Alginate Impressions

7/23/2019 Alginate Impressions

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Alginate Impressions

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Diagnostic Casts



Discussion

• Diagnostic casts are a supplement to the

oral examination.

A. Correct

B. Incorrect



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.



• 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.



• 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.



• Diagnostic casts are used in educating the

patient a!out his&her dental needs and

corresponding treatment plan.



Discussion

• An alginate impression is a ''''''''''''

mold of the teeth.

A. (ositi$e

B. )egati$e



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.



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.



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.



• *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



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.



• 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.



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



• 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.



• "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.



Discussion

• Care should !e ta%en in sha%ing a

5dustless6 can of alginate.

A. Correct

B. Incorrect



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.



Discussion

• 1o: increasing the temperature of the

#ater used to mix alginate material #ill0

A. Decrease the setting time

B. Increase the setting time



• ,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.



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.



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



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



• 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



• 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/



• 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



• @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



• a!el impression 4 store in humidor

• @epeat procedure for opposite arch

• (our impressions immediately after



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



"!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



• 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

Alginate Impressions

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