Irreversible Hydrocolloid

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

Preliminary Impressions

Irreversible Hydrocolloid Preliminary Impressions

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

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

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

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

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

Measuring Alginate Fluff the powder before measuring Ensure no large voids

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

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

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

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

Mixing

Fill Tray

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

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

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

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

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

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

Evaluating Irreversible Hydrocolloid Impressions Properly mixed Smooth surface

Evaluating Irreversible Hydrocolloid Impressions Tray centered over ridge

Evaluating Irreversible Hydrocolloid Impressions No significant tissue/tooth contact

Evaluating Irreversible Hydrocolloid Impressions No-large voids in the impression

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

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

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

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

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

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

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

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

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

Two Pour Technique Separate impression from cast after 30 minutes

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

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

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

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

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

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