Chapter 46 Impression Materials Copyright 2003 Elsevier Science

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. Power. Point® 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 Copyright 2003, Elsevier Science (USA). All rights reserved.

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 § Impressions are negative reproductions of dental structures. Copyright 2003, Elsevier Science (USA). All rights reserved.

Classification of Impressions § Preliminary 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 post‑treatment records. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -1 Example of a final impression. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -2 Example of a bite registration. Copyright 2003, Elsevier Science (USA). All rights reserved.

Impression Trays § Must be sufficiently rigid to: • Carry the impression material into the oral cavity. • Hold the material in close proximity to the teeth. • Avoid breaking during removal. • Prevent warping of the completed impression. Copyright 2003, Elsevier Science (USA). All rights reserved.

Characteristics of Impression Trays § Quadrant tray § § • Covers one half of the arch. Section tray • Covers the anterior portion of the arch. Full arch tray • Covers the entire arch. 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Table 46 -1 Types of Stock Trays Copyright 2003, Elsevier Science (USA). All rights reserved.

Tray Selection Criteria § Feel comfortable to the patient. § 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -3 Examples of quadrant, section, and fullarch impression trays. Copyright 2003, Elsevier Science (USA). All rights reserved.

Tray Adhesives § VPS adhesives (blue) • For polyvinyl siloxane and polyether impression materials. § Rubber Base Adhesive (brown) • Used with rubber base impression materials. § Silicone Adhesive (orangish-pink) • Used with silicone impression materials. Copyright 2003, Elsevier Science (USA). All rights reserved.

Hydrocolloid Impression Materials § Hydro means water. § Colloid means gelatin substance. § Material used to obtain preliminary and final impressions. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Makeup of Alginate § Potassium alginate • 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. § Trisodium phosphate • Added to slow down the reaction time for mixing. Copyright 2003, Elsevier Science (USA). All rights reserved.

Makeup of Alginate- cont’d § Diatomaceous earth • A filler that adds bulk 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -7 Examples of packaging for alginate. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -8 Scoop and water measure for alginate. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -12 An alginate impression. Copyright 2003, Elsevier Science (USA). All rights reserved.

Reversible Hydrocolloid § An impression material that changes its physical state from a sol to a gel and then back to a sol. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Conditioning Bath for Reversible Hydrocolloid § Three Compartments • • • 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Types of Reversible Hydrocolloid § Tray material • Packaged in plastic tubes. Each tube has enough material to fill a full arch, watercooled 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Application of Reversible Hydrocolloid Impression Material 1. A stock water-cooled tray is selected, making sure 2. 3. 4. 5. 6. 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Elastomeric Impression Materials § A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Forms of Elastomeric Materials- cont’d § Regular and heavy-bodied • Often referred to as tray‑type materials, they are much thicker. As the names imply, they are used to fill the tray. Their stiffness helps to force the light‑bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation. Copyright 2003, Elsevier Science (USA). All rights reserved.

Basic Impression Technique 1. The material selected depends upon the dentist’s 2. 3. 4. 5. 6. 7. 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

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 • The last stage occurs from 1 to 24 hours. Copyright 2003, Elsevier Science (USA). All rights reserved.

Types of Elastomeric Materials § § Polysulfide Polyether Silicone Polyvinyl siloxane Copyright 2003, Elsevier Science (USA). All rights reserved.

Polysulfide Impression Material § Chemical makeup • Base: Mercaptan polysulfide. • Cross-linking agent: Sulfur and/or lead peroxide. • Catalysts: Copper hydroxides, zinc peroxide, organic hydroperoxide. • Fillers: Zinc sulfate, lithopone, or calcium sulfate dihydrate. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Polyether Impression Material § Chemical makeup • • Base: Polyether Cross-linking agent: Sulfate Catalysts: Glycol-based plasticizers Filler: Silica Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Silicone Impression Material § Chemical makeup • Base: Poly dimethyl siloxane • Cross-linking agent: Alkyl ortho silicate or organo hydrogen siloxane • Catalyst: Organo tin compounds • Filler: Silica Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Polyvinyl Siloxane Impression Material § Chemical makeup • Base: Silicone polym • Catalyst: Chloroplatinic acid • Filler: Silica Copyright 2003, Elsevier Science (USA). All rights reserved.

Manipulation and Technique Considerations for Polyvinyl Siloxane 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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Occlusal Registration § An accurate registration of the normal centric relationship of the maxillary and mandibular arches. Also commonly referred to as the bite registration. Copyright 2003, Elsevier Science (USA). All rights reserved.

Types of Occlusal Registration § Wax bite • Useful when the diagnostic casts are trimmed. • The most common technique is to use a softened baseplate wax. Copyright 2003, Elsevier Science (USA). All rights reserved.

Fig. 46 -27 Wax bite registration. Copyright 2003, Elsevier Science (USA). All rights reserved.

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. Copyright 2003, Elsevier Science (USA). All rights reserved.

Types of Occlusal Registration- cont’d § Zinc oxide-eugenol (ZOE) bite registration paste • ZOE paste has little to no resistance to bite closure and is a fast-setting material. • Material is supplied in a paste system and dispensed onto a paper pad, mixed, and placed onto a gauze tray for the patient to bite into. Copyright 2003, Elsevier Science (USA). All rights reserved.