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Impression material is a?
An accurate negative reproduction of the mouth.
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A positive reproduction is made by?
pouring dental stone or other suitable material into impression.
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The positive reproduction is called a?
model or cast
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Bite registrations are Taken by the?
dentist or dental assistant.
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A bite restorations Make a reproduction of the?
occlusal relationship between the maxillary and mandibular teeth.
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The final impression is only taken by the?
dentist
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________ provide an accurate registration between the maxillary and mandibular arches.
Bite registration
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What is the function of Impression Materials?
- to record accurately the dimensions of oral tissues and their spatial relationships
- A material in the plastic state is placed against oral tissues to set.
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Is the impression material reversible or irreversible?
Irreversible Hydrocolloid
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Model?
After setting, the impression is removed from the mouth and is used to make a replica of the oral tissues.
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Ideal Impression Materials Properties?
- Ease of manipulation and reasonable cost
- Adequate flow properties
- Appropriate setting time and characteristics
- Sufficient mechanical strength not to tear (high resistance) or permanently deform during removal
- Good dimensional accuracy
- A moldable or plastic material that can adapt to the teeth and tissues
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examples of Whole arch trays?
half/quad/tri [triple] tray occlusal check/ temp crn
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Stock trays or custom-made trays?
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Perforated tray:
- Holes in the tray create a mechanical lock to hold the material in place.
- mechanical interlocking
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Smooth tray:
Interior of the tray is painted or sprayed with an adhesive to hold the impression material
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Quadrant tray
Covers one half of the arch.
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Section tray
Covers the anterior portion of the arch.
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Full arch tray
Covers the entire arch.
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Perforated tray
Holes in the tray create a mechanical lock to hold the material in place.
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Smooth tray
Interior of the tray is painted or sprayed with an adhesive to hold the impression material.
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Tray Selection Criteria:
- Feel comfortable to the patient.
- Extends slightly beyond the facial/buccal surfaces of the teeth. 2-3mm around
- Extends approximately 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch.
- Is sufficiently deep to allow 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth.
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Types of impression materials:
- Elastic/Flexible
- Inelastic/ Rigid
- Hydrocolloid
- Irreversible Hydrocolloid
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Example of Elastic/Flexible Impression Materials:
- Elastomeric:
- Polyether, Polysulfide & Silicone
- Aqueous:
- Reversible(Agar) Hydrocolloid
- Irreversible (Alginate)Hydrocolloid
- *Final impression
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Example of Rigid Impression Materials:
- *For edentulous
- Zinc oxide-eugenol
- Inelastic/ Rigid
- Not used very much
- Impression compound
- Impression plaster
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Hydrocolloid Impression Materials:
- Hydro = water
- Colloid = means glue-like material / gelatin substance
- Composed of two or more substances: one substance does not go into solution but is suspended within another substance [fruit in jello]
- Hydrocolloids used in dentistry are reversible and irreversible
- Used to obtain preliminary and final impressions.
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Irreversible Hydrocolloid:
- [you can never go back]
- Also called alginate hydrocolloid or just alginate
- Easy to manipulate
- Requires no special equipment
- Reasonably accurate
- low cost
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Most widely used impression material in dentistry?
Irreversible Hydrocolloid
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How is Alginate supplied?
Bulk Cans and premeasured single use packets
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What are the Uses of Alginate: Irreversible Hydrocolloid?
- Impressions for study models.
- Impressions of opposing arch.
- To make working models to make teeth whitening trays, mouth guards, custom trays
- To have impression of unprepped teeth. Used to make temporary crowns.
- NOT USED FOR FINAL IMPRESSIONS OF CROWNS/BRIDGES.
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Alginate pros?
- 1.Ease of mixing
- 2.Minimum equipment necessary
- 3.Flexibility of the of the set material
- 4.Low cost.
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Alginate cons?
- 1. Low tear strength (rip easily)
- 2. Does not transfer much detail. Can not be used for final impressions of crowns/bridges.
- 3. Lacks stability due to water content.
- 4. Synersis: loss of water content.
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**Composition of Alginate?
- Potassium alginate: 15% to 20% [highest content]: Comes from seaweed; is also used in foods such as ice cream as a thickening agent.
- Calcium sulfate: Reacts with the potassium alginate to form the gel.
- Tri-sodium phosphate: Added to slow down the reaction time for mixing - retardent.
- Diatomaceous earth: A filler that adds bulk and flexibility to the material.
- Zinc oxide: Adds bulk to the material.
- Potassium titanium fluoride: Added so as not to interfere with the setting and surface strength
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The first physical phase of Alginate?
is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form.
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The second physical phase of Alginate is?
a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.
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Physical Properties of Alginate:
- Comes in different setting times:
- Regular/Normal, Sets in 4-5 minutes. Start to finish
- Fast Set, Sets in approx 2 minutes: Temperature of H2O
- Shelf life affected by heat and humidity:Store in cool dry area. Shelf life of alginate is approximately 1 year
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Alginate is _________.
Irreversible Hydrocolloid
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Powder is mixed with _______ causing a ______.
- cool water
- chemical reaction.
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______water will shorten setting time.
Heated
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_______ water will lengthen setting time
Colder
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Trays used for alginate?
Perforated or lock rim trays.
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When wrapping the tray in a moist napkin is to maintain ___% humidity.
100
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An adult mandibular impression generally requires?
two scoops of powder and two measures of water.
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An adult maxillary impression generally requires?
three scoops of powder and three measures of water.
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Normal set alginate
Working time of 2 minutes and a setting time of up to 41/2 minutes after mixing.
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Fast set alginate
Working time of 11/4 minutes and a setting time of 1 to 2 minutes.
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Working time
The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth.
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Setting time
The time required for the chemical action to be completed.
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Explain the procedure to the patient:
- The material will feel cold, there is no unpleasant taste, and the material will set quickly.
- Breathe deeply through your nose to help you relax and be more comfortable.
- Use hand signals to communicate any discomfort.
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Alginate: Mixing procedure:
- 1. Pick trays that will fit patients mouth. Try in. Use wax on tray if needed. Give patient instructions.
- 2. Mix alginate powder with cool water, 1:1 ratio, vigorously against the side of the rubber bowl until a smooth creamy mix results. Regular set: mix in 45 sec
- . Fast set: mix in 30 sec.
- Load tray… from side/pressing/wet finger
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Regular set for a kid we use ___ water.
- hot
- accelerate the setting time
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What will an unacceptable impression look likejQuery11240742170391663474_1519765727148?
- 1. premature set = too much powder = fluff / hot h2o / took too long
- 2. slow set: 2 much and 2 cold h2o
- 3. grainy/lumpy = mixing issue
- 4. voids = Air bubbles = spread thin layer on occl. Surface 1st. Large and small
- 5. distortion: Dbl imprint & movement
- 6. torn = 2 thin a mix
- 7. excessive amounts = GAG!
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An Acceptable Alginate Impression looks?
- The impression tray is centered over the central and lateral incisors.(midline)
- There is a complete "peripheral roll," which includes all of the vestibular areas.
- The tray is not "overseated," which would result in exposure of areas of the impression tray.
- The impression is free from tears (high tear strength) or voids.
- There is sharp anatomic detail of all teeth and soft tissues.
- The retromolar area, lingual frenum, tongue space, and mylohyoid ridge are reproduced in the mandibular impression.
- The hard palate and tuberosities are recorded in the maxillary impression.
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Synersis:
loss of water content.
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Acceptable mandibular tray should:
- Cover all teeth and retromolar pad
- Be 4 mm wider than the buccal and lingual portions of the posterior and the labial and lingual portions of the anterior teeth
- Allow the teeth to be centered and yet comply with the previous requirement
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Acceptable maxillary tray should:
- seated at the most posterior border and then continue seating parallel to the axis of the central incisors
- the excess alginate flows both in a labial or buccal direction but not in a palatal direction
- Palatal vault recorded
- Break the peripheral seal by running a finger around the edge and remove the impression with a rapid, firm pull
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Iodophor:
universal disinfectant
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Alginate issues Will set up too quickly if:
- Too much powder to water ratio.
- Room temp and water temp are too high.
- Took too long mixing or loading tray.
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After impression has been removed from patient mouth….
- Rinse the impression with cool water
- Cut away any loose alginate
- Disinfect alginate,
- Rinse impression again with cold water
- Remove excess water.
- Pour immediately or store by wrapping in loosely in damp paper towel or seal in a plastic bag for up to 5 days.(no more than 24hrs)
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Disinfection of Alginate:
- Guidelines recommend all impressions be rinsed and disinfected.
- Sodium hypochlorite, iodophor, glutaraldehyde, solutions have been used.
- Hypochlorite bleach 10:1/10 mins.
- Some manufacturers add disinfectants to the alginate powder.
- Immersion of alginate impressions for 10 minutes or as recommended [ or as per directions]
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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.
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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.
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