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right 2003, Elsevier Science (USA). All rights reserved. Chapter 46 Impression Materials Copyright 2003, Elsevier Science (USA). All rights reserved. No part of this product may be reproduced or transmitted in any form or by any means, electronic or mechanical, including input into or storage in any information system, without permission in writing from the publisher. PowerPoint ® presentation slides may be displayed and may be reproduced in print form for instructional purposes only, provided a proper copyright notice appears on the last page of each print-out. Produced in the United States of America ISBN 0-7216-9770-4

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Impression Materials Chapter 46Chapter 46
Impression Materials
Copyright 2003, Elsevier Science (USA).
All rights reserved. No part of this product may be reproduced or transmitted in any form or by any means, electronic or mechanical, including input into or storage in any information system, without permission in writing from the publisher.
PowerPoint® presentation slides may be displayed and may be reproduced in print form for instructional purposes only, provided a proper copyright notice appears on the last page of each print-out.
Produced in the United States of America
ISBN 0-7216-9770-4
Introduction
Impression materials are used to obtain an impression of teeth and/or the surrounding oral tissues.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Definition of Impressions
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Classification of Impressions
Taken either by the dentist or an expanded-function dental assistant.
Used to make a reproduction of the teeth and surrounding tissues.
Used to make (1) diagnostic models, (2) custom trays, (3) provisional coverage, (4) orthodontic appliances, and
(5) pretreatment and posttreatment records.
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Classification of Impressions- cont’d
Final impressions
Taken by the dentist.
Used to make the most accurate reproduction of the teeth and surrounding tissues.
Used to make indirect restorations, partial or full dentures, and implants.
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Fig. 46-1 Example of a final impression.
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Classification of Impressions- cont’d
Bite registrations
Taken by the dentist or dental assistant.
Make a reproduction of the occlusal relationship between the maxillary and mandibular teeth.
Provide an accurate registration of the patient’s centric relationship between the maxillary and mandibular arches.
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Fig. 46-2 Example of a bite registration.
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Impression Trays
Carry the impression material into the oral cavity.
Hold the material in close proximity to the teeth.
Avoid breaking during removal.
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Characteristics of Impression Trays
Section tray
Full arch tray
Perforated tray
Holes in the tray create a mechanical lock to hold the material in place.
Smooth tray
Interior of the tray is painted or sprayed with an adhesive to hold the impression material.
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Table 46-1 Types of Stock Trays
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Tray Selection Criteria
Extends slightly beyond the facial surfaces of the teeth.
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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Fig. 46-3 Examples of quadrant, section, and full-arch impression trays.
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Tray Adhesives
Rubber Base Adhesive (brown)
Silicone Adhesive (orangish-pink)
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Hydrocolloid Impression Materials
Hydro means water.
Irreversible Hydrocolloid
Material that cannot return to a solution state after it becomes a gel.
Alginate is the irreversible hydrocolloid most widely used for preliminary impressions.
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Makeup of Alginate
Potassium alginate
Comes from seaweed; is also used in foods such as ice cream as a thickening agent.
Calcium sulfate
Trisodium phosphate
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Makeup of Alginate- cont’d
Diatomaceous earth
Zinc oxide
Potassium titanium fluoride
Added so as not to interfere with the setting and surface strength.
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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.
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Packaging and Storing of Alginate
Containers about the size of a coffee can are the most commonly used form of packaging.
Premeasured packages are more expensive, but save time by eliminating the need for measurement of the powder.
Shelf life of alginate is approximately 1 year.
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Fig. 46-7 Examples of packaging for alginate.
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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.
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Alginate Settings
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.
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.
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Altering the Setting Times of Alginate
Cooler water can increase the setting time if additional time is needed for the procedure.
Warmer water can reduce or shorten the setting time of the procedure.
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Water-to-Powder Ratio
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.
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Fig. 46-8 Scoop and water measure for alginate.
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Taking an Alginate Impression
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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An Acceptable Alginate Impression
The impression tray is centered over the central and lateral incisors.
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 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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Fig. 46-12 An alginate impression.
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Reversible Hydrocolloid
An impression material that changes its physical state from a sol to a gel and then back to a sol.
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Chemical Makeup of Reversible Hydrocolloid
85% water
13% agar
Agar is an organic substance derived from seaweed.
Additional chemical modifiers are added to aid in the handling characteristics.
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Conditioning Bath for Reversible Hydrocolloid
The first bath is for liquefying the semisolid material. A special water bath called a “hydrocolloid conditioner” at 212° F liquefies the material. After liquefying, the preset thermostat cools the temperature to 150° F automatically.
The second bath becomes a storage bath that cools the material, readying it for the impression. At this temperature, the tubes are waiting for use.
A third bath is kept at 110° F/44° C for tempering the material after it has been placed in the tray.
Three Compartments
Types of Reversible Hydrocolloid
Tray material
Packaged in plastic tubes. Each tube has enough material to fill a full arch, water-cooled tray.
Syringe material
Packaged in plastic or glass cartridges that fit a syringe or in preloaded syringe or preformed sticks that refill special hydrocolloid inlay syringes.
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Application of Reversible Hydrocolloid Impression Material
A stock water-cooled tray is selected, making sure that the tray does not impinge on any of the teeth or soft tissue.
Plastic stops are placed in the tray.
Tubing is connected to the tray and to the water outlet for drainage.
The material is liquefied and moved to the storage bath.
The light-bodied material is placed in the syringe, and heavy-bodied material is placed in the tray.
The light-bodied material is expressed around the prepared tooth, and the dentist seats the tray.
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Elastomeric Impression Materials
A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.
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Characteristics or Elastomeric Impression Materials
Base
Packaged as a paste in a tube, as a cartridge, or as putty in a jar.
Catalyst
Also known as the accelerator, is packaged as a paste in a tube, as a cartridge, or as a liquid in a bottle with a dropper top.
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Forms of Elastomeric Materials
Light-bodied
Also referred to as syringe type, or wash type. This material is used because of its ability to flow in and about the details of the prepared tooth. A special syringe, or extruder, is used to place the light-bodied material on and immediately around the prepared teeth.
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Forms of Elastomeric Materials- cont’d
Regular and heavy-bodied
Often referred to as traytype materials, they are much thicker. As the names imply, they are used to fill the tray. Their stiffness helps to force the lightbodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation.
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Basic Impression Technique
The material selected depends upon the dentist’s preference and the type of impression required for the procedure.
The dentist prepares the tooth or teeth for the impression.
The light-bodied material is prepared and loaded into the syringe and transferred to the dentist.
The dentist places the light-bodied material over and around the prepared teeth and onto the surrounding tissues.
The heavy-bodied material is prepared and loaded into the tray and transferred to the dentist.
When the impression material has reached final set, the impression is removed and inspected for accuracy.
The impression is disinfected, placed in a biohazard bag, labeled, and readied for the laboratory technician.
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Curing Stages of Elastomeric Materials
Initial set
The first stage results in stiffening of the paste without the appearance of elastic properties. The material may be manipulated only during this first stage.
Final set
The second stage begins with the appearance of elasticity and proceeds through a gradual change to a solid rubberlike mass. The material must be in place in the mouth before the elastic properties of the final set begin to develop.
Final cure
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Types of Elastomeric Materials
Polysulfide Impression Material
Catalysts: Copper hydroxides, zinc peroxide, organic hydroperoxide.
Fillers: Zinc sulfate, lithopone, or calcium sulfate dihydrate.
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Manipulation and Technique Considerations for Polysulfide Material
Dispense pastes at the top of the mixing pad.
Mix pastes with the tip of a spatula to incorporate the material first.
Transfer the material to the fresh surface of the mixing pad.
Water, saliva, and blood affect polysulfide material.
Impression should be removed quickly after setting-do not rock the tray.
Adhesive must be thin and dry before adding the impression material.
Wait 20 to 30 minutes before pouring the impression for the stress relaxation to occur in the material.
Be careful of glove powder contamination of the impression.
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Polyether Impression Material
Manipulation and Technique Considerations for Polyether Material
Material is very stiff, which makes it difficult to remove without rocking.
When removing the impression, break the seal and rock slightly to prevent tearing.
Water, saliva, and blood affect polyether material.
Added moisture will increase the impression’s marginal discrepancy.
Increased water absorption occurs if a thinning agent is used.
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Silicone Impression Material
Catalyst: Organo tin compounds
Manipulation and Technique Considerations for Silicone Material
The material has a limited shelf life.
The tray requires a special tray adhesive.
No syneresis or imbibition but does respond with shrinkage over time.
The material is more flexible, so there is more chance for distortion during removal.
Wait 20 to 30 minutes before pouring of models for stress relaxation to occur.
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Polyvinyl Siloxane Impression Material
For dimensional stability, this is the best impression material.
Pouring of the model can be delayed up to 7 to 10 days.
Stiffness of the material makes removal of the tray difficult.
Material dispensed using auto-mixing unit and mixing tips.
Manipulation and Technique Considerations for Polyvinyl Siloxane Material
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Occlusal Registration
An accurate registration of the normal centric relationship of the maxillary and mandibular arches. Also commonly referred to as the bite registration.
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Types of Occlusal Registration
Useful when the diagnostic casts are trimmed.
The most common technique is to use a softened baseplate wax.
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Fig. 46-27 Wax bite registration.
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Types of Occlusal Registration- cont’d
Polysiloxane bite registration paste: Supplied both as a paste system and also as cartridges.
The material is fast setting.
There is no resistance to biting forces.
There is no odor or taste for the patient.
It gains dimensional stability over time.
It is convenient to use.
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Types of Occlusal Registration- cont’d
Zinc oxide-eugenol (ZOE) bite registration paste