Dental Materials Flashcards
What is a dental impression used for?
Recording the intra-oral structures
What information do we receive from the dental impression?
Negative imprint of the oral structures from which a positive reproduction can be formed
What is the process of a conventional impression?
- Material is mixed
- Loaded into impressions tray
- Inserted into mouth
- Allowed to set
- Remove from mouth
- Permits a cast to be made
- Device is made of this cast
What are the 2 main uses for dental impressions?
Study casts and construction of dental appliances
Name some forms of dental applicances?
- Orthodontic appliances
- Removable dentures
- Mouth guards and bleaching trays
- Inlays and onlays
- Crowns
- Bridges
What are the requirements for an impressions tray?
- 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
Name the 2 main material types of trays?
Plastic and Metal
Problems caused by a non-rigid impressions tray?
- Tray shape is altered intra-orally
- Distorts the impression material
- Cast inaccurate
Name the 2 main ways impression trays ensure the impression material stays in the tray?
Trat design: - perforations - rim-lock Tray adhesives: - types - usage
How do perforations ensure retention?
Material extruded through holes retaining the material to tray mechanically
How does rim-lock ensure retention?
Retentive feature around extent of tray
What are tray waves and how do they improve retention?
- Periphery waves
- Helps to contain the fluid impression material in stock impression trays
What is greenstick and how does it improve retention?
- Rigid impression material
- Contains the fluid impression material in impression tray
What are the chemical constituents and purposes of the constituents of greenstick?
- Resin and waves for consistency control
- Stearic acid as a plasticiser
- CaCO3 as a filler, colouring agent and controlling rigidity
How is greenstick prepared?
- Transition temp at 55-60C
- Softened by hot water or flame
What is the typical tray adhesive used with alginate?
10-12% toluene in 45-50% isopropanol
What is the mechanism of action of a tray adhesive?
- Based on contact technology
What is the process of tray adhesive use? but, when should they never be used with?
- Applied to tray and allow to dry
- used sparingly
- Periphery covered
Never on metal trays
Name the 2 main presentations of tray adhesive?
Spray and paint on
What are the benefits of special trays?
- Permits equal thickness of impression material
- Dimensional change of impression material theoretically the same in all dimensions
What are special trays made from?
Polymethylmethacrylate or Shellac
What are the specific spacing of the perforations according to material used?
3mm - alginate
2mm - C-silicone
1mm - impression paste
Name the 10 most important properties of impression materials?
- easy to handle
- compatible with oral fluids
- reproduce detail accurately
- good tear resistance
- no adverse effects
- pleasant taste
- easily removable
- easy decontamination
- remain dimensionally table
- compatible with all model construction materials
What is the process of impression decontamination?
- Immediately after removal rinsed under cold running water
- Tray and material immersed in water-based disinfection solution (MFI)
- Impression then rinsed gently with tap water (over-disinfection can lead to changes)
- impression placed in sealed polythene bag and sent to lab
What is alginate chemcially?
Irreversible hydrocolloid
What is a colloid?
A substance which is distributed evenly through a material
What 2 phases can alginate be in?
Dispersed and continuous
What is the chemical equation for alginate?
Sodium and potassium salts + alginic acid forms alginate
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
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
What is the mixing, working and setting times of alginate?
Mixing: 45-60s
Working: 45s (fast) 75s (reg)
Setting: 1-4.5 mins
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
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)
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)
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
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
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
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
What are the common failures of poor alginate mixtures?
- Grainy
- Treating
- Bubbles
- Chalky model
- Distortion
What is the reason for a grainy alginate?
- inadequate or prolonged mixing
- ratio too low
What is the reason for alginate tearing?
- Inadequate bulk
- premature removal
What is the reason for external bubbles on alginate?
Air incorparation
What is the reason for a chalky alginate?
- Inadequate cleaning
- Excess water in impression
- Premature removal
What is the reason for a distorted alginate?
- Delayed pouring of impression
- Tray movement
- Premature removal
Name a commercially available alginate product?
Tropicalgin by Zhermack
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
What is the defintion of a dental cast?
Replica of the structures in the oral cavity
What are dental plasters and dental stones based on?
Gypsum
CaSO4 dihydrate
Crystalline in form
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
Describe the appearance of beta-Ca sulphate hemihydrate?
Porous powder
Irregular shaped particles
Not closely packed together
How does the the crystalline hemihydrate from impact the plaster?
Determines the precise type of plaster produced
Explain the process of dental stone?
Dihydrate is heated to 125C under pressure in presence of water vapour
Describe the appearance of alpha-Ca sulphate hemihydrate
Unformorm shaped particles
Reduced porosity
What are the 5 chemical constituents for dental stone?
CaSO4 hemihydrate Water KSO4 Borax NaCl
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
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
What is the function of NaCl in the dental stone mixture?
Reduces expansion
Extra sites for crystal growth
Keeps crystals closer together
What is the function of CaSO4 dihydrate in the dentals tone mixture?
0.5-1%
Provides nuclei of crystallisation
Acts as an accelerator
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
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
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
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)
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
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
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
What is the difference in setting expansion between plaster and stone?
Plaster:
- 0.3-0.4%
Stone:
- 0.05-0.3%
What are the working and setting time properties for dental stone?
2-3 minute working time
2-3 minute setting time
What is the definition of working time?
The point at which the material can be manipulated into the impression satisfactorily
How can the manufacture manipulate the setting time for htypsum?
KSO4
Borax
NaCl
CASO4 dihydrate
Indications for dental stone (gypsum)?
Study casts for general diagnosis
Working casts:
- denture full and partial
- ortho appliances
What is the definition of a working cast?
Cast onto which the restoration is constructed in the lab
What is the definition of a study cast?
Cast is intended to be used for treatment planning purposes
How compatible is a gypsum-based material?
Compatible with all commonly used impression materials
How can you adjust the behaviour of the dental stone material?
P:L ratio
Water temperature
Degree of spatulation of the mixture
What adverse reactions to the dental stone will excess water procedures?
Aid mixing
Slow setting time
Weakened plaster
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
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
What is the definition of a silicone impression material?
Elastomeric impression material
Condensation reaction with ethyl alcohol given off
Hydrophobic
Name the 5 constituents of silicone impression material?
Dimethyl siloxane Colloidal silica or CuCO3 Stannous octoate Alkyl silicate Colloidal silica
What is the function of dimethyl siloxane in silicone impression material?
low Mr silicone which has reactive terminal hydroxyl end groups
What is the function of CuCO3/Colloidal silica in silicone impression material?
Filler, as silicone polymer is liquid
FIller particles between 5-10 um
What is the function of Stannous octoate in silicone impression material?
Accelerator
What is the function of Alkyl silicate in silicone impression material?
Accelerator
What is the function of Colloidal silica in silicone impression material?
Thickening agent
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
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)
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
How much does silicone shrink?
Proportional to the amount of polysiloxane present
Name the 3 presentation of condensation silicones?
Putty
Putty and light body
Paste/Paste
Explain the mixing technique for condensation silicone?
Mixed with low viscosity paste accelerator
Kneaded into mass of putty
Give 1 trade name for condensation silicones?
Lab Putty (Coltene Whaledent)
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
Name the 2 types of impression composition materials?
Greenstick
Red cake
Give a description of greenstick?
Rigind non-elastic impression material
Used for border moulding of impression trays especially the post dam
Mucocompressive
When to avoid greenstick?
Allergy to colophony (asthma)
Give a description of red cake?
Thermoplastic
Impression Compound (Trade name)
Sheets or sticks
Indicated for first impression of the edentulous arch
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
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%
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
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
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
Name 3 types of occlusal registration materials?
A-silicones/polyether
Higher methacrylates
Waxes
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
Give 2 names of bite reg paste commercial products?
Jet Bite Blue, Coltene Whaledent, Silicone
Memosil 2, Heraeus Kulzer, Silicone
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
What is the definition of coping?
Thin layer of material which covers the preparation to the margins
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
Give 1 example of a commercial name for a higher methacrylate?
DuraLay II (Reliance)
What can higher methacrylates show?
Dough, removed and measured
Indicates amount of interocclusal clearance
What is the definition of an addition silicone impression material
Elastomeric impression material
Termed after setting reaction addition polymerisation reaction
Hydrophobic
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
How can the amount of filler change the category of the addition silicone impression material?
Heavy
Universal
Light-body
What 2 pastes are needed to form an addition silicone impression material?
Base paste
Catalyst paste
What must both pastes share for an addition silicone impression material?
The same consistency to facilitate mixing
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
What reaction will occur if the mixture has moisture contamination for an addition silicone impression material?
Rolled edge of preparation margins
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
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
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
Describe the good properties of an addition silicone impression material?
Highly hydrophobic
V good dimensional stability (best)
Many models can be poured
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
When will the addition silicone impression material increase in stiffness and why?
After 2-3 hrs due to further crosslinking
How to mitigate the poor tear resistance of an addition silicone impression material?
Leave in the mouth for longer
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
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
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
Name the 5 types of presentation for addition silicone impression materials?
Putty Heavy-bodied Universal bodied Light-bodied Extra light-bodied pastes
Give 1 example of a commercially available addition silicone impression material?
Affinis Coltene Whaledent
What is the effect to a model if addition silicones release hydrogen gas as a by product?
Porosity on the die material
What can be used to absorb the hydrogen for an addition silicone impression material?
Palladium
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
What are the 2 main constituents of an impression paste?
Zinc oxide
Eugenol-based impression
Name the 2 main indications for an impression paste?
Making working impression of edentulous arches
Denture relining material
What spacing does impression paste need in a special tray?
1mm
Used in thin sections
Name the 2 pastes used in an impression paste?
Base
Catalyst
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
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
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
What catalyses the setting reaction for an impression paste?
Water
Describe the setting reaction of impression paste?
Similar to ZOE
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
Name 3 good properties of the impression paste?
Rigid impression produced
Good fine detail reproduced
Mucostatic impression
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)
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
Describe the best practice to remove the impression paste from the spatula to the tray?
Warm spatula above temp rosin soften and wipe
What strange sensations can impression paste give to a paitient?
Tingling or mild burning sensation intra-orally
How to avoid the impression paste sticking to the patients extraoral tissues?
Apply petroleum jelly to extraoral features
A lot
Give 1 example of a commercially available impression paste?
Impression paste by SS White
What material can be sued to make a working model?
Gypsum-based
How long will a gypsum-based material cast take to set?
At least 1 hr
How to remove the impression paste from the gypsum-based model?
Immersed in warm water to remove the impression
What type of cast can an impression paste only be sued with?
Gypsum-based model
No separating medium is required
What are the indications for impression plaster?
USed to record endentulous ridges
Name 5 good properties for impression plaster?
Good surface detail Tolerated by patient Small setting expansion Good dimensional stability Hydrophilic
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)
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
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
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
How must the powder for an impression paste be stored?
Airtight tin to stop water entering the tin
What sized spacing is needed for impression plaster in a special tray?
1mm
How long is the working time for impression plaster?
2-3 mins
How do you insert the tray with impression plaster as the impression material?
Tray moved side to side on insertion so material can flow
How to decontaminate impression plaster?
Decontamination procedure follow manufacturer’s instructions
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
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
Name the 5 bases to make a wax?
Animal/vegetable fat Gums FAs Oils Resins
What is the melting point, hardness and role in dental wax for Carnauba?
Organic
84-91
High
Increases melting range and hardness
What is the melting point, hardness and role in dental wax for Ouricury?
Organic
79-84
High
Increases melting range and hardness
What is the melting point, hardness and role in dental wax for Candelilla?
Organic
68-75
High
Increases hardness of paraffin wax
What is the melting point, hardness and role in dental wax for Beeswax?
Organic
62-68
Medium
Common base for many waxes
What is the melting point, hardness and role in dental wax for Japan Wax?
Organic
53
Medium/low
May be substituited for beeswax
What is the melting point, hardness and role in dental wax for Paraffin?
Synthetic
40-51
Medium
Common base wax
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
What is the melting point, hardness and role in dental wax for Ceresin?
77-93
Medium/High
Increases melting range
What is the melting point, hardness and role in dental wax for Montan?
72-90
Medium/high
Increases melting range
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
Origin of the Carnauba wax?
Copernicia palm
Origin of Ouricury wax?
Feather palm
Origin of the Candelilla wax?
Euphorbia antisyphilitica
Origin of the Japan wax?
Really a fat containing glycerides of palmitic and stearic acid
From sumac tree
Lacquer
What is the definition of a lacquer?
Clear or coloured varnish that dries by solvent evaop to produce a hard and durable finish
Origin of Spermaceti wax?
Sperm whale
Origin of bees wax?
Bees
Why can natural waxes have very varying properties within the same wax?
Source difference
Time obtained
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
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
Give 4 examples of microcrystalline waxes?
Ceresin
Ozokerite
Montan
Barnsdahl