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7/23/2019 Alginate Impressions
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Alginate Impressions
&
Diagnostic Casts
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Discussion
• Diagnostic casts are a supplement to the
oral examination.
A. Correct
B. Incorrect
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Background Information
• A recurring requirement in the dental office
is for study models or diagnostic casts of
patient’s teeth and adjacent tissues. Variousrequirements necessitate these models the
most common !eing for diagnostic
purposes. "odels are also required infa!ricating cro#ns and dies for
prosthodontic appliances.
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• A diagnostic cast is an accurate replication
of the anatomic form of the maxillary or
mandi!ular dental arch sho#ing therelationships of the remaining teeth and the
surrounding tissues.
• Diagnostic casts are a supplement to the oralexamination !ut in some #ays they can
re$eal more.
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• Diagnostic casts permit inspection from
perspecti$es that are impossi!le to o!tain
#hen loo%ing in the patient’s mouth.• Diagnostic casts permit extended
o!ser$ations and comparasions far !eyond
the patient’s endurance for holding his&hermouth open and are a$aila!le for study
during the patient’s a!sence.
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• Diagnostic casts are used in educating the
patient a!out his&her dental needs and
corresponding treatment plan.
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Discussion
• An alginate impression is a ''''''''''''
mold of the teeth.
A. (ositi$e
B. )egati$e
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Three steps of obtaining
diagnostic casts• An alginate impression is made directly in
the patient’s mouth producing a negative
mold.• *he impression is poured in dental stone
producing a positi$e cast.
• *he cast is inspected for defects repaired if possi!le and trimmed to the proper si+e andshape on a model trimmer.
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Physical Properties of Alginate
• Alginate is an impression material that is
supplied in po#der form and mixed #ith
#ater.• ,hen set the material is a flexi!le gel
resem!ling ru!!er.
• Its most important characteristic is its
a!ility to re!ound from stresses.
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Composition of Alginate
• Alginate is classified as irreversible
hydrocolloid.
• -ydrocolloid !ecause it consists of particles
of a gelatinous colloidal/ state in #ater
hydro/ and irre$ersi!le !ecause once it has
jelled it cannot !e returned to a liquidsolution.
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• *he alginate particles are compromised of0
• 1alts of alginic acid a product of marine %elp
• An acti$ator usually calium sulfate
• A retarder such as sodium phosphate
• An inert filler to reduce stic%iness produce a
smooth texture and add strength• 2la$oring
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Packaging of Alginate
• Bul% form the most popular
• (re#eighted pac%age the more desira!lechoice #hen temperature change andmoisture are of concern.
• All types of alginate pac%aging must !estored in a cool, dry place.
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• Alginate is sensiti$e to higher temperature
and moisture contamination. *hose
$aria!les cause the alginate to lose strengthduring mixing and !e more apt to distort
upon remo$al from the mouth.
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Mixing Alginate
• 2luff or sha%e the po#der to distri!ute the po#der particles e$enly
• 3se the specific measuring de$ices #ater4 po#der/ pro$ided !y the manufacturerfor mixing
• 2ollo# the manufacturer’s directionregarding the ratio of #ater to po#der.
• 3se exact measurements
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• After the #ater and po#der ha$e !een
measured place the #ater in a clean dry
!o#l. 1ift the po#der into the #ater.Adding the po#der to the #ater ensures the
po#der particles are #et e$enly. If mixed in
re$erse the #ater is added to the po#der/the chemical reaction #ill start early #ith
some particles setting faster than others.
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• "ix the alginate for the specific amount of
time and using a stiff spatula 5s#ipe6 the
alginate mass against the sides of the !o#lto a$oid entrapment of air in the mix.
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Discussion
• Care should !e ta%en in sha%ing a
5dustless6 can of alginate.
A. Correct
B. Incorrect
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etting Time of Alginate
• 1ince alginate reacts or gels chemically
temperature is a major factor in the setting
time. *he colder the temperature of the#ater the longer it ta%es to set7 con$ersely
the higher the #ater temperature the faster it
sets. Ideal #ater temperature is 89 degreesor room temperature.
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Discussion
• 1o: increasing the temperature of the
#ater used to mix alginate material #ill0
A. Decrease the setting time
B. Increase the setting time
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• ,hen ideal conditions exists a fast;setting
type of alginate #ill gel in < to = minutes
and a normal type gels in = to >.? minutes.*he fast;setting type is the most #idely
used.
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Dimensional tability
• Alginate has a tendency after it sets to lose
syneresis/ or a!sor! imbibition/ #ater
depending on the atomosheric conditionssurrounding it.If conditions are dry it loses
#ater 4 shrin%s7 if immersed in #ater it
im!i!es moisture or s#ells.
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Ad!antages of Alginate
• It ma%es an accurate impression
• It allo#s for undercuts
• *he process is not time consuming• It is easy to #or% #ith has good $iscosity 4 is
lo# in adhesi$e qualities
• It causes no great pain to the patient• Inexpensi$e to the dentist
• @equires little armamentarium
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Alginate Impression Procedure
• Assem!le the armamentarium
• (atient drape
• Impression trays• 2lexi!le ru!!er !o#l
• 1tiff spatula
• 1ali$a ejector
• Alginate of choice
• 3tility #ax
• Disinfecting agent
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• 1eat 4 drape the patient
• perator should #ear appropriate ((
• Instruct patient of procedure
• (osition the patient upright 4 inspect mouth
•
u!ricate the patient’s lips• 1elect the appropriate trays
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• Install the #ax
• "old the #ax to the $esti!ule
• -a$e patient rinse mouth• "easure #ater 4 test temperature
• 2luff alginate in can 4 measure into cup
• (repare the alginate• oad tray al#ays ta%ing the mandi!ular arch
first/
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• 1emi;dry the teeth 4 mucosa
• (osition 4 seat the tray
• @emo$e excess alginate
• -old the tray in place for the prescri!ed
time
• @emo$e the tray !y !rea%ing the seal at the
periphery then gi$ing a quic% pull
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• @emo$e remaing pieces of alginate from
mouth 4 allo# patient to rinse
• @inse the impression
• $aluate the impression
• *rim a#ay excess alginate
• *a%e #ax registration !ite
• Disinfect impression
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• a!el impression 4 store in humidor
• @epeat procedure for opposite arch
• (our impressions immediately after
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Criteria for electing Appropriate
Trays• *ray clears all tissues !y at least > mm.
• *ray is long enough to co$er part of retromolar
pads or tu!erosity• *ray sides fall at least > mm short of periphal turn
• *ray sides do not grossly depress any frenum
• (atient should not feel pain or excessi$e pressure
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"!aluation Criteria
• All detail is reproduced including thecomplete peripheral turn and a portion of
the retromolar pads or tu!erosities• Detail is sharp not !lurred or indistinct
• 2ree of $oids in critical areas
• 2ree of large folds of alginate• )o areas #here alginate has pulled a#ay
from the tray
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• 2ree of rips and tears except in interproxinal
areas
• Alginate thoroughly co$ers the tray no tray$isi!le through alginate
• 2ree of !ulges or depressions that indicate a
su!;surface !u!!le• Alginate is smooth not sponge;li%e