Irreversible Hydrocolloid

1. Irreversible Hydrocolloid

2. 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 Date / / Initials_______ Instructor #_____ q Unacceptable q Correctable q Acceptable Student q Unacceptable q Correctable q Acceptable Instructor __________ 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. 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

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

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

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

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

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

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

12. 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

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

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

15. Mixing

16. Fill Tray

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

18. 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

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

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

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

22. Evaluating Irreversible Hydrocolloid Impressions • Properly mixed • Smooth surface

23. Evaluating Irreversible Hydrocolloid Impressions • Tray centered over ridge

24. Evaluating Irreversible Hydrocolloid Impressions • No significant tissue/tooth contact

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

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

27. 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

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

29. 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

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

31. 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

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

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

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

35. Two Pour Technique • Separate impression from cast after 30 minutes

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

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

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

39. 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

40. 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

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