1. Chapter 22 Impression Materials and Laboratory Procedures

2. Impression Trays Designed for obtaining an accurate impression of the area required, creates a model for diagnosing or the lab technician Tray selection: the dentist’s preference and what will provide the most accurate results Quadrant Trays (half arch), section trays (suited for anterior teeth), Full arch(cover the complete arch) See Table 22-1, pg. 359, fig. 22-1

3. Impression Materials Impression is a negative reproduction of the teeth and surrounding structures, when poured up in stone or plaster it creates a positive reproduction of the teeth Model is known as a cast Three types of impressions: Preliminary, Final, Occlusal (bite). See Box 22-1, pg. 360, Fig. 22-2, 22-3, 22-4 pg. 360 also Alginate: irreversible hydrocolloid, contains potassium alginate (derived from seaweed), calcium sulfate, trisodium phosphate, diatomaceous earth, zinc oxide, potassium titanium fluoride Alginate has two physical phases: sol(material is a liquid or semi-liquid form), Gel( material becomes a semisolid Two Types of Sets: Normal Set (2 min wt, 4 ½ min st), Fast set (1 ¼ min Wt, 1-2 min st) Supplied in a powder form that is mixed with water 1:1 ratio

4. Taking Alginate Impressions Always be ready to mix the alginate, load tray, keep patient comfortable Steps are to be taken to gain an accurate impression See Box 22-2, Pg. 361 Always explain to the patient the procedure that: the material will be cold, no unpleasant taste, material will set quickly, breathe deep through the nose, do not talk after the tray has been placed Diagnostic Casts: model that is made from impression Model Plaster: not very strong, easy to trim, clean appearance, excellent for diagnostic, Fig. 22-6, pg 361 Dental Stone: stronger than plaster, more durable, more for lab work fabrication

5. Stone/Plaster Information Have the same chemical formula, physical structures are different Water to Power ratios vary for stone and plaster, can effect the setting time Box 22-2, pg. 362 Pouring Methods: double-pour, box and pour, inverted pour (differ because of the type of base) Model Trimmer: used to trim cast stone/plaster models Anatomic/art Portion of the Casts: fig. 22-9, pg. 363