Impression material is a?
An accurate negative reproduction of the mouth.
A positive reproduction is made by?
pouring dental stone or other suitable material into impression.
The positive reproduction is called a?
model or cast
Bite registrations are Taken by the?
dentist or dental assistant.
A bite restorations Make a reproduction of the?
occlusal relationship between the maxillary and mandibular teeth.
The final impression is only taken by the?
________ provide an accurate registration between the maxillary and mandibular arches.
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.
Is the impression material reversible or irreversible?
After setting, the impression is removed from the mouth and is used to make a replica of the oral tissues.
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
examples of Whole arch trays?
half/quad/tri [triple] tray occlusal check/ temp crn
Stock trays or custom-made trays?
- Holes in the tray create a mechanical lock to hold the material in place.
- mechanical interlocking
Interior of the tray is painted or sprayed with an adhesive to hold the impression material
Covers one half of the arch.
Covers the anterior portion of the arch.
Full arch tray
Covers the entire arch.
Holes in the tray create a mechanical lock to hold the material in place.
Interior of the tray is painted or sprayed with an adhesive to hold the impression material.
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.
Types of impression materials:
- Inelastic/ Rigid
- Irreversible Hydrocolloid
Example of Elastic/Flexible Impression Materials:
- Polyether, Polysulfide & Silicone
- Reversible(Agar) Hydrocolloid
- Irreversible (Alginate)Hydrocolloid
- *Final impression
Example of Rigid Impression Materials:
- *For edentulous
- Zinc oxide-eugenol
- Inelastic/ Rigid
- Not used very much
- Impression compound
- Impression plaster
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.
- [you can never go back]
- Also called alginate hydrocolloid or just alginate
- Easy to manipulate
- Requires no special equipment
- Reasonably accurate
- low cost
Most widely used impression material in dentistry?
How is Alginate supplied?
Bulk Cans and premeasured single use packets
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.
- 1.Ease of mixing
- 2.Minimum equipment necessary
- 3.Flexibility of the of the set material
- 4.Low cost.
- 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.
**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
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.
The second physical phase of Alginate is?
a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.
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
Alginate is _________.
Powder is mixed with _______ causing a ______.
- cool water
- chemical reaction.
______water will shorten setting time.
_______ water will lengthen setting time
Trays used for alginate?
Perforated or lock rim trays.
When wrapping the tray in a moist napkin is to maintain ___% humidity.
An adult mandibular impression generally requires?
two scoops of powder and two measures of water.
An adult maxillary impression generally requires?
three scoops of powder and three measures of water.
Normal set alginate
Working time of 2 minutes and a setting time of up to 41/2 minutes after mixing.
Fast set alginate
Working time of 11/4 minutes and a setting time of 1 to 2 minutes.
The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth.
The time required for the chemical action to be completed.
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.
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
Regular set for a kid we use ___ water.
- accelerate the setting time
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!
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.
loss of water content.
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
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
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.
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)
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]
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
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