Impressions in removable partial dentures/dental courses

Impressions inImpressions in
removable partialremovable partial
denturesdentures
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

Impression : a negative likeness or copyImpression : a negative likeness or copy
in reverse of the surface of an object; anin reverse of the surface of an object; an
imprint of the teeth and adjacentimprint of the teeth and adjacent
structures for use in dentistrystructures for use in dentistry

Diagnostic impressionsDiagnostic impressions
Permit analysis of contour of hard and softPermit analysis of contour of hard and soft
tissuestissues
Types of restorations on abutment teethTypes of restorations on abutment teeth
Determination of need for surgicalDetermination of need for surgical
correction of exostosis, frena, tuberositiescorrection of exostosis, frena, tuberosities
and undercutsand undercuts
Serve as blueprint for placement ofServe as blueprint for placement of
restorations, recontouring of teeth and restrestorations, recontouring of teeth and rest
seat preparationseat preparation

Permit analysis of patients occlusionPermit analysis of patients occlusion
Adequacy of interarch spaceAdequacy of interarch space
Presence of overerupted, malposed teethPresence of overerupted, malposed teeth
and tuberosity interference.and tuberosity interference.

Material of choice for diagnosticMaterial of choice for diagnostic
impressionimpression
Irreversible hydrocolloid (alginate)Irreversible hydrocolloid (alginate)

Technique for Making
Diagnostic Impressions
1)Position of patient and Dentist1)Position of patient and Dentist
2)Impression Trays2)Impression Trays
a) selectiona) selection
b) Checking trays for Correct sizeb) Checking trays for Correct size
c) Extending impression traysc) Extending impression trays
3)Control of Gagging3)Control of Gagging
4)Control of saliva4)Control of saliva

Technique for Making
Diagnostic Impressions
Contd
)Manipulation of the impression material)Manipulation of the impression material
6)Making the Impressions6)Making the Impressions
7)Removal of Impression from the mouth7)Removal of Impression from the mouth
8)Inspecting the Impression8)Inspecting the Impression
9)Cleaning the impression9)Cleaning the impression
10)Disinfecting the impression10)Disinfecting the impression
11)Poring the cast11)Poring the cast

Tray Selection for Diagnostic
Impressions
 Tray of choice - Rim lock tray because it is rigidTray of choice - Rim lock tray because it is rigid
- it confines the impression material, helping to- it confines the impression material, helping to
force it into all the areas to be included in theforce it into all the areas to be included in the
impression.impression.
 Perforated trays are rigid, but do not confine thePerforated trays are rigid, but do not confine the
material as well as the rim lock tray .material as well as the rim lock tray .
 Disposable plastic trays - too flexible to ensureDisposable plastic trays - too flexible to ensure
the accuracy of impression and cast that isthe accuracy of impression and cast that is
needed for removable partial denturesneeded for removable partial dentures

Extending an Impression Tray
 The modeling plastic is softened in a 60°The modeling plastic is softened in a 60° CC (140° water(140° water
bath, kneaded, and adapted to the tray partially removedbath, kneaded, and adapted to the tray partially removed
several times to prevent the locking of the tray into theseveral times to prevent the locking of the tray into the
undercuts.undercuts.
 Frequently an impression tray that has a correct width isFrequently an impression tray that has a correct width is
too short to cover the entire desired impression area.too short to cover the entire desired impression area.
The impression tray can be lengthened by the use ofThe impression tray can be lengthened by the use of
modeling plastic .modeling plastic .
 After the modeling plastic has been chilled, it is relievedAfter the modeling plastic has been chilled, it is relieved
to provide approximately 5 to 7 mm of clearance & thento provide approximately 5 to 7 mm of clearance & then
coated with alginate adhesivecoated with alginate adhesive

Extending an Impression Tray
Extending an
Impression Tray

Working properties of AlginateWorking properties of Alginate
Easy to use and inexpensiveEasy to use and inexpensive
Available as bulk and preweightedAvailable as bulk and preweighted
quantityquantity
Deteriorates rapidly at high temperatureDeteriorates rapidly at high temperature
and humidityand humidity
Is contaminated by gypsumIs contaminated by gypsum
Accuracy not affected by changes in waterAccuracy not affected by changes in water
to powder ratioto powder ratio

Cont.Cont.
Ideal temp of water 22degreeCIdeal temp of water 22degreeC
Cooler water will provide more workingCooler water will provide more working
timetime

Storage of impressionStorage of impression
Measurable distortion if not poured withinMeasurable distortion if not poured within
12 minutes12 minutes

Technique of making alginateTechnique of making alginate
impressionsimpressions

Position of patient and dentistPosition of patient and dentist
Dentist position-standingDentist position-standing
Patient position-uprightPatient position-upright
Occlusal plane parallel to floorOcclusal plane parallel to floor
Patients mouth is at same level as dentistsPatients mouth is at same level as dentists
elbowelbow
Stand behind the patient for maxillaryStand behind the patient for maxillary
impressionimpression

Checking trayChecking tray
Clearance of 5-7mm between tray and theClearance of 5-7mm between tray and the
ridgeridge
Tray should cover all anatomic landmarksTray should cover all anatomic landmarks
or can be modifiedor can be modified

GaggingGagging

Methods to prevent gaggingMethods to prevent gagging
Seating patient in upright positionSeating patient in upright position
Correcting palatal area with modellingCorrecting palatal area with modelling
plasticplastic
Not overfilling the tray with alginateNot overfilling the tray with alginate
Seating the posterior part firstSeating the posterior part first
Patient to keep eyes open duringPatient to keep eyes open during
procedureprocedure
Use of astringent mothwash and coldUse of astringent mothwash and cold
waterwater

Control of salivaControl of saliva
Use of gauze packsUse of gauze packs
Saliva ejectionSaliva ejection
15mg propantheline bromide 30min before15mg propantheline bromide 30min before
procedureprocedure

Mixing impression materialMixing impression material
Hand spatulationHand spatulation
Mechanical spatulationMechanical spatulation
Mechanical spatulation under vacuumMechanical spatulation under vacuum

Inspecting the impressionInspecting the impression
Alginate sticking to teethAlginate sticking to teeth
Alginate pulling away from trayAlginate pulling away from tray
VoidsVoids
Layered impressionLayered impression
Granular impressionGranular impression
Inadquate extensionInadquate extension
Contact between teeth and trayContact between teeth and tray

ProblemsProblems
Error. Using irreversible hydrocolloid that has beenError. Using irreversible hydrocolloid that has been
frozen, even when it is stored in its original,sealedfrozen, even when it is stored in its original,sealed
container.container.
Problem: Freezing may alter the setting time of theProblem: Freezing may alter the setting time of the
material drastically.material drastically.
Solution: In the winter, when temperatures in some partsSolution: In the winter, when temperatures in some parts
of the country are considerably below freezing,of the country are considerably below freezing,
irreversible hydrocolloid should be tested before use.irreversible hydrocolloid should be tested before use.

.. Error: Using irreversible hydrocolloid that has beenError: Using irreversible hydrocolloid that has been
stored in defective packaging or in an unsealed containerstored in defective packaging or in an unsealed container
after being opened for first use.after being opened for first use.
Problem: Moisture contamination due to water uptakeProblem: Moisture contamination due to water uptake
from the atmosphere can accelerate or retard the settingfrom the atmosphere can accelerate or retard the setting
time and cause rapid deterioration of physical andtime and cause rapid deterioration of physical and
chemical properties of the irreversible hydrocolloid.chemical properties of the irreversible hydrocolloid.44
Solution: Test the irreversible hydrocolloid before using itSolution: Test the irreversible hydrocolloid before using it

Solution: Use prepackaged irreversibleSolution: Use prepackaged irreversible
hydrocolloid to eliminate this error, even thoughhydrocolloid to eliminate this error, even though
it is more costly than a can of irreversibleit is more costly than a can of irreversible
hydrocolloid or bulk irreversible hydrocolloid. Ifhydrocolloid or bulk irreversible hydrocolloid. If
bulk irreversible hydrocolloid is used, separatebulk irreversible hydrocolloid is used, separate
and weigh amounts for individual use; then sealand weigh amounts for individual use; then seal
each portion in an airtight container such as aeach portion in an airtight container such as a
specimen containers. In addition, use aspecimen containers. In addition, use a
dedicated mixing bowl and spatula only fordedicated mixing bowl and spatula only for
mixing irreversible hydrocolloid. When in doubtmixing irreversible hydrocolloid. When in doubt
about the deterioration of the irreversibleabout the deterioration of the irreversible
hydrocolloid, test it before usehydrocolloid, test it before use

Error: Using a mix of irreversible hydrocolloidError: Using a mix of irreversible hydrocolloid
that is too thick.that is too thick.
Problem: A thick mix of irreversible hydrocolloidProblem: A thick mix of irreversible hydrocolloid
may set before it is fully seated in the mouth.may set before it is fully seated in the mouth.
When this happens, the irreversible hydrocolloidWhen this happens, the irreversible hydrocolloid
will set under pressure. When irreversiblewill set under pressure. When irreversible
hydrocolloid sets as pressure is applied, it ishydrocolloid sets as pressure is applied, it is
always distorted.always distorted.66

The irreversible hydrocolloid may not flow into theThe irreversible hydrocolloid may not flow into the
interproximal spaces between the teeth or pick up theinterproximal spaces between the teeth or pick up the
anatomy of the soft tissues. This error may also result inanatomy of the soft tissues. This error may also result in
the creation of drag marks in the impression and on thethe creation of drag marks in the impression and on the
cast during seating of the impression. The marks will notcast during seating of the impression. The marks will not
fill in because the material is too stiff to flow after it isfill in because the material is too stiff to flow after it is
seated.seated.
Solution: Follow the manufacturer's instructions forSolution: Follow the manufacturer's instructions for
water/powder proportions by weight rather than bywater/powder proportions by weight rather than by
volume.volume.

Error: Attempting to control the setting time ofError: Attempting to control the setting time of
irreversible hydrocolloid by altering theirreversible hydrocolloid by altering the
water/powder ratio.water/powder ratio.55
''66
Problem: If the mixture is thin one time and thickProblem: If the mixture is thin one time and thick
another time, a standardized procedure cannotanother time, a standardized procedure cannot
be established for seating the impression tray.be established for seating the impression tray.
The resulting inconsistency can causeThe resulting inconsistency can cause
unreliable results, in addition to other problemsunreliable results, in addition to other problems
(see errors 9 and 10).(see errors 9 and 10).

Solution: Control the water temperature to varySolution: Control the water temperature to vary
the setting time of irreversible hydrocolloidthe setting time of irreversible hydrocolloid
mixes. Always use the manufacturer'smixes. Always use the manufacturer's
recommended watertopowder ratio. Use waterrecommended watertopowder ratio. Use water
heated to more than room temperature to makeheated to more than room temperature to make
the irreversible hydrocolloid set faster; use waterthe irreversible hydrocolloid set faster; use water
chilled to lower than room temperature tochilled to lower than room temperature to
increase the working time.increase the working time.77
A 10°F increase orA 10°F increase or
decrease in the water temperature will increasedecrease in the water temperature will increase
or decrease the working time by approximatelyor decrease the working time by approximately
40 seconds.40 seconds.

Error: Failing to adequately mix the irreversibleError: Failing to adequately mix the irreversible
hydrocolloid.hydrocolloid.
Problem: If irreversible hydrocolloid is not mixed long orProblem: If irreversible hydrocolloid is not mixed long or
thoroughly enough to completely saturate all of thethoroughly enough to completely saturate all of the
powder with water, pockets of dry or partially wetpowder with water, pockets of dry or partially wet
irreversible hydrocolloid can cause distortions.irreversible hydrocolloid can cause distortions.
Solution: Hand mix the irreversible hvdrocolloidSolution: Hand mix the irreversible hvdrocolloid
thoroughly for 60 seconds. Alternately, vacuum mix thethoroughly for 60 seconds. Alternately, vacuum mix the
irreversible hydrocolloid for 15 seconds with at least 25irreversible hydrocolloid for 15 seconds with at least 25
inches of vacuuminches of vacuum

Error: Allowing partially mixed irreversible hydrocolloidError: Allowing partially mixed irreversible hydrocolloid
from around the top of the mixing bowl to befrom around the top of the mixing bowl to be
incorporated into the mix as the tray is loaded.incorporated into the mix as the tray is loaded.
Problem: Dry irreversible hydrocolloid particles absorbProblem: Dry irreversible hydrocolloid particles absorb
water when the impression is washed. The dry particleswater when the impression is washed. The dry particles
expand as they get wet and set. If a pocket of dry orexpand as they get wet and set. If a pocket of dry or
partially wet irreversible hydrocolloid is in contact with apartially wet irreversible hydrocolloid is in contact with a
tooth or other critical area when the impression is made,tooth or other critical area when the impression is made,
dry material will expand after impression is removeddry material will expand after impression is removed
from mouth and washed, resulting in inaccuracies.from mouth and washed, resulting in inaccuracies.55
''66
Solution: Make certain that partially mixed or drySolution: Make certain that partially mixed or dry
irreversible hydrocolloid powder is not incorporated intoirreversible hydrocolloid powder is not incorporated into
the mix for the impression.the mix for the impression.

Impressions in removable partial dentures/dental courses

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