4. Definition
A dental impression material is a negative record of the tissue of the
mouth.
The negative reproduction of the tissue given by the impression material
is filled up with dental stone or other model materials to get a positive
cast.
it is used to
reproduce the form
the teeth and the
surrounding
tissues.
6. Die is The positive reproduction of a single tooth
cast or model it is when several teeth or a whole
of the arch is reproduced , called
7. Advantages of using a cast or model
1) models provide a
three-dimensional view
of the oral structures .
2)Many restorations or
appliance are best
constructed on a cast.
3) Saving valuable
clinical time
9. Desirable properties of an impression materials
Biocompatible to the dentist and patient
Acceptable to the patient
Have a pleasant taste , odor, consistency and color
Should set quickly once placed in the mouth
Accurate surface detail
Manipulation should be easy
12. Impression tray
impression tray:
Is The metallic or plastic carrier ,which are use to take
impression of natural teeth & their supporting oral
tissues by the impression materials
13. Impression compound
Impression compound :is
one of the oldest impression
materials .
It can be described as rigid,
reversible impression
material which sets by
physical change on heat.
On a applied heat ,it softens
and on cooling it hardens.
14. cont’s
it is mainly used for making impressions of
edentulous ridges.
modeling compound or modeling plastic
17. Indications
1. used for taking primary
impressions of the edentulous
ridge prior to the construction
of a custom-made impression
tray for complete dentures.
2. Bite registration
Giordano, Gen Dent 2000
18. Requirements of ideal impression compound
be plastic
Biocompatible
Harden uniformly when cooled with out distortion
Exhibit a smooth glossy surface after flaming
Withstand trimming
Should not boil
19. manipulation
Sticks:
Small amount of compound (stick compound) can be softened
over a flame .
Cakes:
Larger amounts of compound are softened in warm water in a
thermostatically controlled water path.
21. Loading the tray:
The softening is loaded onto the tray and quickly
seated on to the tissue to be recorded.
Any delay can cause
the impression to harden prematurely.
22. Precautions
Prolonged impression in water path causes the
compound to become brittle.
overheating in water makes the compound sticky
and difficult to handle.
the impression is removed from the mouth only
after it has completely cooled and hardened.
Then disinfect the compound.
24. Advantages of the compound
The material can be reused a number of times.
accuracy can be improved by flaming the surface.
The material has sufficient body to support itself especially
peripheral portions.
25. Disadvantages
Records less detail because of its high viscosity.
compresses soft tissue during impression.
Distortion due to its poor dimensional stability
Difficult removing if the there are severe undercuts.
27. Indications Zinc oxide-eugenol
1. Temporary filling
2. Temporary cementation
3. Root canal filling material
4. For full arch edentulous impression
without or minor undercut
5. Bite registration
29. Manipulation
Equal length of the two paste is extruded
Mixed with stainless steel spatula in paper
pad or glass slab
Mixing time 45-60 s
Working time 3-5 min
30. Non-Eugenol Pastes
NON-EUGENOL PASTE: developed to overcome
the burning sensation caused by eugenol .
Used in eugenol irritant patients
31. Elastomeric Impression Materials
A material that is used when an extremely accurate
impression is essential.
The term elastomeric means having elastic or rubberlike
qualities.
35. 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.
39. Non-aqueous elastomers
They are soft and rubber like and far more stronger
and stable than the hydrocolloids.
They are liquid polymers which can be converted to
solid rubber at room temperature.
These materials are most accurate and dimensionally
stable impression materials available in dentistry.
42. Supplied as
Base and catalyst
GENERAL PROPERTIES OF ELASTOMERIC MATERIALS
Excellent reproduction of surface details
They are generally hydrophobic
Coefficient of thermal expansion is high
The shelf life is two years
43. How you can Control of gagging?
1) seat the patient in an upright position.
2) rinse cold water or mouthwash before impression is
made.
3) The impression tray should not be overfilled with
impression material.
44. 4) The posterior portion of the impression tray
should be seated first. Then, the anterior portion
of the tray should be rotated into position. this
permits excess impression material to be
displaced in an anterior direction away from the
soft plate and airway.
45. Cont’s
5. The patient should be instructed to keep the
eyes open during the impression producer.
6. The patient should be directed to breath
through the nose. the dentist should encourage
slow, deep breaths.
7.use topical /spray anaesthesia to numb the area
47. is a naturally occurring, white powdery mineral with the
chemical name calcium sulphate dehydrate (CaSQ4·2H2O).
Their main uses are for:
◦ casts or models
◦ Dies
◦ investments
Gypsum:
48. Conti…….
models and dies should be accurate replicas of the
patient’s hard and soft tissues.
models and dies are prepared
using materials which are initially
fluid and can be poured into the
impression, then harden to form a
rigid replica.
49. Requirements of dental cast materials:
dimensional accuracy
adequate mechanical properties
be fluid at the time it is poured
be sufficiently strong to resist accidental fracture and
abrasion
be compatible with all the other materials with which it
comes into contact
50. Manipulation and setting characteristics
Plaster and stone powders are mixed with water to
produce a workable mix.
(CaSO4)⋅H2O+3H2O→2CaSO4⋅2H2O
Calcium sulphate hemihydrate + water
Calcium sulphate dihydrate
51. Considerable quantities of air may be incorporated
during mixing and this may lead to porosity within the
set material.
Air porosity may be reduced either by:
◦ vibrating the mix in order to bring air bubbles to the
surface
52. For hand mixing u need:
◦ clean rubber or plastic
bowl
◦ spatula
53. Factors which control the setting times of gypsum products can be divided
into:
1)controlled by manufacturers:
the concentration of nucleating agents in the hemihydrate powder
Chemical accelerator
2)controlled by the operator:
Temperature
W/P ratio
mixing time
Control of setting time:
A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.
Hydrocolloid impression materials
Hydro means water.
Colloid means gelatin substance.
Material used to obtain preliminary and final impressions.
The two types of hydrocolloids used in dental impressions are agar and alginate. Agar is a reversible hydrocolloid because it can pass
repeatedly between highly viscous gel and low viscosity sol simply through heating and cooling.
However, alginate once converted to the gel form cannot be converted back into the sol, and is therefore said to be irreversible hydrocolloid material.
Agar and alginate may be used independently or in combination to record crown impressions.
Agar was first introduced into dentistry for recording crown impressions in 1937 by Sears1 and was the first elastic impression material available.
It is not commonly used in dental practice today however, because of the need for expensive conditioning baths and water cooled
trays.
Alginate, unlike agar, does not require any special equipment. Being easy to use and inexpensive it is popular for less critical applications
Eg. Apposing casts and study models.
Alginate and agar produce impressions with reasonable surface detail. They are both relatively hydrophilic and are not displaced from wet surfaces as easily as the elastomers2.
However, in respect of recording crown preparations these materials have two major disadvantages.
Firstly, very poor dimensional stability because of the ready loss or imbibition of water on standing in dry or wet environments
respectively.
Secondly, low tear resistance which can be a real problem when attempting to record the gingival sulcus.
Some work supports the use of combined reversible and irreversible hydrocolloid impression systems.3,4
These systems are used in a way similar to the putty-wash technique for silicone rubbers described later in this article, with the agar injected around the preparation to capture surface detail and the more viscous alginate in the impression tray.
The advantages of this combination system compared with agar or alginate used individually is the minimisation of equipment required to record an agar impression (no water cooled tray is needed) and the fact that agar is more compatible with gypsum model materials than
alginate. It is also relatively cheap in comparison to many synthetic elastomers. Lin et al.5 demonstrated that the accuracy of this combination system is better than either the reversible or irreversible materials used separately and is comparable to that of polysulphide impression materials. However, the problems of low tear resistance and poor dimensional stability still apply resulting in the need for impressions to be cast up immediately.
For these reasons, most practitioners tend to reject the hydrocolloids in favour of the synthetic elastomers to produce accurate
and stable impressions.
