1 impression materials
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Impression Material
Dr.Mohammed.M.Heskul, DDS,MSc.
The 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 Material
The 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 Material
Impression materials are classified as:
Impresstion Material
• Flexible
• Rigid
Undercuts
Impresstion Material
Rigid: 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 Material
Flexible : can be used in there are or (are not) undercuts,so it
used most frequently.
(Dentulous-edentulous…prepared – non prepared teeth)
Desirable Properties of Impression Materials
Impresstion Material
1- Ease of manipulation and reasonable cost
2- Adequate flow and wetting properties
3- Appropriate setting time and characteristics
4- Sufficient mechanical strength—elastic recovery and resistant to
tearing during removal.
5- Good dimensional accuracy—stable over time
6- Taste and odor acceptable to patient
7- Safe—not 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.
Imp
ress
ion
Ma
teria
ls
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien, Dental Materials & their Selection 1997
ALGINATE Hydrocolloid Impression
Materials…
Alginate is one of the most widely used aqueous dental impression
materials.
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.
ALGINATE…
when properly mixed by hand, should develop a smooth, creamy ,
no voids consistency free of graininess
Normal set : 2 – 4m.15s
Fast set 1-2 m
Because 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…
MIXINC AND SETTING TIMES
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.
ALGINATE…
Na/K alginate
Calcium sulfate to react with Na alginate.
Sodium phosphate retarder
Diatamaceous earth control flexibilty
Pigments colour
Phenylanaline sweetner
INGREDIENTS
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.
ELASTIC RECOVERY
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
FLEXIBILITY
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.
REPRODUCTION OF DETAILS.
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
Objectives for Taking Alginate Impressions
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.
Mixing the Alginate
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.
Steps after Making the Impression
A- 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 Impressions
A- 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 Impressions
B- 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 Impressions
B- 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 Impressions
B- 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 Impressions
C- 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 Impressions
C- 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 Impressions
C- 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 Impressions
C- 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.
Troubleshooting Alginate Impressions
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
Alginate Substitute Impression Materials
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,
100°C, and becomes a gel again by cooling to 43.3°C.
Once the gel has been converted to a sol, it remains fluid for extended
periods (all day) by being stored at 65.7°C.
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.
Agar Hydrocolloid Impression Matyerials
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.
Elastomeric 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.
Addition Silicone Impression Materials
1- A low-molecular-weight silicone with terminal vinyl groups
2- reinforcing filler
3- chloroplatinic acid catalyst
1- low-molecular-weight silicone with silane hydrogens
2- reinforcing filler
First Second
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.
Addition 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.
Condensation Silicone 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
Polysulfide Impression Materials
The Impression immersed in appropriately diluted solution for 10 M.
Except for chlorine dioxide (3M)
Disinfection of Elastomeric impression
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 Materials
Impression compound
- Heated over aflame or hot water until softened.
- Pressed.
- Held firmly.
- Removed.
- Fracture or deformation indicates
undesirable undercut areas in the cavity.
Rigid Impression Materials
Impression compound
Elastomeric impression materials eliminated the use of Zeo for
edentulous impressions.
Two pastes
Set time:3-5
Material is not strong
Zinc Oxide-Eugenol
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 Registeration
- 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
Elastomeric Material for Bite Registration
THanks
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