a) Surface reproducibility; b) Dimensional stability.
4. Use of material:
a) Ease of mixing ; b) Working time;
c) Setting time; d) Handling of the material.
5. Compatible with model materials
6. Economics of material
a) Cheap; b) Long shelf life;
c) Accuracy (save redoing impression)
Physical Phases of Alginate
§ The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form.
§ The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.
Good surface detail
Reaction is faster at higher temperatures
Elastic enough to be drawn over the undercuts, but tears over the deep undercuts
Not dimensionally stable on storing due to evaporation
Non toxic and non irritant
Setting time can depend on technique
Alginate powder is unstable on storage in presence of moisture or in warm temperatures
Causes for Distortion and Dimensional Change of Alginate
§ If an alginate impression is stored in water or in a very wet paper towel, the alginate will absorb additional water and expand. This condition is called imbibition.
§ If an alginate impression remains in the open air, moisture will evaporate from the material, causing it to shrink and distort. This condition is called syneresis.
§ Working time
• The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth.
§ Setting time
• The time required for the chemical action to be completed.
Instructions Taking a Complete Dental Impression
1. Select an appropriately sized dental tray for the upper teeth. The tray should fit snugly in the patient's mouth without causing strain on the jaws or teeth.
2. Mix the impression material according to the instructions on the package. Prepare a timer for the required set time as soon as you begin mixing. The set time includes the time it takes to mix the material and pour the tray, as well as the time in the patient's mouth. The impression begins to set as soon as it is mixed.
3. Apply adhesive to the inside of the dental tray. If the tray is perforated, the impression material will fill the holes and bind securely to the tray without adhesive.
4. Apply a small amount of wax to the outer edges of the dental tray. This will protect the patients mouth, as well as provide a tighter seal and a better impression.
5. Fill the dental tray with impression material.
6. Wipe a small amount of impression material on the occlusal surfaces of the upper teeth to prevent bubbling in the impression.
7. Use a dental mirror to gently pull the patient's cheek aside and insert the dental tray. The dental mirror is smaller than your fingers and allows you more maneuverability and the patient less discomfort.
8. Press the dental tray firmly onto the teeth, securing the tray tightly against the front and back teeth to get an accurate impression.
9. Allow the impression material to set. Remember to remain relaxed. Call out the time remaining to let your patient know exactly where he or she is in the process.
10. Remove the tray from the patient's mouth when the timer you set in Step 2 goes off. Wiggle the tray slightly to loosen the dental tray from the teeth, but do not wrench as this will cause defects in the mold.
11. Inspect the mold to determine that there are no bubbles and that all occlusal surfaces have been accurately represented.
12. Disinfect the mold using an antibacterial spray and rinse.
13. Wrap the mold in a wet paper towel and place in a plastic bag with the patient's name on it.
TEST FOR INITIAL LEVEL OF KNOWLEDGE
1. For a patient 28 years produced laminar RPD. Objectively: the teeth are high, stable. Alveolar process moderately atrophied. Which impression material to use in this case?
A. Upin *
2. A patient 49 years with generalized periodontitis moderate severity. Dentist made non-removable dentures. Which impression material should be applied in this case?
A. Upin, stomalgin *
B. Gypsum dentol-C;
C. Stens, ortokor;
D. Sielast-69 stomafleks;
E. Akriloksid, Protakril-M.
3. Describe the main advantages of alginate materials:
A high precision, low shrinkage;
B. Easy to use in the clinic;
C. The high ductility and low elasticity;
D. Strong connection with perforated impression trays, low toxicity;
E. High flexibility. *
4. A patient 75 years with edentulous jaws, used to dentures 10 years. Objectively: the lower third of the face is reduced, alveolar process on the upper and lower jaws are atrophied, the palate is flat, mucous membrane atrophied. What kind of impression material is best to use for functional impressions in this case?
A. Alginate material
E. The silicone material.*
5. Which difference between functional and anatomic impression:
A. Anatomical print complements functional;
B. The differences between them;
C. The difference between them is negligible
D. They have difference techniques of taking;*
E. Functional anatomy print supplements.
6. One of the stages of complete dentures is adjustments of individual tray and removal of functional impression. Which of these materials is carried for edges of individual tray?
7. The patient 60 years old in order to prosthetics. Objective: partially edentulous jaws. Other teeth I-II degree of mobility. Dentist will make partial denture on the lower jaw. Which impression material prefer?
A. Stomalgin *
8. Impression its:
A printout of the upper and lower jaw and teeth
B. Displaying oral tissues for impression materials;
C. Positive display tissue prosthetic area
D. Negative display tissue prosthetic area;*
E. An impression of the teeth, the mucous membranes, mouth on impression materials.
9. M.A. Napadov divides impression materials into the following groups:
A plaster, silicone, alginate, polymerized, thermoplastic;
B. crystallized, polymerized, elastic, silicone, thermoplastic;
C. curatives, firm, elastic, thermoplastic, hydrocolloid;
D. Hard, soft, flexible, thermoplastic, hydrophobic
E. hardening, thermoplastic, elastic*
Special-purpose Training Tests for study the topic level testing
1. The patient is made sintered metal bridge on 47, 45 teeth. Preparation of teeth done ledge. Which of the materials will get a quality impression?
C. Sielast-05 *
2. Specify the main drawback of alginate materials:
A. swelling in the water
B. Low elasticity;
C. Significant and rapid shrinkage;*
D. Low accuracy;
E. greater strength
3. Which of the following dental materials is an example of an aqueous elastometric?
A. Impression compound
B. ZOE impression paste
D. Irreversible hydrocolloid *
E. Addition silicone
4. Which of the following is an example of an inelastic impression material?
B. ZOE impression paste *
D. Addition silicone
5. A 73-year-old patient consults a dentist about total edentia. Objectively: there is insignificant regular atrophy of the alveolar process of mandible, the process is covered with mucous membrane of moderate elasticity. According to Keller's classification, such manifestations are characteristic for the following type of edentulous jaw:
D First *
6. Women 32 year-old went to the doctor in order to prosthetics. After a physical examination selected prosthesis with metal-ceramic crowns. Which impression material should be used:
B. "Stomafleks" *
7. Woman has not been to the dentist for several years. It was found that she needed extensive restorative treatment to which she agreed. You were asked to take impressions as the first step of her care. The impression material of choice would be: