1. Irreversible
Hydrocolloid

2. Date / / Initials_______ Instructor #_____
Student ____________________
Preliminary Alginate Impressions
Date / / Initials_______ Instructor #_____
q Unacceptable q Correctable q Acceptable Student
q Unacceptable q Correctable q Acceptable Instructor __________
q Accurate recording of all critical anatomy
q Material properly mixed as indicated by impressions
q Minimum of voids
q Trays properly selected and centered over the ridges
q Minimal areas where trays have contacted tissues
Diagnostic Cast Evaluation
q No significant bubbles or flaws in stone
q Base approximately parallel to ridge and approximately l/2 inches thick (minimum)
q Evidence of a dense stone surface
q Clean and well trimmed
q Includes all anatomical surfaces

4. Preliminary Impressions

5. Irreversible Hydrocolloid Preliminary Impressions

6. Selection of a Stock Tray
5 -7 mm between tray & tissues
Bulk for strength & accuracy of material
Just short of vestibule
Slightly beyond vibrating line

7. Stock Tray Selection Compound on peripheries if needed
Extension only to provide coverage of critical anatomy
Not for displacing vestibular tissues

8. Pre-Measure Material Infection control
Do not take containers to your operatory
Do not handle containers with contaminated gloves/hands

9. Handling the Material
Do not leave containers open in a humid environment
Humidity & high temperatures cause deterioration

10. Use Separate Bowls
Gypsum can cause acceleration of setting of alginate
Alginate contamination can decrease strength of casts
Alginate
Stone

11. Measuring Alginate Fluff the powder before measuring
Ensure no large voids

12. Measuring Alginate Do not tap the scoop more than once or twice
Compacts the powder
Thicker mix

13. Preparations Measuring by weight is more accurate than by volume
Ratio of 1 scoop powder : 1 measure water
3 scoops of powder is sufficient for most arches

14. Regulating Set Time Regulate with water temperature
Water/powder ratio can affect tear strength & viscosity

15. Mixing Alginate Mix for up to 45 seconds Smooth creamy consistency
No lumps or powder should remain

16. Mixing

17. Fill Tray

18. Making the Impression Lightly dry the teeth & mucosa
Don’t dessicate the teeth
Alginate may stick

19. Making the Impression
Wipe alginate onto the occlusal surfaces of any teeth

20. Making the Impression
Don't bottom out on the teeth or the residual ridge
Distort the tissue or move teeth
Stone leaks between alginate & tray & produces distorted cusp

21. Making the impression
Wait to remove impression until the material is firm
Approximately one minute after initial set

22. Removal Lift lip up to break the seal against tissues
Several drops of water
Remove rapidly, to prevent significant permanent deformation

23. Impression Storage Wrap in a damp towel Pour within 12 minutes
Wring to eliminate excess water
Pour within 12 minutes
Minimizes distortion
Support impression by handle or tray until cast poured

24. Evaluating Irreversible Hydrocolloid Impressions
Properly mixed
Smooth surface

25. Evaluating Irreversible Hydrocolloid Impressions
Tray centered over ridge

26. Evaluating Irreversible Hydrocolloid Impressions
No significant tissue/tooth contact

27. Evaluating Irreversible Hydrocolloid Impressions
No-large voids in the impression

28. Evaluating Irreversible Hydrocolloid Impressions
All critical anatomy recorded
Hamular notches
Retromolar pads
Vestibules, etc.

29. Disinfection Rinse the impression
Place in zip lock bag, pour in disinfectant to cover all surfaces
Seal for 10 minutes
Remove and rinse prior to pouring stone

30. Mixing Stone Weigh powder Measure water Vacuum mix
Less time to complete than hand mixing
Stronger cast

31. Two pour technique Pour stone into impression
Wait for stone to set (~ 30 minutes)
Invert impression with set first pour onto base stone
Superior surface strength

32. Two Pour Technique
Use vibrator & flow the stone into the impression slowly
Modulate speed of pouring by tilting the tray back and forth

33. Two Pour Technique If impression fills too quickly-voids
To delay filling:
Tilt impression in opposite direction of the flow of the stone
Reduce speed of vibrator
Press impression less firmly against vibrator

34. Two Pour Technique
Leave rough areas on the exposed surface of the stone
Helps attach base

35. Two Pour Technique Make a patty of stone
Invert impression with the first pour onto the base
Adapt new stone to the existing stone

36. Two Pour Technique
Trim excess stone from the base with the spatula while the stone is still soft

37. Two Pour Technique
Separate impression from cast after 30 minutes

38. Trimming Casts Model moist for trimming
Debris from trimmer will not attach

39. Trimming Casts Soak the model by immersing in slurry water
just base of cast contacting tap water

40. Trimming Casts
Prolonged immersion in tap water can lead to erosion of the cast

41. Trimming Diagnostic Casts
Cast should be minimum of 10-12mm (.5 inch) in thinnest part
Trim the base on the model trimmer parallel to ridges
Leave the mucous membrane reflection intact for making a custom tray

42. Trimming Master Casts
Boxed and trimmed with a 3mm wide by 3mm deep land area
Aids in processing of acrylic
Diagnostic casts (no land area)
Used for making custom trays
Land area omitted so material is easier to trim & remove from the cast

43. Outline of Bases for Trimmed Casts
Follow the contour of the ridges, with rounded angles