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After performing the laboratory/clinical exercises in this chapter, the student will be able to do the following:
1. Briefly discuss the rationale for dental hygienists to learn the preparation and technique of addition silicone impression material.
2. Recall the reasons for using addition silicone impression material.
3. Explain the tray preparation that is necessary for use of addition silicone impression material.
4. Summarize the steps involved in:
- Preparing the putty (tray) material
- Preparing the wash (syringe) material
addition silicone impression material
This chapter addresses the manipulation of addition silicone (polyvinylsiloxanes or polysiloxanes) impression material. This is one of the four types of impression materials discussed in Chapter 8, Impression Materials. This material commonly involves the use of an automix gun, as shown in Figure 8.14. Use of the automix gun eliminates hand mixing with a spatula and paper mixing pad.
Addition silicone impression material is generally used as a “final impression material” for the fabrication of crowns and bridges. Dental hygienists may (or may not) take this type of impression depending on their state practice act. From time to time, however, even those who do not take this type of impression may find themselves assisting with this procedure. An advantage of this material is that it does not need to be poured immediately after the impression is taken. Its stability and accuracy make it a very popular material.
II. Procedure for the Double-Mix Putty-Wash Technique
The double-mix impression technique uses two different viscosities of impression material. One is very thick and is used in the tray. The second has a low viscosity. It is syringed on and around the tissues of interest. The tray is seated immediately after the syringe material is injected into place. Typically, the tray and syringe materials are prepared simultaneously by two people.
A. Tray Preparation (Table 30.1)
TABLE 30.1. Armamentarium for Addition Silicones
1. A plastic stock tray is selected and painted with a tray adhesive. This adhesive aids in retention of the impression material in the tray. Use an adhesive from the same manufacturer as the impression material.
2. Be sure to coat the facial, lingual, and occlusal surfaces of the inside of the tray, as shown in Figure 30.1.
3. Allow approximately 10 minutes to air-dry so that the adhesive becomes tacky.
FIGURE 30.1. Stock impression tray coated with adhesive.
B. Preparing the Automix Gun
The automix gun is prepared by loading the cartridge and installing the mixing tip. The system must be ready to dispense material when needed.
1. Load the cartridge into the gun.
2. Twist off the sealing cap. Save the cap.
3. Dispense a pea-sized amount of material onto a paper towel by squeezing the handle. This ensures that the base and catalyst materials have not set and clogged either opening of the cartridge. Wipe the end of the cartridge.
4. Install a new mixing tip, and twist it into the locked position.
5. After use of the automix system, remove the used mixing tip, and replace the cap.