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Impression Material Dr.Mohammed.M.Heskul, DDS,MSc.

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Impression Material

Dr.Mohammed.M.Heskul, DDS,MSc.

Impresstion MaterialThe function of impression material is to record accurately the dimensions of oral tissues and their spatial relationships. In making an impression, a material in the plastic state is placed against the oral tissues to set . After setting, the impression is removed from the mouth and is used to make a replica of the oral tissues

Impresstion MaterialThe impression gives a negative reproduction of these tissues. A positive reproduction is obtained by pouring dental stone or other suitable material into the impression and allowing it to harden. The positive reproduction is called a model or cast when large areas of the oral tissues are involved or a die when single or multiple tooth preparations are recorded the relationships between a tooth.

Impresstion MaterialImpression materials are classified as:

Flexible Rigid

Undercuts

Impresstion MaterialRigid: is restricted to applications in areas where no undercuts exist.

- If there is undercut: on setting, it would be locked in place and could not be removed over the bulge of the tooth without fracturing. - A rigid material can be removed from a tooth prepared for a full crown or from an edentulous.

Impresstion MaterialFlexible : can be used in there are or (are not) undercuts,so itused most frequently. (Dentulous-edentulousprepared non prepared teeth)

Impresstion MaterialDesirable Properties of Impression Materials1- Ease of manipulation and reasonable cost 2- Adequate flow and wetting properties 3- Appropriate setting time and characteristics 4- Sufficient mechanical strengthelastic recovery and resistant to tearing during removal. 5- Good dimensional accuracystable over time 6- Taste and odor acceptable to patient 7- Safenot toxic or irritating. 8- No significant degradation of properties as a result of disinfection. 9- Compatibility with all die and cast materials. 10- good shelf life.

PlasterNon-elastic

Compound Waxes

Impression Materials

ZnO - Eugenol

Agar (reversible)Aqueous Hydrocolloids Alginate (irreversible) Polysulfide Condensation

Elastic Non-aqueous ElastomersSilicones

AdditionPolyetherOBrien, Dental Materials & their Selection 1997

ALGINATE Hydrocolloid Impression MaterialsAlginate is one of the most widely used aqueous dental impression materials.

ALGINATE

The wide use of alginates results from : 1) The ease of mixing and manipulate. 2) The minimum equipment necessary.

3) The flexibility of the set impression. 4) Their accuracy if properly handled. (5) Their low cost.

ALGINATEMIXINC AND SETTING TIMES

when properly mixed by hand, should develop a smooth, creamy , no voids consistency free of graininessNormal set : 2 4m.15s

Fast set 1-2 mBecause the setting occurs as a result of a chemical reaction, an increase in the temperature of the water used to prepare the mix shortens the working and setting times.

ALGINATE

The proportions of powder and water also affect the setting times.

Thinner mixes increase the time required for the material to set.

ALGINATE

A problem with alginate impressions is loss of accuracy with increased time of storage.

The set alginate is a hydrocolloid gel that contains large quantities of water. This water evaporates if the impression is stored in air, and the impression shrinks. If the impression is placed in water, it absorbs water and expands. Therefore, storage in either air or water results in serious changes in dimensions and a loss of accuracy. Storage in humid air approaching 100 relative humidity results in the least dimensional change

ALGINATE

Alginate gels, however, shrink even under conditions of 100 relative humidity as a result of a process caned syneresis, in which water forms on the surface of the impression.

Fortunately, syneresis occurs rather slowly, and alginate impressions prepared from modern products usually can be stored under conditions of 100 relative humidity for up to 5 days without serious dimensional changes.

INGREDIENTS

Na/K alginate Calcium sulfate to react with Na alginate. Sodium phosphate retarder Diatamaceous earth control flexibilty Pigments colour Phenylanaline sweetner

ELASTIC RECOVERY

Alginates have elastic recovery of 96-98 prcnt. 2 - 4 percent permentant deformation THUS . Alginate is flexible but not perfectly elastic. ANSI-ADA specifications require at least 95 percent elastic recovery when Alginate is compressed 20 prcnt for 5 sec.

FLEXIBILITY ANSI-ADA set limit of 5 20 percent at the time a model or die is prepeared in the impression. Relative amount of water powder ratio affects flexibility. Thicker mixes result in low flexibility

REPRODUCTION OF DETAILS. ADA Specifications recommend that alginate must have the minimum capabilities of transferring a line only 0.075 mm wide to a gypsum model or die material.

Objectives for Taking Alginate Impressions

All teeth in the upper and lower arch The entire alveolar process The retromolar area of the lower arch The area of the hamular notch in the upper arch . A detailed, undistorted, and bubble-free reproduction of the oral tissues

Mixing the Alginate

With a stiff, wide-bladed spatula. the alginate powder is stirred with water. The mix is spatulated vigorously against the side of the rubber bowl until smooth, creamy mix results, which is free of voids.

Steps after Making the Impression

1. Rinse the impression with cool water. 2. Cut away any unsupported alginate. 3. Disinfect alginate impression. One method is to soak it in hypochlorite bleach Diluted 10:1 with water for 10 minutes. 4. Rinse disinfected impression with cold water. 5. Remove excess water.

Steps after Making the Impression

6. Proceed to pour gypsum model , or if storage is necessary, wrap loosely in a wet paper towel or seal in a plastic bag for up to 5 days. 7. If stored, the impression should be placed so that the tray supports the alginate. Thus, the tray side of the impression is against the laboratory bench.

Troubleshooting Alginate ImpressionsA- If the alginate set before a satisfactory impression was obtained, several factors could be contributing to this problem:

incorrect dispensing of powder and liquid (not aerating the powder before dispensing) .An unusually high room temperature .

Too much time used in loading the tray and inserting the impression.

Troubleshooting Alginate ImpressionsA- If the alginate set before a satisfactory impression was obtained, several factors could be contributing to this problem: solution for delaying the setting: is to reduce the temperature of the mix water rather than use a thinner mix, which results in lower tear strength.

Troubleshooting Alginate ImpressionsB- If the alginate impression contained several large voids in critical areas, what can be done to avoid this problem? 1- During the dispensing and mixing of the alginate, the powder is add to the water and often an initial wetting of the powder by water is accomplished by squeezing the alginate between the blade of the spatula and the side of the rubber mixing bowl, which minimizes incorporation of voids.

Troubleshooting Alginate ImpressionsB- If the alginate impression contained several large voids in critical areas, what can be done to avoid this problem? 2-When filling the tray, add alginate at one location, and force the alginate to flow into other portions of the tray.

Troubleshooting Alginate ImpressionsB- If the alginate impression contained several large voids in critical areas, what can be done to avoid this problem? 3- As a special precaution, a portion of alginate can be spread over the occlusal surface of the teeth before the loaded tray is inserted.

Troubleshooting Alginate ImpressionsC- If the alginate impression had a large amount of material in the posterior palatal area and did not record adequately the area of the vestibule, several factors could be involved: 1- The posterior of the tray may not have been seated first followed by the anterior, which allowed a large portion of the alginate to flow into the palatal area (which also could make the patient gag).

Troubleshooting Alginate ImpressionsC- If the alginate impression had a large amount of material in the posterior palatal area and did not record adequately the area of the vestibule, several factors could be involved: 2- Inadequate alginate may have been placed in the tray.

Troubleshooting Alginate ImpressionsC- If the alginate impression had a large amount of material in the posterior palatal area and did not record adequately the area of the vestibule, several factors could be involved: 3- The lip may not have been pulled out gently to allow alginate to flow into the vestibule.

Troubleshooting Alginate ImpressionsC- If the alginate impression had a large amount of material in the posterior palatal area and did not record adequately the area of the vestibule, several factors could be involved: 4- The impression must be seated gradually to give the alginate time to flow.

Alginate Substitute Impression Materials

Alginate substitute impression materials are addition silicone impression materials that are formula ted to provide characteristics similar to alginate impression materials.

Alginate Substitute Impression Materials

Agar Hydrocolloid Impression Matyerials

Agar hydrocolloid was the first successful flexible aqueous impression material used in dentistry.

Agar Hydrocolloid Impression Matyerials

The flexibility of the material at the time it is removed from the mouth allows impression of undercut areas . It yields accurate impressions.

Agar Hydrocolloid Impression Matyerials

Agar impression material is supplied as a gel in 1- a collapsible tube: is used with a water-cooled impression tray . 2- a number of cylinders in a glass jar: is used with a syringe.

Agar Hydrocolloid Impression Matyerials

The agar gel is converted to a sol by heating in water, usually boiling, 100C, and becomes a gel again by cooling to 43.3C. Once the gel has been converted to a sol, it remains fluid for extended periods (all day) by being stored at 65.7C.

Agar Hydrocolloid Impression Matyerials

Agar impressions are highly accurate at the time of removal from the mouth but shrink when stored in air or 100% relative humidity and expand when stored in water as with alginate. The least dimensional change occurs when the impressions are stored in 100% humidity; however, prompt pouring of plaster or stone models is recommended.

Elastomeric Impression Materials

polysulfides, condensation silicones polyethers, addition silicones addition silicone-polyether hybrid * elastomeric impression materials dominate the market mainly as a result of their greater accuracy, dimensional stability with time, and ability to record detail as compared with the hydrocolloid materials.

Addition Silicone Impression Materials

-vinyl polysiloxanes . -Devloped as alternative to polysulfide and condensation silicones. - supplied as low-, medium-, high-, or very high-viscosity (putty) material. - The material is supplied as a two-paste or a two-putty system.

First1- A low-molecular-weight silicone with terminal vinyl groups2- reinforcing filler 3- chloroplatinic acid catalyst

Second1- low-molecular-weight silicone with silane hydrogens2- reinforcing filler

Addition Silicone Impression Materials

Because no volatile byproduct (such as water or ethanol) is formed in this reaction, minimal dimensional change occurs during polymerization. Increases in temperature lengthen the rate of reaction and shorten the setting time.

Addition Silicone Impression Materials

If hydroxyl groups are present in the addition silicone, a side reaction occurs that results in the formation of hydrogen. The hydrogen is released gradually from the set impression material and produces bubbles in gypsum dies prepared less than 1 hour, or epoxy dies less than 24 hours, after the impression is taken.

Addition Silicone Impression Materials

Hydrophilic silicones wet the oral tissues better than earlier hydrophobic materials and permit gypsum models and dies to be prepared with fewer air bubbles.

Addition Silicone Impression Materials

Hand Mixing Automixing or dual- cartridge systems

Addition Silicone Impression Materials

Automixing or dual- cartridge systems: During extrusion through the static mixing tip, the two pastes are folded over each other and exit the tip in a mixed condition.

The mixing tip is left on until the next mix, at which time it is replaced by a new tip

Addition Silicone Impression Materials

Properties: Less dimensional change higher elastic recovery

Addition Silicone Impression Materials

Properties: The dimensional change in 24 hours of about -0.1% is very low. The elastic recovery at the time of removal from the mouth of about 99.8% (permanent deformation of 0.2%) is the highest of all the impression materials.

The percent flow values of the addition silicones are likewise low. These properties indicate the superior accuracy of the addition silicones.

Addition Silicone Impression Materials

- The working time is short for the addition silicones. - Setting time: 2-10 (according to the manufacturer). - Flexibility is low to moderate.

- Removal of addition silicone impressions from undercut areas may present difficulties because of this stiffness, and extra space should be provided for the impression material when a custom tray is used.

Condensation Silicone Impression Materials

Condensation silicone impression materials are not used commonly in the dental office but rather as an accurate duplicating material in the dental laboratory. This impression material is supplied as a base and an accelerator

Condensation Silicone Impression Materials

The dimensional change during 24 hours after setting is relatively high.

About 50% of the dimensional change occurs during the first hour after setting, and the remaining 50% occurs between 1 and 24 hours.

Polysulfide Impression Materials

Three types are available and are classified as low, medium, and high viscosity The permanent deformation values of 2% to 3% (elastic recovery of 97% to 98%) indicate that compression during removal of the impression material should be kept to a minimum. shrinkage 0.3-0.4 during the first 24 hours

Disinfection of Elastomeric impression

The Impression immersed in appropriately diluted solution for 10 M. Except for chlorine dioxide (3M)

Rigid Impression MaterialsImpression compound

Principle application for a check impression to determine whether the cavity preparation contains UNDERCUTS that would cause problem in cast gold alloy restoration.

Rigid Impression MaterialsImpression compound

- Heated over aflame or hot water until softened. - Pressed. - Held firmly. - Removed. - Fracture or deformation indicates undesirable undercut areas in the cavity.

Zinc Oxide-Eugenol

Elastomeric impression materials eliminated the use of Zeo for edentulous impressions. Two pastes Set time:3-5 Material is not strong

Elastomeric Material for Bite Registeration

Bite Registration : In the past: by wax.

Factors limited using wax: 1- Distortion on removal 2- release of internal stress on storage. 3- High flow properties. 4- large dimensional change.

Elastomeric Material for Bite Registration

- Elastomeric impression materials ideally should : Be fast setting. Be mousselike in the tray. No taste or odor. be Rigid on set. Be easy to trim

THanks