries within the denture base material) ```
250
What is the alternative to dibutyl phthalate and why is it needed?
Potential carcinogen | Citrates or benzoate esters
251
What must you ensure not to happen with the PMMA powder?
Not contaminated as a small amount will activate the reaction
252
What is MMA?
``` Liquid monomer 100.3C BP Toxic if inhaled for long time Flammable Well-ventilated room ```
253
What are the 4 chemical constituents of MMA and their function?
``` Methylmethacrylate (monomer) Hydroquinone (inhibitor – prevents monomer polymerising during storage Ethylene glycol dimethacrylate (substituted for the main monomeric component) (cross-linking agent) Dibutyl phthalate, butyl and octyl methacrylate (plasticizer) ```
254
What chemical can be added to MMA to act as an accelerator?
N,N dimethyl p-toluidine N,N-dihydroxyethyl-p- toluidine Undergo cold curing polymerisation
255
What can methylmethacrylate be substituted for to remove irritation?
Ethyl and butylmethacrylate
256
What is the function of hydroquinone?
React with any random free radicals to prevent premature reaction from UV or free radicals Produces stabilised free radicals
257
How to improve the wear, fracture resistance, cracking and crazing of PMMA?
By adding cross-linking polymers such as diethylene glycol dimethacrylate Different monomer units can react with another growing chain, therefore linking the chains
258
What are the role of plasticisers in the PMMA/MMA mixture?
Vary mechanical properties Prevent interaction between polymer molecules Causes problems when plasticiser runs out the denture becomes harder and can migrate into oral fluid
259
What are the biocompatibility of phthalates?
Poor Carcinogenic Look for alternative plasticisers such as esters octyl or butyl methacrylate Methacrylates less likely to leach, but failure of polymerisation will causes leaching and hardening of denture base
260
How should PMMA sheets be stored?
sheets are stored in the refrigerator in | the dark before heat processing in the normal way
261
Name the 3 types of PMMA acrylic polymerisation methods?
Cold Chemical Self-cure
262
Explain the setting reaction of a PMMA acrylic resin?
Initiated by an organic peroxide such as benzoyl peroxide Free radicals produced either by heating or reacting with a chemical accelerator such as an organic amine Highly exothermic reaction Heat is slow to dissipate as processing is carried out in a plaster mould
263
What causes gaseous porosity of PMMA acrylic resin?
``` Temperature must be carefully controlled as the volatile monomer may vaporise during processing Gas bubbles may be produced and can become entrapped in the denture base resin ```
264
How much polymerisation shrinkage occurs for PMMA acrylic?
Shrinkage equates to 6% for the recommended 3:1 polymer:monomer mix Dimensional change must be compensated for during the manufacturing process otherwise the final denture or appliance will not fit Internal strains are set up within the material as a result
265
What are the mechanical properties of PMMA?
Low tensile strength Low elastic modulus Flexes in use (fracture overtime, due to cyclic loading - fatigue fracture)
266
What does cross-linking ensure for the structure of PMMA?
Cross-linking agents help to ensure that there is a network of molecules rather than long chains or branched chains that reduce the strength of the final material
267
What is the fracture toughness of PMMA acrylic?
Low | Brittle on impact
268
What are the thermal properties of PMMA?
High coefficient of thermal expansion Low glass transition temp Low thermal conductivity Low thermal diffusivity
269
Why can low glass transition temp be problematic with ceramic teeth?
Due to the difference in coefficient of thermal expansion | Ceramic teeth may be lost due to variations in contraction and expansion of the materials during thermal cycling
270
What consequences do low heat diffusivity and gaseous porosity cause to the patient?
Hot food sensation reduced | Oral mucosa become less keratinised (unprotected)
271
Describe the dimensional stability of PMMA?
PMMA absorbs fluid, causing expansion by 2% Polymer shrinkage compensated for expansion Keep denture wet as drying out can cause shrinkage and crazing Water sorption cause discolour and stain Colour stability is good
272
What is the GS P:L ratio for PMMA acrylic?
Heat-cured process, powder:monomer ratio should be about 3 | or 3.5:1 by volume or 2.5:1 by weight
273
What occurs if the polymer to monomer ratio is too high for PMMA?
insufficient monomer | to wet the polymer a granular resin structure results
274
What occurs if the monomer ratio is too high for PMMA?
Increased shrinkage
275
What problems arise from residual monomer presence?
Irritant to oral soft tissues | Acts as a plasticiser softening the polymer
276
What problems are caused by the plasticisier softening the denture polymer?
Denture base weaker and more flexible Fracture may result Polymer may creep under load over the long term and deform the denture base More marked with cold-cure acrylics and can create greater problems Crosslinking agents may be added in an attempt to minimize this effect Loss of material due to water solubility is low. Presence of organic solvents such as alcohols and chloroform has an adverse effect on methacrylates
277
What is the definition of crazing and what causes it?
Fine cracks on the surface of the acrylic Localised areas of plastic deformation of the polymer caused by stress relief of internal strain
278
What is the definition of crack and what causes it?
Crack is formed as a result of brittle fracture as the walls of voids in the region are thin in the region of the fracture Crack grows under externally applied load eventually leading to a continuous crack Areas filled with microscopic voids and a crack may result if the crazed area can no longer support stress
279
What do tensile stresses cause in PMMA dentures?
Tensile stresses will also cause rupture of the polymer chains leading to a weakened denture
280
What are the 4 causes of crazing?
Heat Action of organic solvents Differences in coefficients of thermal expansion around (dissimilar) inclusions that form stress concentrations Loss of moisture (contract and expand during dry at wet cycle - reduced by crosslinking)
281
Name 3 ways to prevent crazing of PMMA dentures?
Not allowed to dry out Finished denture always supplied in water Patient advised to store in water
282
How are small BVs mimicked in a denture base?
Small fibres of red acrylic
283
What shades are denture bases?
Mucosa-coloured
284
How to increase wettability of the denture base?
Triethoxysilane
285
When would clear acrylic be used for a denture?
Improved appearance for more discerning patient | Processed in 2 stages
286
How is radiodensity created in a PMMA denture?
Originally radiolucent | Achieved by addition of 10-15% bismuth or uranyl salts
287
What are the detrimental effects of increasing radiopacity?
Increasing transverse deflection Increasing water sorption Handling of the unset polymer more difficult
288
What are the 6 other properties of PMMA?
``` Low density Light weight Easier to wear No taste or smell Cheap Easy to process ```
289
Name the 5 types of acrylic (based on means of curing)?
``` Heat cured Cold cured Light cured Injection technique High impact ```
290
Explain the process of formation of heat cured acrylic?
Polymer and monomer are mixed to form a sand like mixture initially Becomes tacky as polymer starts to dissolve Left in container until dough stage is reached
291
What is the dough stage for heat cured acrylic?
Does not stick and snaps when pulled apart | Failure to pack the mixture into the mould at the dough stage will result in the material becoming too ribbery and stiff
292
What factors affect the time to achieve dough time?
Particle size of the polymer - smaller the bead diameter, the more rapidly the dissolution of the bead in the monomer, reaction therefore proceeds more quickly Molecular weight of the polymer - lower molecular weight, faster the reaction will proceed Higher temperature produces a quicker reaction Presence of a plasticiser - reduces the dough time Polymer/monomer ratio - higher ratio, shorter the dough time Type of polymer – permeation of the monomer is greater with a granular polymer, dissolves more readily and reaction time is quicker
293
How to add colour to the acrylic?
``` Added colouring agent Can be added to polymer beads or powder Little needed as intense If colour agent on polymer bead surface add slowly to the monomer Can lead to streaking ```
294
Explain the process of processing of heat cured acrylics?
``` Excess of acrylic dough is placed into the part of the flask containing the teeth Flask is closed and placed into a press Pressure applied so that the dough is forced into all parts of the mould Excess is expressed out of the press ```
295
How to avoid shrinkage porosity?
Excess of acrylic dough is required otherwise shrinkage porosity will result Placed into the flask with a thin polythene sheet Flask is opened and the excess removed Known as trial packing May be repeated several times until no excess is expressed At last closure the polythene sheet is removed with any residual excess
296
Explain the process of heat-cured processing?
Essential that sufficient acrylic dough is tamped into place and remains under pressure during the processing Otherwise any air voids incorporated during the packing will not collapse Leads to a source of porosity and weakness Flask is finally closed and placed under pressure in a water bath most commonly 73°C for 8 hours or longer Normally carried out in the laboratory overnight for convenience Temperature of the water bath is slowly raised to reduce the risk of the monomer vaporising otherwise gaseous porosity may occur Near complete conversion of the monomer results with a minimum amount of unreacted monomer remaining When polymerisation cycle is complete, flask is removed from the water bath and allowed to cool slowly at room temperature before being opened Slow cooling prevents stresses forming by plastic deformation within the polymer as there is a difference of contraction between the gypsum and acrylic Also allows some stress-relieving flow of the material Higher the curing temperature the acrylic is more likely to distort due to more residual stress
297
What temperature is necessary for processing of heat-cured acrylic?
Monomer heated will become vapourised Polymerisation is exothermic so flask hotter than water bath Slow processing to allow dissipation Gypsum absorbs heat Follow manufacturer's processing instructions
298
Explain the process of divestment of the PMMA denture?
Denture carefully removed from the gypsum model avoiding flexure and breakage Acrylic flash removed and non-tissue bearing surfaces are polished
299
Explain the process of polishing the PMMA denture?
Soft brown rubber points used Kept moving to stop heat burning or distorting the denture Fibres removed using sharp scalpel blade Stain resistance can be problematic Heat can cause denture to melt, can change properties
300
Explain what you would use to finish the PMMA denture?
Finish with rubber points and wheels or sandpaper Pumice slurry: - crushed porous volcanic stone that is a highly siliceous glass - slurry should be made up with water to a thin paste - moved quickly over the surface at high speed to prevent the build up of heat
301
Explain what you would use to polish the PMMA denture?
Tripoli Calcium carbonate (whiting or precipitated chalk) used in suspension with water
302
What other dental appliances are constructed with acrylic?
Occlusal splints
303
Explain the injection technique for denture formation?
Designed to maintain pressure on the acrylic as it cures in an attempt to overcome the large volumetric shrinkage of PMMA Wax sprue which is added to the denture Denture is flasked and the wax boiled out High pressure injection cylinder is connected to the flask Acrylic is mixed and placed into the cylinder. Injected into the mould under pressure when at the desired consistency High pressure is maintained during the polymerisation reaction so more material is pushed into the flask to compensate for the polymerisation shrinkage
304
Give an example of an commercially available injection moulding system?
Ivoclar vivadent
305
What is added to PMMA to create a high-impact acrylic?
Butadiene-styrene rubber (reinforcing agent) is added to confer some resistance to fracture Rubber particles are grafted onto the MMA to become incorporated into the acrylic matrix Powder liquid presentation Processed like hear cured Longer lifespan and performance More expensive
306
What is the initiator for a cold-cured acrylic?
Tertiary amine
307
What is the catalyst for a cold-cured acrylic?
N,N dimethyl-p-toluidine | Sulphinic acid are
308
What is present in TII cold cure resin powder and liquid?
``` Powder: - polymethylmethacrylate - benzoyl peroxide - Pigments Liquid: - methylmethacrylate - di-n-butylphthalate - amine ```
309
What is present in TII cold cure resin powder and liquid?
``` Powder: - polyethyl methacrylate - benzoyl peroxide - pigments Liquid: - butyl methacrylate - amine ```
310
Indications for TII cold-cured acrylic?
MMA hypersensitive patients
311
What is difference between TII and TI cold cured acrylic?
Less irritant to soft tissues Softening temp is lower to 67C rather than 90 Greater risk of distortion
312
Describe the polymerisation efficiency of TII cold cured acrylic and what does this cause?
Residual monomer remains (3–5%) as polymerisation process is less efficient than heat-curing Due to the lower molecular weight of the polymer chains and the lack of propagation of the chain during the polymerisation process Residual monomer acts as a plasticiser which softens the material Inferior mechanical properties result Eventually properties achieve same level as heat after all leached out Leaching on oral mucosa is a cause of irritation Polymer beads smaller to facilitate the monomer dissolving the polymer
313
Why does TII cold cured acrylic have problems with porosity and how to minimise it?
Due to air dissolved in the monomer which is not soluble in the polymer at room temperature May be reduced by polymerising the material under pressure Need excess material within the mould to ensure that the prosthesis will remain under pressure during the curing process and ensure that porosity is minimised
314
What are the mechanical properties of cold cured acrylics?
Cold cured acrylics are not as strong as those that are heat cured (c80%) Due to lower molecular weight of the formed polymer so less conversion of the monomer to polymer occurs More initial deformation and creep Slower recovery seen Less build up of internal strain occurs as no external heat source is used
315
Describe the stability of cold-cured acrylics?
Poorer long-term colour stability due to presence of tertiary amine Only 0.1% dimensional change seen on polymerisation Due to the reduced level of conversion of the monomer Greater exothermic reaction than heat-cured materials due to an excess of initiator Initiator which contributes most significantly to the exothermic reaction
316
What are the indications for cold cured acrylics?
Removable orthodontic appliances Minor denture repairs or relines (laboratory) Chairside relines
317
Describe light-cured acrylic presentation and constituents?
Cured by the application of visible light energy Presented as a prefabricated sheet of material which can be adapted to the surface of a model Urethane dimethacrylate and high molecular weight acrylic resin monomers are blended with an organic filler of acrylic beads
318
How to improve handling for light cured acrylics?
Microfine silica is added to optimise handling Forms an interpenetrating polymer network when cured
319
Explain the setting reaction for light cured acrylics?
Camphorquinone, accelerator (amines) and pigments are also required Supplied fully compounded in a light tight package Technician lays down the material on the model or denture being constructed or modified, moulding it into the desired shape Placed into a light box and cured for c5–10 minutes Surface of the material must be treated with a barrier chemical such as carboxymethylcellulose to prevent oxygen inhibition of the polymerization reaction as process is carried out in air
320
Indications for light cured acrylics?
Baseplates of the denture on which a conventional PMMA suprastructure is added Orthodontic appliances “Gum work” portion of metal-based partial dentures Repair of fractured acrylic dentures Hard relines Construction of special (impression) trays
321
What is a flexible denture?
Biocompatible nylon thermoplastic Claimed to be flexible and unbreakable
322
Name 2 commercially available flexible dentures?
Sunflex partials | Valplast flexible partials
323
Indications for flexible dentures?
Allergic to MMA
324
Explain the process of formation of a flexible denture?
Denture is placed in very hot water for a minute prior to placement to fit the denture initially or if clasp adjustments are required Thermoplastic material so will soften and on cooling gain its new shape Nylon material is microscopically porous so aesthetic issues arise in use as the denture base is more difficult to adjust and polish
325
What problems can occur when using dental stone casts and an articulator?
Continuous expansion Lose accuracy Add something to stop it AE8
326
Which materials to use when flasking a CD?
Plaster of Paris for the base Na alginate as the separator Dental stone as the topper
327
What is the ideal space between the tray and the dental arch?
5-7mm
328
Name 3 things metal files aim to remove?
Necrotic material from lumen of canals Hard tissue from canal walls Microorganisms that have penetrated dentinal tubules
329
Name 3 barriers to fully cleaning the root canal system?
Complex anatomy Biofilm Smear layer
330
What makes complex root canal anatomy hard to clean?
Many connection | Complex at apical 1/3
331
What is the definition of biofilm?
Dense aggregate of cocci, rod and filamentous forms embedded in an ECM on the root canal walls Can colonise: - necrotic material in lumen of RC - in dentinal tubules
332
How to remove biofilm before RCT?
Mechanical removal via instrumentation and irrigation | Not easily disrupted
333
What is the definition of the smear layer?
1-2um thick, amorphous, irregular and granular on dentinal surface Composed of inorganic and organic particles, coagulated proteins, pulp tissue, blood cells and microorganisms Caused by instrumentation of the canals
334
Explain the process in removing the smear layer?
By using chelating agents Recommend to remove as: - remove bacteria and nutrients - it impedes irrigation
335
Name the 8 functions of endodontic irrigants?
Lubricate files to facilitate passage into canal Wet canal walls and flush debris Contain any dentinal shavings in suspension so facilitating their removal from canals (prevents apical impaction of debris) Facilitate dissolution of organic mater Remove smear layer Aid cleaning of area inaccessible to mechanical cleansing methods Disinfect RCS Neutralise endotoxins
336
Name the 2 groups of endodontic irrigants?
Clean and expose bacterial contaminates | Used to disinfect RCS
337
Name 2 irrigants for cleaning?
EDTA | Citric acid
338
What is the definition of citric acid?
Chelating agent Removes calcified tissue and detach biofilms from root canal walls 10-50%
339
What is the definition of EDTA?
``` Synthetic aa or Na salt of EDTA ethylenediamine tetra-acetic acid Demineralise and soften root canal wall dentine by 20-50um Neither cidal or static Kill bacteria by starving from metal ions (chelates metal ions) Non-toxic Non-corrosive Not effective against smear layer alone 15-17% Never mix with NaOCl ```
340
Name a commercial product of EDTA?
ENdo-Solution EDTA Cerkamed dental-medical
341
What is the function of EDTA gel?
Coat endodontic files Lubricate and removes smear layer making canal prep easier and faster Increased viscosity is better for holding debris in suspension
342
What is the definition of EDTA gel?
Contains carbamide or urea peroxide causing effervesce Elevator action helps to remove debris Bubbles when in contact with NaOCl Oxygen kills anaerobic bacteria
343
Name a commercially available EDTA gel?
Glyde File Prep Dentsply Maillefer EDTA + carbamide peroxide
344
When should you not use chelating materials?
Initially to negotiate canals as a false can may be cut iatrogenically
345
How should you use chelating materials within the root canals?
Thoroughly washed from RCS as retention will continue softening the dentine Are self-limiting Chelating + disinfecting irrigant Provides a cleaner surface
346
Name 4 types of irrigants for disinfection?
NaOCl Iodine potassium iodine Chlorhexidine Other potent phenolic disinfecting agents High bactericidal concentrations close to toxic dose
347
What is the definition of NaOCl?
Potent organic tissue solvent that is proteolytic and dissolves necrotic organic material Releases free CL which has bactericidal effects Cl breaks peptide bonds dissolving proteins into aas Aas degraded by hydrolysis by chloramine mol Chloramines are antibacterial Oxidising and hydrolysing agent pH> 11 No effect on smear layer (Ca) High pH denatures proteins Hydroxyl ions damage bacterial lipid and membranes + DNA
348
Explain how to use NaOCl?
Breaks down components during use Must be replaced as i loses its efficacy Dwell time of at least 30 mins Biofilm must be disrupted to reach bacteria Canal must be flushed long after canal prep has ceased for this disinfectant to be effective
349
What are the components of the NaOCl solution?
No diff between 0.5-5% solutions for antibacterial effects But efficiency of weak solutions decreases rapidly High conc disinfecting process is faster, untoward damage can occur, as it is more toxic More effective if solution is warmed, as more Cl is released
350
What are the characteristics of NaOCl?
High surface tension than water, so does not wet canal well Walls are not fully covered and the full biofilm may not by disrupted Higher conc = thicker sol Not effective at killing all microorganisms Enterococcus faecalis can't be killed
351
When using NaOCl, what should you be wary about?
Bleaching clothes Unpleasant taste Irritant to eyes, skin and oral mucosa Bleaching will lighten any stained tooth tissue
352
Name 2 commercially available NaOCl?
``` Parcan Sol (Septodont) 3% Chlorax (CerKamed Dental-Medical) 2% or 5.25% ```
353
What instrument to be used with NaOCl?
Ultrasonic instrument | Acoustic streaming enhances cleaning effect
354
What are the side effects if disinfecting irrigants come in contact with anything bar root canals?
``` Severe inflammation + tissue necrosis Neurological damage Facial atrophy Anaphylaxis Airway problems ```
355
What are the clinical manifestations for extracanal extrusion of endodontic irrigants?
``` Immediate serve pain Profuse bleeding from within canal Rapid swelling and Oedema Ecchymosis 2nd infection Paresthesia Persistent pain ```
356
Explain the 9 step process the manage extracanal extrusion?
1. Stop irrigating and consider giving additional LA 2. Immediate irrigation with sterile water or saline for 5-10 mins 3. Dress root canal with non-setting CaOH and access cavity 4. Analgesic advice (paracetamol 500mg) 5. Prescribe antibiotics only if signs of systemic involvement 6. Consider referral to oral and maxillofacial specialist for special care 7. Fully inform patient of event and the potential sequalae 8. Write up detailed notes 9. DATIX form
357
Explain how to reduce the risk of extracanal extrusion?
Use a side exiting endodontic irrigating needle Do not bind tightly in the canal so that irrigating fluid may pass in a coronal direction Keep needle and syringe moving while performing, slow and gentle irrigation Use finger pressure
358
What is the definition of Chlorhexidine digluconate?
``` Cationic bis-biguanide Wide bacterial range (greater than NaOCl) static at 0.2% cidal at 2% Causes cell wall decomposition leading to loss of cellular components Not dissolve organic tissue Negative healing effect Increases odds of failure Result in anaphylaxis ```
359
Why is Chlorhexidine digluconate better than NaOCl?
Kills microorganisms that NAOCl can't | Safer
360
Explain how chlorhexidine digluconate works?
Binds to hydroxyapatite on the root canal walls Used as final soak Good substantivity of about 12 hrs after application
361
What reaction occurs between Chlorhexidine digluconate and NaOCl?
Acid-base reaction seen with NaOCl forming an insoluble precipitate 4-chloroaniline Stains dentine Carcinogenic Difficult to remove (can block canals) Can be overcome by irrigating with sterile water CHX breaks down when heated to form PCA
362
Name 2 commercially alleviable chlorhexidine digluconate products?
R4 (Septodont) 20% in denatured alcohol | Gluco-Chex 2.0% (Cerkamed Dental-Medical)
363
Name 2 forms a chlorhexidine digluconate gel?
Hibiscrub (Regent Medical) 4% | Gluco-Chex 2.0% Gel (Cerkamed Dental-Medical)
364
What is the definition of Iodine Potassium Iodide?
``` Organic and releases iodine Iodine is a potent antibacterial agent with broad spectrum action Bact/fung/tuberculo/vuru and sporicidal Effective for 2 days Penetrate dentinal tubules ```
365
Explain how Iodine Potassium Iodide works?
Attacks proteins, nucleotides and FAs leading to cell death | Low tox, but patient allergic to iodine
366
What is the formulation of Iodine Potassium Iodide?
Irrigating sol 2% iodine in 4% aqueous potassium iodide such as Videne (Adams)
367
What is the definition of H202?
Degrades to form water and oxygen producing hydroxyl free radicals Effective against bacteria, yeasts and viruses as it attack the proteins and DNA Not reduce bacterial load in RCS significantly Oxygen may penetrate into periarticular tissues causing surgical emphysema due to effervesce Not used in contemporary endo
368
What is the definition of hypochlorous acid?
Less toxic than NaOCl Similar to NaOCl Dissociates in sol into hypochlorite ions but the reduced level of discolouration compared to NaOCl means that any adverse effects are reduced NaOCl is more efficient as more Cl is available between the sol of same conc
369
What is the definition of electronically activated water?
Sol of hypochlorous acid Generated via process of electrolysis from water and NaCl by an electrochemical device Safer than other solution as if less irritant if extruded into he periradicular tissues Cidal pH 5-7 Sterilox
370
Name and give characteristics of non-active irrigants?
``` Sterile water LA solution Lubricate files and carries sward in sol No disinfectant prop Not recommended for sole irrigant ```
371
What is the definition of a co-irrigant?
More than 1 irrigant to enhance effect Usually consist of an acid or chelating agent + NaOCl dissolve smear and assist in biofilm destruction + disinfect
372
What is the definition of Ozone?
Sterilising of water supplies Sterilising agent Effective and toxic dose very close Gas delivered down a handpiece
373
Explain how the Ozone device works?
Area sealed from the surroundings and residual gas is drawn back to the generator and neutralised using a Pl filter Deliver ozone down fine tip directly into canal for very short time
374
Name 2 device names for Ozone?
Healozone CurOzone | Prozone W%H
375
What is the definition of bacterial photodynamic therapy?
Impossible to consistently disinfect enter RCS due to: - anatomy - disinfectants are ineffective against some organisms Combo of photo-sensitiser and specific wavelength is effect against all oral microorganisms
376
What is the definition of a photo-sensitiser?
Different wavelengths of activation Tolonium Cl (relative of toluidine blue O) Conc between 13-80 ug/ml Lower surface tension so can wet and penetrate into the dentinal tubules No problem with extracanal extrusion
377
What is the definition of a light source?
``` Laser diode or LED Red light at 635nm +/- 2nm Light exists photo-sensitiser mols Minimal heat Light delivered via a tapered endodontic tip ```
378
Explain the mechanism of action for Bacterial PDT?
Photo-sensitiser is preferentially taken up by rapidly dividing cells such as microorganisms Chemical must be in contact or in very close proximity to bacteria Taken up by the liposomes on cell walls When light energy is applied photo-sensitiser molecule becomes excited and free oxygen radicals produced Singlet oxygen species is a protoplasmic poison which causes oxidative injury to bacterial cell wall Leads to death of microorganism Photo-sensitiser returns to its unexcited state - causes no further effect when light switched off No collateral damage seen to any surrounding tissues Resistant strains cannot be build up Both light and photo-sensitiser are ineffective when used separately. Also viricidal and fungicidal
379
Name 2 commercially available bacterial PDT?
CumdentPACT Cumdente Dental Concepts Laser diode PAD Plus Denfotex Research LED
380
What is the aim of root canal preparation?
Remove as many microorganisms as possible Shape root canal to provide a uniform sized dead space to facilitate its subsequent obturation using stand sixed cones of plastic material and its adaptation to root canal walls to achieve a seal Avoid ledges, perforations zips and canal transportation
381
What are metal files used for?
Remove: - necrotic material from lumen of root canals - hard tissue from root canal walls - microorganisms that have penetrated dentinal tubule Facilitate penetration of disinfecting agents so they reach the microorganisms in RCS
382
What force to files exert onto the RCS?
All files tend to straighten within a curved canal and exert a lateral force on the root canal wall
383
How can files be different?
``` Shape Tapers Length Cutting Non-cutting tips Sade edged Colour/number coded ```
384
name 2 types of endodontic files?
Hand - composed of stainless steel or nickel-titanium | Rotary - only nickel-titanium in a speed-reducing, torque controlled handpiece
385
Describe the anatomy of an endodontic file?
Both have cutting edges along the length of the file Handle/attachment for drill Silicone stop
386
Explain how the cutting edge of the endodontic file cuts?
Cuts when its radial lands are in contact with canal wall Lead angle determines cutting efficiency Radial land areas required for conventional helically fluted files because they prevent the file from over-engagement in the canal Lock of radial land areas reduces friction File may fracture if suddenly engaged Radial lands are important for files that have +ve rake angles Designed so that radial lands can't screw themselves into wall Debris directed towards coronal canal so not compacted apically
387
What is the definition of a rake angle?
Angle of action of the cutting blade us similar to a snow plough which is forces downwards towards surface of road
388
What is the definition of stainless steel files?
Alloy of iron, carbon and chromium + nickel Forms an invisible passivation layer of chromium oxide on surface when exposed to air If scratched, code later rapidly reforms preventing degrade Prevents rusting in presence of water
389
How are stainless steel files manufactured?
Machine shaped directly from a stainless steel wire Machined into a blank of the desired shape Greater # of twists greater the work hardening
390
What are the stainless steel file properties?
Do not bend easily Bend file prior to introduction Bending instrument will further work harden the metal making it more brittle leading to fracture
391
What is the definition of a nickel-titanium files (NiTi)
500% more flexible than stainless steel and 3 times stronger Corrosion resistant Hand and rotary instruments available
392
What are the 2 NiTi temperature dependent crystal structures?
Austenite - high temp or parent phase, cubic structure | Martensite - low temp, monoclinic structure
393
What are the properties of NiTi alloy?
Superelasticity and shape memory effect Occur due to austenite to martensite transition induced by stress or temp (martensitic transformation) Under certain other condition other phase my be present (R-phase)
394
What is the definition and properties of austenite NiTi alloy?
Superelasticity due to austenite NiTi Austenite can be transformed to martensite by stress, termed stress-induced martensite transformation Allows complete recovery of deformation up to 8% strain Stress-induced martensite state is not stable so retransformation back to austenite phase so spring back to original shape Lower elastic modulus than stains steel Higher torque values at fracture
395
What are the indications for Austenite NiTi files?
Shape straight or slightly curved canals Pathfinding instruments as compensation for the decreased torque resistance caused by small diameter files Profile
396
What is the definition and properties of martensitic NiTi alloy?
Softer and more ductile than austenitic Easily deformed and exhibits shape memory effect when heated Pseudoplastic Fatigue crack growth resistance is higher than stable austenite Hyflex
397
What are the properties of gold and blue heat-treated instruments?
Heat treat martensitic alloy Blue colour due to titanium oxide left after heat Controlled memory effect Enhanced flexibility and cyclic fatigue resistance compared with conventional NiTi and M-Wire Greater angle of rotation but lower torque at fracture Preferred un serve curved canals Pre-bendable to bypass ledges
398
Name 2 commercially available gold/blue heat treated instruments
Rotary system: ProTaper Gold (Dentsply Sirona) • Reciprocating motion: Reciproc Blue (VDW) & WaveOne Gold (Dentsply Sirona)
399
Explain the manufacturing process of NiTI endodontic instruments?
Conventional NiTi alloys are ground to make files opposed to twisted Lead to defects n the surface so potentially causing decreased fracture resistance, cutting efficiency and corrosion resistance Electropolishing sometime used to remove surface defects causing by grinding (improves above problems)
400
Explain how to choice between different endodontic files?
Rotary systems are much more efficient than hand techniques • Hand files sometimes preferred to negotiate very curved root canals although newer rotaries may be used these days • Engine driven NiTi endodontic instruments result in significantly less canal transportations compared to stainless steel hand instruments • Selection of material of which file is made and its method of construction is critical in determining performance of instrument
401
What factors do stainless steel endodontic files depend on?
Composition of material Geometry of file Way in which it is loaded
402
What are the contraindication for use of a stainless steel endodontic file?
Anticlockwise twisting as this increases twisting resulting in brittle fracture NaOCl and EDTA reduce cutting ability so files should be rinsed Long prep times prolong immersion of instruments in these solutions in the canal and start process of degrad
403
Name 3 ways a file may break?
Sharp curve - cyclic fatigue Overuse - flexural fatigue In rotation while instruments is prevented from moving - torsional fatigue
404
What is the definition of torsional stress? how to reduce it?
Evert cutting action in the canal | Torque controller so that the rotation of file is stopped prior to receiving excessive torque
405
Explain the decontamination process for endodontic files?
Debris retained on file after use is called swarf • May contain neural tissue with prions • Proteins that cannot be destroyed by the usual methods of surgical disinfection • Theoretically associated with new-variant Creutzfeldt–Jakob disease ( nvCJD ) • Endodontic files should therefore be considered as single use • Incidence of instrument separation is decreased • Autoclaving can decrease the cutting ability of some files and may result in metal fatigue
406
What are the 2 parts for inter-visist temporisation?
Canal medicaments | Temporary dressings
407
Explain why inter-visit temporisation is necessary?
Signs/symptoms Further opportunity to disinfect the RCS by placing a medicament with antimicrobial prop Cases which require root formation to complete
408
Name 6 types of inter-visit canal medicaments?
``` Steroid/antibiotic combo Non-setting CaOH Chlorhexidine Phenol or derivatives Halogens Formaldehyde ```
409
Indications for steroid/antibiotic paste?
Irreversible pulpitis | Intracanal dressing between appointments
410
Name 1 commercially available steroid/antibiotic paste and its constituents?
OdontoPaste (Australian Dental Manufacturing) Ledermix Constituents: - Clindamycin hydrochloride 5% - triamcinolone acetonide 1% - CaOH
411
Explain how the steroid/antibiotic paste works?
Acts topical only killing bacteria adjacent to vital tissue Steroid suppresses any inflamm response Permits bacteria at a distance from surface of lesion to proliferate - leads to death of pulp
412
Why can endodontic steroid paste be useful for irreversible pulpitis?
When sufficient analgesia can't be gained to fully extirpate vital tissue Only effective when it is in contact with vital tissue so rational is debatable
413
What are the pros of using steroid/antibiotic paste + non-setting CaOH?
Ledermix Synergistic Placed separately - too viscous Place steroid/antibiotic paste on a paper point to carry it into canal followed by syringing non-setting CaOH
414
Give a description of non-setting CaOH?
Intracanal medicaments Active chemical provided as a slurry in a water base Methylcellulose based Facilitate removal of the products from the canal Radiopaque pH is 12
415
Explain how non-setting CaOH works?
Bactericidal: - slow acting antimicrobial agent has therapeutic effect after being in situ at least a day - effective disinfection in most cases of infected necrotic cases seen in a week Neutralises acidic endotoxins Inhibits osteoclastic activity due to high pH - useful in cases of inflamm root resorption Hydrolyses lipid component of bacterial LPS - renders bacteria inactive and reduces toxic effect from debris Denatures proteins in RCS May activate CA-dependent adenosine triphosphate reaction assoc with hard tissue formation stimulation periradicular healing
416
Name the 6 indications for non-setting CaOH?
Inter-visit intracanal medicament - disinfect canal system Controls exudation in persistent infection Partial pulpotomy - create a calcific barrier to maintain vitality of tooth Apexogenesis - continue root formation in vital tooth Apexification - induces apical closure of non-vital immature teeth - dressing replaced every 6 weeks until hard tissue barrier forms Resorption - inhibits activity of osteoclasts die to high pH so arresting inflamm process
417
Name the 3 contraindication for non-setting CaOH?
Cause calcification of canal if left in situ > 6 month | Increases risk of root fracture due to denaturing the collagen
418
What is the mode of delivery of non-setting CaOH?
Past inside a tube Fine endodontic Needle (Navvi tip) attached to a Luer lock syringe Deliver paste into canal Consistency of paste must be as thick as possible to fill RCS Can be difficult to remove Effectively removed with citric acid or EDTA as alkaline CaOH reacts with acid
419
Name 1 commercial produce for non-setting CaOH?
UltraCal by Ultradent
420
What are the advantages of non-setting CaOH PLUS points over non-setting CaOH?
``` Greater release of CaOH and so more effective Points ready to use No mixing Easy to apply and remove No smearing ```
421
Give a description of chlorhexidine?
Incorporated into gutta percha Activ point (Roeko) is a 5% chlorhexidine diacetate Placed in canal for 1-3 weeks Conform to ISO specification for GP points for size and diameter which matches shape to that of root canal Drop of sterile water is sued to accelerate release of the chlorhexidine Same effects as a chlorhexidine irrigant
422
Give a description of phenol?
Effective antimicrobials Strong antiseptics Short duration for effect Protoplasmic poison and works at an optimal conc of 1-2%
423
Give 3 examples of phenols?
Para-monochlorphenol Thymol Cresol
424
What did studies show about the use of phenols as disinfectants?
Not able to fully disinfect the RCS after 2 weeks Due to insufficient vapour released for effective antimicrobial action when the products placed on a cotton pellet in pulp chamber
425
Give 1 commercially available phenol product and its constituents?
``` Cresophene - Septodont Constituents: - para-chlorophenol - dexamethasone with thymol and camphor High tox and carcinogenic Obsolete in endodontic practice ```
426
Give a description of halogens?
Antimicrobial Chlorine-containing products (chloramines) Iodine more popular such as iodine potassium iodide Releases vapours 2% iodine prep quicker at reducing bacterial load than CaOH Can prevent E. faecalis growth within 1-2 hrs
427
Contraindications for iodine halogens?
Iodine hypersensitivity
428
Give a description of formaldehyde?
Caustinerf Forte - Septodont Toxicity of formaldehyde containing medicaments Not justified
429
Give 7 key properties needed for a good coronal temporisation?
``` Coronal seal must be perfect - to prevent bacterial ingress Function Aesthetics Strong to withstand occlusal loads Low solubility High wear resistance Longevity ```
430
Name 5 materials used for inter-visit coronal temporisation?
``` GIC Zinc polycarboxylate cement Reinforced zinc oxide eugenol cement Zinc oxide containing putties Semi-permanent material - forming a core using a resin-mod glass ionomer cement, resin composite or amalgam ```
431
What to consider when placing a coronal termporisation material?
Need to consider final restorative material viz resin composite definitive restoration and use of a eugenol-containing cement
432
Name 2 types of coronal protection?
Tightly fitting copper | Orthodontic band
433
What is the function of obturating material?
Prevents ingress of microorganisms by creating a seal at both coronal and apical ends, lateral canals and dentinal tubules Completely fills dead space removing all air which could expand or contract in a pressurised environment
434
Give a description of Gutta percha?
Consists of polyisoprene which comes from rubber tree Polyisoprene has 2 isomeric forms: - cis = rubber - trans = GP Trans exists in 2 phases: - alpha phase is heated and used molten - beta are GP points or cones used at room temperature Mixed with other chemicals to enhance handling
435
Give a comparison between alpha and beta phase for trans polyisoprene?
Beta phase is formed when GP cooled quickly whereas alpha phase is formed if material is cooled slowly Alpha form is denser and has better thermoplastic characteristics
436
Name the 4 constituents for GP and their functions?
Gutta percha Zinc Oxide - filler and antimicrobial Resins - Plasticiser Metal sulphates - radiopacity
437
What are the physical properties of GP?
``` Highly biocompatible Minimal tissue changes Inert Minimal toxicity Dimensionally stable and packable Thermoplastic softening at 60-65C and melting at 100C Stretchable Antibacterial Radiopaque No heat sterilisation Oxidises on light exposure - degrades and becomes brittle Lacks rigidity Poor adaption Shrinkage 2% ```
438
Explain how to sterilise GP?
Using NaOCl | Do not use acetone or alcohol to disinfect as it can be absorbed
439
What is the presentation of GP?
Points Cones Several different sizes Different tapers
440
What are the manufacturing tolerances for GP?
Subjected to ISO standards Cones are made to a tolerance of +/- 0.05mm Different products are composed of different proportions of chemicals creating variations in brittleness and stiffness
441
Explain the cold obturation technique for GP?
GP + endodontic seal to fill root canal Cold lateral condensation - GS Cone which corresponds in size to canal prep is coated with a root canal prep and introduced into root canal then pushed laterally to create space so that next cone can be placed Other accessory cones coated with seaer are then introduced into canal one at a time Continue until root canal is fully obturated Adjust GP cone with scalpel blade Use liquid GP - allows material to flow into irregularities of RCS GuttaFlow - Roeko (GP + addition cross-linking poly(dimethyl siloxane) 30um particle size - 0.2% shrinkage
442
Name the 8 chemical constituents for GuttaFlow and their functions?
``` GP powder - obturating component ZInc oxide - filler and radiopacity Zirconium dioxide - filler and radiopacity Silicone oil - binder + consistency Paraffin ol - binder + consistency Colloidal silver - inhibit reinfection Hexachloroplatinic acid - catalyst Colouring agent - colour ```
443
Explain the technique for warm GP?
Used at high temperatures as pellets Conjugation with gun 150-230C Narrower gauge = lower temperature Once at temp molten material can be expressed out of needle of gun into canal Secure apical stop before suing molten GP - to prevent extrusion Good for obturating anatomical irregularities
444
What are some present techniques to cut GP?
``` Heat used to cut GP Heating over bunsen burner: - naked flame - burning other objects - tempers steel of instrument = damage SYstem B sears GP cleanly Wire inside probe heats up quickly Easy and sade ```
445
Name 4 other obturation systems?
Real Seal 1 : - good for latex sensitivity Thermafil: - softened GP flow into RC
446
What obturation product is indicated for patients sensitive to latex?
Real Seal 1 Polyester with barium sulphate and silicate as radiopaque filler Core is resin based with a Resilon outer coating No rubber or rubber-based materials Soluble in chloroform and my be removed like GP
447
Give a description of ENdoREZ?
EndoREZ: - hydrophilic - dual cured resin obturation system based on UDMA and triethylene glycol dimethacrylate - polymerisation similar to resin composite - base and catalyst presentation - takes 20 mins can be sped up by accelerator - filler for radiopacity - master + accessory then light cure
448
Give a description of SmartSeal?
Smartseal: - hydrophobic polymer, - swell when water absorbed, - hoop system prevents excess swelling - flexible - points and sealer
449
What are the shortcoming of Silver points?
DO not fully obturate canal Rely on RC sealer Prone to corrosion Corrosion products high tox and can leach Permeate dentinal tubules Difficult to remove as they tend to fracture Rigid so can't adapt to walls
450
What is the definition of an endodontic sealer?
Paste coated onto endodontic point prior to its insertion into RC Paste/paste presentation Used sparingly Prvenets extracanal extrusion and decreases amount of sealer needed
451
What is the function of the endodontic sealer?
- Lubricate and facilitate full placement of master point +/- accessory cones • Fills voids between obturation points • Fills and seals lateral canals and passes through lateral canals to root surface - seen radiographically as a ‘puff’ on side of root • Provide a disinfectant action if they contain an active component
452
Name and describe the 4 physical properties all endodontic sealers must display?
Flow - determines ability to effectively fill voids between master cone and accessory cones and any accessory canals may be obturated. • Film thickness - should be minimal as sealer is by far most likely material to degrade • Solubility - most sealers are soluble and are absorbed to some extent when exposed to tissue fluid, keep to a minimum • Radiodensity - should also be radiopaque
453
Name 6 types of endodontic sealers?
``` Zinc oxide eugenol Calcium hydroxide Epoxy resin GIC Poly(dimethyl siloxanes) Tricalcium silicate cements ```
454
Give a description of Zinc oxide eugenol endodontic sealers?
Good results with cold techniques Small particle size to enhance flow Weak Porous Susceptible to decomposition in tissue fluids Lose volume as eugenol and zinc oxide are released Resins/rosins added to decrease dissolution Can act as sensitising agent Zinc oxide antimicrobial and cytotoxic Other added chemicals: - germicides - antiseptic - Canada balsam - increases adhesion to dentine - corticosteroids - suppress inflamm - paraformaldehyde - antimicrobial
455
Name the chemical composition of Zinc oxide eugenol endodontic sealer?
``` Powder: Zinc oxide - filler Silver - radiopacity Oleoresins - viscosity Staybelite resin - binder Dithymoliodide - antiseptic Bismuth subcarbonate/subiodide/trioxide/sulphate - radiopacity Sodium borate - filler Thymol iodide - antiseptic Oils and waxes Liquid: - eugenol - cement former - canada balsam - viscosity - polymerised resin - reinforcing agent ```
456
Give a description of CaOH endodontic sealers?
``` Dissociates into an ionic form and may confer an antimicrobial effect and promote healing sealer must dissolve so leaving voids in obturated material Sealer is more soluble Poor cohesive strength ```
457
Name the chemical components for CaOH endodontic sealers?
``` Base: - CaOH - cement - Zinc Oxide - cement Activator: - Barium sulphate - radio - Titanium dioxide - filler/colour - Zinc stearate - binder ```
458
Give a description of epoxy resin endodontic sealers?
``` Good flow and sealing ability High dimensional stability Low shrinkage Sufficient working time Adhesion to other materials and dentine Antibacterial properties Less porous and have greater hardness Their lower solubility and greater film thickness may prove problematic if the material needs to be removed Soluble in chloroform which facilitates removal least toxic of all endodontic sealers Allergy ```
459
Name the chemical components for Epoxy resin-based endodontic sealer?
``` Base: - silver powder - radio - bismuth oxide - radio - hexamethylenetetramine - hardener - titanium oxide - colour/filler Catalyst: - bisphenoldiglycidyl ether - cement former ```
460
Explain the setting reaction for epoxy resin endodontic sealer?
Addition polymerisation reaction in which epoxides and amine react to form long chains • No residual monomer remains with no by-products • Diamines present in cement provide high dimensional stability • Exothermic reaction • Poly(addition) reaction is temperature dependent and takes a substantial amount of time • Extended working time provided c4 hours
461
Give a description of GIC endodontic sealers?
Modified GICs • Low toxicity and induce little tissue irritation • Cytotoxic but this and any inflammatory responses decrease with time • Adhere to dentine but may be less good at sealing • Physical properties are better than zinc oxide eugenol with less coronal leakage • Leach fluoride which is taken up by dentine • More susceptible to dissolution if exposed to liquids before maturation is complete
462
What are the chemical constituents for polydimethylsiloxane endodontic sealers?
``` Polydimethylsiloxane - Active component Silicon oil - Binder Paraffin base oil - Binder Platinum salt- Catalyst Zirconium dioxide - Filler ```
463
Give a description of polymethylsiloxane endodontic sealer?
Insoluble so not resorbed - contraindicated in deciduous teeth • Dimensionally stable although there is an initial slight expansion on setting • Thin film thickness and good flow characteristics allows material to flow into tubules and fins • Excellent biocompatibility • Cannot bond to dentine • No antibacterial properties
464
Give 1 commercially available polydimethylsiloxane endodontic sealer
RoekoSeal Difficult to use with heated techniques as heat will decrease working time
465
Give the properties of tricalcium silicate based endodontic sealer?
``` Bioactive • Stimulates bone regeneration (hydroxyapatite formation) • Promotes periradicular healing • Mineralisation of dentine • Biocompatible • Adhesion to dentine and GP • pH 11 & CaOH2 release – antimicrobial • Dimensionally stable ```
466
Give 1 commercially available tricalcium silicate based endodontic sealer?
``` Use with GP points • Any obturation technique • BioRoot™ RCS (Septodont) • 1 spoon to 5 drops • Working time c15 mins • Setting time <4 hours • 45µm film thickness ```
467
Give a desctiption of formaldehyde containing obturating pastses?
Paraformaldehyde decomposes to give its monomer which is a water soluble protein denaturing agent • Highly toxic, genotoxic, mutagenic and carcinogenic • Cause severe inflammatory reactions and necrosis with direct tissue contact • Cause permanent injury if applied to neural tissue on extrusion outwith root canal space May be transported to other parts of the body • Allergenic which causes contact dermatitis and has also caused type 1 anaphylaxis • Leaching occurs for a long time and results in chronic inflammation • Prevents or delays healing and masks inflammatory process
468
Give 1 commercially available ZOE containing obturating pastes?
TubliSeal EWT - SybroEndo - ZOE

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