1. Dr.linda Maher

2. 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.

3. 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.

5. 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)

6. ARE Stock trays Custom trays

7. 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.

8. REQUIREMENTS FOR IDEAL IMPRESSION MATERIAL: 1\should have pleasant taste and color 2\be biocompatible to oral tissue (non-toxic-non irritant – not carcinogenic) 3\be compatible with die and casting material 4\economic 5\adequate shelf life for storage 6\easy to use 7\elastic properties for easy removal from the mouth 8\dimentional stability

9. Impression materials ElasticsNon-elastics hydrocolloidselastomers Reversible (agar( Irreversible (alginate) - polysulfide -polyether -silicone waxcompound

10. 1\ELASTIC IMPRESSION MATERIALS CLASSIFIED INTO : 1\hydrocolloids 2\elastomeric COLLOIDS: Glue like materials composed of two or more substances in which one substance does not go into solution but is suspended within another substance.

12. HYDROCOLLOIDS: Water based colloids REVERSIBLE 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

13. ALGINATE IRREVERSIBLE hydrocolloid IT COMES IN FORM OF POWDER WHICH IS TO BE MIXED WITH WATER USES: Preliminary impression. Used to take an impression of the dental arches

14. ADVANTAGES: Easy to manipulate Non toxic Non irritant Compatible with gypsum Acceptable odor Sufficiently fluid

15. DISADVANTAGES Not very accurate Dimensionally unstable Poor shelf life

16. MANIPULATION 1\SELECTION OF THE TRAY 1\Used with stock trays 2\The tray should cover all the teeth and extend into facial and lingual vestibules 3\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

17. 2\HANDLING THE MATERIAL 1\Do not handle containers with contaminated gloves/hands 2\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

18. 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

19. 4\MIXING: Mix for up to 45 seconds Have Working time (from beginning of mix to seating in the mouth) of 2-5 minutes Smooth creamy consistency No lumps or powder should remain

21. REGULATING SETTING TIME: setting time (2-5)minutes Regulate 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.

22. 5\FILLING and LOADING THE TRAY:

23. 6\MAKING IMPRESSION: Wait to remove impression until the material is firm WAIT Approximately one minute after initial setting before removal of the tray from the mouth

24. 7\REMOVE FROM PATIENTS MOUTH: Lift lip up to break the seal against tissues Remove rapidly, to prevent significant permanent deformation

25. 7\IMPRESSION STORAGE: 1\rinse the impression with water 2\evaluate the impression 3\spray with a suitable disinfecting solution 4\Wrap in a wet towel (squeeze the towel after wetting it with water to eliminate excess water) 5\Pour within an hour

26. EVALUATING IMPRESSION 1\Tray centered over ridge

27.  2\No significant tissue/tooth contact

28. 3\No-large voids in the impression

29. 4\All critical anatomy recorded

30. Thank you,