Irreversible Hydrocolloid Essay Example

is the time it takes to complete the uniform blending of components.

Adequate spatulation (mixing with spatula) produces a smooth, creamy mixture with a minimum of voids or air pockets. Lower water to powder ratio increases strength, tear resistance, and consistency; decreases working and setting times and flexibility. A Lower water temperature increases working and setting times. If not mixed properly it will produce a grainy mixture and will result in a poor recording of the details. This set of instructions herein is provided to give you the ability to make a negative impression of any mouth you wish.

Although the reasons for constructing an impression may vary, the materials are primarily the same. The instructions and materials below are for use in dentistry. First prepare your work space by gathering the required materials, seat your patient and review patient history, then put on your personal protective equipment which includes but is not limited to the following: protective gown, goggles, mask, and gloves. Nitrile gloves are considered thicker and stronger but any glove that completely protects your hands and wrists from splashes is preferred.

1. Select the largest tray that will fit comfortably into the patient's mouth. Impression tray types: metal stock trays, disposable plastic trays. They must have retentive features: mechanical - rim lock, perforated or chemical - adhesive spray.

2. Prepare the patient’s mouth by rinsing and drying the patient's teeth. Note that if the teeth are too dry the alginate will stick.

3. Measure correct amount of water (plastic cylinder) for the size tray being used and pour in bowl.

4. Measure out alginate (scoop), because the alginate is such a light powdery substance using the spatula to

tap on cup to make sure it is packed, and then level it off, leaving no voids in the powder is essential in having enough material to make a correct impression, then pour it into the bowl with the water. Always add powder to water.

5. Immediately after pouring stir the mixture to moisten all the powder so the mixture will not fly out. Hold bowl in hand and firmly press the mixture against the side of bowl while turning the bowl with your hand, until the mixture is of a smooth consistency and homogeneous (uniformly mixed). Make sure to work quickly at this stage so the alginate does not set up before getting it into the patient’s mouth!

?6. Quickly take the mixture on the spatula and load the tray pushing the alginate into tray firmly so as to not incorporate air pockets in the alginate. ??

7. Have patient relax facial muscles and lean a little forward (so material doesn’t go down patient’s throat), then insert your finger into corner of patient’s mouth, first right side then left side to extend patient’s lips over edges of tray. Seat tray starting from posterior (back molars) to anterior (front teeth). Rolling the tray forward while seating it will also prevent any of the mixture from going down their throat. ?

8. Approx. 1 min. after stickiness vanishes, (about 3.5 min. from beginning of mix), remove tray with one quick motion. (Wiggling set impression from the mouth will cause excessive distortion.) Rinse, disinfect and store impression in humid environment (can wrap in moist paper towel). When the tray is removed from the mouth, it retains a three dimensional impression of

the teeth. You now have your negative impression, or reverse image of the tooth. Pour with stone or gypsum within 15 minutes. ??

Plaster molds (positive impressions) are made from a mixture of water and gypsum powder. Used for dental applications since the 1700’s, gypsum is finely divided calcium sulfate dihydate. Different types of plasters are used depending on application: impression plaster is used to record the shape of the teeth; model plaster is used to make durable models of the oral cavity. In this way a positive model of the teeth can be made. This positive model made from the negative impression mold is called a cast. The cast is used by the dentist for study purposes.

Evaluation of the patient, the selection of the best impression tray, proper mixing of alginate impression materials, proper impression technique, controlling the patient’s gag reflex, and the quality of the impression are the ultimate goals in producing a great dental impression. If done correctly the impression should ensure a perfect fit for whatever purpose you have in mind. Your impression will never be more precise than the original!