IMPRESSION MATERIALS AND TECHNIQUE Flashcards
dental impression
an imprint or negative likeness
dental impression i made from
semi fluid material allowed to set
THE IDEAL IMPRESSION MATERIAL
(16)
easy to mix and handle
suitable working time
suitable setting time
compatible with die and stone
not toxic or allergenic to the pt
dimensionally stable on setting
accurate to record the fine details
has acceptable odor and taste
adequate strength
adequate shelf life
economical
ready to be disinfected w/o loss of accuracy
fluid or plastic when inserted into the mouth
it must be an exact record of all the aspects
other teeth and tissue surrounding
it must be free from air bubbles especially in the finish line area
IMPRESSION
CRITERIA
(3)
*exact duplication of prepared tooth, including uncut tooth beyond finish line
*accurate reproduction other teeth and tissues, permit cast articulation and restoration contouring
*free of bubbles especially in the finish line and occlusal surfaces of other teeth
IMPRESSION MATERIAL PROPERTIES
wettability
viscosity
pseudoplasticity
viscoelastic
WETTABILITY:
ability of liquid to flow over a solid surface
-related to surface energy of the solid and surface tension of the liquid
-contact angle of wetting
contact angle > 90:
surface not wetted
hydrophobic
contact angle <
90:
surface
wetted
hydrophilic
viscosity
resistance of a liquid to flow or motion. reverse of fluidity
-related to the unset, liquid material
liquids and viscosity:
newtonian:
pseudoplastic:
viscosity constant
decrease viscosity with increase shear rate
pseudoplasticity
shear thinning
-material does not flow until under pressure
-less viscous with increased shear rate
why same material used in tray and syringe
viscoelastic
characteristic of sloid that behaves as an elastic solid and viscous liquid
-related to the set impression
-mechanical properties dependent on loading rate
-mechanical properties dependent on loading rate
(4)
-associated with viscous nature
-as increase load rate, properties improved
-increase tear strength and elastic limit
-quick removal, decreased distortion
A
ACCURACY=
ABILITY TO REPLICATE THE INTRAORAL
SURFACE DETAILS
B
DIMENSIONAL STABILITY =
ABILITY TO RETAIN ITS
ABSOLUTE DIMENSIONAL SIZE OVER TIME.
C. TEAR RESISTANCE =
ABILITY TO RESIST TEARING IN
THIN SECTIONS (SUCH AS THROUGH THE FEATHER-
EDGED MATERIAL WITHIN THE GINGIVAL SULCUS).
IMPRESSION MATERIALS
ELASTIC
(5)
FIRST ELASTIC IMPRESSION MATERIAL (REVERSIBLE HYDROCOLLOID
IRREVERSIBLE HYDROCOLLOID (ALGINATE)
POLYSULFIDE RUBBER
VINYL POLY SILOXANES
POLYETHERS
IMPRESSION MATERIALS
RIGID
THE FIRST IMPRESSION MATERIALS WERE MOST POPULAR THE PREVIOUS CENTURY
-PLASTER OF PARIS
-IMPRESSION PLASTER
-GUTTA PERCHA
-MODELING COMPOUND=IMPRESSION COMPOUND= MODELING PLASTIC
-VARIOUS WAXES
NOT COMMONLY USED NOW WITH THE EXCEPTION OF RECORDING ATROPHIC
EDENTULOUS RIDGES (ESP. MANDIBULAR)
irreversible
chemical rxn, cannot revert to preset state. primary bonds
reversible
(2)
-softens under heat and solidifies when cooled
-secondary bonds, no chemical change
inelastic
(2)
-rigid, cannot be removed from undercuts
-edentulous impressions
elastic (2)
-can be removed from undercuts without distortion
-dentate impressions
Nonelastic
(4)
Zinc oxide eugenol
Impression Compound
Gypsum (Plaster)
Impression wax
Elastic
Hydrocolloids
(2)
Agar
Alginate
Elastic
Non-aqueous
elastomers
(4)
Polysulfides
Polyethers
Addition
silicone
Condensation
silicone
aqueous elastomerics
-water major component
-hydrocolloid
hydrocolloid
(2)
-irreversible (alginate): not for fixed
-reversible (agar): used for fixed (not commonly used today)
non aqueous elastomerics (polymers)
(3)
-polysulfide
-vinyl polysiloxane
-polyesther
NON-AQUEOUS ELASTOMERIC
MATERIALS
“ELASTIC POLYMERS”
(3)
-polysulfide
-vinyl polysiloxane (VPS)
-polyether (PE)
TRAY SELECTION
CRITERIA
(4)
- FEEL COMFORTABLE TO THE PATIENT
- EXTENDS SLIGHTLY BEYOND THE FACIAL SURFACES OF
THE TEETH - EXTENDS APPROXIMATELY 2 TO 3 MM BEYOND THE THIRD
MOLAR. RETROMOLAR. OR TUBEROSITY AREA OF THE
ARCH. - IS SUFFICIENTLY DEEP TO ALLOW 2 TO 3 MM OF
MATERIAL BETWEEN THE TRAY AND INCISAL OR OCCLUSAL
EDGES OF THE TEETH.
IMPRESSION
TRAYS
(4)
1
RIGIDITY IMPORTANT
2
STOCK TRAYS
a. PLASTIC, METAL;
PERFORATED/RIMMED
b. COMPLETE ARCH, QUADRANT
DUALARCH
3. CUSTOM ACRYLIC RESIN TRAYS
(MADE 24H IN ADVANCE)
a.PHOTO-CURED (TRIAD)
THERMOFORMED
AUTO-CURED
b. BETTER FIT
c.LESS MATERIAL WASTE
d. CONTROLLED THICKNESS OF MATERIAL
e. INCREASED ACCURACY, ESPECIALLY FPD’S
4 ADHESION TO TRAY
a. PREVENT IMPRESSION DISTORTION DUE TO MATERIAL PULLING AWAY FROM TRAY
b. MECHANICAL PERFORATIONS
c. ADHESIVE MATERIAL
1) SPECIFIC FOR EACH MATERIAL (INCLUDING ALGINATE)
2) SHOULD ALWAYS USE, EVEN WITH PERFORATED TRAY
3) APPLY AND DRY ~
15 MIN
VPS adhesives (blue)
for polyvinyl siloxane and polyether impression materials
rubber base adhesive (brown)
used with rubber base impression materials
silicone adhesive (orange-pink)
used with silicone impression materials
impression must be sufficiently rigid to (4)
*CARRY THE IMPRESSION MATERIAL
iNTO THE ORAL CAVITY
*HOLD THE MATERIAL IN CLOSE PROXIMITY TO THE TEETH
* AVOID BREAKING DURING REMOVAL
* PREVENT WARPING OF THE COMPLETED IMPRESSION
PRELIMINARY
IMPRESSIONS
goal
a filly or overextended impression of the arch, with all the anatomical landmarks
good impressions are —, not —
made, taken
IRREVERSIBLE HYDROCOLLOID
(ALGINATE)
WAS DEVELOPED AS A SUBSTITUTE FOR THE AGAR IMPRESSION:
MATERIAL WHEN ITS SUPPLY BECAME SCARCE DURING WORLD WAR II
BASED ON A NATURAL SUBSTANCE
From
SEAWEED
RACTED FROM CERTAIN BROWN
WHEN THE SOLUBLE ALGINATES ARE MIXED WITH WATER,
THEY FORM
A SOL QUITE READILY
ALGINATE IMPRESSION MATERIALS ARE HYDROPHILIC, SO MOIST TISSUE
SURFACES ARE NOT A PROBLEM.
BASIC IMPRESSION
TECHNIQUE
(7)
THE MATERIAL SELECTED DEPENDS UPON THE
DENTIST’S PREFERENCE AND THE TYPE OF IMPRESSION
REQUIRED FOR THE PROCEDURE
THE DENTIST PREPARES THE TOOTH OR TEETH FOR THE
IMPRESSION
THE LIGHT-BODIED MATERIAL IS PREPARED AND
LOADED INTO THE SYRINGE AND TRANSFERRED TO THE
DENTIST
THE DENTIST PLACES THE LIGHT-BODIED MATERIAL
OVER AND AROUND THE PREPARED TEETH AND ONTO
THE SURROUNDING TISSUES.
5
THE HEAVY-BODIED MATERIAL IS PREPARED AND
LOADED INTO the tray and transferred TO THE
DENTIST
6
WHEN THE IMPRESSION MATERIAL HÀS REACHED FINAL
SET. THE IMPRESSION IS REMOVED AND INSPECTED
FOR ACCURACY
7
THE IMPRESSION IS DISINFECTED, PLACED IN A
BIOHAZARD BAG, LABELED,
AND READIED FOR THE
LABORATORY TECHNICIAN.
Composition and Setting Reaction of Alginate
*ALGINATE IS PROVIDED AS A POWDER, WHICH CONTAINS THE
FOLLOWING INGREDIENTS:
(9)
*POTASSIUM OR SODIUM ALGINATE:
*CALCIUM SULPHATE DIHYDRATE:
*ZINC OXIDE:
*POTASSIUM TITANIUM FLUORIDE:
*DIATOMACEOUS EARTH:
*TRISODIUM PHOSPHATE:
*COLORING AGENTS
*FLAVORING AGENTS
*POTASSIUM OR SODIUM ALGINATE:
DISSOLVES IN WATER AND
REACTS WITH CALCIUM IONS
*CALCIUM SULPHATE DIHYDRATE:
A REACTOR, REACTS WITH
POTASSIUM ALGINATE TO FORM A DIHYDRATE INSOLUBLE ALGINATE
GEL
*ZINC OXIDE:
FILLER PARTICLES, AFFECTS PROPERTIES AND SETTING
TIME
*POTASSIUM TITANIUM FLUORIDE:
ACCELERATOR, COUNTERACTS
THE INHIBITING EFFECT OF THE HYDROCOLLOID ON THE SETTING OF
STONE; ENSURES GOOD QUALITY SURFACE OF THE CAST
*DIATOMACEOUS EARTH:
FILLER PARTICLES, CONTROLS THE
CONSISTENCY OF THE MIX AND THE FLEXIBILITY OF THE SET
ALGINATE
*TRISODIUM PHOSPHATE:
RETARDER, CONTROLS THE SETTING TIME
TO PRODUCE EITHER REGULAR OR FAST-SET ALGINATES
Technique:
THE FIRST STEP OF MANIpulation
OF WATER AND POWDER
ATION IS TO PREPARE A PROPER MIX
THE MEASURED POWDER IS SIFTED INTO PREMEASURED WATER THA
HAS ALREADY BEEN POURED INTO A CLEAN RUBBER BOWL
E
THE WATER IS ADDED FIRST TO WET THE MIXING BOWL AND TO ENSURE
COMPLETE WETTING OF POWDER PARTICLES
CARE SHOULD BE TAKEN TO AVOID INCORPORATING AIR INTO THE MIX.
THE MIXING TIME IS PARTICULARLY IMPORTANT; 45 SEC TO 1 MIN IS
GENERALLY SUFFICIENT, DEPENDING ON THE BRAND AND TYPE OF
ALGINATE (FAST-SET OR REGULAR-SET)
CONTAMINANTS, SUCH AS SMALL AMOUNTS OF GYPSUM LEFT IN THE
BOWL FROM A PREVIOUS MIX OF PLASTER OR STONE, CAN
ACCELERATE THE SET.
THE TRAY MUST FIT THE PATIENT’S ARCH SO THAT THERE IS
SUFFICIENT BULK OF MATERIAL.
THE THICKNESS OF THE
ALGINATE IMPRESSION BETWEEN THE TRAY AND THE TISSUES
SHOULD BE AT LEAST 3 MM
MOST MANUFACTURERS RECOMMEND A SPECIFIC DISINFECTANT
SUCH AS IODOPHOR, BLEACH, OR GLUTARALDEHYDE, WHICH
SHOULD BE USED ACCORDING TO THE MANUFACTURER’S
DIRECTIONS.
THE CURRENT PROTOCOL FOR DISINFECTING HYDROCOLLOID
IMPRESSIONS RECOMMENDED BY THE CENTER FOR DISEASE
CONTROL IS TO USE HOUSEHOLD BLEACH (1 TO 10 DILUTION),
IODOPHORS, OR SYNTHETIC PHENOLS AS DISINFECTANTS. AFTER
THE IMPRESSION IS RINSED THOROUGHLY, THE DISINFECTANT CAN
BE SPRAYED LIBERALLY ON THE EXPOSED SURFACE. THE
IMPRESSION IS THEN WRAPPED IMMEDIATELY IN A DISINFECTANT-
SOAKED PAPER TOWEL AND PLACED IN A SEALED PLASTIC BAG FOR
10 MIN.
FINALLY, THE WRAPPED IMPRESSION IS REMOVED FROM THE
BAG, UNWRAPPED, RINSED, AND SHAKEN TO REMOVE
EXCESS WATER.
THE STONE CAST SHOULD BE KEPT IN CONTACT WITH THE
IMPRESSION PREFERABLY FOR 60 MIN, BEFORE THE
IMPRESSION IS SEPARATED FROM THE CAST,
IT IS WISE TO SEPARATE THE CAST FROM THE IMPRESSION
WITHIN À REASONABLE PERIOD OF TIME SO THAT
DESICCATION OF THE HYDROCOLLOID DOES NOT OCCUR,
THEREBY CAUSING ABRASION OF THE GYPSUM CAST DURING
ITS REMOVAL.
TWO MAJOR FACTORS THAT AFFECT THE SHELF LIFE OF
ALGINATE IMPRESSION MATERIALS ARE STORAGE
TEMPERATURE AND MOISTURE CONTAMINATION FROM
AMBIENT AIR.
FINISHING THE DIAGNOSTIC
CAST
the diagnostic cast should be separated from the impression — after its initial set
one hour
FINISHING THE DIAGNOSTIC
CAST
care should be taken while
removing the material from the undercut areas
FINISHING THE DIAGNOSTIC
CAST
small nodules and prohections on the impression surface
should be removed
ELASTOMERIC IMPRESSION MATERIALS
THESE ARE ELASTIC IMPRESSION MATERIALS CALLED
*NON-AQUEOUS” ELASTIC IMPRESSION MATERIALS:
DISTINGUISHED FROM THE HYDROCOLLOIDS WHICH ARE
AQUEOUS MATERIALS.
ELASTOMERIC IMPRESSION MATERIALS
THEY ARE SYNTHETIC
RUBBER
ELASTOMERIC IMPRESSION MATERIALS
* THEY OFFER POTENTIAL SOLUTIONS TO THE TWO MAIN
PROBLEMS ASSOCIATED WITH HYDROCOLLOIDS:
- POOR TEAR RESISTANCE
- POOR DIMENSIONAL STABILITY
POLYSULFIDE
(2)
IS AN ELASTOMER THAT IS ALSO KNOWN AS “MERCAPTAN” OR
SIMPLY
“RUBBER BASE”
THE IMPRESSION MATERIAL IS PACKAGED IN TWO TUBES: A
BASE AND AN ACCELERATOR
POLYSULFIDE
COMPOSITION:
(2)
THE BASE CONTAINS A LIQUID POLYSULFIDE POLYMER MIXED
WITH AN INERT FILLER
THE ACCELERATOR WHICH IS USUALLY LEAD PEROXIDE MIXED
WITH SMALL AMOUNTS OF SULFUR AND ACTS AS AN OXIDATION
INITIATOR.
VINYL POLYSILOXANE IMPRESSION
MATERIAL
chemical makeup (4)
base: poly dimethyl siloxanr
cross linking agent: alkyl ortho silicate or organo hydrogen siloxane
catalyst: organo tin compounds
filler: silica
MANIPULATION AND TECHNIQUE
CONSIDERATIONS FOR VINYL POLYSILOXANE
MATERIAL
(5)
THE MATERIAL HÀS A LIMITED SHELF LIFE
THE TRAY REOUIRES À SPECIAL TRAY ADHESIVE
NO SYNERESIS OR IMBIBITION BUT DOES RESPOND
WITH SHRINKAGE OVER TIME
THE MATERIAL IS MORE FLEXIBLE,
SO THERE IS MORE
CHANCE FOR DISTORTION DURING REMOVAL
* WAIT 20 TO 30 MINUTES BEFORE POURING OF MODELS
FOR STRESS RELAXATION TO OCCUR.
Manipulation and Technique
Considerations
For Vinyl Polysiloxane
(4)
- FOR DIMENSIONAL STABILITY,
THIS IS THE BEST
IMPRESSION MATERIAL - POURING OF THE MODEL CAN BE DELAYED UP TO 7 TO
10 DAYS - STIFFNESS OF THE MATERIAL MAKES REMOVAL OF THE
TRAY DIFFICULT. - MATERIAL DISPENSED USING AUTO-MIXING UNIT AND
MIXING TIPS.
VINYL POLYSILOXANE
MANIPULATION AND TECHNIQUE
CONSIDERATIONS
BEST IMPRESSION MATERIAL FOR DIMENSIONAL
STABILITY
POURING SHOULD BE DELAYED AT LEAST
4 HOURS
FOR H2 OUT-GASSING
POURING CAN BE DELAYED UP TO 7-TO-10 DAYS
B.
(OR INDEFINITELY)
STIFFNESS MAKES REMOVAL DIFFICULT.
C.
MOST MATERIAL DISPENSED USING AUTO-MIXING
GUN AND MIXING TIPS
VINYL POLYSILOXANE (VPS
NOT PVS)
1.ADDITION REACTION: A + B- C
NO BY-PRODUCTS
2. LIGHT, MEDIUM, OR HEAVY-BODIED PASTES,
HEAVY-BODIED PUTTY
OR
3.AUTOMATIC MIXING,
UNIFORM MIX
a. LESS AIR
b.DECREASED MIX TIVE
C.MIXING TIPS NOT ALWAYS INTERCHANGEABLE
(CHECK COLOR CODE)
4. HYDROPHOBIC
a. DRY ORAL FIELD
b. SURTACTANTS ADDED, IMPROVED POURING
LESS CAST BUBBLES
5. SULFUR, POLYMERIZATION INHIBITION
a. LATEX GLOVES, RETRACTION CHEMICALS
6. H, GAS RELEASE
a.
SECONDARY REACTION
NOT A BY-PRODUCT
b
15-30 MIN POUR DELAY
C. PLATINUM H, SCAVENGERS
7. excellent elastic recovery from undercuts
8. dimmensionally stable
a. poor delay
b. multiple pours
monophase
medium body, tray and syringe
dual phase
-heavy/medium
-medium/light
putty wash
-make putty impression prior to preparation
-putty used as custom tray
-light or medium body, syringe
POLYETHER
(7)
- base + caralyn: addition
- light, medium, heavy body
- hand, auto-mix or electronic-mix system
- DIFFICULT REMOVAL FROM MOUTH OR CAST
UNDERCUT BLOCKOUT
INITIALLY THOUGHT DUE TO HIGHER PE STIFFNESS
REFORMULATED, LESS STIFF THAN VPS
EVEN THOUGH LOWER STIFFNESS, STILL HIGHER REMOVAL FORCE
MATERIAL STIFFNESS AND IMPRESSION REMOVAL DIFFICULTY NOT
CORRELATED (WALKER ET AL 2012, J PROS) - HYDROPHILIC: LIKELY REASON FOR IMPRESSION REMOVAL DIFFICULTY
HIGHER INTERACTIONS FORCES WITH IMPRESSED SURFACE - HIGH ELASTIC RECOVERY
- DIMENSIONAL STABILITY
POUR DELAY
MULTIPLE POUR
POLYETHER
MANIPULATION AND TECHNIQUE CONSIDERATIONS
(5)
EXCELLENT IMPRESSION ACCURACY AND DIMENSIONAI
STABILITY
STIFF AND THEREFORE DIFFICULT TO REMOVE WITHOUT
ROCKING
BREAK SEAL AND ROCK SLIGHTLY TO PREVENT TEARING: LOW
TEAR RESISTANCE
NEGATIVELY AFFECTED BY H2O, SALIVA, AND BLOOD
(1
SINCE IT IS HYDROPHOBIC, MOISTURE INCREASES
MARGINAL DISCREPANCY
(2) INCREASED WATER ABSORPTION OCCURS IF USE
THINNING AGENTS
CAN BE DISPENSED FROM AUTOMATED EXTRUDER
AND MIXER (ESPE PENTAMIX)
POLYETHER IMPRESSION
MATERIAL
chemical makeup
(4)
*BASE: POLYETHER
* CROSS-LINKING AGENT: SULFATE
*CATALYSTS: GLYCOL-BASED PLASTICIZERS
* FILLER: SILICA
MANIPULATION AND TECHNIQUE
CONSIDERATIONS FOR POLYETHER
MATERIAL
(5)
*MATERIAL IS VERY STIFF WHICH MAKES IT DIFFICULT TO REMOVE
WITHOUT ROCKING
*WHEN REMOVING THE IMPRESSION, BREAK THE SEAL AND ROCK
SLIGHTLY TO PREVENT TEARING.
* WATER, SALIVA,
AND BLOOD AFFECT POLYETHER MATERIAL
* ADDED MOISTURE WILL INCREASE THE IMPRESSION’S MARGINAL
DISCREPANCY
* INCREASED WATER ABSORPTION OCCURS IF A THINNING AGENT IS
USED.
IMPRESSION TECHNIQUE
(4)
-load reusable intraoral impression syringe
-load disposable intraoral syringe
-use intraoral syringe tip on automix unit
-inject into sulcus, push material ahead of tip to reduce bubbles
IMPRESSION TECHNIQUE
(4)
- AIR SYRINGE, DRIVE MATERIAL, INTO SULCUS AND
PREP DETAIL - TRAY, WITH DRIED ADHESIVE, LOADED FROM
DISPENSER. (ASST DOES THIS WHILE DENTIST
SYRINGES AROUND PREP - TRAY IS SEATED AND HELD WITH NO DOWNWARD
PRESSURE FOR ~4-6 MIN - ONCE SET, REMOVE AS QUICKLY AND STRAIGHTLY
AS POSSIBLE, REDUCE PERMANENT
DEFORMATION.ION
bubbles at finish line unacceptable impression
cause:
Lifting intra-oral tip while syringing or
presence of moisture.
Tacky, unset VPS material in preparation area
cause:
solution:
Cause: Sulfur contamination from gloves or retraction chemical.
Solution: Wash and dry preparation
IMPRESSION DISINFECTION
-disinfectant-soaked paper towel/plastic bag, 10 min
-VPS not adversely affected
-hydrocolloids (imbition:expansion after 10 min)
-polysulfide, polyether (potential expansion, increase exposure time)
THE FUTURE: DIGITAL
IMPRESSIONS
(2)
*less focus on research and development of impression materials
*digital impressions, scan and then send electronic file
some current systems:
(3)
- CEREC PRIMESCAN, OMNICAM OR BLUECAM (SIRONA)
- ITERO ELEMENT (ALIGN TECHNOLOGY)
- LAVA TRUE DEFINITION SCANNER (MIDMARK)
