1. DA 122 Dental Materials

2.  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.

3.  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 heatagar seaweed  Agar: reversible  extracted from cell walls of brown algae  Alginate: irreversible  extracted from certain red algae

4.  Common uses:  Final impressions for fixed prosthodontics  Special Properties:  Made from agar  Thermal reaction causes change from gel to sol  Can go from gel to sol to gel  Accurate  Economical  Requires much equipment

5.  Tubes of gel boil for 10 minutes  Boiling unit  Material becomes liquid (sol) and remains in that state in water bath of 150 ⁰ F until ready to use  Conditioning unit  Tray material is moved to cooler water (110 ⁰ F) 5 minutes before use  Cooling unit  Material is placed in mouth in trays which are cooled with water flowing through trays during impression

6.  Armamentarium  Conditioning unit  Trays with attachment hoses  Carpules or syringes  Tubes of tray material  Preparation Time:  10 minutes boiling unit  Hours to days in storage unit  5 minutes in conditioning unit  Setting Time:  5 minutes in the mouth

7.  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

8.  Armamentarium  Flexible rubber bowl  Stiff, broad spatula  Powder and scoop  68 ⁰F * 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

9.  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

10.  Appearance:  Creamy, smooth  Thick  Homogeneous  Rubbery hard when set  Common Brand Names:  Alginate  Jeltrate  Tropicalgin