Impression Materials and Techniques Flashcards
what is an analogue impression
- a negative likeness or copy in reverse of the surface of an object
- an imprint of the teeth and adjacent structures for use in dentistry
- made from soft semi fluid material allowed to set
what is an impression technique
a method and manner used in making a negative likeness
what is an impression tray
a device that is used to carry, confine, and control impression material while making an impression
what is the ideal impression material
- easy to mix and handle
- suitable working time
- suitable setting time
- compatible with die and stone materials
- not toxic or allergic to the patient
- dimensionally stable
- accurate to record the fine details
- acceptable odor and taste
- adequate stretch
- adequate shelf life
- ready to be disinfected without loss of accuracy
- fluid or plastic when inserted into the mouth
- it must be an exact record of all the aspects
- economic
what is impression criteria
- exact dupliction of the prepared teeth
- including uncut tooth structure beyond finish line
- accurate reproduction of the other teeth and tissues, permit cast articulation and restoration contouring
- free of air bubbles especially in the finish line and occlusal surfaces
- extended enough to capture the vestibule, tuberosities and retromolar pad
what is wettability
ability of liquid to flow over a solid surface
what is wettability related to
surface energy of the solid and surface tension of the liquid
what is the contact angle of wettability
- hydrophobic: contact angle >90 degrees, surface not wetted
- hydrophilic: contact angle <90 degrees, surface wetted
what is viscosity and what is it related to
- resistance of liquid to flow
- reverse of fluidity
- related to unset, liquid material
what are liquid and viscosity categorized as
- newtonian
- none-newtonian
what is newtonian
a fluid viscosity is not affected by shear rate
- viscosity is constant
what is a none- newtonian
a fluid that does not follow
- viscosity can be changed
what is pseudoplasticity
- shear thinning
- reduce viscosity with increase share
- material does not flow until under pressure
- less viscous with increased share
what is viscoelasticity
- characteristic of solid that behaves as an elastic solid and a viscous fluid
- related to the set impression
- mechanical properties depending on loading rate
what are the mechanical properties depending on loading rate in viscoelasticity
- associated with viscus nature
- as increased load rate, properties improved
- increased tear strength and elastic limit
- quick removal, decreased distrortion
what is accuracy
ability to replicate the intra oral surface details
what is dimensional stability
ability to retain its absolute dimensional size over time
what is tear resistance
ability to resist tearing in thin sections, such as through the feather edge material within the gingival sulcus
describe nonelastic impression materials
- rigid, cannot be removed from undercuts
- edentulous impressions
describe elastic impression materials
-can be removed from undercuts without distortion
- dentate impressions
what are the two types of impression materials
- nonelastic
- elastic
what are the types of nonelastic impression materials
- plaster
- impression compound
- zinc oxide eugenol
- impression waxes
what are the types of elastic impression materials
- hydrocolloids
- non aqueous elastomers
what are the non aqueous elastomers
-condensation silicone
- polysulfides
- polyethers
- addition silicone
what are the types of hydrocolloids
- agar reversible
- alginate irreversible
what are the nonelastic/rigid impression materials popular in previous century
-plaster of paris
- impression plaster
- gutta percha
- modeling compound
- ZOE
- various waxes
the first nonelastic/rigid impression materials were popular in the previous century and arent used now with the exception of:
recording atrophic edentulous ridges or flappy ridges
what are the elastic impression materials and the year
- reversible hydrocolloid - first impression material 1925
- irreversible hydrocolloid 1940
- polysulfide rubber 1950
- vinyl poly siloxanes 1970
- polyether 1975
describe aqueous elastomeric hydrocolloids
- water is the major component
- hydrocolloid
- reversible and irreversible
- reversible is not commonly used today
describe none- aqueous elastomeric polymers
- polysulfide
- vinyl polysiloxane
- polyether
describe reversible hydrocolloid
- softens under heat and solidifies when cooled
- secondary bonds
- no chemical change
describe irreversible hydrocolloid
- chemical reaction that cannot revert to preset state
- primary bonds
describe aqueous elastomeric - hydrocolloids
- colloidal materials, agar, or alginate dissolved in water
- sol to gel
describe sol to gel reaction in agar and alginate
- agar: reversible due to temperature change
- alginate: irreversible chemical reaction
what are the properties related to gel network in aqueous elastomeric hydrocolloids
- evaporation (shrinkage)
- syneresis: gel relaxation; water extruded from gel - shrinkage
- inhibition: absorption of water causing expansion
what consistencies do elastic polymers come in
light, medium, heavy and putty
what are the types of elastic polymers
- polysulfide or rubber base PS
- vinvyl polysiloxane VPS
- polyether PE
what is the chemical setting reaction in none aqueous elastomeric
- condensation polymerization: by product is H2O or -OH
- addition polymerization: no by product
what is the tray selection criteria
- feel comfortable to the patient
- extended slightly beyond the facial/buccal surfaces of the teeth
- extend approximately 2-3mm beyond the 3rd molar, retromolar, or tuberosity
- sufficiently deep to allow 2-3mm of material between the tray and the occlusal/incisal edges
- sufficiently rigid
the impression tray must be sufficiently rigid to:
- carry the impression material into the oral cavity
- hold the material in close proximity to the teeth
- avoid breaking during removal
- prevent wrapping of the completed impression
what are the types of impression trays
- stock trays
- custom trays
describe stock trays
- plastic or metal; perforated or rimmed
- complete arch, quadrant, or dual arch
- dentate or edentulous arch
describe custom trays
- made 24 hours in advance
- light cured, auto cured, thermoformed
- better fit
- less material waste
- controlled thickness of mateiral
- increased accuracy
what is impression tray retention and adhesion for
to prevent impression distortion due to material pulling away from tray
what gives retention and adhesion in impression trays
- mechanism perforations or rims
- chemical adhesion
what are the adhesive materials for retention and adhesion in impression trays
- specific for each material; including alginate
- should always be used
- apply and dry
what is the goal of preliminary impressions
a fully or overextended impression of the arch, with all anatomical landmarks
what is the purpose of preliminary impressions
- evaluate arch form
- anatomical landmarks
- musculature
- hard and soft tissue anomalies
- restorative space
- diagnostic wax up
- fabrication of custom tray
what is the final impression material selected based on
the type of impression required for the procedure
what is tissue retraction
in the final impression single or double cord technique; cord/s removed right before impression making
where is the light bodied consistency dispensed in the final impression
into the sulcus, over and around the prepared teeth and onto the surrounding tissue
describe the final impression with the custom tray
- the custom tray with dried adhesive loaded with medium or heavy bodied consistency and tray is seated with no downward pressure approximately 4-6 minutes
- once set remove as quickly and straight as possible
- the impression is disinfected, inspected for accuracy, placed in a biohazard bag, labeled and ready for the lab tech
what is the purpose of tissue manipulation for gingival retraction
to atraumatically displace gingival tissue to allow access for impression material to record the finish line and provide sufficient thickness of the impression
what are the techniques for tissue manipulation for gingival retraction
- mechanical
- chemo- mechanical
- surgical
- surgical not widely used
what is an example of chemo mechanical tissue manipulation for gingival retention
impregnated cords
what are examples of surgical techniques for tissue manipulation and gingival retraction
- electrosurgery
- rotary curettage
- laser
what are the classifications of retraction cords dependent on and describe each
- configuration: twisted, knitted, plain
- surface finish: waxed, unwaxed
what is the chemo mechanical technique
- pack the retraction cord, soaked in hemostatic agent then dried using cord packing instrument
- double vs single cord technique
- remove cord/s after 4 minutes
- impression material injected into the sulcus
what is the double vs single cord technique
- two knitted cords with different diameters are used
- smaller diameter will be deep into the sulcus
what was irreversible hydrocolloid/alginate developed for and where is it from
a substitute for agar impressino material when its supply became scarce during WWII
- based on a nature substance extracted from brown seaweed
when irreversible hydrocolloid/alginates are mixed with water what do they form
a sol gel
is alginate hydrophobic or hydrophilic
hydrophilic
what is the composition of alginate
- soluble alginates
- calcium sulphate: reactor, insoluble calcium alginate
- zinc oxide: filler
- potassium titanium fluoride: accelerator
- diatomaceous earth: filler, provides strength and stiffness
- sodium phosphate: retarder
- coloring and flavouring agent
describe the chemical reaction in alginate
Na alginate + CaSO4 -> Ca alginate + Na2SO4
alginate is a powder which contains the following reacting ingredients:
- potassium or sodium alginate (15-20%): reacts with calcium ions
- calcium sulphate dihydrate (14-20%) reacts with potassium alginate to form a dihydrate insoluble alginate gel
what is the technique using alginate
- powder: liquid ratio
- add water first
- avoid incorporating air into the mix
- mixing time is 45-60 seconds, based on fast set or regular set
- contaminants such as gypsum may accelerate the set
- thickness of alginate should be 3mm
what is the recommended technique for alginate impression disinfectin
-1:10 dilution of household bleach
- impression then wrapped immediately in soaked paper towel and sealed bag
how long should the stone cast set after pouring the alginate impression
60 minutes
what are the 2 major factors that affect the shelf life of the impression
storage temperature and moisture
how should the diagnostic cast be cleaned up after taken out of impression
- small nodules and projections on the impression surface should be removed
- casts should be trimmed and mounted
what are dimensional changes in the impression caused by
delay in pouring the impression
what is distortion caused by
moving the tray during setting, premature removal of tray, not removing with a snap , delay pouring cast
what can tearing be caused by
impression removed before it sets, slow rate of removal, thin mix used, deep undercuts, not enough material in tray
what is loss of detail from
premature tray removal from mouth
how is non aqueous elastic material distinguished from hydrocolloids
hydrocolloids are aqueous
what are elastomeric impression materials made of
synthetic rubber
what problems do elastomeric impression materials solve with hydrocolloids
- poor tear resistance
- poor dimensional stability
describe polysulfide
- AKA mercaptan or simply rubber
- provided as two tubes as base and accelerator
- requires a custom tray
- longer setting time, malodor, stain clothes
what is the composition of polysulfide
- base: polysulfide polymer mixed with inert fillers
- catalyst: lead dioxide mixed with small amounts of sulfur and act as oxidation initiator
describe vinyl polysiloxane
- limited shelf life
- requires special tray adhesive
- provided as auto mix unit, syringe, and mixing tips
- no syneresis, or imbition however respond with shrinkage over time
- more flexible, so there is more chance for distortion during removal
- best dimensional stability among impression materials
what is the impression technique with vinyl polysiloxane
- wait 20-30 minutes before pouring for stress relaxation. it can be delayed up to 7-10 days
- stiffness makes removal of tray more difficult
what is the composition of addition silicon in vinyl polysiloxane
- base: poly dimethyl siloxane
- catalyst: polyvinyl siloxane- platinum salt
- cross linking agent: alkyl ortho silicate or organo hydrogen siloxane
- filler: silica
what is the manipulation and technique of vinyl polysiloxane
- addition reaction, no by product
- automix: uniform mixing, less air, less mixing time
-sulfur inhibit the polymerization: latex gloves retards the setting - hydrophobic: dry field needed, surfactant added: improves wettability and less cast bubbles
- elastic recovery from undercuts
describe the H2 release in vinyl polysiloxane manipulation and technique
- secondary reaction not a byproduct
- 15-30 min delay in pouring
- platinum act as H2 scavengers
what effects the dimensional stability of vinyl polysiloxane
multiple pours
- delayed pouring
describe polyether
- hydrophilic
- high elastic recovery
- provided as hand, auto mix unit or electronic mixing
- light, medium and heavy body consistencies
- difficult removal from mouth or cast
why is it difficult to remove polyether from mouth or cast
- undercut block out
- less stiff than VPS
- material stiffness and harder removal are not correlated
how should you prevent tearing in polyether
break the seal and rock slightly
how do water, saliva and blood affect polyether material
increase the marginal discrepancy
when does increased water absorption occur in polyether
if a thinning agent is used
what is the composition of polyether
- base: polyether
- catalyst: glycol based plasticizers
- cross linking agent: sulfate
- filler: silica
describe polyether manipulation and technique
- addition reaction, no by product
- short setting time
- excellent accuracy and dimensional stability
- dimensional stability: affected by multiple pours and delayed pouring
which are the tear strengths of PS? VPS? PE?
PS: highest
- VPS: adequate
- PE: adequate
what tray do you use with PS? VPS? PE?
- PS: custom
- VPS: custom or stock
- PE: custom or stock
what is the working/setting time of PS? VPS? PE?
- PS: 3-6/8-10
- VPS: 2-4/4-6
- PE: 3/6
what is the pour time of PS? VPS? PE?
- PS: 1 hour
- VPS: 7 days
- PE: 7 days
what is the moisture toelrance/ pouring ease of PS? VPS?PE?
- PS: acceptable
- VPS: poor/adequate
- PE: very good
what is the cause of voids
- lifting intra oral tip while syringing or presence of moisture
what is the cause of tacky unset VPS material in the preparation area
- early removal or sulfur contamination from gloves
what are the effects of disinfectant soaked paper towel for 10 mins on eaach material
- no adverse effect on VPS
- potential expansion with increased exposure time for PS and PE
- imbition and expasion for alginate
it is better to ______ the impression than soaked paper towel
rinse and spray
what are the acceptable disinfectants
- glutaraldehyde
- iodophors
- sodium hypochlorite
- synthetic phenols
- dual or synergized quaternaries
- sodium bromide
- chlorine
what is GPT-9
-a digital impression
- a digital scan
- intra oral scanners
- scan then send electronic file
what is a digital scan
capturing the optimal image directly of the patients anatomy or indirectly of a definitive cast of the anatomy
what is a digital impression
- not a negative likeness or copy in reverse of the surface of an object
