Chapters 46 Impression Materials 47 Lab Materials and Procedures

1. Chapters • 46 Impression Materials • 47 Lab Materials and Procedures

2. Alginate Impressions • Preliminary Impressions • Show teeth and surroundings tissue • Used for diagnostic aids • Should fluff canister before using, (material settles and packs down) • Negative reproduction of the teeth and surrounding tissues

3. Rubber Base • Final Impressions • Most Accurate impressions • Measure equal amounts of catalyst and base material • Homogeneous mix • Catalyst incorporated into base when mixing • Elastomeric impression material

4. Types of Trays • Full • Quadrant and triple trays • Section (anterior) • Plastic/metal • Perforated/solid • Stock • Custom • Vacuum formed

5. Ratio for mixing Alginate • Maxillary—3 scoops of powder to 3 measures of water • Mandibular—2 scoops of powder to 2 measures of water • Too much water makes a thin mix and takes a long time to set • Too little water makes a stiff mix and set to quickly • Plaster (gypsum product)

6. Loading Alginate Trays • Mandibular trays—two increments (one on each side of tray) • Maxillary trays—one increment from the posterior

7. Removing Trays • Mandibular trays—firm lifting motion • Maxillary trays—release posterior and then anterior

8. Seating Trays • Press posterior down first • Always explain to patient what you are doing • Take mandibular impression first (patient will have better understanding of what is taking place) • Patient should be seated in the most upright position.

9. Seating Cont. • Ask patient to swallow before seating tray, (this removes excess saliva and possible air bubbles) • Ask patient to lean forward when tray is placed. • Ask patient to breath through their nose • Have patient lift feet off of chair, if they gag

10. After removing trays • Rinse patients mouth out • Rinse with water and shake off excess • Spray impression with disinfectant • Wrap in wet paper towel, if you can not pour immediately • Place patient’s name with impressions

11. Pour Methods for Plaster • Inverted pour – one large mix in single step • Box pour – surrounded with box of wax • Double pour – (fab mold)– anatomic first and art portion second

12. Setting Time • Things that can affect setting time of alginate • Water temp—(warmer the water, the faster the set time) • Water to powder ratio (the more powder the faster the set) • Normal set or fast set alginate

13. Dental Labs • Most labs are in a separate area of the office, usually the back of office or the basement. • Well ventilated • Items might include: • Model trimmers • Vaccum formers • Lab burs and handpiece

14. Models • Two portions of the cast • Anatomic portion is created from the alginate impression, shows teeth and tissues • Art portion forms the base of the cast • Trimmed models • Maxillary model will be pointed at the anterior portion • Mandibular model will be rounded at the anterior portion • Positive reproduction of teeth and surrounding tissues

15. Bite Registrations • Reproduction of the occlusal relationship of the maxillary and mandibular teeth, (when mouth is occluded) • Can be preformed or made in lab office