HYDROCOLLOID IMPRESSION MATERIALSDA 122 Dental Materials

DEFINITION OF HYDROCOLLOID A hydrocolloid has colloid particles

spread throughout water and depending on the quantity of water available can take on different states, e.g., gel ( semi-solid) or sol (liquid).

Dental hydrocolloids exist in two forms: a sol (a more or less viscous liquid) and a gel (an elastic solid). The impression material is introduced into the mouth as a sol and converts into a gel through either a chemical or a thermal process.

DEFINITION (CONTINUED) Hydrocolloids can be either

irreversible(single-state) or reversible. For example, agar, a reversible hydrocolloid of seaweed extract, can exist in a gel and sol state, and alternate between states with the addition or elimination of heat

Agar: reversibleextracted from cell walls of brown algae

Alginate: irreversibleextracted from certain red algae

REVERSIBLE HYDROCOLLOID Common uses:

Final impressions for fixed prosthodontics

Special Properties:Made from agarThermal reaction

causes change from gel to sol

Can go from gel to sol to gel

AccurateEconomicalRequires much

equipment

REVERSIBLE HYDROCOLLOID PROCESS Tubes of gel boil for 10

minutes Boiling unit

Material becomes liquid (sol) and remains in that state in water bath of 150⁰ F until ready to use Conditioning unit

Tray material is moved to cooler water (110⁰ F) 5 minutes before use Cooling unit

Material is placed in mouth in trays which are cooled with water flowing through trays during impression

REVERSIBLE HYDROCOLLOID Armamentarium

Conditioning unitTrays with

attachment hosesCarpules or

syringesTubes of tray

material

Preparation Time:10 minutes

boiling unitHours to days in

storage unit 5 minutes in

conditioning unit Setting Time:

5 minutes in the mouth

IRREVERSIBLE HYDROCOLLOID Common Uses:

Study models (casts) Counter models Preliminary

impressions for F/F and P/P

Orthodontic appliances Splints, mouthguards,

custom trays

ALGINATE Ratio: powder/water

3:3 Maxillary or 2:2 Mandibular

Special Properties: Water-based Economical Easy to use Comfortable for

patient Elastic properties Sets by chemical

reaction with water Made from

seaweed and kelp

IRREVERSIBLE HYDROCOLLOID Armamentarium

Flexible rubber bowl Stiff, broad spatula Powder and scoop 68⁰F* and

measuring vial Appropriate

impression trays *Note: warmer

water sets faster; cooler water sets slower

Clean-up Let material set;

then peel it off spatula and bowl

Wipe bowl with damp paper towel

Be sure bowls and spatulas are completely clean and dry before using

MIXING ALGINATE: TECHNICALLYWATER IN BOWL; POWDER INTO WATER

Mix Surface: Flexible rubber

bow Mix instrument:

Broad, alginate spatula

Mix Time: Type I (FAST) =

30 – 45 seconds Type II (regular) =

60 seconds Work Time:

2 ¼ minutes Initial Set:

2 ½ minutes Final Set:

3 ¾ minutes

ALGINATE Appearance:

Creamy, smoothThickHomogeneousRubbery hard

when set

Common Brand Names:Alginate JeltrateTropicalgin