Dr.linda Maher. DENTAL IMPRESSION is a negative record of the tissues in the mouth. it is used to reproduce the form of the teeth and surrounding tissues.

IMPRESSION MATERIALS

Dr.linda Maher

DENTAL IMPRESSION is a negative record of the tissues in the mouth. it is used to reproduce the form of the teeth and surrounding tissues.

IMPRESSION MATERIALS:materials used for making the impression these materials should be in a moldable

state that can adapt to the teeth and tissues.Within a specific period of time , the material

must set to semi solid ,elastic or rigid state.Elastics are preferable more than rigid

materials because they flex from the tissues easily.

IMPRESSION TRAY:Are used to carry the impression

material to the mouth and support it until it sets. then removed from the mouth and poured into dental plaster or stone.

TYPES OF TRAYS:1\stock trays(they are ready made trays-

can be plastic or metallic)2\Custom trays(constructed in the lab for

individual patient)

ARE

Stock trays

Custom trays

DENTAL REPLICA MODELS(CAST)A positive reproduction of the teeth

and tissue. it is formed when a plaster or stone is poured into the impression and hardened.

REQUIREMENTS FOR IDEAL IMPRESSION MATERIAL:

1\should have pleasant taste and color2\be biocompatible to oral tissue (non-toxic-

non irritant – not carcinogenic)3\be compatible with die and casting material4\economic5\adequate shelf life for storage6\easy to use7\elastic properties for easy removal from the

mouth8\dimentional stability

Impression materials

Elastics Non-

elastics

hydrocolloids

elastomers

Reversible(agar(

Irreversible

(alginate)

-polysulfid

e-

polyether-silicone

wax compound

1\ELASTIC IMPRESSION MATERIALS CLASSIFIED INTO : 1\hydrocolloids 2\elastomericCOLLOIDS:Glue like materials composed of two

or more substances in which one substance does not go into solution but is suspended within another substance.

HYDROCOLLOIDS:Water based colloidsREVERSIBLE HYDROCOLLOIDS:((AGAR))Set by temperature change into gel like

material .when heated , liquefied into their original form

IRREVERSIBLE HYDROCOLLOIDS((ALGINATE))

Set by chemical reaction and cannot be revered back

ALGINATEIRREVERSIBLE hydrocolloidIT COMES IN FORM OF POWDER

WHICH IS TO BE MIXED WITH WATER

USES: Preliminary impression.Used to take an impression of the

dental arches

ADVANTAGES:Easy to manipulateNon toxic Non irritantCompatible with gypsumAcceptable odorSufficiently fluid

DISADVANTAGESNot very accurateDimensionally unstablePoor shelf life

MANIPULATION1\SELECTION OF THE TRAY1\Used with stock trays2\The tray should cover all the teeth and

extend into facial and lingual vestibules3\The tray should be deep enough to

provide at least 2mm of space for alginate

4\the tray better to be perforated for more adhesion of alginate

2\HANDLING THE MATERIAL• 1\Do not handle containers with

contaminated gloves/hands2\Do not leave containers open in a

humid environment 3\Use separate bowls for alginate

and stones Gypsum can cause acceleration of setting of alginate

3\MEASURING THE ULGINATE:

Fluff the powder before measuring

Measuring by weight is more accurate than by volume

Mostly the Ratio is 1 scoop powder : 1 measure

water (differ according to manufacturer)

3 scoops of powder is sufficient for most arches

4\MIXING:Mix for up to 45 secondsHave Working time (from

beginning of mix to seating in the mouth) of 2-5 minutes

Smooth creamy consistency No lumps or powder should

remain

REGULATING SETTING TIME:setting time (2-5)minutesRegulate with water

temperature(setting time can be lengthened by using cold water or shortened by using warm water)

Water/powder ratio can affect the set but also adversely affect the physical properties and there for is not recommended.

5\FILLING and LOADING THE TRAY:

6\MAKING IMPRESSION:Wait to remove impression until the

material is firmWAIT Approximately one minute

after initial setting before removal of the tray from the mouth

7\REMOVE FROM PATIENTS MOUTH:

Lift lip up to break the seal against tissues

Remove rapidly, to prevent significant permanent deformation

7\IMPRESSION STORAGE:1\rinse the impression with water2\evaluate the impression3\spray with a suitable

disinfecting solution4\Wrap in a wet towel

(squeeze the towel after wetting it with water to eliminate excess water)

5\Pour within an hour

EVALUATING IMPRESSION1\Tray centered over ridge

2\No significant tissue/tooth contact

3\No-large voids in the impression

4\All critical anatomy recorded

Thank you,