AM: Seminar 50 min

1

• AM Seminar (50 min)
• Irreversible hydrocolloid impression Quiz (30
  min, 20 min Discussion 50 min)
• 1100 Sign out SKU-1 and SKU-2 typodonts
  (Marjorie Pre-Clinical Lab 3218)
• Ensure typodont intact, have screwdrivers
• Keep boxes, all materials with typodonts to
  return in December
• Do not Print on Boxes
• Irreversible hydrocolloid experiments
• Demo of mixing irreversible hydrocolloid
  impressions/pouring casts
• Have bowls, spatulas, Whip Mix vacuum mixing
  bowls
• PM Lab Typodont impression Pour Max. cast
• Evaluate impression/cast yourself, then assessed
  by instructors, sign formative evaluations

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 _____

3
Today

• Questions from last day
• Course Outline - online
• Manuals Page 97-103
• Readings - excellent
• Questions about irreversible hydrocolloid or
  trimming casts?

4
Next Week

• Surveying
• Readings in VS, Manual
• In class, sort yourself by row, depending on your
  seminar leader

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
• Dont 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
• 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